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Physical Review BPhysical Review B is the APS journal devoted to condensed matter and materials physics. Our goal is to publish the most important, stimulating, and useful papers for our international community of researchers spanning many subdisciplines. We welcome your comments and suggestions via feedback@aps.org. More...
Structure, structural phase transitions, mechanical properties, defects
S. Miga, W. Kleemann, J. Dec, and T. Łukasiewicz
Isothermal aging above the ferroelectric phase-transition temperature, Tc≈410 K , causes the charge-disordered uniaxial crystal Sr0.40Ba0.60Nb2O6 to become trapped in metastable nanopolar states at any finite wait time. However, backward extrapolation of the isothermal relaxation of its axial...
[Phys. Rev. B 80, 220103
] Published Fri Dec 11, 2009
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E. Hüger, H. Schmidt, J. Stahn, B. Braunschweig, U. Geckle, M. Bruns, and A. Markwitz
The investigation of atomic mobilities in transient metastable phases is a challenging task in diffusion science. For amorphous silicon carbonitrides we identified a transient metastable bonding configuration by Fourier-transform infrared spectroscopy on samples annealed in a defined time-temperatur...
[Phys. Rev. B 80, 220101
] Published Wed Dec 9, 2009
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Marcel H. F. Sluiter
Several tetrahedrally close-packed (tcp) phases, such as β-W , β-Ta , and β-U , are believed to be stabilized by impurities. Here we analyze the various ways in which impurities can be dissolved in tcp structures paying special attention to interstitial configurations in the β-W (A15) struc...
[Phys. Rev. B 80, 220102
] Published Wed Dec 9, 2009
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Inhomogeneous, disordered, and partially ordered systems
First-principles determination of low-temperature order and ground states of Fe-Ni, Fe-Pd, and Fe-Pt
Sergey V. Barabash, Roman V. Chepulskii, Volker Blum, and Alex Zunger
While the binary Fe-X (X=Ni,Pd,Pt) alloys are among the most widely applied bimetallics, open questions remain regarding whether and which of their compounds are stable at low T . Based on density-functional theory and first-principles cluster expansions that are “filtered” against structur...
[Phys. Rev. B 80, 220201
] Published Wed Dec 16, 2009
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Magnetism
K. Kuepper, M. Raekers, C. Taubitz, M. Prinz, C. Derks, M. Neumann, A. V. Postnikov, F. M. F. de Groot, C. Piamonteze, D. Prabhakaran, and S. J. Blundell
Electronic and magnetic properties of the charge ordered phase of LuFe2O4 are investigated by means of x-ray spectroscopic and theoretical electronic structure approaches. LuFe2O4 is a compound showing fascinating magnetoelectric coupling via charge ordering. Here, we identify the spin ground st...
[Phys. Rev. B 80, 220409
] Published Fri Dec 18, 2009
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Shinichi Watanabe, Ryusuke Kondo, Seiichi Kagoshima, and Ryo Shimano
![]() [Phys. Rev. B 80, 220408
] Published Thu Dec 17, 2009
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I. Mirebeau, I. Goncharenko, H. Cao, and A. Forget
![]() [Phys. Rev. B 80, 220407
] Published Mon Dec 14, 2009
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Gia-Wei Chern and Natalia Perkins
Motivated by recent interest in quasi-one-dimensional compound CaV2Osub>4 , we study the ground states of a spin-orbital chain characterized by an Ising-like orbital Hamiltonian and frustrated interactions between S=1 spins. The on-site spin-orbit interaction and the Jahn-Teller effect compete with i...
[Phys. Rev. B 80, 220405
] Published Thu Dec 10, 2009
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N. Kida, D. Okuyama, S. Ishiwata, Y. Taguchi, R. Shimano, K. Iwasa, T. Arima, and Y. Tokura
Electric-field (E) drive of magnetic resonance in a solid has been a big challenge in condensed-matter physics and emerging spintronics. We demonstrate the appearance of distinct magnetic excitations driven by the light E component in a hexaferrite Ba2Mg2Fe12O22 . In the conical-spin state even...
[Phys. Rev. B 80, 220406
] Published Thu Dec 10, 2009
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M. Matusiak, E. M. Tunnicliffe, J. R. Cooper, Y. Matsushita, and I. R. Fisher
We report measurements of the thermoelectric power (TEP) for a series of Pb1−xTlxTe crystals with x=0.0 to 1.3%. Although the TEP is very large for x=0.0 , using a single-band analysis based on older work for dilute magnetic alloys we do find evidence for a Kondo contribution of 11–18 μ...
[Phys. Rev. B 80, 220403
] Published Wed Dec 9, 2009
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M. Gloanec, S. Rioual, B. Lescop, R. Zuberek, R. Szymczak, P. Aleshkevych, and B. Rouvellou
We report on the temperature dependence of ferromagnetic resonance (FMR) measurements on NiFe/FeMn bilayer. This includes investigations about the angular distribution of the resonance, HR , and that of the linewidth, ΔH . By considering the domain-wall formation model, the exchange-bias field, ...
[Phys. Rev. B 80, 220404
] Published Wed Dec 9, 2009
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Superfluidity and superconductivity
A. Tsurumaki and Z. Hiroi
![]() [Phys. Rev. B 80, 220505
] Published Tue Dec 22, 2009
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M. Le Tacon, T. R. Forrest, Ch. Rüegg, A. Bosak, A. C. Walters, R. Mittal, H. M. Rønnow, N. D. Zhigadlo, S. Katrych, J. Karpinski, J. P. Hill, M. Krisch, and D. F. McMorrow
![]() [Phys. Rev. B 80, 220504
] Published Mon Dec 21, 2009
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D. H. Ryan, J. M. Cadogan, C. Ritter, F. Canepa, A. Palenzona, and M. Putti
Powder neutron-diffraction measurements on both SmFeAsO and the fluorine-doped superconductor, SmFeAsO0.85F0.15 , show that the Sm sublattice orders magnetically. In both cases we observe a simple layered antiferromagnetic arrangement of the ∼0.5μB Sm moments. This provides direct evidence tha...
