Fe-磷属元素化物超导体中能隙表面束缚态证明可能的$s^{\pm}$波配对
Possible $s^{\pm}$-wave pairing evidenced by midgap surface bound states in Fe-pnictide superconductors
摘要：
考虑粒子与空穴之间的非对称界面散射，建立了铁磷属元素化物超导体隧道谱的唯象理论。结果表明，与反相$s^{\pm}$波配对一致，Fe-磷属元素化物超导体[100]表面存在明显的零能表面束缚态.然而，与$d$波铜氧化物超导体中的[110]束缚态相反，这些束缚态是由于隧穿电子和$s^{\pm}$配对的垂直于界面的动量不守恒而产生的，因此它们只能存在于[100]方向附近边缘取向的小窗口（$\sim \pm 6^{\circ}$）中。我们的结果解释了为什么在隧道谱中经常观察到零偏压电导峰，当它消失时，出现两个相干峰。这些结果提供了明确的信号，以测试可能的$s^{\pm}$波配对的Fe-磷属元素化物超导体。
英文摘要：
A phenomenological theory of tunneling spectroscopy for Fe-pnictide superconductors is developed by taking into consideration of asymmetric interface scattering between particle and holes. It is shown that in consistent with anti-phase $s^{\pm}$-wave pairing, appreciable zero-energy surface bound states exist on the [100] surface of Fe-pnictide superconductors. However, in contrast to the [110] bound states in $d$-wave cuprate superconductors, these bound states arise as a result of non-conservation of momentum perpendicular to the interface for tunneling electrons and the $s^{\pm}$ pairing, and hence they can only exist in a small window ($\sim \pm 6^{\circ}$) in the orientation of edges near [100] direction. Our results explain why zero-bias conductance peak is often observed in tunneling spectroscopy and when it disappears, two coherent peaks show up. These results provide unambiguous signals to test the possible $s^{\pm}$-wave pairing in Fe-pnictide superconductors.
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