Three Phases in the 3D Abelian Higgs Model with Nonlocal Gauge Interactions

We study the phase structure of the 3D nonlocal compact U(1) lattice gauge theory coupled with a Higgs field by means of Monte-Carlo simulations. The nonlocal interactions among gauge variables are along the temporal direction and mimic the effect of local coupling to massless particles. We found that in contrast to the 3D local abelian Higgs model which has only one phase, the present model exhibits the confinement, Higgs, and Coulomb phases separated by three second-order transition lines emanating from a triple point. This result is quite important for studies on electron fractionalization phenomena in strongly-correlated electron systems. Implications to them are discussed

Deconfinement Phase Transition in a 3D Nonlocal U(1) Lattice Gauge Theory

We introduce a 3D compact U(1) lattice gauge theory having nonlocal interactions in the temporal direction, and study its phase structure. The model is relevant for the compact QED$_3$ and strongly correlated electron systems like the t-J model of cuprates. For a power-law decaying long-range interaction, which simulates the effect of gapless matter fields, a second-order phase transition takes place separating the confinement and deconfinement phases. For an exponentially decaying interaction simulating matter fields with gaps, the system exhibits no signals of a second-order transition.Comment: 4 pages, 5 figures, typos correcte

Possible high TcT_c superconductivity in La3_3Ni2_2O7_7 under high pressure through manifestation of a nearly-half-filled bilayer Hubbard model

Inspired by a recent experiment showing that La$_3$Ni$_2$O$_7$ exhibits high $T_c$ superconductivity under high pressure, we theoretically revisit the possibility of superconductivity in this material. We find that superconductivity can take place which is essentially similar to that of the bilayer Hubbard model consisting of the Ni $3d_{3z^2-r^2}$ orbitals. Although the coupling with the $3d_{x^2-y^2}$ orbitals degrades superconductivity, $T_c$ can still be high enough to understand the experiment thanks to the very high $T_c$ reached in the bilayer Hubbard model.Comment: 3 figures, 5 page