Institute for Advanced Study, Tsinghua University, Beijing 100084, China.
State Key Laboratory of Low Dimensional Quantum Physics, Tsinghua University, Beijing 100084, China.
Phys Rev Lett. 2018 May 25;120(21):215702. doi: 10.1103/PhysRevLett.120.215702.
Tricriticality, as a sister of criticality, is a fundamental and absorbing issue in condensed-matter physics. It has been verified that the bosonic Wilson-Fisher universality class can be changed by gapless fermionic modes at criticality. However, the counterpart phenomena at tricriticality have rarely been explored. In this Letter, we study a model in which a tricritical Ising model is coupled to massless Dirac fermions. We find that the massless Dirac fermions result in the emergence of a new tricritical point, which we refer to as the chiral tricritical point (CTP), at the phase boundary between the Dirac semimetal and the charge-density wave insulator. From functional renormalization group analysis of the effective action, we obtain the critical behaviors of the CTP, which are qualitatively distinct from both the tricritical Ising universality and the chiral Ising universality. We further extend the calculations of the chiral tricritical behaviors of Ising spins to the case of Heisenberg spins. The experimental relevance of the CTP in two-dimensional Dirac semimetals is also discussed.
三重临界点是凝聚态物理中的一个基本且引人入胜的问题，它与临界点类似。已经证实，玻色子 Wilson-Fisher 普遍类可以通过无能隙费米子模式在临界点发生变化。然而，三重临界点的对应现象很少被探索。在这封信中，我们研究了一个模型，其中一个三重临界点 Ising 模型与无质量狄拉克费米子耦合。我们发现，无质量狄拉克费米子导致在 Dirac 半金属和电荷密度波绝缘体之间的相边界处出现一个新的三重临界点，我们称之为手征三重临界点（CTP）。从有效作用的泛函重整化群分析中，我们得到了 CTP 的临界行为，这与三重临界点 Ising 普遍和手征 Ising 普遍都有定性的不同。我们进一步将 Ising 自旋的手征三重临界行为的计算扩展到海森堡自旋的情况。还讨论了 CTP 在二维 Dirac 半金属中的实验相关性。
