Charge-density waves in rubidium blue bronze Rb_0.3MoO₃ observed by scanning tunneling microscopy

Using low-temperature scanning tunneling microscopy under ultrahigh vacuum, high-resolution topographical images were obtained on a cleaved (2̅ 01) surface of a rubidium blue bronze (Rb_0.3MoO₃) single crystal. Only molecular lattice was observed at room temperature. At temperatures of 63 and 78 K, well below the charge density wave (CDW) transition temperature in Rb_0.3MoO₃, underlying molecular lattice and CDW superlattice were observed simultaneously in topographical constant current images. The amplitude of the CDW modulation is about 0.1 Å along b. On the Fourier transform of these images, both main Bragg spots (molecular lattice related) and satellite spots (CDW superlattice related) coexist unambiguously. The average projection of the CDW wave vector on the (2̅ 01) surface deduced by Fourier transform is consistent with the bulk value obtained previously by other techniques. Our results show clearly that the Peierls phase of the quasi-one-dimensional blue bronze can be studied by STM.