Dynamic critical exponents as an emergent property at interacting topological quantum critical points

Abstract

In standard studies of quantum critical points (QCPs), the dynamic critical exponent $z$ is introduced as a fundamental parameter along with global symmetries to identify universality classes. Often, the dynamic critical exponent $z$ is set to be one as the most natural choice for quantum field theory representations, which further implies emergence of higher space-time symmetries near QCPs in many condensed matter systems. In this article, we study a family of topological quantum critical points (tQCPs) where the $z=1$ quantum field theory is prohibited in a fundamental representation by a protecting symmetry, resulting in tQCPs with $z=2$. We further illustrate that when strong interactions are properly taken into account, the stable weakly interacting gapless tQCPs with $z=2$ can further make a transition to another family of gapless tQCPs with dynamic critical exponent $z=1$, without breaking the protecting symmetry. Our studies suggest that dynamic critical exponents, as well as the degrees of freedom in fermion fields, can crucially depend on interactions in topological quantum phase transitions; in tQCPs, to a large extent, they are better thought of as emergent properties.

6 pages, 2 figures

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