Nonreciprocal Terahertz Second-Harmonic Generation in Superconducting NbN under Supercurrent Injection
Nonreciprocal Terahertz Second-Harmonic Generation in Superconducting NbN under Supercurrent Injection
复制标题
超导氮化铌在超电流注入下的非互易太赫兹二次谐波发生
DOI：
10.1103/physrevlett.125.097004
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发表时间：
2020-08-28
影响因子：
8.6
通讯作者：
Shimano, Ryo
中科院分区：
文献类型：
--
作者：
Nakamura, Sachiko;Katsumi, Kota;Shimano, Ryo
在s波超导体NbN薄膜中观察到太赫兹（THz）频率范围内的巨大二次谐波产生，其中时间反转(T)和空间反转(P)对称性同时被超电流注入打破。我们证明了当电流方向反转时，二次谐波信号的相位发生反转；也就是说，信号被归因于在P和T对称性被破坏的情况下发生的非互反响应。高温信号的温度依赖性表现为尖锐共振，这是由太赫兹电场在非谐波钉钉电位下驱动的涡旋运动造成的。在0.48太赫兹入射2.8 kV/cm的相对较弱的太赫兹电场下，在约1 Oe的磁场冷却下，厚度为25 nm的NbN薄膜中，ti - sHG的最大转换率接近10（-2）。
Giant second-harmonic generation in the terahertz (THz) frequency range is observed in a thin film of an s-wave superconductor NbN, where the time-reversal (T) and space-inversion (P) symmetries are simultaneously broken by supercurrent injection. We demonstrate that the phase of the second-harmonic signal flips when the direction of supercurrent is inverted; i.e., the signal is ascribed to the nonreciprocal response that occurs under broken P and T symmetries. The temperature dependence of the SH signal exhibits a sharp resonance, which is accounted for by the vortex motion driven by the THz electric field in an anharmonic pinning potential. The maximum conversion ratio ti sHG reaches approximate to 10(-2) in a thin film NbN with the thickness of 25 nm after the field cooling with a very small magnetic field of approximate to 1 Oe, for a relatively weak incident THz electric field of 2.8 kV/cm at 0.48 THz.