巡游费米子系统量子相变的重整化φ ^6模型
Renormalized phi^6 model for quantum phase transitions in systems of itinerant fermions
摘要：
我们研究了量子涨落和热涨落对巡游费米子系统中量子相变性质的影响，主要关注这些相变的顺序。我们的方法是基于一组流方程推导的功能重整化群框架内，其中的序参量被保留作为唯一的自由度，并在有效势参数化与φ ^6的形式允许一阶和二阶的情况。我们发现一种趋势，把裸模型内的一阶转变为二阶转变后占序参量波动。我们计算了在量子相变附近作为非热控制参数a_2的函数的一级和二级相边界线T_c。我们分析了当系统被调谐到接近量子三临界的情形时，控制Tc线形状的移位指数psi的交叉，其中二阶相变线终止于量子三临界点。
英文摘要：
We study the impact of quantum and thermal fluctuations on properties of quantum phase transitions occurring in systems of itinerant fermions with main focus on the order of these transitions. Our approach is based on a set of flow equations derived within the functional renormalization group framework, in which the order parameter is retained as the only degree of freedom, and where the effective potential is parametrized with a phi^6 form allowing for both first and second order scenarios. We find a tendency to turn the first order transitions within the bare model into second order transitions upon accounting for the order parameter fluctuations. We compute the first and second order phase boundary lines T_c as a function of a non-thermal control parameter a_2 in the vicinity of a quantum phase transition. We analyze crossovers of the shift exponent psi governing the shape of the T_c line when the system is tuned close to a quantum tricritical scenario, where a second order phase transition line terminates at a quantum tricritical point.
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