论文标题
在MoiréBiLayer中用激子掺杂Mott绝缘子：分数超流体，中性费米表面和Mott Transition
Doping a Mott insulator with excitons in moiré bilayer: fractional superfluid, neutral Fermi surface and Mott transition
论文作者
论文摘要
在本文中，我们探讨了在MoiréBiLayers的背景下将中性激子掺杂到Mott绝缘子中引起的可能阶段。我们考虑只有通过层间排斥而结合在一起的两个Moiré层，并且有一个u（2）$ \ times $ u（2）对称。两层的密度可以调节为$ n_t = x，n_b = 1-x $，$ n_t+n_b = 1 $。 $ x = 0 $ limit是一个层偏光莫特绝缘子，可以通过以密度$ x $的掺杂层间激子来达到小$ x $制度。在WSE $ _2 $ -HBN-WSE $ _2 $/ws $ _2 $ System中，充电差距可以保持在小$ x $的有限元。为了捕获自旋和激子自由度的交织，我们提出了一个四种风味的自旋模型。除了明显的单激子冷凝阶段的可能性外，我们还确定了具有分数的更奇特的物理：（i）我们分别为两层定义了自旋间隙$Δ_T，δ_b$。只要任一层的自旋隙都是有限的，单激子冷凝是不可能的，我们只能具有配对的激子冷凝。如果两个自旋差距都是有限的，则可以是分数激子超流体，并与$ z_2 $旋转液体共存配对激子冷凝。将提供有关此类阶段的数值证据。 （ii）如果$ x = 0 $的层极化莫特绝缘子在u（1）带有Spinon fermi表面的自旋液体中，则在$ x> 0 $的自然相位是由费米子激子形成的中性费米表面。在这个异国情调的相位，有金属的反流传输以及层极化的弗里德尔振荡。我们在一个维度上的数值模拟观察到了这种中性费米表面相的类似物。 （iii）通过在带宽调谐的MIT的通用类中调整$ x $，可能会有金属 - 绝缘体过渡（MIT）。我们为这种连续的莫特过渡提供了一种理论，并预测了普遍的阻力电阻率。
In this paper we explore possible phases arising from doping neutral excitons into a Mott insulator in the context of moiré bilayers. We consider two moiré layers coupled together only through inter-layer repulsion and there is a U(2)$\times$ U(2) symmetry. The densities of the two layers can be tuned to be $n_t=x,n_b=1-x$ with $n_t+n_b=1$. $x=0$ limit is a layer polarized Mott insulator and small $x$ regime can be reached by doping inter-layer excitons at density $x$. Charge gap can remain finite at small $x$, as is demonstrated experimentally in the WSe$_2$-hBN-WSe$_2$/WS$_2$ system. To capture the intertwinement of the spin and exciton degree of freedom, we propose a four-flavor spin model. In addition to the obvious possibility of single exciton condensation phase, we also identified more exotic physics with fractionalization: (I) We define spin gap $Δ_t, Δ_b$ for the two layers respectively. As long as the spin gap at either layer is finite, single exciton condensation is impossible and we can only have paired exciton condensation. If both spin gaps are finite, it can be a fractional exciton superfluid with paired exciton condensation coexisting with $Z_2$ spin liquid. Numerical evidences for such a phase will be provided. (II) If the layer polarized Mott insulator at $x=0$ is in a U(1) spin liquid with spinon Fermi surface, the natural phase at $x>0$ hosts neutral Fermi surface formed by fermionic excitons. There are metallic counter-flow transport and also Friedel oscillations in layer polarization in this exotic phase. Our numerical simulation in one dimension observes an analog of this neutral Fermi surface phase. (III) There could be a metal-insulator transition (MIT) by tuning $x$ in the universality class of a bandwidth tuned MIT. We provide one theory for such a continuous Mott transition and predicted a universal drag resistivity.