[Phys. Rev. B 80, 220503
] Published Thu Dec 10, 2009
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Electronic structure: wide-band, narrow-band, and strongly correlated systems
M. Mulazzi, J. Miyawaki, A. Chainani, Y. Takata, M. Taguchi, M. Oura, Y. Senba, H. Ohashi, and S. Shin
Soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES) reveals the band dispersion and Fermi surface of bulk ferromagnetic Co(0001). The spectral peak widths are narrower than previously observed in low-energy ARPES experiments. From very general considerations and in contrast to low-energy...
[Phys. Rev. B 80, 241106
] Published Tue Dec 15, 2009
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W. Fan, S. Huang, J. Cao, E. Ertekin, C. Barrett, D. R. Khanal, J. C. Grossman, and J. Wu
We investigated external-stress-induced metal-insulator phase transitions in cantilevered single-crystal VO2 nanobeams at variable temperatures using a combined theoretical and experimental approach. An atomic force microscope was used to measure the force-displacement curve of the nanobeams, whic...
[Phys. Rev. B 80, 241105
] Published Fri Dec 11, 2009
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Naoki Ogawa, Takuya Satoh, Yasushi Ogimoto, and Kenjiro Miyano
/div>Electronic and magnetic dynamics at a single interface of antiferromagnetic manganites, LaMnO3/SrMnO3 , were studied with time-resolved second-harmonic generation and time-resolved nonlinear magneto-optical Kerr effect. The temporal evolution of the respective signals shows clear differences; an op...
[Phys. Rev. B 80, 241104
] Published Thu Dec 10, 2009
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U. Lüders, W. C. Sheets, A. David, W. Prellier, and R. Frésard
Based on the Hubbard model of strongly correlated systems, a reduction in the bandwidth of the electrons can yield a substantial change in the properties of the material. One method to modify the bandwidth is geometrically confined doping, i.e., the introduction of a (thin) dopant layer in a materia...
[Phys. Rev. B 80, 241102
] Published Tue Dec 8, 2009
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Semiconductors I: bulk
Xiuwen Zhang, Giancarlo Trimarchi, Mayeul d’Avezac, and Alex Zunger
Large atomic size mismatch between compounds discourages their binding into a common lattice because of the ensuing cost in strain energy. This central paradigm in the theory of isovalent alloys long used to disqualify alloys with highly mismatched components from technological use is clearly broken...
[Phys. Rev. B 80, 241202
] Published Tue Dec 15, 2009
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Semiconductors II: surfaces, interfaces, microstructures, and related topics
V. V. Solovyev, S. Schmult, W. Dietsche, and I. V. Kukushkin
![]() [Phys. Rev. B 80, 241310
] Published Thu Dec 17, 2009
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A. D. Chepelianskii and D. L. Shepelyansky
![]() [Phys. Rev. B 80, 241308
] Published Wed Dec 16, 2009
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Alexander Seidel and Kun Yang
We calculate the electron spectral functions at the edges of the Moore-Read Pfaffian and anti-Pfaffian fractional quantum Hall states in the clean limit. We show that their qualitative differences can be probed using momentum resolved tunneling, thus providing a method to unambiguously distinguish w...
[Phys. Rev. B 80, 241309
] Published Wed Dec 16, 2009
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P. Degiovanni, Ch. Grenier, and G. Fève
A unified approach to decoherence and relaxation of energy resolved single-electron excitations in integer quantum Hall edge channels is presented. Within the bosonization framework, relaxation and decoherence induced by interactions and capacitive coupling to an external linear circuit are computed...
[Phys. Rev. B 80, 241307
] Published Fri Dec 11, 2009
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S. Matsuzaka, Y. Ohno, and H. Ohno
We studied electron density (n) dependence of the extrinsic spin Hall effect in n -doped GaAs with n raging from 1.8×1016 to 3.3×1017 cm−3 . By scanning Kerr microscopy measurements, we observed spin accumulation near the channel edges in all the samples due to the extrinsic spin Hall ...
[Phys. Rev. B 80, 241305
] Published Wed Dec 9, 2009
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N. Chauvin, C. Zinoni, M. Francardi, A. Gerardino, L. Balet, B. Alloing, L. H. Li, and A. Fiore
We demonstrate that the presence of charges around a semiconductor quantum dot (QD) strongly affects its optical properties and produces nonresonant coupling to the modes of a microcavity. We show that, besides (multi)exciton lines, a QD generates a spectrally broad emission which efficiently couple...
[Phys. Rev. B 80, 241306
] Published Wed Dec 9, 2009
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Surface physics, nanoscale physics, low-dimensional systems
Ferdinand Kuemmeth and Emmanuel I. Rashba
Spin- and angular-resolved photoemission spectroscopy is a basic experimental tool for unveiling spin polarization of electron eigenstates in crystals. We prove, by using spin-orbit coupled graphene as a model, that photoconversion of a quasiparticle inside a crystal into a photoelectron can be acco...
[Phys. Rev. B 80, 241409
] Published Wed Dec 16, 2009
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Abraham Hmiel and Yongqiang Xue
Using first-principles calculations within density-functional theory, we demonstrated shape-dependent electronic properties of [112]-oriented Si nanowires (SiNWs) with monohydride (mh-SiNW) and trihydride (th-SiNW) passivation. We show for both mh-SiNWs and th-SiNWs, an indirect-to-direct band-gap t...
[Phys. Rev. B 80, 241410
] Published Wed Dec 16, 2009
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A. J. M. Giesbers, U. Zeitler, L. A. Ponomarenko, R. Yang, K. S. Novoselov, A. K. Geim, and J. C. Maan
We show that the width of the longitudinal magnetoconductivity peaks in graphene related to the N=1 Landau level displays a power-law type temperature dependence, Δν∝Tκ , with κ=0.37±0.05 . Similarly, the derivative of the Hall conductivity at the plateau transition, (dσxy/dν) , scales...
[Phys. Rev. B 80, 241411
] Published Wed Dec 16, 2009
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Luis Berbil-Bautista, Stefan Krause, Matthias Bode, Antonio Badía-Majós, César de la Fuente, Roland Wiesendanger, and José Ignacio Arnaudas
We report on studies of spin structures that appear around screw and edge dislocations in Dy (0001) films grown on W (110) substrates. By means of spin-polarized scanning-tunneling microscopy, we have observed the formation of vortexlike and lobe-shaped magnetic structures. We have studied the effec...
