Ultracold atoms in superlattices as quantum simulators for a spin ordering model and phenomena

Cold atoms in optical lattices is the application of two formerly distinct aspects of physics: quantum gases from atomic physics and laser theory from quantum optics. Its use to simulate quantum phenomena and models in condensed matter physics is a growing field. The major goal is to use cold fermonic atoms in these superlattices for the simulations. We present here a theoretical proposal for simulating a spin ordering model using fermions. We demonstrate superexchange interaction in the double well and resonating valence bond (RVB) states in kagome lattice which is important for understanding the CuO2 plane of the superconducting cuprates and other magnetic frustrated materials.Comment: 10 page

Superexchange Driven Singlet-Triplet Transition in Quantum Dots Array Embedded in Kagome Lattice System

The envisaged revolutionary impact of the quantum computer has continued to elucidate diverse means to design and build physical quantum computers. In condensed matter physics, one of the means is to design materials to host two-electron quantum dots (QDs) which can be manipulated into singlet-triplet (S-T) transition. This transition which is read as the quantum bits (qubits) that is considered as a possible logic gate for the quantum computers is enhanced by external magnetic field which is a potential source of decohenrence. In the study here therefore, the possibility of using a superexchange induced internal magnetic field to drive the S-T transition in QDs embedded in a kagome lattice system (KLS) is examined. The design is by embedding the two-electron QDs into the frustrated sites of the KLS and then filling the other sites with single electrons. The parameter space of this KLS to achieve the S-T in the QDs array are obtained from the superexchange interaction in correlated  variational  study of the system.   Keywords: frustrated system,  kagome  lattice, quantum dot, singlet-triplet transition, quantum compute

A general theoretical design of semiconductor nanostructures with equispaced energy levels: preliminary report for quantum wells in semiconductor ternary alloys (AxB1-xC)

The purpose of this study is to formulate a general theoretical design of equispaced energy levels for semiconductor nanostructures. Here we present a preliminary report for the design of equispaced energy levels for quantum wells (QWs) in semiconductor ternary alloys (AxB1-xC). The procedure is by mapping the envelope function Schrodinger equation for a realistic QW, with the local conduction-band edges as the potential experienced by an electron in the QW into an effective-mass Schrodinger equation with a linear harmonic oscillator potential by the method of coordinate transformation. The electron effective mass and potential are then obtained as the signatures for the equispaced energy levels for QWs in semiconductor ternary alloys. Keywords: Semiconductor nanostructures, Ternary alloys, Quantum wells, Equispaced energy levels, Effective mass

Superconductivity driven by magnetic instability in CeCu2Si2

The coexistent of superconductivity (SC) with antiferromagnetism (AFM) and ferromagnetism (FM) as U ?? is studied in CeCu2Si2 on application of the Exact Diagonalization technique to the Single site Impurity Anderson Model and the Periodic Anderson Model. The results obtained show that magnetic instability is the key to understanding superconductivity in Heavy Fermion compounds as increasing the onsite coulomb repulsion, U, suppresses all ferromagnetic tendencies and enhances superconductivity. The results obtained here is in qualitative agreement with the inelastic neutron scattering experimental results obtained by Stockert et al (2011) on increasing the copper content in CeCu2Si2. U in this theoretical study behaves as Cu in the inelastic neutron scattering experiment. Keywords: Heavy fermion, antiferromagnetism, superconductivity, ferromagnetism, singlet state energy, triplet state energy

100 Years of Superconductivity: The Past, The Present And The Future Quest for a Generalized Theory

This is a review paper to celebrate the first century (1911 – 2011) of the discovery of superconductivity. The emphasis is on the search for a generalized theory of superconductivity. It is observed here that though there are many theories currently in the literature, there are three domineering mechanisms for the Cooper pair formation (CPF) and their emergent theories of superconductivity. Two of these mechanisms, based on the quantum theory axiom of action-at-a distance, may be only an approximation of the third mechanism which is contact interaction of the wavepackets of the two electrons forming the Cooper pair as envisaged in hadronic mechanics. It is therefore suggested that the future of the search for the theory of superconductivity should be considered from the natural possible bonding in element that at short distances, the CPF is by a nonlinear, nonlocal and nonhamiltonian strong hadronictype interaction due to deep wave-overlapping of spinning particles leading to a Hulthen potential that is attractive between two electrons in singlet couplings while at large distance the CPF is by superexchange interaction which is purely a quantum mechanical effect.Journal of the Nigerian Association of Mathematical Physics, Volume 19 (November, 2011), pp 623 – 63

Comparison of a two electron with a two charged boson variational hubbard interactions

There is growing belief that both the conventional Bose Einstein condensation (CBEC) and non-conventional Bose Einstein condensation (NBEC) can be obtained from repulsive and attractive interactions of bosons respectively. However, there is still no generally accepted model to obtain both condensates. Since results in the literature show that the Hubbard model two electron interactions has both repulsive and attractive regions depending on the interaction strength, we are considering its extension to charged bosons to investigate the possibility of obtaining the condensates from it. As a preliminary investigation, we have compared in this present study, the two electron variational Hubbard Hamiltonian with that modified for charged bosons in N = 2, N x N = 4 x 4 and N x N x N = 5 x 5 x 5 lattices. The results show only slight differences between the cases of the electrons and bosons. The implication that there is possibility of obtaining both condensates from the Hubbard model is then discussed in relation to superconductivity. Keywords: Bose Einstein condensation, superconductivity, Hubbard model, electrons, bosons Global Journal of Pure and Applied Sciences Vol. 12(1) 2006: 119-12