Anomalous metallic state of Cu$_{0.07}$TiSe$_2$: an optical spectroscopy study

TL;DR

This study uses optical spectroscopy to investigate Cu$_{0.07}$TiSe$_2$, revealing an unusual metallic state characterized by a temperature-dependent plasma edge shift, suggesting decreasing effective mass of carriers.

Contribution

It provides the first optical spectroscopy analysis of Cu$_{0.07}$TiSe$_2$, highlighting its anomalous metallic behavior and the temperature dependence of its plasma edge.

Findings

Low carrier density in Cu$_{0.07}$TiSe$_2$

Significant high-energy shift of the plasma edge with decreasing temperature

Indication of decreasing effective mass of carriers at lower temperatures

Abstract

We report an optical spectroscopy study on the newly discovered superconductor Cu$_{0.07}$TiSe$_2$. Consistent with the development from a semimetal or semiconductor with a very small indirect energy gap upon doping TiSe$_2$, it is found that the compound has a low carrier density. Most remarkably, the study reveals a substantial shift of the "screened" plasma edge in reflectance towards high energy with decreasing temperature. This phenomenon, rarely seen in metals, indicates either a sizeable increase of the conducting carrier concentration or/and a decrease of the effective mass of carriers with reducing temperature. We attribute the shift primarily to the later effect.