Scanning Tunneling Microscopy Studies of Layered Correlated Electron Systems: Transition Metal Dichalcogenides and Iridates

Graduate Thesis Or Dissertation

Citations

Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/rr171x267

Abstract

Strongly correlated electron problems, including high temperature superconductivity, colossal magneto-resistivity, charge-density wave, heavy fermion phenomena, etc., have been major research focuses in condensed-matter physics for the past several decades. Involvements of and competitions between different degrees of freedom and energy scales present considerable difficulties for understanding these problems. In this thesis, I have used home-built variable-temperature high resolution (spatial and energy) spectroscopic imaging scanning tunneling microscopes (SI-STM) to study the topography and the local single-particle tunneling spectroscopy in a family of two-dimensional charge-density wave (2D-CDW) materials (TaSe2, TaS2, and NbSe2) and in a newly discovered 5d Mott insulator Sr2IrO4 with strong spin-orbit coupling. In the 2D-CDW materials, we have shown the strong lattice distortion and weak electron modulation accompanying CDW transition, directly opposite to Peierls mechanism. We have also discovered that the 2D-CDW transitions in TaSe2 and TaS2 show involvement of the orbital degree of freedom, shedding light on a long standing puzzle with their electrical resistivity anomalies. In the novel 5d Mott insulator Sr2IrO4 we have found a large insulating gap of 620 meV, indicating a stronger-than-expected correlation effect for a 5d electron system.

Creator