西亚试剂：Electron pairing without superconductivity

Strontium titanate (SrTiO3) is the first and best known superconducting semiconductor1. It exhibits an extremely low carrier density threshold for superconductivity2, and possesses a phase diagram similar to that of high-temperature superconductors3, 4—two factors that suggest an unconventional pairing mechanism. Despite sustained interest for 50 years, direct experimental insight into the nature of electron pairing in SrTiO3 has remained elusive. Here we perform transport experiments with nanowire-based single-electron transistors at the interface between SrTiO3 and a thin layer of lanthanum aluminate, LaAlO3. Electrostatic gating reveals a series of two-electron conductance resonances—paired electron states—that bifurcate above a critical pairing field Bp of about 1–4 tesla, an order of magnitude larger than the superconducting critical magnetic field. For magnetic fields below Bp, these resonances are insensitive to the applied magnetic field; for fields in excess of Bp, the resonances exhibit a linear Zeeman-like energy splitting. Electron pairing is stable at temperatures as high as 900 millikelvin, well above the superconducting transition temperature (about 300 millikelvin). These experiments demonstrate the existence of a robust electronic phase in which electrons pair without forming a superconducting state. Key experimental signatures are captured by a model involving an attractive Hubbard interaction that describes real-space electron pairing as a precursor to superconductivity.钛酸锶是一种异乎寻常的半导体，在其中电子被认为不仅在超导状态下成对，而且在没有超导性的更高温度下也成对。现在，Guanglei Cheng及同事发表了这一系统中在远高于超导转变温度的温度下电子成对的直接证据。作者认为，这些是人们长期寻找的预先形成的电子对，它们在较低温度下凝聚，以在这一系统中产生非传统的超导状态。

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