标题： 无序超导体中预形成库珀对的集体能隙 显示英文标题

标题： Collective energy gap of preformed Cooper-pairs in disordered superconductors

摘要： 在大多数超导体中，向超导态的转变是由电子形成库珀对所驱动的。这些对的凝聚进入一个单一的、相位相干的量子态是在临界温度$T_c$时与它们的形成同时发生的。在一些无序的、非晶态的超导体中出现了一个不同的情景：而不是由配对驱动的转变，在$T_c$以上首先形成非相干的库珀对，导致伪间隙的打开，然后在$T_c$时凝聚成相位相干的超导态。这种两步情景暗示着一个新的能量尺度$\Delta_{c}$，驱动预先形成的对的集体超导转变。在这里，我们通过非晶氧化铟超导薄膜的安德列夫谱学揭示了这个能量尺度。我们在$\pm \Delta_{c}$处观察到两个安德列夫电导峰，这些峰仅在$T_c$以下以及在接近绝缘体转变边缘的高无序薄膜中出现。我们的发现表明，非晶超导薄膜为探索预先形成的库珀对的集体超流转变提供了典型的无序量子系统。 显示英文摘要

摘要： In most superconductors the transition to the superconducting state is driven by the binding of electrons into Cooper-pairs. The condensation of these pairs into a single, phase coherent, quantum state takes place concomitantly with their formation at the transition temperature, $T_c$. A different scenario occurs in some disordered, amorphous, superconductors: Instead of a pairing-driven transition, incoherent Cooper pairs first pre-form above $T_c$, causing the opening of a pseudogap, and then, at $T_c$, condense into the phase coherent superconducting state. Such a two-step scenario implies the existence of a new energy scale, $\Delta_{c}$, driving the collective superconducting transition of the preformed pairs. Here we unveil this energy scale by means of Andreev spectroscopy in superconducting thin films of amorphous indium oxide. We observe two Andreev conductance peaks at $\pm \Delta_{c}$ that develop only below $T_c$ and for highly disordered films on the verge of the transition to insulator. Our findings demonstrate that amorphous superconducting films provide prototypical disordered quantum systems to explore the collective superfluid transition of preformed Cooper-pairs pairs.