[Phys. Rev. B 80, 241408
] Published Mon Dec 14, 2009
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D. A. Siegel, S. Y. Zhou, F. El Gabaly, A. K. Schmid, K. F. McCarty, and A. Lanzara
The crystallographic symmetries and spatial distribution of stacking domains in graphene films on 6H-SiC(0001) have been studied by low-energy electron diffraction and dark-field imaging in a low-energy electron microscope. We find that the graphene diffraction spots from two and three atomic layers...
[Phys. Rev. B 80, 241407
] Published Thu Dec 10, 2009
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Recently published articles in Physical Review B. See the current issues for more. Superfluidity and superconductivity
A. Tsurumaki and Z. Hiroi
![]() [Phys. Rev. B 80, 220505
] Published Tue Dec 22, 2009
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P. M. R. Brydon
![]() [Phys. Rev. B 80, 224520
] Published Tue Dec 22, 2009
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Rinat Ofer and Amit Keren
![]() [Phys. Rev. B 80, 224521
] Published Tue Dec 22, 2009
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M. Schneider, G. Fuchs, K.-H. Müller, K. Nenkov, G. Behr, D. Souptel, and S.-L. Drechsler
The magnetic field dependence of the thermal conductivity κ of a HoNi2B2C single crystal (parallel to [110]; 2lt;T/Klt;10 ; μ0H≤0.4 T ) is reported. It exhibits a characteristic change in the slope of κ(T) at significantly lower temperatures (or lower fields) than the resistively...
[Phys. Rev. B 80, 224522
] Published Tue Dec 22, 2009
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Structure, structural phase transitions, mechanical properties, defects
Oswaldo Diéguez and Nicola Marzari
We have used first-principles calculations to study the structural, electronic, and thermodynamic properties of the three known forms of Rh-S chalcogenides: Rh2S3 , Rh3S4 , and Rh17S15 . Only the first of these materials of interest for catalysis had been studied previously within this approach. ...
[Phys. Rev. B 80, 214115
] Published Tue Dec 22, 2009
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C. M. Fang, M. A. van Huis, and H. W. Zandbergen
The iron carbide Fe7C3 exhibits two types of basic crystal structures, an orthorhombic (o-) form and a hexagonal (h-) one. First-principles calculations have been performed for the basic Fe7C3 forms and for the related θ-Fe3C cementite phase. Accurate total-energy calculations show that t...
[Phys. Rev. B 80, 224108
] Published Tue Dec 22, 2009
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Yu. A. Genenko, J. Glaum, O. Hirsch, H. Kungl, M. J. Hoffmann, and T. Granzow
Migration of charged point defects triggered by the local random depolarization field is shown to plausibly explain aging of poled ferroelectric ceramics providing reasonable time and acceptor concentration dependences of the emerging internal bias field. The theory is based on the evaluation of the...
[Phys. Rev. B 80, 224109
] Published Tue Dec 22, 2009
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Inhomogeneous, disordered, and partially ordered systems
Stefanie Thiem, Michael Schreiber, and Uwe Grimm
In this paper, we report results for the wave packet dynamics in a class of quasiperiodic chains consisting of two types of weakly coupled clusters. The dynamics are studied by means of the return probability and the mean-square displacement. The wave packets show anomalous diffusion in a stepwise p...
[Phys. Rev. B 80, 214203
] Published Tue Dec 22, 2009
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Zahra Naeimi and MirFaez Miri
We study the effects of particle size dispersion on the absorption spectrum of nonfractal random gas of particles and fractal cluster-cluster aggregates. We use the coupled-dipole equations to describe the interaction of particles with the external electromagnetic wave. We express the absorption in ...
[Phys. Rev. B 80, 224202
] Published Tue Dec 22, 2009
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Dynamics, dynamical systems, lattice effects, quantum solids
Jian-Sheng Wang, Xiaoxi Ni, and Jin-Wu Jiang
A generalized Langevin equation with quantum heat baths [quantum molecular dynamics (QMD)] for thermal transport is derived with the help of nonequilibrium Green’s function (NEGF) formulation. The exact relationship of the quasiclassical approximation to NEGF is demonstrated using Feynman diagrams...
[Phys. Rev. B 80, 224302
] Published Tue Dec 22, 2009
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Magnetism
Suman Mandal, S. Banerjee, and Krishnakumar S. R. Menon
The local defect structure of NiO nanoparticles was determined by extended x-ray absorption fine structure method. By using the bulk and surface sensitive characterization techniques, we are able to show that the vacancies mostly reside on the surface of the particles and the distribution of vacanci...
[Phys. Rev. B 80, 214420
] Published Tue Dec 22, 2009
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Peter Thalmeier
![]() [Phys. Rev. B 80, 214421
] Published Tue Dec 22, 2009
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E. Burzo, I. Balazs, L. Chioncel, E. Arrigoni, and F. Beiuseanu
We analyze the effects of doping holmium impurities into the full-Heusler ferromagnetic alloy Co2MnSi . Experimental results, as well as theoretical calculations within density functional theory in the local-density approximation generalized to include Coulomb correlation at the mean-field level sh...
[Phys. Rev. B 80, 214422
] Published Tue Dec 22, 2009
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J.-S. Zhou, J. B. Goodenough, J.-Q. Yan, J.-G. Cheng, K. Matsubayashi, Y. Uwatoko, and Y. Ren
The RVO3 perovskites undergo orbital ordering and orbital-flipping transitions as well as a spin ordering transition. However, the existing model of orbital ordering fails to explain the thermal conductivity, which remains poor and glassy in the orbitally ordered phase. The phonon thermal conducti...
[Phys. Rev. B 80, 224422
] Published Tue Dec 22, 2009
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Electronic structure: wide-band, narrow-band, and strongly correlated systems
Hitesh J. Changlani, Jesse M. Kinder, C. J. Umrigar, and Garnet Kin-Lic Chan
We describe correlator product states, a class of numerically efficient many-body wave functions to describe strongly correlated wave functions in any dimension. Correlator product states introduce direct correlations between physical degrees of freedom in a simple way, yet provide the flexibility t...
