Hawashin Bilal, Eichhorn Astrid, Janssen Lukas, Scherer Michael M, Ray Shouryya
Theoretical Physics III, Faculty of Physics and Astronomy, Ruhr University Bochum, Bochum, Germany.
CP3-Origins, University of Southern Denmark, Odense, Denmark.
Nat Commun. 2025 Jan 2;16(1):20. doi: 10.1038/s41467-024-54884-w.
The understanding of phenomena falling outside the Ginzburg-Landau paradigm of phase transitions represents a key challenge in condensed matter physics. A famous class of examples is constituted by the putative deconfined quantum critical points between two symmetry-broken phases in layered quantum magnets, such as pressurised SrCu(BO). Experiments find a weak first-order transition, which simulations of relevant microscopic models can reproduce. The origin of this behaviour has been a matter of considerable debate for several years. In this work, we demonstrate that the nature of the deconfined quantum critical point can be best understood in terms of a novel dynamical mechanism, termed Nordic walking. Nordic walking denotes a renormalisation group flow arising from a beta function that is flat over a range of couplings. This gives rise to a logarithmic flow that is faster than the well-known walking behaviour, associated with the annihilation and complexification of fixed points, but still significantly slower than the generic running of couplings. The Nordic-walking mechanism can thus explain weak first-order transitions, but may also play a role in high-energy physics, where it could solve hierarchy problems. We analyse the Wess-Zumino-Witten field theory pertinent to deconfined quantum critical points with a topological term in 2+1 dimensions. To this end, we construct an advanced functional renormalisation group approach based on higher-order regulators. We thereby calculate the beta function directly in 2+1 dimensions and provide evidence for Nordic walking.
理解超出金兹堡 - 朗道相变范式的现象是凝聚态物理中的一个关键挑战。一类著名的例子是由层状量子磁体中两个对称破缺相之间假定的无约束量子临界点构成的，比如加压的SrCu(BO)。实验发现了一个弱一级相变，相关微观模型的模拟可以重现这一现象。这种行为的起源多年来一直是相当有争议的问题。在这项工作中，我们证明无约束量子临界点的本质可以通过一种名为“北欧式行走”的新型动力学机制得到最好的理解。北欧式行走表示一种重整化群流，它源自一个在一定耦合范围内平坦的β函数。这会产生一种对数流，它比与不动点的湮灭和复杂化相关的著名行走行为更快，但仍比耦合的一般跑动慢得多。因此，北欧式行走机制可以解释弱一级相变，而且可能在高能物理中也起作用，在那里它可以解决层级问题。我们分析了与2 + 1维中具有拓扑项的无约束量子临界点相关的韦西 - 祖米诺 - 维滕场论。为此，我们基于高阶调节器构建了一种先进的泛函重整化群方法。由此我们直接在2 + 1维中计算β函数，并为北欧式行走提供证据。
