Competing charge density waves and temperature-dependent nesting in 2H-TaSe2

TL;DR

This study uses high-resolution x-ray diffraction to explore the complex charge density wave phases in 2H-TaSe2, revealing temperature-dependent competing orders and a non-monotonic evolution of the Fermi surface nesting vector.

Contribution

It provides detailed experimental evidence of multi-q superstructures and temperature hysteresis in charge density waves, advancing understanding of their interplay and Fermi surface evolution.

Findings

Observation of coexisting commensurate and incommensurate CDW phases

Identification of a temperature hysteresis in the multi-q ordered phase

Non-monotonic evolution of the Fermi surface nesting vector with temperature

Abstract

Multiple charge density wave (CDW) phases in 2H-TaSe2 are investigated by high-resolution synchrotron x-ray diffraction. In a narrow temperature range immediately above the commensurate CDW transition, we observe a multi-q superstructure with coexisting commensurate and incommensurate order parameters, clearly distinct from the fully incommensurate state at higher temperatures. This multi-q ordered phase, characterized by a temperature hysteresis, is found both during warming and cooling, in contrast to previous reports. In the normal state, the incommensurate superstructure reflection gives way to a broad diffuse peak that persists nearly up to room temperature. Its position provides a direct and accurate estimate of the Fermi surface nesting vector, which evolves non-monotonically and approaches the commensurate position as the temperature is increased. This behavior agrees with our recent observations of the temperature-dependent Fermi surface in the same compound [Phys. Rev. B 79, 125112 (2009)].