Optical properties of TlNi2Se2: Observation of pseudogap formation

TL;DR

This study investigates the optical properties of TlNi2Se2, revealing pseudogap formation likely caused by charge-density-wave fluctuations driven by van Hove singularities near the Fermi level.

Contribution

First optical spectroscopy study on TlNi2Se2 revealing pseudogap formation and its possible origin from CDW instability driven by saddle points.

Findings

Observation of pseudogap formation in TlNi2Se2

Similarity of optical spectra to BaNi2As2

Evidence for CDW instability driven by van Hove singularity

Abstract

The quasi-two-dimensional nickel chalcogenides $TlNi_2Se_2$ is a newly discovered superconductor. We have performed optical spectroscopy study on $TlNi_2Se_2$ single crystals over a broad frequency range at various temperatures. The overall optical reflectance spectra are similar to those observed in its isostructure $BaNi_2As_2$. Both the suppression in $R(\omega)$ and the peaklike feature in $\sigma_1(\omega)$ suggest the progressive formation of a pseudogap feature in the midinfrared range with decreasing temperatures, which might be originated from the dynamic local fluctuation of charge-density-wave (CDW) instability. We propose that the CDW instability in $TlNi_2Se_2$ is driven by the saddle points mechanism, due to the existence of van Hove singularity very close to the Fermi energy.