Physical Review B

The depth-resolved x-ray magnetic circular dichroism (XMCD) technique was applied to observe the interfacial and inner magnetic moments in CoFe/MgO and Co₂MnSi(CMS)/MgO. The magnetic moments of the real interface region (two monolayers from the interface) and the inner layers were separately analyze...

We investigate the interaction of femtosecond laser pulses with spins including relativistic corrections. The time-ordered magneto-optical signals corresponding to a pump-probe configuration are calculated in the case of one electron submitted to a magnetic field and evolving in eight levels of the ...

The dynamics of a magnetic vortex are influenced profoundly by nonlinear effects at large and small amplitudes. For example, a strongly driven magnetic vortex is unstable with respect to internal deformation, leading to reversal of its core magnetization. At small amplitudes, a nonlinear response is...

Here we show that the 2.80(8)μ_B Fe⁻¹ block antiferromagnetic order of BaFe₂Se₃ transforms into stripe antiferromagnetic order in KFe₂Se₃ with a decrease in moment to 2.1(1)μ_B Fe⁻¹. This reduction is larger than expected from the change in electron count from Ba²⁺ to K⁺, and occurs with the loss of t...

We report specific heat capacity measurements on a LiFeAs single crystal at temperatures down to 400 mK and magnetic fields up to 9 T. A small specific heat jump at T_c and finite residual density of states at T=0 K in the superconducting (SC) state indicate that there are strong unitary scatterers t...

We have measured the temperature dependence of the absolute value of the magnetic penetration depth λ(T) in a Ca₁₀(Pt₃As₈)[(Fe_1−xPt_x)₂As₂]₅ (x=0.097) single crystal using a low-temperature magnetic force microscope (MFM). We obtain λ_ab(0)≈1000 nm via extrapolating the data to T=0. This large λ and p...

We have determined the Fermi surface in KOs₂O₆ (T_c=9.6 K and B_c2∼32 T) via de Haas–van Alphen (dHvA) oscillation measurements and a band structure calculation. We find effective masses up to 26(1)m_e (m_e is the free electron mass), which are unusually heavy for compounds where the mass enhancement is...

The multipocket Fermi surfaces of iron-based superconductors promote pairing states with both extended s-wave and d-wave symmetry. We argue that the competition between these two order parameters could lead to a time-reversal symmetry-breaking state with s+id pairing symmetry in the iron-based super...

We present highly subwavelength magnetic metamaterials designed for operation at radio frequencies (rf's). A dual-layer design consisting of independent planar spiral elements enables the experimental demonstration of a unit cell size (a) that is ∼700 times smaller than the resonant wavelength (λ₀)....

We describe the crystal growth, crystal structure, and basic electrical properties of Bi₂Te_1.6S_1.4, which incorporates both S and Te in its tetradymite quintuple layers in the motif -[Te_0.8S_0.2]-Bi-S-Bi-[Te_0.8S_0.2]-. This material differs from other tetradymites studied as topological insulators due...

Employing a classical density-functional description of liquid environments, we introduce a rigorous method for the diffusion quantum Monte Carlo calculation of free energies and thermodynamic averages of solvated systems that requires neither thermodynamic sampling nor explicit solvent electrons. W...

Transition-metal oxides with partially filled d shells are typically Mott or charge-transfer insulators with notoriously poor transport properties due to large effective electron/hole masses or due to carrier self-trapping. Employing band-structure calculations and ab initio small-polaron theory for...

Using band symmetry analysis and density functional theory calculations, we reveal the origin of why oxygen vacancy (V_O) energy levels are shallow in some ABO₃ perovskites, such as SrTiO₃, but are deep in some others, such as LaAlO₃. We show that this diverse behavior can be explained by the symmetr...

Studies have shown that many-body interactions among semiconductor excitons can produce distinct features in two-dimensional optical spectra. However, to the best of our knowledge, the dynamics of many-body interactions have not been measured in two-dimensional (2D) spectroscopy studies. Here we mea...

