arXiv subjects

Frank Marsiglio

Publications and source records attributed to Frank Marsiglio.

32 records · Page 2Linked to original sources

arXiv2017

Two and three particles interacting in a one-dimensional trap

We outline a procedure for using matrix mechanics to compute energy eigenvalues and eigenstates for two and three interacting particles in a confining trap, in one dimension. Such calculations can bridge a gap in the undergraduate physics curriculum between single-particle and many-particle quantum systems, and can also provide a pathway from standard quantum mechanics course material to understanding current research on cold-atom systems. In particular we illustrate the notion of "fermionization" and how it occurs not only for the ground state in the presence of strong repulsive interactions, but also for excited states, in both the strongly attractive and strongly repulsive regimes.

cond-mat.quant-gas↗

arXiv2017

Fractional Josephson effect in nonuniformly strained graphene

Nonuniform strain distributions in a graphene lattice can give rise to uniform pseudomagnetic fields and associated pseudo-Landau levels without breaking time-reversal symmetry. We demonstrate that by inducing superconductivity in a nonuniformly strained graphene sheet, the lowest pseudo-Landau levels split by a pairing gap can be inverted by changing the sign of the pairing potential. As a consequence of this inversion, we predict that a Josephson $π$ junction deposited on top of a strained graphene sheet exhibits one-dimensional gapless modes propagating along the junction. These gapless modes mediate single electron tunneling across the junction, giving rise to the $4π$-periodic fractional Josephson effect.

cond-mat.mes-hall↗

arXiv2015

The importance of basis states: an example using the Hydrogen basis

We use a simple system, the electron configuration in a Hydrogen-like atom, to demonstrate the importance of using a complete basis set to provide a proper quantum mechanical description. We first start with what might be considered a successful strategy --- to diagonalize a truncated Hamiltonian matrix, written in a basis consisting of Hydrogen ($Z=1$) basis states. This fails to provide the correct answer, and we then demonstrate that the continuum basis states provided the rest of the true wave function, for the bound ground states. This work then shows, in a relatively simple system, the need to utilize a complete basis set, consisting of both bound and continuum states.

physics.atom-ph↗

arXiv2011

Competition between reduced delocalization and charge transfer effects for a two-band Hubbard model

We use the embedding approach for a dynamical mean-field method to investigate the electronic properties of a semi-infinite two band Hubbard model at half- and quarter-filling. Two effects determine the degree of correlation at the surface: first, there will charge transfer between the surface and the bulk, and, secondly, electrons at the surface are less delocalized due to the reduced coordination number. We determine the result of these two effects and compute the quasiparticle weight. It is shown that depletion of charge from the surface to the bulk at quarter-filling competes with enhanced correlation effects; the net result is that at quarter-filling the quasi particle weight at the surface is approximately equal to the bulk quasi particle weight. Only when the charge transfer approaches zero at large interaction strengths does the quasi particle weight at the surface become lower than that in the bulk.

cond-mat.str-el↗

arXiv2011

Surface effects in doping a Mott insulator

The physics of doping a Mott insulator is investigated in the presence of a solid-vacuum interface. Using the embedding approach for dynamical mean field theory we show that the change in surface spectral evolution in a doped Mott insulator is driven by a combination of charge transfer effects and enhanced correlation effects. Approaching a Mott insulating phase from the metallic side, we show that a dead layer forms at the surface of the solid, where quasiparticle amplitudes are exponentially suppressed. Surface correlation and charge transfer effects can be strongly impacted by changes of the hopping integrals at the surface.

cond-mat.str-el↗

arXiv2010

Metallic surface of a bipolaronic insulator

We investigate the possibility that the surface of a strongly coupled electron-phonon system behaves differently from the bulk when the relevant parameters are inhomogeneous due to the presence of the interface. We consider parameter variations which make the surface either more metallic or more insulating than the bulk. While it appears impossible to stabilize a truly insulating surface when the bulk is metallic, the opposite situation can be realized. A metallic surface can indeed be decoupled from a bipolaronic insulator realized in the bulk.

cond-mat.str-el↗

arXiv2010

Absence of a supercritical regime induced by short-range impurity scattering in gapped graphene

We show that the changes in the electronic density of states (DOS) in graphene induced by impurity scattering with short-range potentials are completely different from those caused by the long-range Coulomb potential. The spectral weight of the state that eventually disappears into the valence band (as the strength of scattering increases) does not transform into a resonance state. Therefore no unusual screening effects related to a redistribution of the density of states in the valence band are observed. The states induced by the short-range impurities in graphene, therefore, have distinctively different properties compared with the long-range potential case. These properties, in fact, closely resemble the case of a short-range single impurity in other bipartite lattices, such as the square, body centered cubic, and simple cubic lattices.