[Phys. Rev. B 80, 245116
] Published Tue Dec 22, 2009
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Semiconductors I: bulk
F. D. Brandão, M. V. B. Pinheiro, G. M. Ribeiro, G. Medeiros-Ribeiro, and K. Krambrock
The nonstoichiometry of the main structural phase of TiO2 (rutile) and its natural n -type conductivity is due to oxygen deficiency, which has been explained in terms of native defects, i.e., oxygen vacancies and titanium interstitials. While the latter has been unambiguously identified by electr...
[Phys. Rev. B 80, 235204
] Published Tue Dec 22, 2009
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O. Volnianska, P. Boguslawski, J. Kaczkowski, P. Jakubas, A. Jezierski, and E. Kaminska
Doping properties of Ag in ZnO were analyzed by first-principles calculations within both the local-density and generalized gradient approximations. The ionization energy of AgZn , about 0.2 eV, is comparable to that of the commonly used group-V acceptors, and is lower than that of two other IB s...
[Phys. Rev. B 80, 245212
] Published Tue Dec 22, 2009
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Surface physics, nanoscale physics, low-dimensional systems
Woo Kyun Kim and Michael L. Falk
Molecular dynamics simulations of frictional sliding in an atomic force microscope (AFM) show a clear dependence of superlubricity between incommensurate surfaces on tip compliance and applied normal force. While the kinetic friction vanishes for rigid tips and low normal force, superlubric behavior...
[Phys. Rev. B 80, 235428
] Published Tue Dec 22, 2009
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J. A. Driscoll and K. Varga
Field emission from carbon nanotubes is studied by propagating the electronic wave function in real time using time-dependent density-functional theory. Complex absorbing potentials have been employed to avoid artificial reflections from the boundaries and to allow long time simulations. Domain deco...
[Phys. Rev. B 80, 245431
] Published Tue Dec 22, 2009
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J. W. Klos, A. A. Shylau, I. V. Zozoulenko, Hengyi Xu, and T. Heinzel
We study the effects of the long-range disorder potential and warping on the conductivity and mobility of graphene ribbons using the Landauer formalism and the tight-binding p -orbital Hamiltonian. We demonstrate that as the length of the structure increases the system undergoes a transition from t...
[Phys. Rev. B 80, 245432
] Published Tue Dec 22, 2009
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R. A. Sepkhanov, M. V. Medvedyeva, and C. W. J. Beenakker
Spin precession has been used to measure the transmission time τ over a distance L in a graphene sheet. Since conduction electrons in graphene have an energy-independent velocity v , one would expect τ≥L/v . Here we calculate that τlt;L/v at the Dirac point ( =charge neutrality point)...
[Phys. Rev. B 80, 245433
] Published Tue Dec 22, 2009
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Kotaro Makino, Atsushi Hirano, Kentaro Shiraki, Yutaka Maeda, and Muneaki Hase
We have used a femtosecond pump-probe impulsive Raman technique to explore the ultrafast dynamics of micelle suspended single-walled carbon nanotubes (SWNTs) in various pH environments. The structures of coherent phonon spectra of the radial breathing modes exhibit significant pH dependence, to whic...
[Phys. Rev. B 80, 245428
] Published Mon Dec 21, 2009
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C. Seifert, D. Skuridina, X. Dou, K. Müllen, N. Severin, and J. P. Rabe
Double layers of a nanographene with defined molecular structure have been self-assembled at the interface between a molecular solution and the basal plane of graphite. Bias-dependent scanning tunnel microscopy allowed nondestructive imaging of the first or the second or both layers. While the first...
[Phys. Rev. B 80, 245429
] Published Mon Dec 21, 2009
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L. Schweitzer
The electronic properties of noninteracting particles moving on a two-dimensional bricklayer lattice are investigated numerically. In particular, the influence of disorder in form of a spatially varying random magnetic flux is studied. In addition, a strong perpendicular constant magnetic field B ...
[Phys. Rev. B 80, 245430
] Published Mon Dec 21, 2009
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Papers recently accepted for publication in Physical Review B (view more). Electronic structure: wide-band, narrow-band, and strongly correlated systems
Layered superconductors as negative refractive-index metamaterials
A. L. Rakhmanov, V. A. Yampolskii, J. A. Fan, Federico Capasso and Franco Nori
We analyze the use of layered superconductors as strongly anisotropic metamaterials, which can possess negative refractive index in a wide frequency range. Superconductors are of particular interest because they have the potential to support low losses, which is critical for applications such as super-resolution imaging. We show that low-Tc (s-wave) superconductors can be used to construct layered heterostructures with low losses for T << Tc. However, the real part of their in-plane effective permittivity is very large, making coupling into the structure difficult. Moreover, even at low temperatures, layered high-Tc superconductors have a large in-plane normal conductivity, producing large losses (due to d-wave symmetry). Therefore, it is difficult to enhance the evanescent modes in either low-Tc or high-Tc superconductors.
Accepted Tue Dec 22, 2009
Metal insulator transition through a semi Dirac point in oxide nanostructures: VO_{2} (001) layers confined within TiO_{2} - TeX Formatting Error: subscript (_) must be in math mode!
Victor Pardo and Warren E. Pickett
Multilayer (TiO2)m/(VO2)n nanostructures (d1 - d0 interfaces with no polar discontinuity) show a metal-insulator transition with respect to the VO2 layer thickness in first principles calculations. For n 5 layers, the system becomes metallic, while being insulating for n = 1 and 2. The metal-insulator transition occurs through a semi-Dirac point phase for n = 3 and 4, in which the Fermi surface is point-like and the electrons behave as massless along the zone diagonal in k-space and as massive fermions along the perpendicular direction. We provide an analysis of the evolution of the electronic structure through this unprecedented insulator-to-metal transition, and identify it as resulting from quantum confinement producing a non-intuitive orbital ordering on the V d1 ions, rather than being a specific oxide interface effect. Spin-orbit coupling does not destroy the semi-Dirac point for the calculated ground state, where the spins are aligned along the rutile c-axis, but it does open a substantial gap if the spins lie in the basal plane.
