Thermal transport and mixed valence in ZrTe3 doped with Hf and Se

Two-dimensional transition metal trichalcogenides (TMTCs) 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. ZrTe3 features the CDW below TCDW = 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 Zr2+ and Zr4+ atoms in ZrTe3 crystals that are reduced by doping in ZrTe3−xSex and Zr1−yHfyTe3. Superconductivity is enhanced via disorder in Te2-Te3 atomic chains that are associated with CDW formation. Hf substitution on the Zr atomic site enhances TCDW due to unperturbed Te2-Te3 chain periodicity and enhanced electron-phonon coupling. Weak electronic correlations in ZrTe3−xSex are likely governed by the lattice contraction effects.