Title: Insulating and metallic phases in the one-dimensional Hubbard-Su-Schrieffer-Heeger model: Insights from a backflow-inspired variational wave function Show Chinese title

Title: 一维Hubbard-Su-Schrieffer-Heeger模型中的绝缘相和金属相：受回流启发的变分波函数的见解

Abstract: The interplay between electron-electron and electron-phonon interactions is studied in a one-dimensional lattice model, by means of a variational Monte Carlo method based on generalized Jastrow-Slater wave functions. Here, the fermionic part is constructed by a pair-product state, which explicitly depends on the phonon configuration, thus including the electron-phonon coupling in a backflow-inspired way. We report the results for the Hubbard model in presence of the Su-Schrieffer-Heeger coupling to optical phonons, both at half-filling and upon hole doping. At half-filling, the ground state is either a translationally invariant Mott insulator, with gapless spin excitations, or a Peierls insulator, which breaks translations and has fully gapped excitations. Away from half-filling, the charge gap closes in both Mott and Peierls insulators, turning the former into a conventional Luttinger liquid (gapless in all excitation channels). The latter, instead, retains a finite spin gap that closes only above a threshold value of the doping. Even though consistent with the general theory of interacting electrons in one dimension, the existence of such a phase (with gapless charge but gapped spin excitations) has never been demonstrated in a model with repulsive interaction and with only two Fermi points. Since the spin-gapped metal represents the one-dimensional counterpart of a superconductor, our results furnish evidence that a true off-diagonal long-range order may exist in the two-dimensional case. Show Chinese abstract

Abstract: 研究了一维晶格模型中电子-电子相互作用与电子-声子相互作用之间的相互作用，采用基于广义Jastrow-Slater波函数的变分蒙特卡罗方法。 在此，费米子部分由一个对声子构型明确依赖的配对乘积态构建，从而以回流启发的方式包含了电子-声子耦合。 我们报告了在存在Su-Schrieffer-Heeger与光学声子耦合的Hubbard模型的结果，分别在半满填充和空穴掺杂的情况下。 在半满填充时，基态要么是平移不变的Mott绝缘体，具有无能隙的自旋激发，要么是Peierls绝缘体，破坏了平移对称性且具有完全有能隙的激发。 在偏离半满填充时，Mott和Peierls绝缘体中的电荷间隙均关闭，使前者转变为常规Luttinger液体（所有激发通道均无能隙）。 后者则保留有限的自旋间隙，仅在高于临界掺杂值时关闭。 尽管与一维相互作用电子的一般理论一致，但在排斥相互作用模型中，具有两个费米点的这种相的存在从未被证明过（具有无能隙的电荷但有能隙的自旋激发）。 由于自旋有隙金属是一维超导体的对应物，我们的结果提供了证据，表明在二维情况下可能存在真正的非对角长程有序。