arXiv:2605.24061

Universal classification of continuous phase transitions with two order parameters

Yilun Xu, Feng-xiao Sun

cond-mat.stat-mechquant-phSubmitted May 22, 2026• Announced May 25, 2026• 0 citations

Abstract

The continuous phase transition, indicated by the macroscopic order parameter and the occurrence of the spontaneous symmetry breaking, is well illustrated based on the Ginzburg-Landau's paradigm. In systems described by one order parameter, the phase diagram is only composed of the normal phase and the ordered phase. However, in systems with two or more order parameters, much richer phase diagrams and critical phenomena may emerge. According to coupling terms of the free energy, we classify the systems with two order parameters into several categories, featuring different patterns of phase diagrams and critical scalings respectively. Our work propose the new avenue to studying and evaluating the complex systems only based on the coupling terms in expressions of free energy.

Related papers

Induced phase transitions and spontaneous symmetry breaking based on the renormalized Ginzburg-Landau theory

Feulefack Ornela Claire, Carlos TSAGUE FOTIO, Keumo Tsiaze Roger Magloire +2 more

In this study, we present theoretical investigations of phase transitions and critical phenomena in materials through the lens of second-order Ginzburg-Landau theory, in conjunction with considerations of symmetry groups and thermal fluctuations. By addressing the residual effects after a renormalization process, a small number of macroscopic degrees of freedom can effectively replace the infinite number of microscopic degrees of freedom, emphasizing the significant role of dimensionality and the intrinsic characteristics of the system in understanding and analyzing transitions. We highlight several non-universal characteristics of continuous phase transitions near the transition temperature, including the non-monotonic relationship between the critical temperature and dimensionality, as well as the enhancement or disappearance of the specific heat jump in complex superconductors. While the resulting expressions for thermodynamic quantities are complex for one-dimensional systems, obeying Mermin-Wagner's theorem, they are considerably simplified for two-dimensional and three-dimensional systems.

arXiv:2507.07534Jul 10, 20250 citations

Superradiance enhances and suppresses fermionic pairing based on universal critical scaling in two order parameters systems

Yilun Xu

Distinguished from the system with one order parameter, systems described by two or more order parameters will manifest more complex and much richer phase diagram and critical phenomena. In systems of two order parameters, the phase transition of one order parameter may influence the strength of another. Focus on the Landau's theory of continuous phase transitions, we give a general physcial quantity to decide the changing rate of the two order parameters based on a general formula of free energy. Taking two-mode Rabi model and the 1D Fermi Dicke model as the examples, we verify our analytical results and show how the superradiant phase transition manipulates the two-spin pairing strength and the superconductor band gap. Our work proposes the new paradigm to study the complex systems with two or more order parameters and provides novel avenue to enhancing or suppressing the desired physical effect by such interplay.

cond-mat.quant-gasCross-listedarXiv:2604.07407Apr 9, 20260 citations

Beyond-Landau Phase Transitions: Topological Order and Deconfined Quantum Criticality — E8 Intelligence Research

Andrew Stewart Caldin

FINDING: Phase transitions exist that violate the Landau paradigm — they occur without any spontaneous symmetry breaking and are instead governed by topological order and deconfined quantum criticality. | MATH: Landau free energy F = F₀ + a(T−T_c)φ² + bφ⁴ + ... (order parameter φ, symmetry-breaking potential). Beyond-Landau transitions: (1) Deconfined quantum criticality (Senthil et al.) — continuous transition between two ordered phases with *different* broken symmetries, no Ginzburg-Landau order parameter connects them; (2) Topological phase transitions — characterized by topological invariants (Chern number C = (1/2π)∮ F d²k, Z₂ invariant ν, winding numbers), not local order parameters; (3) "Zwillingsphasen" (twin phases) — second-order transition between phases without hidden symmetry breaking. | CONNECTION: Topological invariants are integer-valued (C ∈ ℤ, ν ∈ {0,1}) — quantized, not continuous. This is a *discrete* mathematical structure underlying continuous physical transitions Author: Andrew Stewart Caldin, Independent Researcher, UK. Part of the E8 Intelligence Research series. Platform: e8intelligence.com

