Joaquín E. Drut

Is graphene in vacuum an insulator

We present evidence, from lattice Monte Carlo simulations of the phase diagram of graphene as a function of the Coulomb coupling between quasiparticles, that graphene in vacuum is likely to be an insulator. We find a semimetal-insulator transition at alpha_{g};{crit}=1.11+/-0.06, where alpha_{g} approximately 2.16 in vacuum, and alpha_{g} approximately 0.79 on a SiO2 substrate. Our analysis uses the logarithmic derivative of the order parameter, supplemented by an equation of state. The insulating phase disappears above a critical number of four-component fermion flavors 4<N_{f};{crit}<6. Our data are consistent with a second-order transition.

Spin 1/2 Fermions in the Unitary Regime: A Superfluid of a New Type

We study, in a fully nonperturbative calculation, a dilute system of spin 1/2 interacting fermions, characterized by an infinite scattering length at finite temperatures. Various thermodynamic properties and the condensate fraction are calculated and we also determine the critical temperature for the superfluid-normal phase transition in this regime. The thermodynamic behavior appears as a rather surprising and unexpected mélange of fermionic and bosonic features. The thermal response of a spin 1/2 fermion at the BCS-BEC crossover should be classified as that of a new type of superfluid.

Lattice field theory simulations of graphene

We discuss the Monte Carlo method of simulating lattice field theories as a means of studying the low-energy effective theory of graphene. We also report on simulational results obtained using the Metropolis and Hybrid Monte Carlo methods for the chiral condensate, which is the order parameter for the semimetal-insulator transition in graphene, induced by the Coulomb interaction between the massless electronic quasiparticles. The critical coupling and the associated exponents of this transition are determined by means of the logarithmic derivative of the chiral condensate and an equation-of-state analysis. A thorough discussion of finite-size effects is given, along with several tests of our calculational framework. These results strengthen the case for an insulating phase in suspended graphene, and indicate that the semimetal-insulator transition is likely to be of second order, though exhibiting neither classical critical exponents, nor the predicted phenomenon of Miransky scaling.

Quantum Monte Carlo simulations of the BCS-BEC crossover at finite temperature

The quantum Monte Carlo method for spin-

Finite-Temperature Pairing Gap of a Unitary Fermi Gas by Quantum Monte Carlo Calculations

\frac{1}{2}

Thermodynamics of a Trapped Unitary Fermi Gas

fermions at finite temperature is formulated for dilute systems with an

Critical exponents of the semimetal-insulator transition in graphene: A Monte Carlo study

s

Lattice methods for strongly interacting many-body systems

-wave interaction. The motivation and the formalism are discussed along with descriptions of the algorithm and various numerical issues. We report on results for the energy, entropy, and chemical potential as a function of temperature. We give upper bounds on the critical temperature

Momentum distribution and contact of the unitary Fermi gas

{T}_{c}

Renormalization group flow of quartic perturbations in graphene: Strong coupling and large- N limits

for the onset of superfluidity, obtained by studying the finite-size scaling of the condensate fraction. All of these quantities were computed for couplings around the unitary regime in the range