Band-selective third-harmonic generation in superconducting MgB2: Possible evidence for the Higgs amplitude mode in the dirty limit

Sergey Kovalev; Tao Dong; Li-Yu Shi; Chris Reinhoffer; Tie-Quan Xu; Hong-Zhang Wang; Yue Wang; Zi-Zhao Gan; Semyon Germanskiy; Jan-Christoph Deinert; Igor Ilyakov; Paul H. M. van Loosdrecht; Dong Wu; Nan-Lin Wang; Jure Demsar; Zhe Wang

doi:10.1103/PhysRevB.104.L140505

Band-selective third-harmonic generation in superconducting MgB2: Possible evidence for the Higgs amplitude mode in the dirty limit

Sergey Kovalev, Tao Dong, Li-Yu Shi, Chris Reinhoffer, Tie-Quan Xu, Hong-Zhang Wang, Yue Wang, Zi-Zhao Gan, Semyon Germanskiy, Jan-Christoph Deinert, Igor Ilyakov, Paul H. M. van Loosdrecht, Dong Wu, Nan-Lin Wang, Jure Demsar, Zhe Wang

DOI 10.1103/PhysRevB.104.L140505 · Physical Review B

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Abstract

We report on time-resolved linear and nonlinear terahertz spectroscopy of the two-band superconductor MgB2 with a superconducting transition temperature Tc≈36 K. Third-harmonic generation (THG) is observed below Tc by driving the system with intense narrow-band THz pulses. For the pump-pulse frequencies f=0.3, 0.4, and 0.5 THz, the temperature-dependent evolution of the THG signals exhibits a resonance maximum at the temperatures with the resonance conditions 2f=2Δπ(T) fulfilled, for the dirty-limit superconducting gap 2Δπ. In contrast, for f=0.6 and 0.7 THz with 2f>2Δπ(T→0)=1.03 THz, the THG intensity increases monotonically with decreasing temperature. Moreover, for 2f<2Δπ(T→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 π-band superconducting gap, pointing to the importance of scattering for observation of the Higgs mode in superconductors.

Source-reported materials — not catalogue approval

Formula	Reported Tc (K)	Pressure (GPa)	Type
MgB2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	36	Pressure not reported	onset
MgB2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	36	Pressure not reported	onset
NbN Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	—	Pressure not reported	unknown