Fermi surface nesting in several transition metal dichalcogenides

TL;DR

This study uses ARPES to analyze the Fermi surface nesting in transition metal dichalcogenides, revealing complex relationships between nesting vectors, susceptibility, and charge density wave transitions, with implications for doping effects.

Contribution

It provides a detailed comparison of Fermi surface nesting and CDW behavior in several TMDCs using ARPES and tight-binding models, highlighting the non-coincidence of nesting and ordering vectors.

Findings

Nesting vectors are close but do not exactly match CDW wave vectors.

Nesting persists across the CDW transition temperature.

Doping with Cu does not eliminate nesting, suggesting potential for enhanced CDW instability.

Abstract

By means of high-resolution angle resolved photoelectron spectroscopy (ARPES) we have studied the fermiology of 2H transition metal dichalcogenide polytypes TaSe2, NbSe2, and Cu0.2NbS2. The tight-binding model of the electronic structure, extracted from ARPES spectra for all three compounds, was used to calculate the Lindhard function (bare spin susceptibility), which reflects the propensity to charge density wave (CDW) instabilities observed in TaSe2 and NbSe2. We show that though the Fermi surfaces of all three compounds possess an incommensurate nesting vector in the close vicinity of the CDW wave vector, the nesting and ordering wave vectors do not exactly coincide, and there is no direct relationship between the magnitude of the susceptibility at the nesting vector and the CDW transition temperature. The nesting vector persists across the incommensurate CDW transition in TaSe2 as a function of temperature despite the observable variations of the Fermi surface geometry in this temperature range. In Cu0.2NbS2 the nesting vector is present despite different doping level, which lets us expect a possible enhancement of the CDW instability with Cu-intercalation in the CuxNbS2 family of materials.