Vortex states at low temperatures and quantum fluctuations in disordered superconductors

我们研究了具有均匀和强无序的厚(100 Nm)非晶MoxSi1-x&gt；薄膜在低温(T)和高场(B)下的涡旋态。我们发现涡旋-液体相，即所谓的量子涡旋-液体(QVL)相，一直持续到T=0。当在与T→O的QVL相对应的固定场中冷却时，在一定的温度T_q下，电阻率的阿雷尼乌斯曲线上的曲率由下向上变化，这表明液体中的温度主导的涨落与量子驱动的涨落相交叉。此外，QVL相的相对宽度沿B和T轴几乎与正常态的电阻率ρ_n成正比增加，这与QVL相是由强的量子涨落引起的观点一致，这种涨落随着ρ_n的增加而增强。我们还通过测量磁通流动电压δV(T)关于平均电压的起伏分量，研究了涡旋态从热态到量子液体的变化。我们发现了低温液体中的异常涡旋动力学。对于厚膜，由涡旋运动产生的δV(T)在QVL相清晰可见，δV(T)的分布反常不对称，有一条向通量运动方向延伸的尾巴。这一结果表明，在QVL阶段，驱动涡的速度和/或数量起伏很大。我们在那里观察到了很大的宽带噪音。对于薄膜(6 Nm)，在几乎相同的降温条件下也观察到了类似的异常涡旋运动。基于这些结果，我们认为厚膜和薄膜低温液相中的涡旋动力学是由与量子涨落效应有关的共同物理机制所主导的。

We have studied the vortex states at low temperatures (T) and high fields (B) for thick (100 nm) amorphous Mo_xSi_<1-x> films with uniform and strong disorder. We have found that the vortex-liquid phase, so-called the quantum-vortex-liquid(QVL) phase, persists down to T=0. Upon cooling in fixed fields which correspond to the QVL phase at T→O, curvature in the Arrehenius plots of the resistivity changes from downward to upward at certain temperature T_Q, indicative of crossover from temperature dominated to quantum driven fluctuations in the liquid phase. Moreover, the relative width of the QVL phase has been shown to increase along the B and T axes nearly proportional to the normal-state resistivity ρ_n. This is in accord with the view that the QVL phase is caused by strong quantum fluctuations, which are enhanced with increasing ρ_n.We have also studied a change in the vortex dynamics associated with a change in the vortex state from the thermal to quantum liquid by measuring the fluctuating component of the flux-flow voltage δ V(t) about the average voltage. We have found the unusual vortex dynamics in the low-temperature liquid phase. For the thick film, δ V(t) originating from the vortex motion is clearly visible in the QVL phase, where the distribution of δ V(t) is anomalously asymmetric, having a tail which extends to the direction of flux motion. This result implies large velocity and/or number fluctuations of driven vortices in the QVL phase. We have observed large broadband noise there. For the thin (6 nm) film the similar unusual vortex motion is observed in nearly the same reduced-temperature regime. We suggest based on these results that the vortex dynamics in the low-temperature liquid phase of thick and thin films is dominated by common physical mechanisms related to quantum-fluctuation effects.