Accepted Tue Dec 22, 2009
Dielectric breakdown in a Mott insulator: Many body Schwinger Landau-Zener mechanism studied with a generalized Bethe ansatz
Takashi Oka and Hideo Aoki
The nonadiabatic quantum tunneling picture, which may be called the many-body Schwinger-Landau-Zener mechanism, for the dielectric breakdown of Mott insulators in strong electric fields is studied in the one-dimensional Hubbard model. The tunneling probability is calculated by a metod due to Dykhne-Davis-Pechukas with an analytical continuation of the Bethe-ansatz solution for excited states to a non-Hermitian case. A remarkable agreement with the time-dependent density matrix renormalization group result is obtained.
Accepted Tue Dec 22, 2009
Inhomogeneous, disordered, and partially ordered systems
Macroscopic localization lengths of vibrational normal modes in a heuristic DNA model
C. J. Paez, R. Rey Gonzalez and P. A. Schulz
In this work we study the localization of vibrational modes in heuristic models for disordered DNA like molecules. Within such approach, atomic groups are replaced by renormalized sites connected by effective springs. The oscillation amplitudes at each site are considered and the localization degree of the normal modes is analyzed by means of the participation ratio, as well as the relative fluctuation of an ensemble of disorder realizations for normal modes in different frequency ranges. The present results suggest that the dynamical properties at low frequencies are completely different for double strand structures compared to single strand ones. Irrespective to disorder, double strand molecules show normal modes with macroscopic localization lengths at low frequencies, for a wide range of spring constants considered in the literature, in contrast to the strong localization in single strands.
Accepted Tue Dec 22, 2009
Quantitative local environment characterization in amorphous oxides
Alexis Amezaga, Erik Holmstrom, Raquel Lizarraga, Eduardo Menendez Proupin, P. Bartolo Perez and Paolo Giannozzi
We perform density functional theory calculations of electronic core levels to obtain the tellurium X-ray photoelectron spectra in the amorphous solar energy materials CdTeOx (x=0.2,1,2, and 3). We quantify the distribution of local tellurium environments that sum up to the total two-peak structure in the experimental spectrum. The general trend is that the more oxygen neighbors tellurium has the bigger the shift of its core level energy. However, due to the structural complexity, the relation between the core level shift and the number of oxygen neighbors does not obey simple rules. Hence, we show the importance of computer simulations when interpreting X-ray photoelectron spectra in this system in particular, and amorphous oxides in general.
Accepted Tue Dec 22, 2009
Semiconductors I: bulk
Electronic properties of 3R-CuAlO_{2} under pressure: Three theoretical approaches - TeX Formatting Error: subscript (_) must be in math mode!
N. E. Christensen, A. Svane, R. Laskowski, B. Palanivel, P. Modak, A. N. Chantis, M. van Schilfgaarde and T. Kotani
The pressure variation of the structural parameters, u and c/a, of the delafossite CuAlO2 is calculated within the local density approximation (LDA). Further, the electronic structures as obtained by different approximations are compared: LDA, LDA+U, and a recently developed "Quasiparticle self-consistent GW"() approximation. The structural parameters obtained by the LDA agree very well with experiments, but, as expected, gaps in the formal band structure are underestimated as compared to optical experiments. The (in LDA too high lying) Cu-3d states can be down-shifted by LDA+U. The magnitude of the electric field gradient (EFG) as obtained within the LDA is far too small. It can be "fitted" to experiments in LDA+U, but a simultaneous adjustment of the EFG and the gap cannot be obtained with a single U value. QSGW yields reasonable values for both quantities. LDA and QSGW yield significantly different values for some of the band-gap deformation potentials, but calculations within both approximations predict that 3R-CuAlO2 remains an indirect-gap semiconductor at all pressures in its stability range 0 to 36 GPa, although the smallest direct gap has a negative pressure coefficient.
Accepted Tue Dec 22, 2009
Semiconductors II: surfaces, interfaces, microstructures, and related topics
Calculating the trap density of states in organic field effect transistors from experiment: A comparison of different methods
Wolfgang L. Kalb and Bertram Batlogg
The spectral density of localized states in the band gap of pentacene (trap DOS) was determined with a pentacene-based thin-film transistor from measurements of the temperature dependence and gate-voltage dependence of the contact-corrected field-effect conductivity. Several analytical methods to calculate the trap DOS from the measured data were used to clarify, if the different methods lead to comparable results. We also used computer simulations to further test the results from the analytical methods. Most methods predict a trap DOS close to the valence band edge that can be very well approximated by a single exponential function with a slope in the range of 50-60nbsp;meV and a trap density at the valence band edge of 2times;1021nbsp;eV-1cm-3. Interestingly, the trap DOS is always slightly steeper than exponential. An important finding is that the choice of the method to calculate the trap DOS from the measured data can have a considerable effect on the final result. We identify two specific simplifying assumptions that lead to significant errors in the trap DOS. The temperature-dependence of the band mobility should generally not be neglected. Moreover, the assumption of a constant effective accumulation layer thickness leads to a significant underestimation of the slope of the trap DOS.
Accepted Tue Dec 22, 2009
Using randomly distributed charges to create quantum dots
O. Makarovsky, A. G. Balanov, L. Eaves, A. Patane, R. P. Campion, C. T. Foxon and R. J. Airey
Using a combination of modelling and tunneling spectroscopy, we investigate how electrostatic potential fluctuations generated by randomly distributed ionised donors close to a quantum well can produce deep and strongly-confined quantum dot-like potential minima with a rich spectrum of zero-dimensional electronic energy levels. We consider different types of random distribution of donors and how the electronic properties can be controlled and investigated in appropriately-designed double barrier resonant tunneling diodes.
Accepted Tue Dec 22, 2009
Nonlinear photoluminescence spectra from a quantum dot cavity system: Interplay of pump induced stimulated emission and anharmonic cavity QED
Peijun Yao, P. K. Pathak, E. Illes, S. Hughes, S. Munch, S. Reitzenstein, P. Franeck, A. Loffler, T. Heindel, S. Hofling, L. Worschech and A. Forchel
We investigate the power-dependent photoluminescence spectra from a strongly coupled quantum dot-cavity system using a quantum master equation technique that accounts for incoherent pumping, pure dephasing, and fermion or boson statistics. Analytical spectra at the one-photon correlation level and the numerically exact multi-photon spectra for fermions are presented. We compare to recent experiments on a quantum dot - micropillar cavity system and show that an excellent fit to the data can be obtained by varying only the incoherent pump rates in direct correspondence with the experiments. Our theory and experiments together show convincing evidence for stimulated-emission induced broadening and anharmonic cavity-QED.
