Raimundo R. dos Santos

Kondo–attractive-Hubbard model for the ordering of local magnetic moments in superconductors

We consider local magnetic moments coupled to conduction electrons with on-site attraction in order to discuss the interplay between pairing and magnetic order. We probe the ground-state properties of this model on a one-dimensional lattice through pair binding energies and several correlation functions calculated by means of density-matrix renormalization group. A phase diagram is obtained (for fixed electron density 1/3) from which we infer that coexistence between magnetic order and superconductivity is robust at the expense of a continuous distortion of the magnetic arrangement of the local moments as evidenced by a strong dependence of the characteristic wave vector

Introduction to quantum Monte Carlo simulations for fermionic systems

{\mathbf{k}}^{\ensuremath{\ast}}

Modulation of charge-density waves by superlattice structures

on the coupling constants. This allows us to understand some trends of the coexistence, such as the influence of the rare earth on

Ising spin glass in a transverse magnetic field.

{\mathbf{k}}^{\ensuremath{\ast}}

Universality, frustration, and conformal invariance in two-dimensional random Ising magnets

, as observed experimentally in the borocarbides.

Charge-density waves in one-dimensional Hubbard superlattices

We tutorially review the determinantal Quantum Monte Carlo method for fermionic systems, using the Hubbard model as a case study. Starting with the basic ingredients of Monte Carlo simulations for classical systems, we introduce aspects such as importance sampling, sources of errors, and finite-size scaling analyses. We then set up the preliminary steps to prepare for the simulations, showing that they are actually carried out by sampling discrete Hubbard-Stratonovich auxiliary fields. In this process the Green’s function emerges as a fundamental tool, since it is used in the updating process, and, at the same time, it is directly related to the quantities probing magnetic, charge, metallic, and superconducting behaviours. We also discuss the as yet unresolved ‘minus-sign problem’, and two ways to stabilize the algorithm at low temperatures.

First principles study of the ferromagnetism in Ga1−xMnxAs semiconductors

We discuss the interplay between electronic correlations and an underlying superlattice structure in determining the period of charge density waves (CDWs), by considering a one-dimensional Hubbard model with a repeated (nonrandom) pattern of repulsive

Luttinger liquid superlattices: Realization of gapless insulating phases

(Ug0)

FIELD-INDUCED ORDERING IN CRITICAL ANTIFERROMAGNETS

and free

Hole concentration in a diluted ferromagnetic semiconductor

(U=0)