Oct 27, 20260 citations

Phenomenological Free-Energy-Function, Fractal Dimension, and Critical Indices for Phase Transition Systems

Lun‐Biao Xu, Zhijian Wang

Considering the relations between interaction terms in microscopic Hamiltonian and terms in macroscopic Landau's free-energy-function (FEF) of a phase transition system, we propose a modified Landau's phenomenological FEF to deal with critical phenomena. According to scaling symmetry, it is indeed true that, the dimension of interaction space is fractal at critical points for a phase transition system. Following these analyses, we obtain all the critical indices reasonably classified in the classes denoted by , which satisfy all the scaling laws and coincide with experiments. A cogent example is given.

Communications in Theoretical PhysicsOct 1, 19911 citation

Topological Quantum Phase Transitions

M. A. Contínentino

The Landau Paradigm The usual paradigm to describe phase transitions is that of Landau. It is based on an expansion of a free energy functional or an action in terms of an order parameter. Close to the phase transition the order parameter is small, and only terms dictated by symmetry are allowed in this expansion. Associated with this paradigm are many important ideas, such as that of broken symmetry and Goldstone modes. The extension of this paradigm to include quantum phase transitions certainly brought new ideas and progress, as we have seen in this book: the inextricability between the dynamics and static properties, the modified hyperscaling relation with the notion of an effective dimensionality, the role of the uncertainty principle linking energy and temporal fluctuations and so on. The underlying principle here is always that of symmetry. However, as we will see in this chapter, this paradigm is not sufficient to describe certain classes of phenomena that do not involve symmetry changes but are nonetheless still associated with diverging lengths, singularities and critical exponents: features that are clearly related to critical phenomena and phase transitions. We have already met similar behaviour when studying density-driven or Lifshitz transitions. We will see in this chapter that these transitions are much more common and interesting that initially thought. The keyword here is topology, which contains principles and constraints that protect quasi-particle excitations and are still more powerful than those of symmetry. Topological Quantum Phase Transitions We will refer to topological quantum phase transitions (TQPT) as those that separate two phases where at least one of them is topologically non-trivial, as characterised by some topological parameter like a winding number or a Berry phase. In some cases these transitions either give rise to singularities in a thermodynamic quantity or are accompanied by a diverging length. However, differently from Landau-type phase transitions they are not necessarily associated with a symmetry change. Also there is no identifiable order parameter to distinguish between the different phases. Topological quantities are not useful to play the role of an order parameter. They are in general discontinuous at topological transitions and this does not necessarily reflect the nature of the transition. On the other hand, we will show that the renormalisation group is a useful tool to describe TQPT.

Cambridge University Press eBooksJan 1, 20171 citation

Universal Symmetry-Breaking Dynamics at Continuous Phase Transitions: Evidence for a New Dynamical Critical Exponent

Tobias Wiener, Laurin Brunner, Markus Heyl

Uncovering and understanding universal dynamics in matter far from equilibrium remains a key challenge. In this work, we identify a so far unrecognized form of universal behavior that emerges after a sudden symmetry-breaking quench at continuous phase transitions. Our key observation is that the order-parameter fluctuations in Ising models exhibit a compelling temporal collapse across a wide range of system sizes and quench strengths, indicative of an emergent single-variable scaling form. This phenomenon can be explained by introducing a so far unknown dynamical critical exponent for the underlying continuous phase transition. We find evidence for a lower critical effective dimension of this universal regime: it is observed in the 2D quantum and 3D and 4D classical Ising models, but not in the 1D quantum or 2D classical cases. Our results suggest that our observed universal far-from-equilibrium scaling may extend beyond the Ising models studied here and could more broadly characterize systems with non-conserved order parameters, opening new avenues for exploring universal dynamics both theoretically and in current experimental platforms.

quant-pharXiv:2605.07753May 11, 20260 citations