We consider signatures of Abelian and non-Abelian quasiparticle statistics in quantum Hall Fabry-Perot interferometers. When quasiparticles enter and exit the interference cell, for instance due to glassy motion in the dopant layer, the anyonic phase can be observed in phase jumps. In the case of th...

When the dimension of a solid structure is reduced, there will be two emerging effects, quantum confinement and surface effect, which dominate at nanoscale. Based on first-principles calculations, we demonstrate that due to an intriguing interplay between these two dominating effects, the topologica...

We have used first-principles simulations based on time-dependent density functional theory to show that short laser pulses can trigger preferential hydrogen desorption from the upper or lower side of suspended graphane (H-terminated graphene). This control is achieved by using intense ultrashort p-...

We examine the quantum Hall effect in bilayer graphene grown on Cu substrates by chemical vapor deposition. Spatially resolved Raman spectroscopy suggests a mixture of Bernal (A-B) stacked and rotationally faulted (twisted) domains. Magnetotransport measurements performed on bilayer domains with a w...

We present a systematic search for low-energy metastable superhard carbon allotropes by using the recently developed evolutionary metadynamics technique. It is known that cold compression of graphite produces an allotrope at 15–20 GPa. Here we look for all low-enthalpy structures accessible from gra...

Active nanoplasmonic metamaterials support bright and dark modes that compete for gain. Using a Maxwell-Bloch approach incorporating Langevin noise we study the lasing dynamics in an active nanofishnet structure. We report that lasing of the bright negative-index mode is possible if the higher-Q dar...

It is widely believed that carrier-density inhomogeneities (“electron-hole puddles”) in single-layer graphene on a substrate such as quartz are due to charged impurities located close to the graphene sheet. Here we demonstrate by using a Kohn-Sham-Dirac density-functional scheme that corrugations in...

Gapless edge modes hosted by chirally stacked trilayer graphene display unique features when a bulk gap is opened by applying an interlayer potential difference. We show that trilayer graphene with half-integer valley Hall conductivity leads to unbalanced edge modes at opposite zigzag boundaries, re...

We present a study of the second-order nonlinear optical properties of metal-based metamaterials. A hydrodynamic model for electronic response is used, in which nonlinear surface contributions are expressed in terms of the bulk polarization. The model is in good agreement with published experimental...

By eliminating normal fabrication processes, we preserve the bulk insulating state of calcium-doped Bi₂Se₃ single crystals in suspended nanodevices, as indicated by the activated temperature dependence of the resistivity at low temperatures. We perform low-energy electron beam irradiation (<16 ke...

Hydrogenation of deuterium-intercalated quasi-free-standing monolayer graphene on SiC(0001) is obtained and studied with low-energy electron diffraction and high-resolution electron energy loss spectroscopy. While the carbon honeycomb structure remains intact, it is shown that a significant band gap...

We report the results of spin-resolved small-angle neutron scattering (SANS) experiments on the two-phase nanocrystalline alloy NANOPERM. At a saturating applied magnetic field of 1.27 T we observe a cross-shaped angular anisotropy in the non-spin-flip SANS cross section Σ⁺⁺. This feature—for this c...

The depth-resolved x-ray magnetic circular dichroism (XMCD) technique was applied to observe the interfacial and inner magnetic moments in CoFe/MgO and Co₂MnSi(CMS)/MgO. The magnetic moments of the real interface region (two monolayers from the interface) and the inner layers were separately analyze...

We investigate the interaction of femtosecond laser pulses with spins including relativistic corrections. The time-ordered magneto-optical signals corresponding to a pump-probe configuration are calculated in the case of one electron submitted to a magnetic field and evolving in eight levels of the ...

The integrated power and linewidth of a propagating and a self-localized spin-wave mode excited by spin-polarized current in an obliquely magnetized magnetic nanocontact are studied experimentally as functions of the angle θ_e between the external bias magnetic field and the nanocontact plane. It is ...

We study the effect of a time-dependent driving field with a high amplitude on a system composed of two coupled qubits (two-level systems). Using the rotating-wave approximation (RWA) makes it possible to find simple conditions for resonant excitation of the four-level system. We find that the reson...

