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

• Published in: ACS applied electronic materials Vol. 5; no. 9; pp. 4770 - 4777
• Main Authors: Cervasio, Rebecca, Tomarchio, Luca, Verseils, Marine, Brubach, Jean-Blaise, Macis, Salvatore, Zeng, Shengwei, Ariando, Ariando, Roy, Pascale, Lupi, Stefano
• Format: Journal Article
• Language: English
• Published: American Chemical Society 26-09-2023
• Subjects: superconducting gap; THz spectroscopy; optical spectroscopy; electrodynamics of superconductors; nickelates; unconventional superconductivity
• ISSN: 2637-6113; 2637-6113
• DOI: 10.1021/acsaelm.3c00506

The intensive search for alternative noncuprate 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 values in oxides. In the unsolved quest for the physical conditions necessary for inducing superconductivity, we report on a broad-band optical study of a Nd0.8Sr0.2NiO2 film measured using optical and terahertz spectroscopy at temperatures above and below the critical temperature T c ∼ 13 K. The normal-state electrodynamics of Nd0.8Sr0.2NiO2 can be described by a scattering time at room temperature (τ ≃ 1.3 × 10–14 s) and a plasma frequency ωp ≃ 5500 cm–1 in combination with an absorption band in the mid-infrared (MIR), characteristics of transition metal oxides, located around ω0 ∼ 2500 cm–1 and with an amplitude ωp MIR of about 8000 cm–1. The degree of electronic correlation can be estimated using the ratio ωp 2/(ωp 2 + (ωp MIR)2). In the present system, the determined value of 0.32 ± 0.06 indicates a strong electron correlation in the NiO2 plane with similar strength as cuprates. From 300 to 20 K, we observe a spectral weight transfer between the Drude and MIR band, together with a strong increase in the Drude scattering time, in agreement with DC resistivity measurements. Below T c, a superconducting energy gap 2Δ ∼ 3.3 meV can be extracted from the terahertz reflectivity using the Mattis–Bardeen model.