Effects of thermal- and spin- fluctuations on the band structure of purple bronze Li$_2$Mo$_{12}$O$_{34}$

TL;DR

This study investigates how thermal and spin fluctuations influence the electronic band structure of Li$_2$Mo$_{12}$O$_{34}$, revealing temperature-dependent broadening and significant spin effects on high DOS molybdenum sites.

Contribution

It provides the first detailed analysis of thermal disorder and spin fluctuations on the band structure of purple bronze Li$_2$Mo$_{12}$O$_{34}$ using ab-initio DFT-LMTO calculations.

Findings

Thermal disorder causes band broadening at the Fermi level.

Spin polarization shows large exchange enhancement on high DOS Mo sites.

Band structure remains consistent with photoemission data despite disorder effects.

Abstract

The band structures of ordered and thermally disordered Li$_2$Mo$_{12}$O$_{34}$ are calculated by use of ab-initio DFT-LMTO method. The unusual, very 1-dimensional band dispersion obtained in previous band calculations is confirmed for the ordered structure, and the overall band structure agrees reasonably with existing photoemission data. Dispersion and bandstructure perpendicular to the main dispersive direction is obtained. A temperature dependent band broadening is calculated from configurations with thermal disorder of the atomic positions within the unit cell. This leads a band broadening of the two bands at the Fermi energy which can become comparable to their energy separation. The bands are particularly sensitive to in-plane movements of Mo sites far from the Li-sites, where the density-of-states is highest. The latter fact makes the effect of Li vacancies on the two bands relatively small. Spin-polarized band results for the ordered structure show a surprisingly large exchange enhancement on the high DOS Mo sites. Consequences for spin fluctuations associated with a cell doubling along the conducting direction are discussed.