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arXiv:1002.2958 · Journal of the Physical Society of Japan

Polarized Superfluidity in the Imbalanced Attractive Hubbard Model

Akihisa Koga, Philipp Werner

Published May 25, 2010• 26 citations
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Abstract

We investigate the attractive Hubbard model in infinite spatial dimensions by means of dynamical mean-field theory. Using a continuous-time Monte Carlo algorithm in the Nambu formalism as an impurity solver, we directly deal with the superfluid phase in the population imbalanced system. By calculating the superfluid order parameter, the magnetization, and the density of states, we discuss how the polarized superfluid state is realized in the attractive Hubbard model at quarter filling. We find that a drastic change in the density of states is induced by spin imbalanced populations in the superfluid state.

DOI
10.1143/jpsj.79.064401

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We investigate the attractive Hubbard model in infinite spatial dimensions by means of dynamical mean-field theory. Using a continuous-time Monte Carlo algorithm in the Nambu formalism as an impurity solver, we directly deal with the superfluid phase in the population imbalanced system. By calculating the superfluid order parameter, the magnetization, and the density of states, we discuss how the polarized superfluid state is realized in the attractive Hubbard model at quarter filling. We find that a drastic change in the density of states is induced by spin imbalanced populations in the superfluid state.
We investigate the attractive Hubbard model in infinite spatial dimensions by combining dynamical mean-field theory with a strong-coupling continuous-time quantum Monte Carlo method. By calculating the superfluid order parameter and the density of states, we discuss the stability of the superfluid state. In the intermediate-coupling region above the critical temperature, the density of states exhibits a heavy fermion behavior with a quasiparticle peak in the dense system, while a dip structure appears in the dilute system. The formation of the superfluid gap is also addressed.
We study the effects of disorder on an sss-wave superfluid in the attractive Hubbard model using statistical dynamical mean-field theory, which enables us to treat both the correlation effects and the spatial nonuniformity due to disorder in the same framework. The distribution functions of the local density of states and the superfluid order parameter are obtained. From the geometrical average of these quantities, which characterizes the order parameters in disordered systems, we determine the ground-state phase diagram of the attractive Hubbard model with disorder at half-filling and zero temperature. We discuss the superfluid-localization transition and the crossover behavior within the localized phase.
We study the attractive Hubbard model with mass imbalance to clarify low temperature properties of the fermionic mixtures in the optical lattice. By combining dynamical mean-field theory with the continuous-time quantum Monte Carlo simulation, we discuss the competition between the superfluid and density wave states at half filling. By calculating the energy and the order parameter for each state, we clarify that the coexisting (supersolid) state, where the density wave and superfluid states are degenerate, is realized in the system. We then determine the phase diagram at finite temperatures.
We investigate spontaneously symmetry breaking states in the attractive SU(NNN) Hubbard model at half filling. Combining dynamical mean-field theory with the continuous-time quantum Monte Carlo method, we obtain the finite temperature phase diagrams for the superfluid state. When N>2N>2N>2, the second-order phase transition occurs in the weak coupling region, while the first-order phase transition with the hysteresis appears in the strong coupling region. We also discuss the stability of the density wave state and clarify the component dependence of the maximum critical temperature.