Band-selective third-harmonic generation in superconducting MgB${}_2$: Possible evidence for Higgs amplitude mode in the dirty limit

Abstract

We report on time-resolved linear and nonlinear terahertz spectroscopy of the two-band superconductor MgB${}_2$ with the superconducting transition temperature $T_c\approx 36$ K. Third-harmonic generation (THG) is observed below $T_c$ by driving the system with intense narrowband THz pulses. For the pump-pulse frequencies $f=$ 0.3, 0.4, and 0.5 THz, temperature-dependent evolution of the THG signals exhibits a resonance maximum at the temperatures with the resonance conditions $2f=2{\Delta }_{\pi }(T)$ fulfilled, for the dirty-limit superconducting gap $2{\Delta }_{\pi }$. In contrast, for $f=$ 0.6 and 0.7 THz with $2f>2{\Delta }_{\pi }(T\to 0)=1.03$ THz, the THG intensity increases monotonically with decreasing temperature. Moreover, for $2f<2{\Delta }_{\pi }(T\to 0)$ the THG is found nearly isotropic with respect to the pump-pulse polarization. These results suggest a predominant contribution of the driven Higgs amplitude mode of the dirty-limit $\pi$-band superconducting gap, pointing to the importance of scattering for observation of the Higgs mode in superconductors.

5 pages, 3 figures

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• Transient Higgs oscillations and high-order nonlinear light-Higgs coupling in terahertz-wave drivenNbN superconductor
• Contribution of Collective Excitations to Third Harmonic Generation in Multiband Superconductors: the case of MgB${}_2$
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• Phase signatures in third-harmonic response of Higgs and coexisting modes in superconductors
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• Ultrafast dynamics of optically excited charge carriers in the room-temperature antiferromagnetic semiconductor $\alpha$-MnTe
• Amplitude mode in a multi-gap superconductor MgB${}_2$ investigated by terahertz two-dimensional coherent spectroscopy
• Optical response of Higgs mode in superconductors at clean limit: formulation through Eilenberger equation and Ginzburg-Landau Lagrangian
• Terahertz third-harmonic generation of lightwave driven Weyl fermions far from equilibrium
• Higgs and Nambu-Goldstone modes in condensed matter physics
• Higgs physics in superconductors
• Quantum spin dynamics of the honeycomb magnet K${}_2$Co${}_2$TeO${}_6$ in high magnetic fields
• Two-dimensional coherent spectroscopy of disordered superconductors in the narrow-band and broad-band limits
• Third-harmonic generation in superconductors: Role of quantum geometry in the competition between Higgs mode and quasiparticles
• Anomalous terahertz nonlinearity in disordered s-wave superconductor close to the superconductor-insulator transition