arXiv subjects

Luca Dell'Anna

Publications and source records attributed to Luca Dell'Anna.

45 records · Page 3Linked to original sources

arXiv2009

Kondo impurity on the honeycomb lattice at half-filling

We consider a Kondo-like impurity interacting with fermions on a honeycomb lattice at half-filling, as in the case of graphene. We derive from the lattice model an effective one-dimensional continuum theory which has, in general, four flavors with angular momentum mixing in the presence of internode scattering processes and six couplings in the spin-isotropic case. Under particular conditions, however, it can be reduced to a single-coupling multichannel pseudogap Kondo model. We finally calculate, in the presence of an energy dependent Fermi velocity, induced by Coulomb interaction, the critical coupling in the large-N expansion, the magnetic susceptibility and the specific heat.

cond-mat.str-el↗

arXiv2009

Effect of random on-site energies on the critical temperature of a lattice Bose gas

We study the effect of random on-site energies on the critical temperature of a non-interacting Bose gas on a lattice. In our derivation the on-site energies are distributed according a Gaussian probability distribution function having vanishing average and variance $v_o^2$. By using the replicated action obtained by averaging on the disorder, we perform a perturbative expansion for the Green functions of the disordered system. We evaluate the shift of the chemical potential induced by the disorder and we compute, for $v_o^2 << 1$, the critical temperature for condensation. We find that, for large filling, disorder slightly enhances the critical temperature for condensation.

cond-mat.stat-mech↗

arXiv2008

Multiple Andreev reflections in a quantum dot coupled to superconductors: Effects of spin-orbit coupling

We study the out-of-equilibrium current through a multilevel quantum dot contacted to two superconducting leads and in the presence of Rashba and Dresselhaus spin-orbit couplings, in the regime of strong dot-lead coupling. The multiple Andreev reflection (MAR) subgap peaks in the current voltage characteristics are found to be modified (but not suppressed) by the spin-orbit interaction, in a way that strongly depends on the shape of the dot confining potential. In a perfectly isotropic dot the MAR peaks are enhanced when the strength $α_R$ and $α_D$ of Rashba and Dresselhaus terms are equal. When the anisotropy of the dot confining potential increases the dependence of the subgap structure on the spin-orbit angle $θ=\arctan(α_D/α_R)$ decreases. Furthermore, when an in-plane magnetic field is applied to a strongly anisotropic dot, the peaks of the non-linear conductance oscillate as a function of the magnetic field angle, and the location of the maxima and minima allows for a straightforward read-out of the spin-orbit angle $θ$.

cond-mat.mes-hall↗

arXiv2006

Role of the impurity-potential range in disordered d-wave superconductors

We analyze how the range of disorder affects the localization properties of quasiparticles in a two-dimensional d-wave superconductor within the standard non-linear sigma-model approach to disordered systems. We show that for purely long-range disorder, which only induces intra-node scattering processes, the approach is free from the ambiguities which often beset the disordered Dirac-fermion theories, and gives rise to a Wess-Zumino-Novikov-Witten action leading to vanishing density of states and finite conductivities. We also study the crossover induced by internode scattering due to a short range component of the disorder, thus providing a coherent non-linear sigma-model description in agreement with all the various findings of different approaches.

cond-mat.dis-nn↗

arXiv2006

Electrical resistivity near Pomeranchuk instability in two dimensions

We analyze the DC charge transport in the quantum critical regime near a d-wave Pomeranchuk instability in two dimensions. The transport decay rate is linear in temperature everywhere on the Fermi surface except at cold spots on the Brillouin zone diagonal. For pure systems, this leads to a DC resistivity proportional to T^{3/2} in the low-temperature limit. In the presence of impurities the residual impurity resistance at T=0 is approached linearly at low temperatures.

cond-mat.str-el↗

arXiv2006

Disordered d-wave superconductors with interactions

We study the localization properties of disordered d-wave superconductors by means of the fermionic replica trick method. We derive the effective non-linear sigma-model describing the diffusive modes related to spin transport which we analyze by the Wilson-Polyakov renormalization group. A lot of different symmetry classes are considered within the same framework. According to the presence or the absence of certain symmetries, we provide a detailed classification for the behavior of some physical quantities, like the density of states, the spin and the quasiparticle charge conductivities. Following the original Finkel'stein approach, we finally extend the effective functional method to include residual quasiparticle interactions, at all orders in the scattering amplitudes. We consider both the superconducting and the normal phase, with and without chiral symmetry, which occurs in the so called two-sublattice models.

cond-mat.dis-nn↗

arXiv2006

Anomalous dimensions of operators without derivatives in the non-linear sigma-model for disordered bipartite lattices

We consider a generic time-reversal invariant model of fermions hopping randomly on a square lattice. By means of the conventional replica-trick within the fermionic path-integral formalism, the model is mapped onto a non-linear sigma-model with fields spanning the coset U(4N)/Sp(2N), N->0. We determine the proper scaling combinations of an infinite family of relevant operators which control deviations from perfect two-sublattice symmetry. This allows us to extract the low-energy behavior of the density of states, which agrees with earlier results obtained in particular two-sublattice models with Dirac-like single-particle dispersion. The agreement proves the efficacy of the conventional fermionic-path-integral approach to disordered systems, which, in spite of many controversial aspects, like the zero-replica limit, remains one of the more versatile theoretical tool to deal with disordered electrons.

cond-mat.dis-nn↗

arXiv2005

Fermi surface fluctuations and single electron excitations near Pomeranchuk instability in two dimensions

A metallic electron system near an orientational symmetry breaking Pomeranchuk instability is characterized by a ''soft'' Fermi surface with enhanced collective fluctuations. We analyze fluctuation effects in a two-dimensional electron system on a square lattice in the vicinity of a Pomeranchuk instability with d-wave symmetry, using a phenomenological model which includes interactions with a small momentum transfer only. We compute the dynamical density correlations with a d-wave form factor for small momenta and frequencies, the dynamical effective interaction due to fluctuation exchange, and the electron self-energy. At the quantum critical point the density correlations and the dynamical forward scattering interaction diverge with a dynamical exponent z=3. The singular forward scattering leads to large self-energy corrections, which destroy Fermi liquid behavior over the whole Fermi surface except near the Brillouin zone diagonal. The decay rate of single-particle excitations, which is related to the width of the peaks in the spectral function, exceeds the excitation energy in the low-energy limit. The dispersion of maxima in the spectra flattens strongly near those portions of the Fermi surface which are remote from the zone diagonal.

cond-mat.str-el↗

arXiv2001

Quasiparticle conductivities in disordered d-wave superconductors

We study the quasiparticle transport coefficients in disordered d-wave superconductors. We find that spin and charge excitations are generally localized unless magnetic impurities are present. If the system is close to a nesting point in the impurity-scattering unitary limit, the tendency towards localization is reduced while the quasiparticle density of states gets enhanced by disorder. We also show that the residual repulsive interaction among quasiparticles has a delocalizing effect and increases the density of states.

cond-mat.supr-con↗