We investigate single-particle properties of a one-component Fermi gas with a tunable p-wave interaction. Including pairing fluctuations associated with this anisotropic interaction within a $T$-matrix theory, we calculate the single-particle density
of states, as well as the spectral weight, above the superfluid transition temperature $T_{rm c}$. Starting from the weak-coupling regime, we show that the so-called pseudogap first develops in these quantities with increasing the interaction strength. However, when the interaction becomes strong to some extent, the pseudogap becomes obscure to eventually disappear in the strong-coupling regime. This non-monotonic interaction dependence is quite different from the case of an s-wave interaction, where the pseudogap simply develops with increasing the interaction strength. The difference between the two cases is shown to originate from the momentum dependence of the p-wave interaction, which vanishes in the low momentum limit. We also identify the pseudogap regime in the phase diagram with respect to the temperature and the p-wave interaction strength. Since the pseudogap is a precursor phenomenon of the superfluid phase transition, our results would be useful for the research toward the realization of p-wave superfluid Fermi gases.
We review a representation of Hubbard-like models that is based on auxiliary pseudospin variables. These pseudospins refer to the local charge modulo two in the original model and display a local Z_2 gauge freedom. We discuss the associated mean-fiel
d theory in a variety of different contexts which are related to the problem of the interaction-driven metal-insulator transition at half-filling including Fermi surface deformation and spectral features beyond the local approximation. Notably, on the mean-field level, the Hubbard bands are derived from the excitations of an Ising model in a transverse field and the quantum critical point of this model is identified with the Brinkman-Rice criticality of the almost localized Fermi liquid state. Non-local correlations are included using a cluster mean-field approximation and the Schwinger boson theory for the auxiliary quantum Ising model.
We analytically calculate the energy spectrum of a circular graphene quantum dot with radius R subjected to a perpendicular magnetic field B by applying the infinite-mass boundary condition. We can retrieve well-known limits for the cases R, B going
to infinity and B going to zero. Our model is capable of capturing the essential details of recent experiments. Quantitative agreement between theory and experiment is limited due to the fact that a circular dot is not close enough to the experimental geometry, that disorder plays a significant role, and that interaction effects may be relevant.
Motivated by the anomalous temperature dependence of the c-axis resistivity of Sr$_2$RuO$_4$, the dimensional crossover from a network of perpendicular one-dimensional chains to a two-dimensional system due to a weak hybridization between the perpend
icular chains is studied. The corresponding two-orbital Hubbard model is treated within a slave-boson mean-field theory (SBMFT) to take correlation effects into account such as the spin-charge separation on the one-dimensional chains. Using an RPA-like formulation for the Greens function of collective spinon-holon excitations the emergence of quasiparticles at low-temperatures is examined. The results are used to discuss the evolution of the spectral density and the c-axis transport within a tunneling approach. For the latter a regime change between low- and high-temperature regime is found in qualitative accordance with experimental data.
We investigated the vortex dynamics in the non-centrosymmetric superconductor Li_2Pt_3B in the temperature range 0.1 K - 2.8 K. Two different logarithmic creep regimes in the decay of the remanent magnetization from the Bean critical state have been
observed. In the first regime, the creep rate is extraordinarily small, indicating the existence of a new, very effective pinning mechanism. At a certain time a vortex avalanche occurs that increases the logarithmic creep rate by a factor of about 5 to 10 depending on the temperature. This may indicate that certain barriers against flux motion are present and they can be opened under increased pressure exerted by the vortices. A possible mechanism based on the barrier effect of twin boundaries is briefly discussed.
