Mazza Giacomo, Rösner Malte, Windgätter Lukas, Latini Simone, Hübener Hannes, Millis Andrew J, Rubio Angel, Georges Antoine
Department of Quantum Matter Physics, University of Geneva, Quai Ernest-Ansermet 24, 1211 Geneva, Switzerland.
CPHT, CNRS, Ecole Polytechnique, IP Paris, F-91128 Palaiseau, France.
Phys Rev Lett. 2020 May 15;124(19):197601. doi: 10.1103/PhysRevLett.124.197601.
Ta_{2}NiSe_{5} is one of the most promising materials for hosting an excitonic insulator ground state. While a number of experimental observations have been interpreted in this way, the precise nature of the symmetry breaking occurring in Ta_{2}NiSe_{5}, the electronic order parameter, and a realistic microscopic description of the transition mechanism are, however, missing. By a symmetry analysis based on first-principles calculations, we uncover the discrete lattice symmetries which are broken at the transition. We identify a purely electronic order parameter of excitonic nature that breaks these discrete crystal symmetries and contributes to the experimentally observed lattice distortion from an orthorombic to a monoclinic phase. Our results provide a theoretical framework to understand and analyze the excitonic transition in Ta_{2}NiSe_{5} and settle the fundamental questions about symmetry breaking governing the spontaneous formation of excitonic insulating phases in solid-state materials.
Ta₂NiSe₅是承载激子绝缘体基态最有前景的材料之一。虽然已有许多实验观测结果被如此解释，但Ta₂NiSe₅中发生的对称性破缺的确切性质、电子序参量以及对转变机制的实际微观描述却仍未明确。通过基于第一性原理计算的对称性分析，我们揭示了在转变时被打破的离散晶格对称性。我们确定了一个具有激子性质的纯电子序参量，它打破了这些离散晶体对称性，并导致了实验观测到的从正交相到单斜相的晶格畸变。我们的结果提供了一个理论框架，用于理解和分析Ta₂NiSe₅中的激子转变，并解决了关于对称性破缺控制固态材料中激子绝缘相自发形成的基本问题。
