Evgeni Burovski

Critical temperature and thermodynamics of attractive fermions at unitarity

The unitarity regime of the BCS-BEC crossover can be realized by diluting a system of two-component lattice fermions with an on-site attractive interaction. We perform a systematic-error-free finite-temperature simulation of this system by diagrammatic determinant Monte Carlo method. The critical temperature in units of Fermi energy is found to be T(C)/epsilonF=0.152(7). We also report the behavior of the thermodynamic functions, and discuss the issues of thermometry of ultracold Fermi gases.

Quantitative determination of temperature in the approach to magnetic order of ultracold fermions in an optical lattice.

We perform a quantitative simulation of the repulsive Fermi-Hubbard model using an ultracold gas trapped in an optical lattice. The entropy of the system is determined by comparing accurate measurements of the equilibrium double occupancy with theoretical calculations over a wide range of parameters. We demonstrate the applicability of both high-temperature series and dynamical mean-field theory to obtain quantitative agreement with the experimental data. The reliability of the entropy determination is confirmed by a comprehensive analysis of all systematic errors. In the center of the Mott insulating cloud we obtain an entropy per atom as low as 0.77k(B) which is about twice as large as the entropy at the Néel transition. The corresponding temperature depends on the atom number and for small fillings reaches values on the order of the tunneling energy.

Critical Temperature Curve in BEC-BCS Crossover

The strongly correlated regime of the crossover from Bardeen-Cooper-Schrieffer pairing to Bose-Einstein condensation can be realized by diluting a system of two-component fermions with a short-range attractive interaction. We investigate this system via a novel continuous-space-time diagrammatic determinant Monte Carlo method and determine the universal curve Tc/epsilonF for the transition temperature between the normal and the superfluid states as a function of the scattering length with the maximum on the Bose-Einstein condensation side. At unitarity, we confirm that Tc/epsilonF=0.152(7).

High-precision measurement of the thermal exponent for the three-dimensional XY universality class

Simulation results are reported for the critical point of the two-component ϕ4 field theory. The correlation-length exponent is measured to high precision with the result ν=0.6717(3). This value is in agreement with recent simulation results [ Campostrini et al. Phys. Rev. B 63 214503 (2001)] and marginally agrees with the most recent space-based measurements of the superfluid transition in 4He [ Lipa et al. Phys. Rev. B 68 174518 (2003)].

The Fermi-Hubbard model at unitarity

We simulate the dilute attractive Fermi-Hubbard model in the unitarity regime using a diagrammatic determinant Monte Carlo algorithm with worm-type updates. We obtain the dependence of the critical temperature on the filling factorand, by extrapolating to � ! 0, determine the universal critical temperature of the continuum unitary Fermi gas in units of Fermi energy: Tc/F = 0.152(7). We also determine the thermodynamic functions and show how the Monte Carlo results can be used for accurate thermometry of a trapped unitary gas.

Bound state formation and the nature of the excitonic insulator phase in the extended Falicov-Kimball model

Motivated by the possibility of pressure-induced exciton condensation in intermediate-valence Tm[Se,Te] compounds, we study the Falicov-Kimball model extended by a finite

Luttinger liquid of trimers in Fermi gases with unequal masses.

f

Multiparticle Composites in Density-Imbalanced Quantum Fluids

-hole valence bandwidth. Calculating the Frenkel-type exciton propagator we obtain excitonic bound states above a characteristic value of the local interband Coulomb attraction. Depending on the system parameters coherence between

Fermionic trimers in spin-dependent optical lattices

c

Diagrammatic Quantum Monte Carlo for Two-Body Problems: Applied to Excitons

and