Optical Study of BaFe$_2$As$_2$ under pressure: Coexistence of spin-density-wave gap and superconductivity

TL;DR

This study investigates how pressure affects the optical properties of BaFe$_2$As$_2$, revealing the coexistence of spin-density-wave and superconducting phases, with evidence of a superconducting gap opening at high pressure.

Contribution

It provides the first detailed optical analysis of BaFe$_2$As$_2$ under pressure, demonstrating the coexistence of SDW and superconductivity and identifying the superconducting gap.

Findings

Suppression of SDW state with increasing pressure.

Coexistence of SDW and superconductivity at 3.6 GPa.

Observation of a full superconducting gap at 6 K.

Abstract

Temperature-dependent reflectivity measurements in the frequency range 85 - 7000 cm$^{-1}$ were performed on BaFe$_2$As$_2$ single crystals under pressure up to $\sim$5 GPa. The corresponding pressure- and temperature-dependent optical conductivity was analyzed with the Drude-Lorentz model to extract the coherent and incoherent contributions. The gradual suppression of the spin-density wave (SDW) state with increasing pressure and the appearance of the superconducting phase coexisting with the SDW phase at 3.6~GPa were observed. At 3.6~GPa, the reflectivity reaches unity below $\sim$95~cm$^{-1}$ indicating the opening of the superconducting gap and shows a full gap tendency at 6 K.