非平衡破缺对称态：由保留可观测量导出
Nonequilibrium Broken-Symmetry States from Retained Observables
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中文总结 AI 辅助
本文提出将非平衡破缺对称态的动力学选择重构为静态约束变分问题，利用保留可观测量定义约束空间，通过约束Hartree-Fock高效识别光激发Hubbard模型及驱动双交换模型中的非平衡序。
中文摘要 AI 辅助
在平衡态中，破缺对称态由能量与熵之间的竞争所选择。在非平衡态下，缓慢弛豫的可观测量保留着关于制备过程的信息，并可能重塑这种竞争，从而允许出现热力学上不利的序。识别此类态通常需要跟踪缓慢的、依赖协议的动力演化。这里我们将这种动力学选择重新表述为一个静态约束变分问题。一小部分实验可测量或数值可获取的量——粒子数、能量和慢可观测量——定义了约束空间。底层动力学决定了系统在该空间中的位置，而对准粒子占据数和一类指定的候选序同时进行熵最大化则决定了选择何种序。将变分态限制在高斯流形上，可以得到一种计算成本低廉的约束Hartree-Fock实现。对于光激发Hubbard模型，该方法重现了长时间TDHF对正方晶格反铁磁性的抑制，并在三角晶格上识别出非公度螺旋序取代平衡态的$120^\circ$态。对于连续驱动的铁磁双交换模型，在稳态非平衡态（NESS）能量处评估约束序图，揭示了一个有利于Néel序的受限区域。因此，该框架将寻找非平衡破缺对称态转化为一个实用的静态筛选问题，无需对每种制备协议进行模拟。
英文摘要
In equilibrium, broken-symmetry states are selected by the competition between energy and entropy. Out of equilibrium, slowly relaxing observables retain information about the preparation and may reshape this competition, allowing orders that are not thermally favored. Identifying such states ordinarily requires following slow, protocol-dependent dynamics. Here we recast this dynamical selection as a static constrained variational problem. A small set of experimentally measurable or numerically accessible quantities-particle number, energy, and slow observables-defines a constraint space. The underlying dynamics determines where the system lies in this space, while entropy maximization over both quasiparticle occupations and a prescribed class of candidate orders determines which order is selected. Restricting the variational states to the Gaussian manifold yields a computationally inexpensive constrained Hartree-Fock implementation. For photoexcited Hubbard models, the approach reproduces the long-time TDHF suppression of square-lattice antiferromagnetism and identifies incommensurate spiral order in place of the equilibrium $120^\circ$ state on the triangular lattice. For a continuously driven ferromagnetic double-exchange model, evaluating the constrained order map at the stationary NESS energy reveals a restricted region in which Neel order is favored. The framework therefore turns the search for nonequilibrium broken-symmetry states into a practical static screening problem, without requiring simulations of every preparation protocol.
发表机构
- University of Virginia（弗吉尼亚大学）
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