Higgs mode excitation in superconductors by intense terahertz pulse
Higgs mode excitation in superconductors by intense terahertz pulse
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DOI：
10.1117/12.2223010
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发表时间：
2016-05
期刊：
影响因子：
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通讯作者：
Ryusuke Matsunaga;R. Shimano
中科院分区：
文献类型：
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作者：
Ryusuke Matsunaga;R. Shimano
近年来，强太赫兹（THz）脉冲产生技术的发展为在桌面实验中揭示各种材料的超快现象提供了新的机会，并为量子相的超快控制提供了新的途径。本文介绍了金属超导体NbN在强太赫兹脉冲激励下的非平衡动力学研究进展。由于超导间隙能量位于太赫兹频率范围内，强太赫兹脉冲激发可以在间隙边缘瞬间激发高密度准粒子而不注入多余能量。在不激发非相干准粒子的情况下，通过将泵浦频率调谐到间隙能量以下，也可以相干地驱动超导基态。直接探测了这种强烈的低能激发所引起的序参量的超快动力学，揭示了集体激发的性质，即希格斯振幅模式。发现了超导体产生的高效太赫兹高谐波，显示了太赫兹波与希格斯模式之间的非线性耦合。我们还报道了多隙超导体MgB2的实验结果。
Recent development of intense terahertz (THz) pulse generation technique has offered novel opportunities to reveal ultrafast phenomena in a variety of materials on tabletop experiments and provided a new pathway toward ultrafast control of quantum phases. Here we present our recent study of nonequilibrium dynamics in metallic superconductors NbN excited by intense THz pulse. Since the superconducting gap energy is located in the THz frequency range, the intense THz pulse excitation makes it possible to instantaneously excite high-density quasiparticles at the gap edge without injecting excess energies. It has also become possible to coherently drive the superconducting ground state without exciting incoherent quasiparticles by tuning the pump frequency below the gap energy. The ultrafast dynamics of the order parameter induced by such an intense low energy excitation is directly probed, and the nature of a collective excitation, namely the Higgs amplitude mode, is revealed. Efficient THz higher-harmonic generation from a superconductor is discovered, manifesting the nonlinear coupling between the THz wave and the Higgs mode. We also report the experimental results in a multi-gap superconductor MgB2.