论文标题
超导MGB $ _2 $的带选择性第三谐波一代：Higgs振幅模式的可能证据
Band-selective third-harmonic generation in superconducting MgB$_2$: Possible evidence for Higgs amplitude mode in the dirty limit
论文作者
论文摘要
我们报告了两波段超导体MGB $ _2 $的时间分辨线性和非线性Terahertz光谱，超导转换温度$ t_c \ 36 $ k \大约36 $ k。第三级 - 荷尔马克人（THG）在$ t_c $ t_c $ the $ t_c $中被带有Intense narkernense narker narkerband pulses的系统。对于泵浦脉冲频率$ f = $ 0.3，0.4和0.5 thz，THG信号的温度依赖性演变在温度下显示出共振，共振条件$ 2F =2Δ_π（t）$满足，对于dirty-limiT-limit超导通的差距$2δ_π$。相反，对于$ f = $ 0.6和0.7 THz，$ 2F>2Δ_π（t \ rightarrow0）= 1.03 $ thz，随着温度的降低，THG强度单调增加。此外，对于$ 2F <2δ_π（t \ rightarrow0）$，就泵脉冲极化而言，THG几乎是各向同性的。这些结果表明，肮脏的限制$π$ - 带超导差的驱动的希格斯振幅模式的主要贡献，表明散射对于观察超导体中希格斯模式的重要性。
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 $2f=2Δ_π(T)$ fulfilled, for the dirty-limit superconducting gap $2Δ_π$. In contrast, for $f=$ 0.6 and 0.7 THz with $2f>2Δ_π(T\rightarrow0)=1.03$ THz, the THG intensity increases monotonically with decreasing temperature. Moreover, for $2f<2Δ_π(T\rightarrow0)$ 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.
