Higgs mode in the d-wave superconductor Bi2Sr2CaCu2O8+x driven by an intense terahertz pulse

TL;DR

This study reveals the excitation of the Higgs mode in a d-wave superconductor Bi2Sr2CaCu2O8+x using intense terahertz pulses, demonstrating nonlinear optical responses linked to the superconductor's order parameter.

Contribution

First experimental observation of the Higgs mode in a d-wave superconductor driven by terahertz pulses, with detailed polarization-resolved analysis and theoretical comparison.

Findings

Oscillatory optical reflectivity following THz electric field squared

Identification of A1g and B1g symmetry components in nonlinear response

A1g component linked to the Higgs mode of the d-wave order parameter

Abstract

We investigated the terahertz (THz)-pulse driven nonlinear response in the d-wave cuprate superconductor Bi2Sr2CaCu2O8+x (Bi2212) using a THz pump near-infrared probe scheme in the time domain. We have observed an oscillatory behavior of the optical reflectivity that follows the THz electric field squared and is strongly enhanced below Tc. The corresponding third-order nonlinear effect exhibits both A1g and B1g symmetry components, which are decomposed from polarization-resolved measurements. Comparison with a BCS calculation of the nonlinear susceptibility indicates that the A1g component is associated with the Higgs mode of the d-wave order parameter.