Accepted Tue Dec 22, 2009
Magneto optical properties of excitonic complexes of GaAs self assembled quantum dots
M. Abbarchi, T. Kuroda, T. Mano, K. Sakoda and M. Gurioli
We report a detailed experimental investigation of the magneto optical properties of different excitonic complexes (neutral exciton, neutral biexciton and charged exciton) confined in self-assembled GaAs/AlGaAs strain free quantum dots grown by droplet epitaxy, where all piezoelectric effects are lacking. We measured the Land#232; g factor and the diamagnetic coefficient g for several quantum dots spanning an interval of ~ 200 meV of the emission energy. The dependence of g factor and g on quantum dot size and shape is discussed together with a comparison with Stranski-Krastanov and fluctuation induced GaAs quantum dots, as well as with excitons confined in quantum wells.
Accepted Tue Dec 22, 2009
Optical fishnet metamaterials described by effective material parameters
Christoph Menzel, Thomas Paul, Carsten Rockstuhl, Thomas Pertsch, Sergei Tretyakov and Falk Lederer
Although optical metamaterials that show artificial magnetism are mesoscopic systems, they are frequently described in terms of effective material parameters. But due to intrinsic nonlocal (or spatially dispersive) effects it may be anticipated that this approach is usually only a crude approximation and is physically meaningless. In order to study the limitations regarding the assignment of effective material parameters, we introduce a technique to retrieve the frequency-dependent elements of the effective permittivity and permeability tensors for arbitrary angles of incidence and apply the method exemplarily to the fishnet metamaterial. It turns out that for the fishnet metamaterial, genuine effective material parameters can only be introduced if quite stringent constraints are imposed on the wavelength/unit cell size ratio. Unfortunately they are only met far away from the resonances that induce a magnetic response required for many envisioned applications of such a fishnet metamaterial. Our work clearly indicates that the mesoscopic nature and the related spatial dispersion of contemporary optical metamaterials that show artificial magnetism prohibits the meaningful introduction of conventional effective material parameters.
Accepted Tue Dec 22, 2009
Light intensity dependence of photocurrent gain in single crystal diamond detectors
Meiyong Liao, Xi Wang, Tokuyuku Teraji, Satoshi Koizumi and Yasuo Koide
The authors report on the photocurrent gain in a diamond photodetector that has two non-ohmic contacts connected back-to-back. This photocurrent gain strongly depends on both the deep-ultraviolet (DUV) light intensity and the applied voltage. In addition, the gain is accompanied by a slow response. The gain is observed to originate from a metal/diamond interface trap center. Numerical analysis discloses that the photocurrent-voltage characteristics follow thermionic-field emission tunneling at low DUV light intensity and field-emission tunneling at high DUV light intensity. The deep traps are thought to produce a thin interface barrier layer at the metal/diamond interface under DUV illumination, which is responsible for the tunneling processes.
Accepted Tue Dec 22, 2009
Inhomogeneous nuclear spin flips: Feedback mechanism between electronic states in a double quantum dot and the underlying nuclear spin bath
M. Stopa, J. J. Krich and A. Yacoby
We discuss a feedback mechanism between electronic states in a two-electron double quantum dot and the underlying nuclear spin bath. We analyze two pumping cycles for which this feedback provides a force for the Overhauser fields of the two dots to either equilibrate or diverge. Which of these effects is favored depends on the g-factor and Overhauser coupling constant of the material. The strength of the effect increases with the ratio of Overhauser coupling to electron exchange energy and also increases as the external magnetic field decreases.
Accepted Tue Dec 22, 2009
Magnetism
Direct imaging of domain wall interactions in Ni_{80}Fe_{20} planar nanowires - TeX Formatting Error: subscript (_) must be in math mode!
T. J. Hayward, M. T. Bryan, P. W. Fry, P. M. Fundi, M. R. J. Gibbs, D. A. Allwood, M.Y Im. and P. Fischer
We have investigated magnetostatic interactions between domain walls in Ni80Fe20 planar nanowires using magnetic soft X-ray microscopy and micromagnetic simulations. In addition to significant monopole-like attraction and repulsion effects we observe that there is coupling of the magnetization configurations of the walls. This is explained in terms of an interaction energy that depends not only on the distance between the walls, but also upon their internal magnetization structure.
Accepted Tue Dec 22, 2009
Phase diagram of magnetic nanodisks measured by scanning electron microscopy with polarization analysis
S. H. Chung, R. D. McMichael, D. T. Pierce and J. Unguris
We use Scanning Electron Microscopy with Polarization Analysis (SEMPA) to image the magnetic domain structures of individual ferromagnetic nanodisks with different diameters and thicknesses, and thereby determine the phase diagram of the magnetic ground states in these technologically important magnetic structures. Depending on the nanodisk dimensions, we observe magnetic structures based on one of three configurations: a single domain in-plane, a single domain out-of-plane, or a vortex state. By imaging the in-plane and out-of-plane magnetization components of identically prepared Ni80Fe15Mo5 nanodisks with diameters that range from 35 nm to 190 nm and with thicknesses that range from 10 nm to 65 nm, we are able to locate phase boundaries between the three different phases and the triple point. The phase boundaries are not sharply defined, however. Near the boundaries and especially near the triple point, we observe disks in a mixture of the different metastable ground phases, and we observe variations of the basic states, such as a tilted vortex configuration. A magnetic phase diagram generated by a micromagnetic simulation is found to be in good qualitative agreement with the phase diagram determined by the SEMPA measurements. The ability to determine the magnetic phases in sub-100 nm nanodisks enables tailoring material properties and geometry of nanodisks for various potential applications.
