AI 中文总结
研究超导体中太赫兹激光脉冲驱动集体模式的新机制，通过多光子激发路径，结合数值模拟与解析结果，证明位移机制可激发希格斯模式，经实验验证，为控制光学响应参数依赖性提供新视角。
AI 中文摘要
强相位稳定太赫兹（THz）激光脉冲可通过多光子激发路径相干驱动集体模式，其方式不同于线性响应中的标准共振机制。本文表明，在超导体中，当受激准粒子激活超导序参量的（非共振）静态位移时，非线性光学响应会增强，这与不透明材料中相干声子的位移激发完全类似。通过数值模拟与解析结果相结合，证明位移机制在 s 波和 d 波超导体中均可激发希格斯模式。通过超导 s 波 NbN 中非线性一次谐波相位的温度依赖性实验验证了这一预测。还讨论了通过泵浦 - 探测协议可实验获取的长时间序参量弛豫与能量耗散过程的联系。结果为强 THz 场测量并最终控制光学响应在集体自由度上的参数依赖性提供了新视角。
英文摘要
Intense phase-stable terahertz (THz) laser pulses can drive collective modes coherently via multi-photon excitation pathways in a manner different than the standard resonant mechanism operative in linear response. Here we show that in superconductors the nonlinear optical response can be enhanced when excited quasiparticles activate a (non-resonant) static displacement of the superconducting order parameter, in full analogy with the displacive excitation of coherent phonons in opaque materials. By combining numerical simulations with analytical results we demonstrate that the displacive mechanism to excite the Higgs mode is operative in both $s$-wave and $d$-wave superconductors. We validate this prediction experimentally by the temperature dependence of the phase of the nonlinear first harmonic in superconducting $s$-wave NbN. We also discuss how the order-parameter relaxation at large times, which can be experimentally accessed via pump-probe protocols is connected to energy-dissipative processes. Our results offer a novel perspective on the ability of intense THz fields to measure, and eventually control, the parametric dependence of the optical response on collective degrees of freedom.
