Thermal transport and mixed valence in ZrTe$_3$ doped with Hf and Se

TL;DR

This study investigates how doping ZrTe₃ with Hf and Se affects its thermal transport, valence states, charge density waves, and superconductivity, revealing enhanced superconductivity and CDW properties due to disorder and lattice effects.

Contribution

It demonstrates how doping influences mixed valence states, CDW transition temperature, and superconductivity in ZrTe₃, providing insights into tuning properties of TMTCs.

Findings

Doping reduces mixed valence Zr atoms in ZrTe₃.

Superconductivity is enhanced by disorder in Te chains.

Hf substitution increases CDW transition temperature.

Abstract

Two-dimensional transition metal trichalcogenides (TMTC's) feature covalently bonded metal-chalcogen layers separated by the van der Waals (vdW) gap. Similar to transition metal dichalcogenides (TMDCs), TMTCs often host charge density waves (CDWs) and superconductivity but unlike TMDCs atomic chains in the crystal structure give rise to quasi one-dimensional (quasi 1D) conduction. ZrTe$_3$ features CDW below $T_{\textrm{CDW}}$ = 63 K and filamentary superconductivity below 2 K that can be enhanced by pressure or chemical substitution. Here we report the presence of mixed valent Zr$^{2+}$ and Zr$^{4+}$ atoms in ZrTe$_3$ crystals that is reduced by doping in ZrTe$_{3-x}$Se$_x$ and Zr$_{1-y}$Hf$_y$Te$_3$. Superconductivity is enhanced via disorder in Te2-Te3 atomic chains that are associated with CDW formation. Hf substitution on Zr atomic site enhances $T_{\textrm{CDW}}$ due to unperturbed Te2-Te3 chain periodicity and enhanced electron-phonon coupling. Weak electronic correlations in ZrTe$_{3-x}$Se$_x$ are likely governed by the lattice contraction effects.