Nonreciprocal Terahertz Second-Harmonic Generation in Superconducting NbN under Supercurrent Injection
Sachiko Nakamura, Kota Katsumi, Hirotaka Terai, Ryo Shimano
DOI 10.1103/PhysRevLett.125.097004 · Physical Review Letters
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Abstract
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 ηSHG reaches ≈10−2 in a thin film NbN with the thickness of 25 nm after the field cooling with a very small magnetic field of ≈1 Oe, for a relatively weak incident THz electric field of 2.8 kV/cm at 0.48 THz.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| NbN Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 14.5 | Pressure not reported | unknown |
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