We study a model of a large number of strongly coupled phonons that can be viewed as a bosonic variant of the Sachdev-Ye-Kitaev model. We determine the phase diagram of the model which consists of a glass phase and a disordered phase, with a first-order phase transition separating them. We compute the specific heat of the disordered phase, with which we diagnose the high-temperature crossover to the classical limit. We further study the real-time dynamics of the disordered phase, where we identify three dynamical regimes as a function of temperature. Low temperatures are associated with a semiclassical regime, where the phonons can be described as long-lived normal modes. High temperatures are associated with the classical limit of the model. For a large region in parameter space, we identify an intermediate-temperatures regime, where the phonon lifetime is of the order of the Planckian time scale $\hbar/k_B T$.
Two-fluid dynamics in driven YBa$_2$Cu$_3$O$_{6.48}$
$_2$ O $_{6+x}$中某些声子模的相干光激发已被证明在高于$T_c$的温度下诱导类超导层间相干。最近的工作已经将这些现象与约瑟夫森等离子体极化激元的参数激发和放大相关联，约瑟夫森等离子体极化激元在$T_c$以上过阻尼，但通过声子驱动而变得相干。然而，未凝聚准粒子的耗散响应，它不以相同的方式耦合到声子驱动，还没有得到解决。在这里，我们调查的超流密度，$ωσ_2(ω)$，和准粒子的耗散响应，$σ_1(ω)$，通过系统地调整中红外脉冲的持续时间和能量，同时保持峰值字段固定的增强。我们发现，光致超流密度饱和的零温度平衡值的脉冲长于声子退相时间，而耗散分量继续增长，增加脉冲持续时间。我们表明，超流和耗散保持解耦，只要驱动器上，并确定一个最佳的制度的泵脉冲持续时间的超导响应是最大的和耗散最小化。
A Microscopic Description of Displacive Coherent Phonons
本文发展了一种基于哈密顿的激光泵浦诱导位移相干声子的微观描述。该理论捕捉到电子流体上的声子激发的反馈，这在最先进的唯象公式中是缺失的。我们表明，这种反馈导致啁啾在短的时间尺度，即使声子运动是谐波。在长时间内，这种反馈在振荡信号中表现为有限相位。我们将理论应用于BaFe $_2$ As $_2$，解释了最近实验报道的振荡信号中相位的起源，并预测该系统将在更大的能量密度下表现出红移啁啾。我们的理论也打开了从相干声子动力学中提取平衡信息的可能性。