Motivated by the recent experiment in multilayered cuprate superconductors reporting the enhancement of antiferromagnetic order below the superconducting transition temperature, we study the proximity effect of the antiferromagnetic correlation in a bilayer system and also examine the possibility of...

We report specific heat capacity measurements on a LiFeAs single crystal at temperatures down to 400 mK and magnetic fields up to 9 T. A small specific heat jump at T_c and finite residual density of states at T=0 K in the superconducting (SC) state indicate that there are strong unitary scatterers t...

We have measured the temperature dependence of the absolute value of the magnetic penetration depth λ(T) in a Ca₁₀(Pt₃As₈)[(Fe_1−xPt_x)₂As₂]₅ (x=0.097) single crystal using a low-temperature magnetic force microscope (MFM). We obtain λ_ab(0)≈1000 nm via extrapolating the data to T=0. This large λ and p...

Several populations of Cu spherical nanoparticles grown in a silicate glass at different temperatures with respect to the glass transition temperature were studied using high-resolution, low-frequency Raman scattering and optical absorption. The analysis of the spectra shows that the annealing of th...

We report on the strong interaction between graphene and intercalated cobalt revealed by scanning tunneling spectroscopy (STS). A significant difference between pristine graphene and Co-intercalated graphene is identified at high bias voltages in the regime of field emission. For MLg/Co/Pt a resonan...

When the dimension of a solid structure is reduced, there will be two emerging effects, quantum confinement and surface effect, which dominate at nanoscale. Based on first-principles calculations, we demonstrate that due to an intriguing interplay between these two dominating effects, the topologica...

We have used first-principles simulations based on time-dependent density functional theory to show that short laser pulses can trigger preferential hydrogen desorption from the upper or lower side of suspended graphane (H-terminated graphene). This control is achieved by using intense ultrashort p-...

We examine the quantum Hall effect in bilayer graphene grown on Cu substrates by chemical vapor deposition. Spatially resolved Raman spectroscopy suggests a mixture of Bernal (A-B) stacked and rotationally faulted (twisted) domains. Magnetotransport measurements performed on bilayer domains with a w...

We study theoretically the return probability experiment, which is used to measure the dephasing time T₂^*, in a double quantum dot (DQD) in semiconducting carbon nanotubes with spin-orbit coupling and disorder-induced valley mixing. Dephasing is due to hyperfine interaction with the spins of the ¹³C...

Up to now, the crystallographic structure of the magnetoelectric perovskite EuTiO₃ has been considered to remain cubic down to low temperature. Here we present high-resolution synchrotron x-ray powder-diffraction data showing the existence of a structural phase transition, from cubic Pm-3m to tetrag...

We report an experimental and theoretical study of antimony oxide (Sb₂O₃) in its cubic phase (senarmontite) under high pressure. X-ray diffraction and Raman scattering measurements up to 18 and 25 GPa, respectively, have been complemented with ab initio total-energy and lattice-dynamics calculations...

We present a theory of the quantum Griffiths phases associated with the ferromagnetic quantum phase transition in disordered metals. For Ising spin symmetry, we study the dynamics of a single rare region within the variational instanton approach. For Heisenberg symmetry, the dynamics of the rare reg...

We study the ground-state properties of a system of identical classical Coulombic point particles, evenly distributed between two equivalently charged parallel plates at distance d; the system as a whole is electroneutral. It was previously shown that upon increasing d from 0 to ∞, five different st...

Responses from one-dimensional magnetophotonic crystals terminated by gold layers have been studied experimentally. Such a plasmonic magnetophotonic crystal slab supported an optical resonance (optical Tamm state) originating from the periodicity of the magnetophotonic crystal and a surface plasmon ...

In the context of a gas of ultracold atoms with effective spin S=3/2 confined to an elongated trap, we study the one-dimensional Fermi gas interacting via an attractive δ-function potential within the grand-canonical ensemble. The particles can be either unbound or clustered in bound states of two, ...

