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    Université de Fribourg

    Collective modes in excitonic insulators: Effects of electron-phonon coupling and signatures in the optical response

    Murakami, Yuta ; Golež, Denis ; Kaneko, Tatsuya ; Koga, Akihisa ; Millis, Andrew J. ; Werner, Philipp

    In: Physical Review B, 2020, vol. 101, no. 19, p. 195118

    We consider a two-band spinless model describing an excitonic insulator (EI) on the two-dimensional square lattice with anisotropic hopping parameters and electron-phonon (el-ph) coupling, inspired by the EI candidate Ta2NiSe5. We systematically study the nature of the collective excitations in the ordered phase which originates from the interband Coulomb interaction and the el-ph coupling. ...

    Université de Fribourg

    Staggered ordered phases in the three-orbital Hubbard model

    Ishigaki, Kosuke ; Nasu, Joji ; Koga, Akihisa ; Hoshino, Shintaro ; Werner, Philipp

    In: Physical Review B, 2019, vol. 99, no. 8, p. 085131

    We study ordered phases with broken translational symmetry in the half-filled three- orbital Hubbard model with antiferromagnetic Hund coupling by means of dynamical mean-field theory (DMFT) and continuous-time quantum Monte Carlo simulations. The stability regions of the antiferro-orbital (AFO), antiferromagnetic (AFM), and charge density wave (CDW) states are determined by measuring the...

    Université de Fribourg

    Spontaneously orbital-selective superconductivity in a three-orbital Hubbard model

    Ishigaki, Kosuke ; Nasu, Joji ; Koga, Akihisa ; Hoshino, Shintaro ; Werner, Philipp

    In: Physical Review B, 2018, vol. 98, no. 23, p. 235120

    We study a three-orbital Hubbard model with negative Hund's coupling in infinite dimensions, combining dynamical mean-field theory with continuous time quantum Monte Carlo simulations. This model, which is relevant for the description of alkali- doped fullerides, has previously been shown to exhibit a spontaneous orbital-selective Mott phase in the vicinity of the superconducting phase....

    Université de Fribourg

    Superconductivity in the two-band Hubbard model

    Koga, Akihisa ; Werner, Philipp

    In: Physical Review B, 2015, vol. 91, no. 8, p. 085108

    We study the two-band Hubbard model in infinite dimensions by solving the dynamical mean-field equations with a strong coupling continuous-time quantum Monte Carlo method and show that an s-wave superconducting state can be stabilized in the repulsively interacting case. We discuss how this superconducting state competes with the metallic and paired Mott states. The effects of the Hund coupling...