AI 中文总结
该研究用无符号问题的量子蒙特卡罗模拟，研究电荷中性时扭曲双层石墨烯相图，探讨其随扭曲角、应变和温度的变化，分析不同条件下的相变、熵变及能谱函数变化，并讨论实验区分相关相的方法。
AI 中文摘要
我们使用无符号问题的量子蒙特卡罗模拟，研究了电荷中性时扭曲双层石墨烯的相图，它是扭曲角θ、单轴异质应变ε和温度T的函数。在T = 0且零应变时，随着θ向魔角减小，发现从狄拉克半金属到带隙的克莱默斯谷间相干（KIVC）相的连续转变。有限应变下，KIVC相在更小θ时进一步连续转变为各向异性半金属。在KIVC区域，熵随温度急剧上升并在15K≤T≤40K达到平稳。能谱函数随θ连续演化，低温时K点出现能隙，中间温度时能谱函数在狄拉克半金属谱与魔角附近以Γ为中心的无隙准粒子谱之间平滑插值。我们还讨论了如何在实验中区分它们。
英文摘要
We study the phase diagram of twisted bilayer graphene at charge neutrality as a function of twist angle $θ$, uniaxial heterostrain $\varepsilon$, and temperature $T$ using sign-problem-free quantum Monte Carlo simulations. At $T=0$ and zero strain, we find a continuous transition from a Dirac semimetal to a gapped Kramers inter-valley coherent (KIVC) phase as $θ$ decreases toward the magic angle. With finite strain, the KIVC phase undergoes a further continuous transition at smaller $θ$ into an anisotropic semimetal with gapless excitations near the center of the moiré Brillouin zone. In the KIVC regime, the entropy rises sharply with temperature and plateaus at $15\,\text{K} \lesssim T \lesssim 40\,\text{K}$ near the value expected from a Mott-like regime of localized electrons with nearly uncorrelated spin, valley, and orbital degrees of freedom, despite the topological obstruction preventing a localized tight-binding description of the active bands. The spectral function evolves continuously with $θ$: at low $T$, a gap opens at the $K$ points and the minimal gap shifts to $Γ$ as $θ$ decreases; at intermediate $T$, the spectral function smoothly interpolates between a Dirac semimetal spectrum with coherent $K$-point quasiparticles and a spectrum with gapless $Γ$-centered quasiparticles near the magic angle. The later can be a anisotropic or a Mott semimetal and we discuss how to distiguish them in experiment.
Comments20 pages, 8 figures
