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arXiv 1302.2964cond-mat.supr-con
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铁基超导体中的s ~+is态的时间折射对称性破缺

s+is State with Broken Time Reversal Symmetry in Fe-Based Superconductors

Saurabh Maiti, Andrey V. Chubukov

摘要:

分析了强空穴掺杂Ba_{1-x} K_xFe_2As_2在x=1和x ~ 0.4(最佳掺杂)之间超导能隙结构的演化。在后一种情况下,配对状态最有可能是s+-,空穴和电子袋上的间隙符号不同,但两个以伽马为中心的空穴袋上的间隙符号相同(空穴袋上的++状态)。在只有空穴的纯KFe_2As_2(x=1)中,激光ARPES数据显示了另一种s+态,即空穴之间的间隙改变符号(a +态)。我们分析了当x -> 1时++ gap如何转化为+- gap。我们发现,这种转变发生通过一个中间的s+is,状态,其中两个空穴袋上的间隙在相位上相差“φ”,这逐渐涉及从“φ”= pi(+-状态)到φ =0(++状态)。这种状态打破了时间反演对称性,具有巨大的应用潜力。我们计算了集体激发的色散,发现两种不同的Leggett型相模在TRSB态的两个端点处软化。

英文摘要:

We analyze the evolution of the superconducting gap structure in strongly hole doped Ba_{1-x}K_xFe_2As_2 between x=1 and x ~ 0.4 (optimal doping). In the latter case, the pairing state is most likely s+-, with different gap signs on hole and electron pockets, but with the same signs of the gap on the two Gamma-centered hole pockets (a ++ state on hole pockets). In a pure KFe_2As_2 (x=1), which has only hole pockets, laser ARPES data suggested another s+- state, in which the gap changes sign between hole pockets (a +- state). We analyze how ++ gap transforms into a +- gap as x -> 1. We found that this transformation occurs via an intermediate s+is, state in which the gaps on the two hole pockets differ in phase by `phi', which gradually involves from `phi' = pi (the +- state) to phi =0 (the ++ state). This state breaks time-reversal symmetry and has huge potential for applications. We compute the dispersion of collective excitations and show that two different Leggett-type phase modes soften at the two end points of TRSB state.

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