Finite-density phase diagram of a $(1+1)-d$ non-abelian lattice gauge theory with tensor networks

Pietro Silvi1,2, Enrique Rico3, Marcello Dalmonte4,5, Ferdinand Tschirsich1, and Simone Montangero1,6

1Institute for complex quantum systems & Center for Integrated Quantum Science and Technologies (IQST), Universität Ulm, D-89069 Ulm, Germany
2Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck, Austria
3Department of Physical Chemistry, University of the Basque Country UPV/EHU, Apartado 644, E-48080 Bilbao, Spain & IKERBASQUE, Basque Foundation for Science, Maria Diaz de Haro 3, E-48013 Bilbao, Spain
4Institute for Theoretical Physics, University of Innsbruck, A-6020, Innsbruck, Austria & Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences, A-6020 Innsbruck, Austria
5Abdus Salam International Center for Theoretical Physics, Strada Costiera 11, Trieste, Italy
6Institute for Complex Quantum Systems & Center for Integrated Quantum Science and Technologies, Universität Ulm, D- 89069 Ulm, Germany

We investigate the finite-density phase diagram of a non-abelian $SU(2)$ lattice gauge theory in $(1+1)$-dimensions using tensor network methods. We numerically characterise the phase diagram as a function of the matter filling and of the matter-field coupling, identifying different phases, some of them appearing only at finite densities. For weak matter-field coupling we find a meson BCS liquid phase, which is confirmed by second-order analytical perturbation theory. At unit filling and for strong coupling, the system undergoes a phase transition to a charge density wave of single-site (spin-0) mesons via spontaneous chiral symmetry breaking. At finite densities, the chiral symmetry is restored almost everywhere, and the meson BCS liquid becomes a simple liquid at strong couplings, with the exception of filling two-thirds, where a charge density wave of mesons spreading over neighbouring sites appears. Finally, we identify two tri-critical points between the chiral and the two liquid phases which are compatible with a $SU(2)_2$ Wess-Zumino-Novikov-Witten model. Here we do not perform the continuum limit but we explicitly address the global $U(1)$ charge conservation symmetry.


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