We present a sign-problem-free quantum Monte Carlo study of a model that exhibits quantum phase transitions without symmetry breaking and associated changes in the size of the Fermi surface. The model is an Ising gauge theory on the square lattice coupled to an Ising matter field and spinful “orthogonal” fermions at half filling, both carrying Ising gauge charges. In contrast to previous studies, our model hosts an electronlike, gauge-neutral fermion excitation providing access to Fermi-liquid phases. One of the phases of the model is a previously studied orthogonal semimetal, which has ${\mathbb{Z}}_2$ topological order and Luttinger-volume-violating Fermi points with gapless orthogonal fermion excitations. We elucidate the global phase diagram of the model: Along with a conventional Fermi-liquid phase with a large Luttinger-volume Fermi surface, we also find a “deconfined” Fermi liquid in which the large Fermi surface coexists with fractionalized excitations. We present results for the electron spectral function, showing its evolution from the orthogonal semimetal with a spectral weight near momenta $\{\pm \pi /2,\pm \pi /2\}$ to a large Fermi surface.

中文翻译：

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费米表面重建，不破坏对称性

我们提出了一个无符号问题的量子蒙特卡洛模型研究，该模型展示了量子相变而没有对称性破坏以及费米表面尺寸的相关变化。该模型是基于Ising量规的方格理论，耦合到Ising物质场和半填充时有刺的“正交”费米子，均携带Ising量规电荷。与以前的研究相比，我们的模型具有类似电子的，规中性的费米子激发态，提供了进入费米液相的通道。该模型的一个阶段是先前研究的正交半金属，它具有${\mathbb{ž}}_2$具有无间隙正交费米子激发的拓扑阶和违反Luttinger量的费米点。我们阐明了该模型的整体相图：除了具有大Luttinger体积费米表面的常规费米液相外，我们还发现了一种“受限”费米液体，其中大费米表面与分次激发共存。我们给出了电子光谱函数的结果，显示了它从正交半金属的演化，其光谱权重接近动量。$\{\pm \pi /2，\pm \pi /2\}$ 到大费米表面。