FisMat2017 - Submission - View

Abstract's title: Superconductivity, charge-density waves, and antiferromagnetism in the Hubbard-Holstein model
Submitting author: Seher Karakuzu
Affiliation: SISSA
Affiliation Address: Via Bonomea, 265, 34136 Trieste TS
Country: Italy
Oral presentation/Poster (Author's request): Poster
Other authors and affiliations: L. Tocchio (Politecnico di Torino) , S. Sorella (SISSA) , F. Becca (SISSA)

By using variational wave functions and quantum Monte Carlo techniques, we investigate the interplay between electron-electron and electron-phonon interactions in the two-dimensional Hubbard-Holstein model. Here, the ground-state phase diagram is triggered by several energy scales, i.e.,the electron hopping t, the on-site electron-electron interaction U , the phonon frequency ω_{0} , and the electron-phonon coupling g. At half filling, the ground state has antiferromagnetic order for U \gtrapprox 2g 2 /ω_{0} , while it shows charge-density waves for U \lessapprox 2g 2 /ω_{0} ; in the weak-coupling limit, when both U/t and 2g 2 /tω_{0} are small, and ω_{0} /t ≈ 1, a paramagnetic metal emerges. By increasing the value of the phonon energy, the region where the metallic phase is present extends along the transition line between antiferromagnetic and charge-density-wave insulators. Most importantly, pairing correlations develop, indicating the presence of a truly superconducting phase. Moreover, by
hole-doping the charge-density-wave insulator, phase separation occurs; instead, a uniform phase is stabilized when doping the metallic/superconducting phase. In order to minimize size effects, which are particularly large in the weak-coupling limit and in the doped case, we employ an averaging over twisted-boundary conditions.