# Weak metal-metal transition in the vanadium oxytelluride Rb$_{1-\delta}$V$_2$Te$_2$O

## TL;DR

This study synthesizes and characterizes Rb$_{1-eta}$V$_2$Te$_2$O, revealing a weak metal-metal transition likely linked to orbital or spin-density-wave order, with implications for potential superconductivity upon suppression of this order.

## Contribution

It provides the first detailed investigation of Rb$_{1-eta}$V$_2$Te$_2$O, combining experimental and theoretical methods to elucidate its structure, electronic properties, and low-temperature transition.

## Key findings

- Weak metal-metal transition at ~100 K characterized by resistivity and Hall coefficient anomalies.
- Absence of structural superlattice reflections suggests no conventional charge density wave.
- Electronic structure dominated by V-3$d$ orbitals with orbital polarization and multiple Fermi surfaces.

## Abstract

We report the synthesis, crystal structure, physical properties, and first-principles calculations of a vanadium-based oxytelluride Rb$_{1-\delta}$V$_2$Te$_2$O ($\delta\approx0.2$). The crystal structure bears two-dimensional V$_2$O square nets sandwiched with tellurium layers, mimicking the structural motifs of cuprate and iron-based superconductors. The material exhibits metallic conductivity with dominant hole-type charge carriers. A weak metal-to-metal transition takes place at $\sim$100 K, which is conformably characterized by a slight kink/hump in the electrical resistivity, jumps in the Hall and Seebeck coefficients, a minute drop in the magnetic susceptibility, and a small peak in the heat capacity. Neither Bragg-peak splitting nor superlattice reflections can be detected within the resolution of conventional x-ray diffractions. The band-structure calculations show that V-3$d$ orbitals dominate the electronic states at around Fermi energy where a $d_{yz}/d_{xz}$ orbital polarization shows up. There are three Fermi-surface sheets that seem unfavorable for nesting. Our results suggest an orbital or spin-density-wave order for the low-temperature state and, upon suppression of the competing order, emergence of superconductivity could be expected.