We present ab initio calculations of the skew-scattering contribution to the spin Hall effect for freestanding fcc Au(111) films. Their thickness is varied between 1 and 32 monolayers, and Pt atoms are considered as substitutional impurities and adatoms. The obtained spin Hall angle drastically chan...

The concept of dynamical symmetries is used for formulation of the renormalization group approach to the Kondo effect in the Anderson model with repulsive and attractive interaction U in the Kondo and mixed valence regimes. It is shown that the generic local dynamical symmetry of the Anderson Hamilt...

Using ab initio calculations, we have identified stable group-V dopant-vacancy complexes complexes in ZnO consisting of interstitial dopants surrounded by three V_Zn (D_I-3V_Zn with D=P, As, or Sb). In contradiction with previous reports, our calculations show that the acceptor level of group-V dopant–...

Light-matter coupling is investigated by rotating, by an angle θ, the polarization of linearly polarized microwaves with respect to the long axis of GaAs/AlGaAs Hall bar electron devices. At low microwave power P experiments show a strong sinusoidal variation in the diagonal resistance R_xx vs θ at t...

Phenomenological models suggest that thin epitaxial SrTiO₃ films on silicon will exhibit ferroelectric behavior as a result of compressive strain. However, such models do not include atomic-scale interface effects, which can dramatically alter the predicted behavior. In this paper, we use density fu...

We present a theory of the quantum Griffiths phases associated with the ferromagnetic quantum phase transition in disordered metals. For Ising spin symmetry, we study the dynamics of a single rare region within the variational instanton approach. For Heisenberg symmetry, the dynamics of the rare reg...

We have performed broadband zero-field and magneto-infrared spectroscopy of the three dimensional topological insulator Bi_0.91Sb_0.09. The zero-field results allow us to measure the value of the direct band gap between the conducting L_a and valence L_s bands. Under applied field in the Faraday geometr...

SrPt₂As₂ single crystals with CaBe₂Ge₂-type structure were synthesized by self-melting technique. X-ray diffraction, transmission electron microscopy, electrical resistivity, magnetic susceptibility, specific heat, and optical spectroscopy measurements were conducted to elucidate the properties of S...

We present highly subwavelength magnetic metamaterials designed for operation at radio frequencies (rf's). A dual-layer design consisting of independent planar spiral elements enables the experimental demonstration of a unit cell size (a) that is ∼700 times smaller than the resonant wavelength (λ₀)....

The phantom force is an apparently repulsive force, which can dominate the atomic contrast of an AFM image when a tunneling current is present. We described this effect with a simple resistive model, in which the tunneling current causes a voltage drop at the sample area underneath the probe tip. Be...

We present ac susceptibility and specific-heat measurements taken on samples of LiHo_xY_1−xF₄ in the dilute limit: x=0.018, 0.045, 0.080, and 0.12. Susceptibility measurements show glassy behavior including wide absorption spectra that continually broaden with decreasing temperature. Dynamical scaling...

The competition between intertube hopping processes and density-density interactions is investigated in one-dimensional quantum dipolar bosons systems of N coupled tubes at zero temperature. Using a phenomenological bosonization approach, we show that the resulting competition leads to an exotic qua...

We show that a three-dimensional topological insulator doped with magnetic impurities in the bulk can have a regime where the surface is magnetically ordered but the bulk is not. This is in contrast to conventional materials where bulk ordered phases are typically more robust than surface ordered ph...

We derive an approximate analytical solution of the self-consistency equations of the bosonic dynamical mean-field theory (B-DMFT) in the strong-coupling limit. The approach is based on a linked-cluster expansion in the hybridization function of normal bosons around the atomic limit. The solution is...

Employing a classical density-functional description of liquid environments, we introduce a rigorous method for the diffusion quantum Monte Carlo calculation of free energies and thermodynamic averages of solvated systems that requires neither thermodynamic sampling nor explicit solvent electrons. W...

