Weak-coupling theory of pair density wave instabilities in transition metal dichalcogenides
Weak-coupling theory of pair density wave instabilities in transition metal dichalcogenides
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DOI：
10.1103/physrevb.107.224516
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发表时间：
2022-09
影响因子：
3.7
通讯作者：
D. Shaffer;F. Burnell;R. Fernandes
中科院分区：
文献类型：
--
作者：
D. Shaffer;F. Burnell;R. Fernandes
实现对密度波（PDW）相位的可能性，其中库珀对具有有限的动量，提出了一个有趣的挑战，已经在各种各样的系统中进行了研究。在传统的超导体中，只有当外部场提升费米表面的自旋简并度，导致以不相称的动量形成对时，这才有可能。在这里，我们研究了第二种可能性，可能与过渡金属dichalcogenides，其中费米表面由一对口袋集中在$\pm K$点的布里渊区，以及在$\Gamma$点的中央口袋。在这三个口袋是相同的限制，配对磁化率在非零波矢量$\pm \mathbf{K}$有对数发散，允许弱耦合分析的PDW不稳定性。我们发现，排斥电子相互作用联合收割机产生有效的吸引力的相互作用，在单重态和三重态PDW通道，只要$\Gamma$口袋存在。由于这些PDW通道与均匀超导通道解耦，它们可能成为系统的主要非常规配对不稳定性。在解决线性化的间隙方程，我们发现，PDW不稳定性是强大的对小三角翘曲的$\pm K$口袋和小失谐之间的$\Gamma$和$\pm K$口袋，影响PDW过渡的塞曼磁场影响均匀超导过渡的类似方式。我们还得到了金兹伯格-朗道自由能的PDW带隙动量$\pm \mathbf{K}$，分析了FF型和LO型PDW基态出现的条件和后果。我们的分类在每个基态的诱导订单揭示了不寻常的阶段，包括一个奇频电荷2 e $超导体在LO型PDW。
The possibility of realizing pair density wave (PDW) phases, in which Cooper pairs have a finite momentum, presents an interesting challenge that has been studied in a wide variety of systems. In conventional superconductors, this is only possible when external fields lift the spin degeneracy of the Fermi surface, leading to pair formation at an incommensurate momentum. Here, we study a second possibility, potentially relevant to transition metal dichalcogenides, in which the Fermi surface consists of a pair of pockets centered at the $\pm K$ points of the Brillouin zone as well as a central pocket at the $\Gamma$ point. In the limit where these three pockets are identical, the pairing susceptibility has a logarithmic divergence at the non-zero wave-vectors $\pm \mathbf{K}$, allowing for a weak-coupling analysis of the PDW instability. We find that repulsive electronic interactions combine to yield effective attractive interactions in the singlet and triplet PDW channels, as long as the $\Gamma$ pocket is present. Because these PDW channels decouple from the uniform superconducting channel, they can become the leading unconventional pairing instability of the system. Upon solving the linearized gap equations, we find that the PDW instability is robust against small trigonal warping of the $\pm K$ pockets and small detuning between the $\Gamma$ and $\pm K$ pockets, which affect the PDW transition in a similar way as the Zeeman magnetic field affects the uniform superconducting transition. We also derive the Ginzburg-Landau free energy for the PDW gaps with momenta $\pm \mathbf{K}$, analyzing the conditions for and consequences of the emergence of FF-type and LO-type PDW ground states. Our classification of the induced orders in each ground state reveals unusual phases, including an odd-frequency charge-$2e$ superconductor in the LO-type PDW.