Accepted Tue Dec 22, 2009
Effect of electrical current pulses on domain walls in Pt/Co/Pt nanotracks with out of-plane anisotropy: Spin transfer torque versus Joule heating
M. Cormier, A. Mougin, J. Ferre, A. Thiaville, N. Charpentier, F. Piechon, R. Weil, V. Baltz and B. Rodmacq
The effect of electrical current pulses on magnetic domain walls is studied in a nanometer-scale magnetic track defined in a He+-irradiated Pt/Co(0.5nbsp;nm)/Pt film with out-of-plane anisotropy. Current pulses in a wide range of intensities and durations are shown to result either in track demagnetization, or in polarity-independent domain wall propagation, due to Joule heating during the current pulse. None of the expected spin transfer effects is shown to occur. To explain this, the spin-dependent current density distribution in the stack is evaluated, in the frame of an adapted Fuchs-Sondheimer model. The spin-polarized current density in the cobalt layer is shown to be unexpectedly low as compared to the charge current in the whole stack, which causes Joule heating. This is explained by a low electron transmission at Co/Pt interfaces, as is deduced from resistance measurements on a series of samples with different cobalt thicknesses. This leads us to emphasize that the balance between spin and total charge current densities should be carefully considered when addressing spin transfer torque effects.
Accepted Tue Dec 22, 2009
Raman signature of the U(1) Dirac spin liquid state in the spin-\frac{1}{2} kagome system - TeX Formatting Error: frac only valid in math mode
Win Kog Ho, ZhengXin Liu, Tai Ng Kai and Patrick A. Lee
We followed the Shastry-Shraiman formulation of Raman scattering in Hubbard systems and considered the Raman intensity profile in the spin-1/2 "perfect" kagom#233; lattice herbertsmithite ZnCu3(OH)6Cl2, assuming the ground state is well-described by the U(1) Dirac spin-liquid state. In the derivation of the Raman T-matrix, we found that the spin chirality term appears in the A2g channel in the kagom#233; lattice at the t4/(wi-U)3 order, but (contrary to the claims by Shastry and Shraiman) vanishes in the square lattice to that order. In the ensuing calculations on the spin-1/2 kagom#233; lattice, we found that the Raman intensity profile in the Eg channel is invariant under an arbitrary rotation in the kagom#233; plane, and that in all (A1g, Eg, and A2g) symmetry channels the Raman intensity profile contains broad continua that display power-law behaviors at low energy, with exponent approximately equal to 1 in the A2g channel and exponent approximately equal to 3 in the Eg and the A1g channels. For the A2g channel, the Raman profile also contains a characteristic 1/w singularity, which arose in our model from an excitation of the emergent U(1) gauge field.
Accepted Tue Dec 22, 2009
ac- and dc driven noise and I-V characteristics of magnetic nanostructures
O. A. Tretiakov and Aditi Mitra
We study a structure consisting of a ferromagnetic (F) layer coupled to two normal metal (N) leads. The system is driven out of equilibrium by the simultaneous application of external DC and AC voltages across the N/F/N structure. Using the Keldysh diagrammatic approach, and modeling the ferromagnet as a classical spin of size S >> 1, we derive the Langevin equation for the magnetization dynamics and calculate the noise correlator. We find that the noise has an explicit frequency dependence in addition to depending on the characteristics of the AC and DC drive. Further, we calculate the current-voltage characteristics of the structure to O(1/S2) and find that the nonequilibrium dynamics of the ferromagnetic layer gives rise to corrections to the current that are both linear and nonlinear in voltage.
Accepted Tue Dec 22, 2009
Relaxation mechanism for ordered magnetic materials
C. Vittoria, S. D. Yoon and A. Widom
We have formulated a relaxation mechanism for ferrites and ferromagnets (insulators and metals) whereby the coupling between the magnetic motion and lattice is based purely on continuum arguments concerning magnetostriction. This theoretical approach contrasts with previous mechanisms based on microscopic formulations of spin-phonon interactions employing a discrete lattice. Our model explains for the first time the scaling of the intrinsic ferromagnetic resonance linewidth with frequency, with temperature { 1/Ms(T) } and the anisotropic nature of magnetic relaxation in ordered magnetic materials. Here, Ms(T) is the thermal saturation magnetization. Without introducing adjustable parameters, our model is in reasonable quantitative agreement with experimental measurements of the intrinsic magnetic resonance linewidths of important class of ordered magnetic materials including both insulators and metals.
Accepted Tue Dec 22, 2009
Origin of ferromagnetism in molybdenum dioxide from ab initio calculations
Jawad Nisar, Xiangyang Peng and Rajeev Ahuja
We have performed spin polarized calculations of the unexpected ferromagnetism (FM) in ultrathin films of molybdenum dioxide (MoO2) within the framework of density functional theory. It is found that the ideal bulk MoO2 is metallic and non-magnetic. Bulk MoO2 with Mo vacancy, O vacancy, Mo interstitial or O interstitial remains to be non-magnetic. Using slab calculation, we observed ferromagnetism in both oxygen rich and poor MoO2 (100) surfaces with average surface magnetic moment 1.53 and 0.69 mu B per surface Mo atom, respectively. The partial density of states of surface Mo atom at the Fermi level (EF) is much larger than that of the Mo atom in the center of the slab and in bulk MoO2, which indicates that ferromagnetism in surface (100) is due to Stoner instability. Enrichment of oxygen at the surface is found to be more favorable for ferromagnetism in MoO2 (100). The 2p-states of surface oxygen atoms are significantly hybridized with the 4d states of Mo atoms and are appreciably spin-polarized.
Accepted Tue Dec 22, 2009
Surface physics, nanoscale physics, low-dimensional systems
Electron phonon coupling in graphene antidot lattices: An indication of polaronic behavior
Nenad Vukmirovic, Vladimir M. Stojanovic and Mihajlo Vanevic
We study graphene antidot lattices - superlattices of perforations (antidots) in a graphene sheet - using a model that accounts for the phonon-modulation of the p-electron hopping integrals. We calculate the phonon spectra of selected antidot lattices using two different semi-empirical methods. Based on the adopted model, we quantify the nature of charge carriers in the system by computing the quasiparticle weight due to the electron-phonon interaction for an excess electron in the conduction band. We find a very strong phonon-induced renormalization, with the effective electron masses exhibiting nonmonotonic dependence on the superlattice period for a given antidot diameter. Our study provides an indication of polaronic behavior and points to the necessity of taking into account the inelastic degrees of freedom in future studies of transport in graphene antidot lattices.
