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arXiv:2401.11702 · Physical review. B./Physical review. B

Gapless symmetry-protected topological phases and generalized deconfined critical points from gauging a finite subgroup

Lei Su, Meng Zeng

Published Jun 5, 2024• 21 citations
arXivHTMLPDF

Abstract

This work taps into the idea of gauging finite subgroups of global symmetries in conventional systems to obtain unconventional phases and phase transitions, greatly expanding the conventional Landau paradigm. Assisted by analytical anomaly computations and numerical density-matrix renormalization group calculations, the authors map the ordinary superfluid-insulator transition of the Bose-Hubbard model to novel phase transitions between exotic topological and/or symmetry-breaking phases. The general framework has potential applications in cold atom experiments and digital quantum simulators.

DOI
10.1103/physrevb.109.245108

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This work taps into the idea of gauging finite subgroups of global symmetries in conventional systems to obtain unconventional phases and phase transitions, greatly expanding the conventional Landau paradigm. Assisted by analytical anomaly computations and numerical density-matrix renormalization group calculations, the authors map the ordinary superfluid-insulator transition of the Bose-Hubbard model to novel phase transitions between exotic topological and/or symmetry-breaking phases. The general framework has potential applications in cold atom experiments and digital quantum simulators.
Recently, a generalized Landau paradigm has been proposed, in which a broad class of "unconventional" phase transitions lying beyond the original symmetry-breaking framework of Landau are understood as the symmetry-breaking transitions of generalized symmetries. In particular, in (1+1)D, such "topological" or "deconfined" transitions can be mapped to the symmetry-breaking transitions of non-invertible symmetries. How to extract the universal dynamical properties of the transitions from this understanding? In this paper, we follow the Ginzburg-Landau philosophy and develop a field-theoretic description of such critical points in terms of the fluctuations of local order parameters, now of non-invertible symmetries. The Symmetry Topological Field Theory formalism plays a central role in our analysis, allowing us to identify the algebra of local order parameters from the Lagrangian algebra of a (2+1)D topological order. We illustrate the key ideas and the full steps of this generalized Ginzburg-Landau procedure using the transitions between gapped phases with a simple non-invertible symmetry --- the Rep(S3S_3S3​) symmetry.
We outline a holographic framework that attempts to unify Landau and beyond-Landau paradigms of quantum phases and phase transitions. Leveraging a modern understanding of symmetries as topological defects/operators, the framework uses a topological order to organize the space of quantum systems with a global symmetry in one lower dimension. The global symmetry naturally serves as an input for the topological order. In particular, we holographically construct a String Operator Algebra (SOA) which is the building block of symmetric quantum systems with a given symmetry G in one lower dimension. This exposes a vast web of dualities which act on the space of G-symmetric quantum systems. The SOA facilitates the classification of gapped phases as well as their corresponding order parameters and fundamental excitations, while dualities help to navigate and predict various corners of phase diagrams and analytically compute universality classes of phase transitions. A novelty of the approach is that it treats conventional Landau and unconventional topological phase transitions on an equal footing, thereby providing a holographic unification of these seemingly-disparate domains of understanding. We uncover a new feature of gapped phases and their multi-critical points, which we dub fusion structure, that encodes information about which phases and transitions can be dual to each other. Furthermore, we discover that self-dual systems typically posses emergent non-invertible, i.e., beyond group-like symmetries. We apply these ideas to 1+1d 1 + 1 d quantum spin chains with finite Abelian group symmetry, using topologically-ordered systems in 2+1d 2 + 1 d . We predict the phase diagrams of various concrete spin models, and analytically compute the full conformal spectra of non-trivial quantum phase transitions, which we then verify numerically.
