Department of Physics and Astronomy, Ames Laboratory, Iowa State University, Ames, IA, USA.
Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI, USA.
Nat Mater. 2018 Jul;17(7):586-591. doi: 10.1038/s41563-018-0096-3. Epub 2018 Jun 4.
'Sudden' quantum quench and prethermalization have become a cross-cutting theme for discovering emergent states of matter. Yet this remains challenging in electron matter, especially superconductors. The grand question of what is hidden underneath superconductivity (SC) appears universal, but poorly understood. Here we reveal a long-lived gapless quantum phase of prethermalized quasiparticles (QPs) after a single-cycle terahertz (THz) quench of a NbSn SC gap. Its conductivity spectra is characterized by a sharp coherent peak and a vanishing scattering rate that decreases almost linearly towards zero frequency, which is most pronounced around the full depletion of the condensate and absent for a high-frequency pump. Above a critical pump threshold, such a QP phase with coherent transport and memory persists as an unusual prethermalization plateau, without relaxation to normal and SC thermal states for an order of magnitude longer than the QP recombination and thermalization times. Switching to this metastable 'quantum QP fluid' signals non-thermal quench of coupled SC and charge-density-wave (CDW)-like orders and hints quantum control beneath the SC.
“突发”量子淬火和预热化已成为发现物质新状态的跨学科主题。然而，这在电子物质中仍然具有挑战性，特别是在超导体中。超导性（SC）之下隐藏着什么的重大问题似乎是普遍存在的，但理解得很差。在这里，我们揭示了在 NbSn SC 能隙的单次太赫兹（THz）淬火后，预热准粒子（QP）的长寿命无能隙量子相。其电导率谱的特征是存在尖锐的相干峰和消失的散射率，该散射率几乎呈线性减小至零频率，在完全耗尽凝聚态时最为明显，而在高频泵浦时则不存在。在临界泵浦阈值以上，这种具有相干输运和记忆的 QP 相作为一种异常预热平台持续存在，而无需弛豫到正常和 SC 热态，其时间比 QP 复合和热化时间长一个数量级。切换到这种亚稳态“量子 QP 流体”标志着耦合的 SC 和电荷密度波（CDW）样有序的非热淬火，并暗示了 SC 之下的量子控制。
