热无序晶格的拓扑鲁棒性：从平均结构到系综电子性质
Topological robustness of thermally disordered lattices: From average structures to ensemble electronic properties
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中文总结 AI 辅助
本文以Bi$_2$Se$_3$为例，通过分子动力学与蒙特卡洛模拟揭示有限温度下拓扑鲁棒性源于构型系综分布而非平均结构，并发现带反转在600 K以上仍保持。
中文摘要 AI 辅助
能带拓扑通常归属于单一晶体结构，然而在有限温度下，晶体是热无序构型的系综，其带隙存在涨落。我们以Bi$_2$Se$_3$作为代表性拓扑绝缘体，通过缩放自旋轨道耦合对每个从头算分子动力学快照中的能带序进行分类，探究热平均结构是否能忠实代表这一系综。平均结构在两方面失效：它遗漏了瞬时对称性破缺在单个构型中产生的类Rashba自旋劈裂，并且显著低估了带隙重整化；而由谐波蒙特卡洛构型组成的小型系综则能同时再现带隙的平均值和涨落范围。利用带反转存活概率，我们发现Bi$_2$Se$_3$的带反转在高达600 K的每个采样构型中均保持，超过该温度后，单个构型在平均带隙闭合之前便已跨越进入正常能带序。因此，有限温度下的拓扑鲁棒性是构型分布的性质，而非任何单一结构的性质。
英文摘要
Band topology is usually assigned to a single crystal structure, yet at finite temperature a crystal is an ensemble of thermally disordered configurations with a fluctuating band gap. We ask whether the thermally averaged structure is a faithful proxy for this ensemble, taking Bi$_2$Se$_3$ as a representative topological insulator and classifying band ordering in each ab initio molecular dynamics snapshot by scaling the spin-orbit coupling. The averaged structure fails in two ways: it misses the Rashba-like spin splitting that instantaneous symmetry breaking produces in individual configurations, and it substantially underestimates the band-gap renormalization, whereas a small ensemble of harmonic Monte Carlo configurations reproduces both the mean and the spread of the gap. Using a band-inversion survival probability, we find that the band inversion of Bi$_2$Se$_3$ holds in every sampled configuration up to 600 K, above which individual configurations cross into normal band ordering well before the average gap closes. Topological robustness at finite temperature is thus a property of the distribution over configurations rather than of any single structure.
发表机构
- McMaster University（麦克马斯特大学）
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