paper

Optical Properties of Superconducting Nd0.8Sr0.2NiO2 Nickelate

arXiv:2203.16986

Abstract

The intensive search for alternative non-cuprate high-transition-temperature ( $T_{c}$ ) superconductors has taken a positive turn recently with the discovery of superconductivity in infinite layer nickelates. This discovery is expected to be the basis for disentangling the puzzle behind the physics of high $T_{c}$ in oxides. In the unsolved quest for the physical conditions necessary for inducing superconductivity, we report an optical study of a Nd $_{0.8}$ Sr $_{0.2}$ NiO $_{2}$ film measured using optical spectroscopy, at temperatures above and below the critical temperature $T_{c} \sim 13$ K. The normal-state electrodynamics of Nd $_{0.8}$ Sr $_{0.2}$ NiO $_{2}$ , is described by the Drude model characterized by a scattering time just above $T_{c}$ ( $I ¨ \sim 1.7 \times 1 0^{- 14}$ s) and a plasma frequency $I ¨ _{p} = 8500$ cm $^{- 1}$ in combination with an absorption band in the Mid-Infrared (MIR) around $I ¨ _{0} \sim 4000$ cm $^{- 1}$ . The MIR absorption indicates the presence of strong electronic correlation effect in the NiO $_{2}$ plane similarly to cuprates. Below $T_{c}$ , a superconducting energy gap ( $2 I^$ ) of $\sim 3.2$ meV is extracted from the Terahertz reflectivity using the the Mattis-Bardeen model. From the Ferrel-Glover-Thinkam Rule applied to the real part of the optical conductivity, we also estimate a London penetration depth of about 490 nm, in agreement with a type-II superconductivity in Nd $_{0.8}$ Sr $_{0.2}$ NiO $_{2}$ Nickelate.

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