Charge density wave in superfluid

We study the phase diagram of a dipolar Fermi gas at half-filling in a cubic optical lattice with dipole moments aligned along the $z$ axis. The anisotropic dipole-dipole interaction leads to the competition between ${p}_{z}$ -wave superfluid and nematic charge-density-wave (CDW) orders at low temperatures. We find that the superfluid phase survives with weak interactions and the CDW phase dominates with strong interactions. In-between, the supersolid phase appears as a balance between superfluid and CDW orders. The superfluid density is anisotropic in the supersolid and superfluid phases. In the CDW phase, there is a semimetal-to-insulator transition with increase of the interaction strength. Experimental implications are discussed.We study the phase diagram of a dipolar Fermi gas at half-filling in a cubic optical lattice with dipole moments aligned along the $z$ axis. The anisotropic dipole-dipole interaction leads to the competition between ${p}_{z}$-wave superfluid and nematic charge-density-wave (CDW) orders at low temperatures. We find that the superfluid phase survives with weak interactions and the CDW phase dominates with strong interactions. In-between, the supersolid phase appears as a balance between superfluid and CDW orders. The superfluid density is anisotropic in the supersolid and superfluid phases. In the CDW phase, there is a semimetal-to-insulator transition with increase of the interaction strength. Experimental implications are discussed.

arXiv:1312.1751Physical Review BMay 20, 201415 citations

Wave Kinetic Description of Superfluidity

José Tito Mendonça

Brazilian Journal of PhysicsJun 2, 20141 citation

Disorder-induced charge-density-wave–superfluid transition in SU(N) Fermi systems

Masaru Sakaida, Norio Kawakami

We investigate $\mathrm{SU}(N)$ attractive Fermi systems with disorder using a Bogoliubov-de Gennes method at zero temperature with particular focus on the SU(3) case. The charge correlation function, the distribution function of the superfluid (SF) order parameter, and the free energy are calculated for a two-dimensional square lattice system at half filling. From the disorder average of these quantities, we find that disorder triggers a transition from the charge-density-wave (CDW) phase to the SF phase; disorder suppresses the CDW order, making the SF state stable. This disorder-driven phase transition is of first order and is unique for SU(3) systems; it has not been observed for the disordered SU(2) systems studied so far. We elucidate the properties of the CDW-SF transition from the disorder-averaged density of states and the distribution function of the particle density and thus obtain the ground-state phase diagram. We also address the SU(4) case and find that the CDW state is driven directly to the Anderson localized state, but the SF phase is not stabilized. We argue what will be expected for generic $N$ cases.We investigate $\mathrm{SU}(N)$ attractive Fermi systems with disorder using a Bogoliubov-de Gennes method at zero temperature with particular focus on the SU(3) case. The charge correlation function, the distribution function of the superfluid (SF) order parameter, and the free energy are calculated for a two-dimensional square lattice system at half filling. From the disorder average of these quantities, we find that disorder triggers a transition from the charge-density-wave (CDW) phase to the SF phase; disorder suppresses the CDW order, making the SF state stable. This disorder-driven phase transition is of first order and is unique for SU(3) systems; it has not been observed for the disordered SU(2) systems studied so far. We elucidate the properties of the CDW-SF transition from the disorder-averaged density of states and the distribution function of the particle density and thus obtain the ground-state phase diagram. We also address the SU(4) case and find that the CDW state is driven directly to the Anderson localized state, but the SF phase is not stabilized. We argue what will be expected for generic $N$ cases.

