Dresden 2026 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 86: Correlated Magnetism – Spin Liquids II

TT 86.4: Talk

Thursday, March 12, 2026, 15:45–16:00, CHE/0091

Monopole condensation in U(1) Dirac spin liquids: AFM and VBS orders — •João C. Inácio¹ and Fakher Assaad^{1, 2} — ¹Institut für Theoretische Physik und Astrophysik, Universität Würzburg, 97074 Würzburg, Germany — ²Würzburg-Dresden Cluster of Excellence ct.qmat, Am Hubland, 97074 Würzburg, Germany

Quantum spin liquids are states of matter where quantum fluctuations prohibit magnetic order down to zero temperature. Such states cannot be described by conventional mean-field theories. In U(1) Dirac spin liquids (DSL), the low-energy degrees of freedom are emergent gauge fields coupled to fractionalised spinon excitations. Spinons behave like Dirac fermions coupled to a compact U(1) gauge field, giving rise to QED_3. Within this framework instanton excitations of the gauge fields, i.e. monopoles, are central to understand the spin liquid state. Monopoles carry antiferromagnetic (AFM) or valence bond solid (VBS) charge leading to a Dirac mass upon their condensation, creating a large competition between different magnetic orders. We study a U(1) lattice gauge theory coupled to phonons by the means of exact fermionic quantum Monte Carlo simulations in order to understand this competition. By doing a scan over the spinon-phonon coupling (g) and the gauge field fluctuations (J) we are able to create a phase diagram where AFM, VBS and DSL phases coexist.

Keywords: Dirac spin liquids; spin-phonon coupling; Lattice Gauge theories; Auxiliary field quantum Monte Carlo