Comment on "Terahertz time-domain spectroscopy of transient metallic and superconducting states" (arXiv:1506.06758)

TL;DR

This paper critiques a model of terahertz spectroscopy measurements of transient states, showing that under realistic conditions, the measured response closely approximates the optical conductivity, supporting its use in experiments.

Contribution

The authors demonstrate that the response function measured by terahertz spectroscopy is nearly equivalent to optical conductivity in practical scenarios, clarifying the method's validity.

Findings

The difference between response function and optical conductivity is small under realistic conditions.

Time-domain terahertz spectroscopy provides a good estimate of optical conductivity in transient phases.

Supports the use of terahertz spectroscopy for studying light-induced superconducting states.

Abstract

We comment on the model proposed by Orenstein and Dodge in arXiv:1506.06758v1, which describes time-domain terahertz measurements of transiently generated, high-electron-mobility (or superconducting) phases of solids. The authors' main conclusion is that time-domain terahertz spectroscopy does not measure a response function that is mathematically identical to the transient optical conductivity. We show that although this is correct, the difference between the measured response function and the microscopic optical conductivity is small for realistic experimental parameters. We also show that for the experiments reported by our group on light-induced superconducting-like phases in cuprates and in organic conductors, the time-domain terahertz yields a very good estimate for the optical conductivity.