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arXiv 1703.02541cond-mat.supr-concond-mat.str-el
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对密度波超导态中的Higgs模

Higgs Modes in the Pair Density Wave Superconducting State

Rodrigo Soto-Garrido, Yuxuan Wang, Eduardo Fradkin, S. Lance Cooper

摘要:

对密度波(PDW)超导态已被提出来解释在化合物La $_{2-x}$ Ba $_x$ CuO $_4$在$x=1/8$(Phys.Rev.Lett. 99,127003)。在这种状态下,超导序参量是空间调制的,与通常的超导(SC)状态(其中序参量是均匀的)形成鲜明对比。在这项工作中,我们研究的振幅(希格斯)模式在单向PDW状态的属性。为此,我们考虑耦合到费米准粒子费米面的PDW型态的唯象模型。与具有单个希格斯模式的常规超导体相比,单向PDW超导体具有两个希格斯模式。虽然在PDW状态下费米表面基本上保持无带隙,但我们发现PDW希格斯模衰减为费米子准粒子需要超过能量阈值。我们表明,这种抑制阻尼PDW状态是由于运动学。结果,两个希格斯模式中只有一个被显著阻尼。此外,受实验相图的启发,我们讨论了在PDW和均匀SC态共存的制度中Higgs模的混合。这些结果应该可以直接观察到的拉曼光谱,在动量分辨电子能量损失光谱,并在共振非弹性X射线散射,从而提供证据的PDW状态。

英文摘要:

The pair density wave (PDW) superconducting state has been proposed to explain the layer- decoupling effect observed in the compound La$_{2-x}$Ba$_x$CuO$_4$ at $x=1/8$ (Phys. Rev. Lett. 99, 127003). In this state the superconducting order parameter is spatially modulated, in contrast with the usual superconducting (SC) state where the order parameter is uniform. In this work, we study the properties of the amplitude (Higgs) modes in a unidirectional PDW state. To this end we consider a phenomenological model of PDW type states coupled to a Fermi surface of fermionic quasiparticles. In contrast to conventional superconductors that have a single Higgs mode, unidirectional PDW superconductors have two Higgs modes. While in the PDW state the Fermi surface largely remains gapless, we find that the damping of the PDW Higgs modes into fermionic quasiparticles requires exceeding an energy threshold. We show that this suppression of damping in the PDW state is due to kinematics. As a result, only one of the two Higgs modes is significantly damped. In addition, motivated by the experimental phase diagram, we discuss the mixing of Higgs modes in the coexistence regime of the PDW and uniform SC states. These results should be observable directly in a Raman spectroscopy, in momentum resolved electron energy loss spectroscopy, and in resonant inelastic X-ray scattering, thus providing evidence of the PDW states.

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