The Landau paradigm—classifying phases by local order parameters and transitions by spontaneous symmetry breaking—has long been understood to be incomplete. Deconfined quantum critical points (DQCPs), topological orders, and symmetry-protected phases resist Landau characterization. A candidate structural pattern now emerging across the cond-mat.str-el corpus is that the failure of the Landau paradigm is not merely an exception but a systematic consequence of three interlocking mechanisms: (1) the presence of non-invertible symmetries whose breaking generates order parameters obeying generalized algebraic structures rather than group representations; (2) the role of anomaly type—specifically the position of the Lieb-Schultz-Mattis (LSM) anomaly class in the Lyndon-Hochschild-Serre spectral sequence—in determining whether a critical point is dual to ordinary symmetry breaking or to non-invertible symmetry breaking; and (3) excitation-density control as the decisive factor separating phases that merely enter the topological regime from those that develop genuine topological order. This synthesis draws on six papers from cond-mat.str-el and one from cond-mat.mes-hall (as a mechanistic comparator), all posted within the last 30 days. The thesis is presented as a *heuristic structural reading*, not a derivation from a shared formalism: the cited papers use distinct mathematical frameworks (fusion categories, spectral sequences, sequential circuits, tensor networks, quadratic fermion mappings), and we argue that these frameworks share a common organizational principle—the algebra of defects and condensable objects—rather than a common Lagrangian. The primary falsification path is explicit: if a direct DQCP transition between twin phases (as defined by [corpus:arxiv:2605.31601v1]) can be shown to be continuously connected to a hidden symmetry-breaking transition upon deformation of the Hamiltonian, the structural independence of beyond-Landau transitions claimed here would be overturned. Numerical DMRG or tensor-network studies on the specific models of [corpus:arxiv:2606.06343v1] and [corpus:arxiv:2605.27672v1] with explicitly broken categorical symmetry would constitute such a test. --- Authorship: Saluca Agentic AI Research Team (Saluca LLC). AI-drafted from arXiv preprint corpus on the date in the filename. Cited arXiv preprints: 2605.27166v1, 2605.27193v1, 2605.27672v1, 2605.31601v1, 2605.31602v1, 2606.05856v1, 2606.06343v1, 2606.11303v1, 2606.11527v1
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The phase transition between gapped topological phases represents a class of unconventional criticality beyond the Landau paradigm. However, recent research has shifted attention to topological phases without a bulk gap, where the phase transitions between them are still elusive. In this work, based on large-scale density-matrix renormalization-group techniques, we investigate the critical behaviors of the extended quantum XXZXXZXXZ model obtained by the Kennedy-Tasaki transformation. Using fidelity susceptibility as a diagnostic, we obtain a complete phase diagram, which includes both topological nontrivial and trivial gapless phases. Furthermore, as the XXZXXZXXZ-type anisotropy parameter $\mathrm{\ensuremath{\Delta}}$ varies, both the critical points hc{h}_{c}hc​ and correlation length exponent $\ensuremath{\nu}$ remain the same as in the $\mathrm{\ensuremath{\Delta}}=0$ case, characterized by c=3/2c=3/2c=3/2 (Ising plus free boson) conformal field theory. Our results indicate that fidelity susceptibility can effectively detect and reveal a stable unconventional critical line between the topologically distinct gapless phases for general $\mathrm{\ensuremath{\Delta}}$. This work serves as a valuable reference for further research on phase transitions within the gapless topological phase of matter.
The Landau paradigm is a central dogma for understanding phase and phase transitions in condensed matter systems, yet for decades it has been known that a variety of quantum phases exist beyond the framework. Is there a more general framework that provides a systematic understanding of phase and phase transitions in quantum many-body systems? Recent developments of the notion of generalized symmetry and generalized gauging seem to point to a way to generalize the Landau Paradigm. In this essay, we discuss how `beyond Landau' phases and phase transitions can be captured by a generalized Landau paradigm in terms of the breaking of generalized symmetries, often induced by the generalized gauging procedure facilitated through the topological holography formalism. We also discuss what needs to be understood to make the generalized Landau paradigm useful in the study of quantum phase and phase transitions.