Physical Review AJul 31, 20144 citations

Hard core bosons on the dual of the bowtie lattice

Wanzhou Zhang, Laixi Li, Wenan Guo

We study the zero-temperature phase diagram of hardcore bosons on the dual of the bowtie lattice. Two types of striped diagonal long-range order (striped order I and striped order II) are discussed. A state with type-II striped order and superfluidity is found, even without nearest-neighbor repulsion. The emergence of such a state is due to the inhomogeneity and the anisotropy of the lattice structure. However, neither the translational symmetry nor the symmetry between sublattices of the original lattice is broken in this state. In this paper, we restrict a ``solid state'' of lattice bosons as a diagonal long-range-ordered state breaking either the translational symmetry of the original lattice or the symmetry of different sublattices. We thus name such a phase a striped superfluid phase. In the presence of a nearest-neighbor repulsion, we find two striped charge-density-wave phases with boson density $\ensuremath{\rho}=1/2$ (with striped order I) and $\ensuremath{\rho}=2/3$ (with striped order II), respectively, when the hopping amplitude is small compared with the repulsion. The striped charge-density wave I state is a solid, in which the translational symmetry of the original lattice is broken. We observe a rather special first-order phase transition showing an interesting multiloop hysteresis phenomenon between the two striped charge-density-wave phases when the hopping term is small enough. This can be accounted for by the special degeneracy of the ground states near the classical limit. The striped superfluid phase reappears outside the two striped charge-density-wave phases. The transition between the striped charge-density wave I and striped superfluid phases is first order while the transition between striped charge-density wave II and the striped superfluid phases is continuous. We find that the superfluid stiffness is anisotropic in the striped superfluid states with and without repulsion. In the striped superfluid state with repulsion, the superfluid stiffness is subject to different types of anisotropy in the region near half filling and above 2/3 filling.We study the zero-temperature phase diagram of hardcore bosons on the dual of the bowtie lattice. Two types of striped diagonal long-range order (striped order I and striped order II) are discussed. A state with type-II striped order and superfluidity is found, even without nearest-neighbor repulsion. The emergence of such a state is due to the inhomogeneity and the anisotropy of the lattice structure. However, neither the translational symmetry nor the symmetry between sublattices of the original lattice is broken in this state. In this paper, we restrict a ``solid state'' of lattice bosons as a diagonal long-range-ordered state breaking either the translational symmetry of the original lattice or the symmetry of different sublattices. We thus name such a phase a striped superfluid phase. In the presence of a nearest-neighbor repulsion, we find two striped charge-density-wave phases with boson density $\ensuremath{\rho}=1/2$ (with striped order I) and $\ensuremath{\rho}=2/3$ (with striped order II), respectively, when the hopping amplitude is small compared with the repulsion. The striped charge-density wave I state is a solid, in which the translational symmetry of the original lattice is broken. We observe a rather special first-order phase transition showing an interesting multiloop hysteresis phenomenon between the two striped charge-density-wave phases when the hopping term is small enough. This can be accounted for by the special degeneracy of the ground states near the classical limit. The striped superfluid phase reappears outside the two striped charge-density-wave phases. The transition between the striped charge-density wave I and striped superfluid phases is first order while the transition between striped charge-density wave II and the striped superfluid phases is continuous. We find that the superfluid stiffness is anisotropic in the striped superfluid states with and without repulsion. In the striped superfluid state with repulsion, the superfluid stiffness is subject to different types of anisotropy in the region near half filling and above 2/3 filling.

arXiv:1003.6070Physical Review BOct 28, 20105 citations

We study the phase diagram of a dipolar Fermi gas at half-filling in a cubic optical lattice with dipole moments aligned along the

z

axis. The anisotropic dipole-dipole interaction leads to the competition between

{p}_{z}

-wave superfluid and nematic charge-density-wave (CDW) orders at low temperatures. We find that the superfluid phase survives with weak interactions and the CDW phase dominates with strong interactions. In-between, the supersolid phase appears as a balance between superfluid and CDW orders. The superfluid density is anisotropic in the supersolid and superfluid phases. In the CDW phase, there is a semimetal-to-insulator transition with increase of the interaction strength. Experimental implications are discussed.

We investigate

\mathrm{SU}(N)

attractive Fermi systems with disorder using a Bogoliubov-de Gennes method at zero temperature with particular focus on the SU(3) case. The charge correlation function, the distribution function of the superfluid (SF) order parameter, and the free energy are calculated for a two-dimensional square lattice system at half filling. From the disorder average of these quantities, we find that disorder triggers a transition from the charge-density-wave (CDW) phase to the SF phase; disorder suppresses the CDW order, making the SF state stable. This disorder-driven phase transition is of first order and is unique for SU(3) systems; it has not been observed for the disordered SU(2) systems studied so far. We elucidate the properties of the CDW-SF transition from the disorder-averaged density of states and the distribution function of the particle density and thus obtain the ground-state phase diagram. We also address the SU(4) case and find that the CDW state is driven directly to the Anderson localized state, but the SF phase is not stabilized. We argue what will be expected for generic

N

cases.