Accepted Tue Dec 22, 2009
Spatiotemporal dynamics of optically generated electron hole excitations in single walled carbon nanotubes
J. H. Gronqvist, M. Hirtschulz, A. Knorr and M. Lindberg
A method for studying spatially and temporally resolved many-body dynamics of charge carriers in carbon nanotubes is presented. We derive coherent, spatially inhomogeneous Bloch equations for charge carrier dynamics in an optically excited carbon nanotube. By solving the equations of motion numerically under spatially inhomogeneous excitation conditions, we also demonstrate a striking difference in carrier drift velocity for excitation at the exciton resonance and above the band edge.
Accepted Tue Dec 22, 2009
Superfluidity and superconductivity
Nonlocal transport in normal metal/superconductor hybrid structures: Role of interference and interaction
J. Brauer, F. Hubler, M. Smetanin, D. Beckmann and H. v.Lohneysen
We have measured local and non-local conductance of mesoscopic normal-metal/superconductor hybrid structures fabricated by e-beam lithography and shadow evaporation. The sample geometry consists of a superconducting aluminum bar with two normal-metal wires forming tunnel contacts to the aluminum at distances of the order of the superconducting coherence length. We observe subgap anomalies in both local and non-local conductance that quickly decay with magnetic field and temperature. For the non-local conductance both positive and negative signs are found as a function of bias conditions, indicating at a competition of crossed Andreev reflection and elastic cotunneling. Our data suggest that the signals are caused by a phase-coherent enhancement of transport rather than dynamical Coulomb blockade.
Accepted Tue Dec 22, 2009
Scanning SQUID microscopy of vortex clusters in multiband superconductors
Taichiro Nishio, Vu Hung Dao, Qinghua Chen, Liviu F. Chibotaru, Kazuo Kadowaki and Victor V. Moshchalkov
In a new type of superconductors, type-1.5 materials, vortices emerge in clusters, which make characteristic evolution with increasing magnetic field. These novel vortex clusters and their field dependence are directly visualized by scanning SQUID microscopy at very low vortex densities in MgB2 single crystals. Our observations are elucidated by simulations based on a two-gap Ginzburg-Landau (GL) theory in the type-1.5 regime.
Accepted Tue Dec 22, 2009
Kink antikink vortex transfer in periodic plus-random pinning potential: Theoretical analysis and numerical experiments
W. V. Pogosov, H. J. Zhao, V. R. Misko and F. M. Peeters
The influence of random pinning on the vortex dynamics in a periodic square potential under an external drive is investigated. Using numerical experiments and theoretical approach, we found several dynamical regimes of vortex motion that are different from the ones for a regular pinning potential. Vortex transfer is controlled by kinks and antikinks, which either preexist in the system or appear spontaneously in pairs and then propagate. When kinks and antikinks collide, they annihilate. We provide clear physical interpretations of the observed features.
Accepted Tue Dec 22, 2009
Rinat Ofer and Amit Keren
We describe two different nuclear quadrupole resonance (NQR) based techniques, designed to measure the local asymmetry of the internal electric field gradient η and the tilt angle α of the main NQR principal axis ẑ from the crystallographic axis ĉ . These techniques use the dependence o...
[Phys. Rev. B 80, 224521
] Published Tue Dec 22, 2009
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P. M. R. Brydon
We examine the appearance of a spontaneous bulk spin current in a triplet superconductor in contact with a metallic ferromagnet. The spin current results from the spin flip of Cooper pairs upon reflection from the interface with the ferromagnet, and is shown to display strong similarities to the spo...
[Phys. Rev. B 80, 224520
] Published Tue Dec 22, 2009
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A. Tsurumaki and Z. Hiroi
[Phys. Rev. B 80, 220505
] Published Tue Dec 22, 2009
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Peter Thalmeier
The acoustic Faraday rotation in the 4f paramagnet Tb3Ga5O12 has recently been observed by Sytcheva (unpublished). As in earlier examples the rotation angle per unit length of transverse acoustic modes was found to depend linearly on sound frequency. Existing theories for this effect consistent...
[Phys. Rev. B 80, 214421
] Published Tue Dec 22, 2009
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M. Le Tacon, T. R. Forrest, Ch. Rüegg, A. Bosak, A. C. Walters, R. Mittal, H. M. Rønnow, N. D. Zhigadlo, S. Katrych, J. Karpinski, J. P. Hill, M. Krisch, and D. F. McMorrow
[Phys. Rev. B 80, 220504
] Published Mon Dec 21, 2009
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Mathias Duckheim, Dmitrii L. Maslov, and Daniel Loss
We derive boundary conditions for the electrically induced spin accumulation in a finite, disordered two-dimensional semiconductor channel. While for dc electric fields these boundary conditions select spatially constant spin profiles equivalent to a vanishing spin-Hall effect, we show that an in-pl...
[Phys. Rev. B 80, 235327
] Published Fri Dec 18, 2009
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J. K. Asbóth, A. R. Akhmerov, A. C. Berceanu, and C. W. J. Beenakker
We calculate the transmission of electrons and holes between two normal-metal (N) electrodes, separated over a distance L by an impurity-free superconductor (S) with d -wave symmetry of the order parameter. Nodal lines of vanishing excitation gap form ballistic conduction channels for coupled ele...
[Phys. Rev. B 80, 224517
] Published Fri Dec 18, 2009
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L. Benfatto, E. Cappelluti, and C. Castellani
In this paper we provide a comprehensive analysis of different properties of pnictides both in the normal and superconducting state, with a particular focus on the optimally doped Ba1−xKxFe2As2 system. We show that, by using the band dispersions experimentally measured by angle-resolved photoemi...
[Phys. Rev. B 80, 214522
] Published Fri Dec 18, 2009
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V. V. Solovyev, S. Schmult, W. Dietsche, and I. V. Kukushkin
[Phys. Rev. B 80, 241310
] Published Thu Dec 17, 2009
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Shinichi Watanabe, Ryusuke Kondo, Seiichi Kagoshima, and Ryo Shimano
[Phys. Rev. B 80, 220408
] Published Thu Dec 17, 2009
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