Using ultrahigh magnetic fields up to 170 T and polarized midinfrared radiation with tunable wavelengths from 9.22 to 10.67 μm, we studied cyclotron resonance in large-area graphene grown by chemical vapor deposition. Circular polarization dependent studies reveal strong p-type doping for as-grown g...

We systematically investigate magnetic reversal of permalloy islands in a square spin-ice geometry with in situ Lorentz microscopy. Differential phase imaging reveals the presence of a flux channel similar to a Dirac string between the magnetic charge monopoles during the reversal. Analysis of the p...

A number of recent experiments have used torsional oscillators to study the behavior of solid helium. The oscillator frequencies increased at temperatures below 200 mK, an effect attributed to decoupling of a fraction of the helium mass—the signature of a “supersolid” phase. However, helium's shear ...

It has been suggested that after being gapped by a small symmetry-breaking field, the Majorana quasiparticles localized on the surface of a class DIII topological insulator will exhibit a thermal Hall effect that arises from a gravitational Chern-Simons term. We critically examine this idea, and arg...

Superlattices (SLs) in monolayer and bilayer graphene, formed by spatially periodic potential variations, lead to a modified bandstructure with extra finite-energy and zero-energy Dirac fermions with tunable anisotropic velocities. We theoretically show that transport in a weak perpendicular (orbita...

We have experimentally studied the nonlinear nature of electrical conduction in monolayer graphene devices on silica substrates. This nonlinearity manifests itself as a nonmonotonic dependence of the differential resistance on applied dc voltage bias across the sample. At temperatures below ∼70 K, t...

We investigate the pairing in iron pnictides in the coexistence phase, which displays both superconducting and antiferromagnetic orders. By solving the pairing problem on the Fermi surface reconstructed by long-range magnetic order, we find that the pairing interaction necessarily becomes angle depe...

We study the Anderson impurity problem in a mesoscopic setting, namely the “Anderson box,” in which the impurity is coupled to finite reservoir having a discrete spectrum and large sample-to-sample mesoscopic fluctuations. Note that both the weakly coupled and strong coupling Anderson impurity probl...

Electron doping of a 122-type iron pnictide BaFe₂As₂ by substituting the Ba site with an aliovalent ion (indirect doping), which had been unsuccessful by conventional solid-state synthesis methods, was achieved by a nonequilibrium film growth process. The substitution with La was substantiated by a ...

The Heusler-derived multiferroic alloy Ni_50−xCo_xMn₄₀Sn₁₀ has recently been shown to exhibit, at just above room temperature, a highly reversible martensitic phase transformation with an unusually large magnetization change. In this work the nature of the magnetic ordering above and below this transf...

The low-temperature magnetic behavior of the double-layered ruthenate Sr₃Ru₂O₇, as grown from a eutectic Sr₂RuO₄-Sr₃Ru₂O₇ system, was investigated via zero- and transverse-field muon-spin rotation. The gradual increase of the muon relaxation rate observed below 2.5 K, even in the absence of applied ...

Highly sp³-bonded, nearly hydrogen-free carbon-based materials can exhibit extremely low friction and wear in the absence of any liquid lubricant, but this physical behavior is limited by the vapor environment. The effect of water vapor on friction and wear is examined as a function of applied norma...

We investigate the magnetic polarization of the Ir 5d dopant states in the pnictide superconductor Ba(Fe_1−xIr_x)₂As₂ with x=0.027(2) using Ir L₃ edge x-ray resonant magnetic scattering (XRMS). Despite the fact that doping partially suppresses the antiferromagnetic transition, we find that magnetic or...

Magnetic properties of YbAl₃C₃ with the hexagonal ScAl₃C₃-type structure have been investigated by the magnetization (M) and specific-heat (C) measurements under magnetic fields (H). YbAl₃C₃ is reported to show a spin-gap state, which is considered to be ascribed to a magnetic dimer formed in the or...

We report a systematic study of the hyperfine interaction between the electron spin of a single nitrogen-vacancy (NV) defect in diamond and nearby ¹³C nuclear spins, by using pulsed electron-spin resonance spectroscopy. We isolate a set of discrete values of the hyperfine coupling strength ranging f...