无序二维薄膜中超导-绝缘体转变的起源
Origin of the superconductor-insulator transition in disordered two-dimensional films
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中文总结 AI 辅助
本研究探究无序二维薄膜中超导-绝缘体转变的起源，通过分析宽范围无序度下的薄层电阻与超流刚度演化，明确SIT附近有限温度转变仍为BKT型，零温转变由量子相位涨落驱动。
中文摘要 AI 辅助
理论预测，超导到绝缘体的转变（SIT）源于安德森局域化与超导性之间的竞争：安德森局域化倾向于使单粒子波函数局域化，而超导性则在超导序参量中建立长程关联。在二维（2D）超导薄膜中，电阻消失的转变温度$T_\text{c}$满足$R_\text{\Box}(T_\text{BKT}){=}0$，该转变由别列津斯基-科斯特利茨-索利斯（BKT）机制决定，且满足$T_\text{BKT}< T_{c0}$，其中$T_{c0}$为平均场转变温度。在弱无序样品中，$T_\text{BKT}\lesssim T_{c0}$；而随着无序度增加，在SIT附近$T_\text{BKT}\ll T_{c0}$。有限温度转变是否在整个交叉过程中保持BKT特性仍是一个开放问题。在此，我们在宽范围的无序强度$W$上研究了薄层电阻$R_\text{\Box}(T)$和超流刚度$J_s(T)$的演化。我们证实，即使在SIT附近，超导态到阻态的有限温度转变仍为BKT型。然而，当无序度接近临界值时，零温超流相位刚度$J_s(0)$会迅速消失，而$T_{c0}$仍保持有限，我们将此归因于量子相位涨落作为零温转变的驱动力。在Haviland、Liu和Goldman实验发现该现象三十年后，我们的测量结果阐明了二维薄膜中SIT的起源。
英文摘要
Theory predicts the superconductor-to-insulator transition (SIT) to emerge from the competition between Anderson localization, which tends to localize single-particle wavefunctions, and superconductivity, which establishes long-range correlations in the superconducting order parameter. In two-dimensional (2D) superconducting films, the transition temperature $T_\text{c}$ at which resistance vanishes, $R_\Box(T_\text{BKT}){=}0$, is set by the Berezinskii-Kosterlitz-Thouless (BKT) mechanism and satisfies $T_\text{BKT}< T_{c0}$, where $T_{c0}$ is the mean-field transition temperature. In weakly disordered samples $T_\text{BKT}\lesssim T_{c0}$, whereas increasing disorder drives $T_\text{BKT}\ll T_{c0}$ near the SIT. Whether the finite-temperature transition retains its BKT character throughout this crossover remains an open question. Here, we investigate the evolution of both sheet resistance $R_\Box(T)$ and superfluid stiffness $J_s(T)$ over a wide range of disorder strength $W$. We establish that even near the SIT, the finite-temperature transition from the superconducting to the resistive state remains of BKT type. However, as disorder approaches the critical value, the zero temperature superfluid phase stiffness, $J_s(0)$, is found to vanish rapidly while $T_{c0}$ remains finite, which we attribute to quantum phase fluctuations as the drive for the zero-temperature transition. Three decades after its experimental discovery by Haviland, Liu, and Goldman, our measurements clarify the origin of the SIT in 2D films.
