Probing d-wave superconducting gap of high-$T_\mathrm{c}$ cuprate $\mathrm{Bi}_2\mathrm{Sr}_2\mathrm{Ca}_2\mathrm{Cu}_3\mathrm{O}_{10+\delta}$ by resonant inelastic X-ray scattering

TL;DR

This study uses resonant inelastic X-ray scattering to measure the d-wave superconducting gap in an overdoped cuprate, revealing a momentum-dependent gap size of about 130 meV and demonstrating RIXS as a bulk-sensitive technique for gap symmetry analysis.

Contribution

The paper demonstrates the effectiveness of high-resolution RIXS in probing the superconducting gap and its symmetry in high-Tc cuprates, providing a bulk-sensitive alternative to surface-sensitive methods.

Findings

Superconducting gap size of approximately 130 meV.

Clear suppression of spectral weight below Tc at small momentum transfers.

Support for d-wave symmetry of the superconducting gap.

Abstract

The superconducting gap is a characteristic feature of high-T$_c$ superconductors and provides crucial information on the pairing mechanism underlying high-temperature superconductivity. Here, we employ high-resolution resonant inelastic X-ray scattering (RIXS) at the Cu $L_3$-edge to investigate the superconducting gap in the overdoped cuprate $\mathrm{Bi}_2\mathrm{Sr}_2\mathrm{Ca}_2\mathrm{Cu}_3\mathrm{O}_{10+\delta}$ ($T_\mathrm{c}$ = 107 K). By analyzing antisymmetrized, temperature-dependent RIXS spectra over a range of in-plane momentum transfers, we observe a clear suppression of low-energy spectral weight below T$_c$, indicative of superconducting gap formation. This suppression is most pronounced at small momentum transfers ($|\boldsymbol{q}_\parallel| \leq 0.18$ r.l.u.) and corresponds to a gap size of approximately 2$\Delta_0 \sim$ 130 meV. Comparison with theoretical calculations of the momentum-dependent charge susceptibility supports a d-wave symmetry of the superconducting gap, while an isotropic s-wave gap fails to reproduce key experimental features. These findings establish RIXS as a powerful, bulk-sensitive probe of superconducting gap symmetry and highlight its utility for studying materials beyond the reach of surface-sensitive techniques such as ARPES and STM.