无热力学极限的量子相变
Quantum phase transitions without thermodynamic limits
摘要：
对有限维量子系统引入了一种新的微正则平衡态。平衡的特征是哈密顿量的期望值在水平面上均匀分布。提出的平衡态的显着特点是，相应的态密度是能量的连续函数，因此热力学函数是有限量子系统定义良好。然而，态密度一般不是一个解析函数。它表明，通用的量子系统，因此表现出二阶（连续）相变在有限的温度。
英文摘要：
A new microcanonical equilibrium state is introduced for quantum systems with finite-dimensional state spaces. Equilibrium is characterised by a uniform distribution on a level surface of the expectation value of the Hamiltonian. The distinguishing feature of the proposed equilibrium state is that the corresponding density of states is a continuous function of the energy, and hence thermodynamic functions are well defined for finite quantum systems. The density of states, however, is not in general an analytic function. It is demonstrated that generic quantum systems therefore exhibit second-order (continuous) phase transitions at finite temperatures.
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