含1 1/3价铜的二维超导体CuS的结构和电子性质
Structural and Electronic Properties of the 2D Superconductor CuS with 1 1/3-valent Copper
摘要：
我们提出了第一原理计算的结构和电子性质的硫化铜铜蓝材料。对称性降低的结构转变被很好地再现。然而，这种转变的微观起源尚不清楚。计算结果坚定地表明，迄今为止，该化合物中有争议的Cu化合价为1.33。我们还认为，最近报道的高温超导CuS不太可能发生在化学计量的无缺陷材料，因为确定的Cu价太接近1，以确保接近莫特-哈伯德状态和超交换自旋波动相当大的强度。另一方面，可以想象一个相关的系统，在相同的结构基序中每个Cu具有更多的空穴（$e.g.$，由于缺陷或O杂质），在这种情况下，超交换和与CuS费米表面相比扩大的组合可能会导致非常规的超导性，类似于HTSC铜酸盐，但与它们不同的是，具有$f$波对称性。
英文摘要：
We present first principle calculations of the structural and electronic properties of the CuS covellite material. Symmetry-lowering structural transition is well reproduced. However, the microscopic origin of the transition is unclear. The calculations firmly establish that the so far controversial Cu valency in this compound is 1.33. We also argue that recently reported high-temperature superconductivity in CuS is unlikely to occur in the stoichiometric defect-free material, since the determined Cu valency is too close to 1 to ensure proximity to a Mott-Hubbard state and superexchange spin fluctuations of considerable strength. On the other hand, one can imagine a related system with more holes per Cu in the same structural motif ($e.g.$, due to defects or O impurities) in which case combination of superexchange and an enlarged compared to CuS Fermi surface may lead to unconventional superconductivity, similar to HTSC cuprates, but, unlike them, of an $f$-wave symmetry.
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