Optical spectroscopy study of Nd(O,F)BiS2 single crystals

TL;DR

This optical spectroscopy study of Nd(O,F)BiS2 single crystals reveals a simple metallic response with low plasma energy, indicating weak electronic correlations and ruling out exotic pairing mechanisms or charge density wave instabilities.

Contribution

First optical spectroscopy analysis of Nd(O,F)BiS2 single crystals showing weak correlations and clarifying electronic structure and superconducting pairing mechanisms.

Findings

Plasma frequency estimated at 2.1 eV, lower than first-principles predictions for x=0.5 doping.

Energy scales of interband transitions match first-principles calculations.

Absence of strong correlation effects and charge density wave instability.

Abstract

We present an optical spectroscopy study on F-substituted NdOBiS$_2$ superconducting single crystals grown using KCl/LiCl flux method. The measurement reveals a simple metallic response with a relatively low screened plasma edge near 5000 \cm. The plasma frequency is estimated to be 2.1 eV, which is much smaller than the value expected from the first-principles calculations for an electron doping level of x=0.5, but very close to the value based on a doping level of 7$\%$ of itinerant electrons per Bi site as determined by ARPES experiment. The energy scales of the interband transitions are also well reproduced by the first-principles calculations. The results suggest an absence of correlation effect in the compound, which essentially rules out the exotic pairing mechanism for superconductivity or scenario based on the strong electronic correlation effect. The study also reveals that the system is far from a CDW instability as being widely discussed for a doping level of x=0.5.