cond-mat.mes-hall↗

arXiv2009

Emerging nonequilibrium bound state in spin-current-local-spin scattering

Magnetization reversal is a well-studied problem with obvious applicability in computer hard-drives. One can accomplish a magnetization reversal in at least one of two ways: application of a magnetic field, or through a spin current. The latter is more amenable to a fully quantum mechanical analysis. We formulate and solve the problem whereby a spin current interacts with a ferromagnetic Heisenberg spin chain, to eventually reverse the magnetization of the chain. Spin-flips are accomplished through both elastic and inelastic scattering. A consequence of the inelastic scattering channel, when it is no longer energetically possible, is the occurrence of a new entity: a non-equilibrium bound state (NEBS), which is an emergent property of the coupled local plus itinerant spin system. For certain definite parameter values the itinerant spin lingers near the local spins for some time, before eventually leaking out as an outwardly diffusing state. This phenomenon results in novel spin-flip dynamics and filtering properties for this type of system.

cond-mat.mes-hall↗

arXiv2006

Electron-phonon vs. electron-impurity interactions with small electron bandwidths

It is common practice to try to understand electron interactions in metals by defining a hierarchy of energy scales. Very often, the Fermi energy is considered the largest, so much so that frequently bandwidths are approximated as infinite. The reasoning is that attention should properly be focused on energy levels near the Fermi level, and details of the bands well away from the Fermi level are unimportant. However, a finite bandwidth can play an important role for low frequency properties: following a number of recent papers, we examine electron-impurity and electron-phonon interactions in bands with finite widths. In particular, we examine the behaviour of the electron self energy, spectral function, density of states, and dispersion, when the phonon spectral function is treated realistically as a broad Lorentzian function. With this phonon spectrum, impurity scattering has a significant non-linear effect.

cond-mat.str-el↗

arXiv2005

Sum Rule Anomaly from Suppression of Inelastic Scattering in the Superconducting State

In the conventional BCS description of a superconductor the kinetic energy increases in the superconducting state. We describe the observed decrease in kinetic energy by adopting a simple model of electrons whose elastic scattering rate undergoes a sharp decrease as the temperature is lowered below Tc. This phenomenology has been suggested by other experiments, particularly microwave conductivity. We find that such a decrease accounts for the observed increase; a study of these different phenomena over a wide range of high Tc materials would confirm this correlation.

cond-mat.supr-con↗

arXiv2005

Proximity effect in clean strong/weak/strong superconducting tri-layers

Recent measurements of the Josephson critical current through LSCO/LCO/LSCO thin films showed an unusually large proximity effect. Using the Bogoliubov-de Gennes (BdG) equations for a tight binding Hamiltonian we describe the proximity effect in weak links between a superconductor with critical temperature $T_c$ and one with critical temperature $T_c$', where $T_c>T_c$'. The weak link (N') is therefore a superconductor above its own critical temperature and the superconducting regions are considered to have either s-wave or d-wave symmetry. We note that the proximity effect is enhanced due to the presence of superconducting correlations in the weak link. The dc Josephson current is calculated, and we obtain a non-zero value for temperatures greater than $T_c$' for sizes of the weak links that can be almost an order of magnitude greater than the conventional coherence length. Considering pockets of superconductivity in the N' layer, we show that this can lead to an even larger effect on the Josephson critical current by effectively shortening the weak link.

cond-mat.supr-con↗

arXiv2003

Self-Consistent Modification To The Electron Density Of States Due To Electron-Phonon Coupling In Metals

The "standard" theory of a normal metal consists of an effective electron band which interacts with phonons and impurities. The effects due to the electron-phonon interaction are often delineated within the Migdal approximation; the properties of many simple metals are reasonably well described with such a description. On the other hand, if the electron-phonon interaction is sufficiently strong, a polaron approach is more appropriate. The purpose of this paper is to examine to what degree the Migdal approximation is self-consistent, as the coupling strength increases. We find that changes in the electron density of states become significant for very large values of the coupling strength; however, there is no critical value, nor even a crossover regime where the Migdal approximation has become inconsistent. Moreover, the extent to which the electron band collapses is strongly dependent on the detailed characteristics of the phonon spectrum.

cond-mat.str-el↗

arXiv2002

Superconductivity in Ba_2Sn_3Sb_6 and SrSn_3Sb_4

Resistivity and ac magnetic susceptibility measurements on Ba2Sn3Sb6 and SrSn3Sb4 indicate that these Zintl compounds display a transition to a superconducting phase at Tc = 3.9 K. The Meissner effect was observed for Ba2Sn3Sb6 under an applied field of 25 Oe. The signatures for superconductivity, such as high and low velocity conduction electrons and lone pairs, are present for both of these compounds.

cond-mat.supr-con↗

arXiv2002

Expansion in the "distance" from Hc2(T) line for the mixed state of BCS superconductors

We develop a description of the mixed state of type II superconductivity valid within a wide range of temperatures and external magnetic fields. It is based on the quasiclassical version of microscopic BCS theory and employs an expansion in the "distance" from the Hc2(T) line. We prove that in a clean metal with spherical Fermi surface and isotropic pairing interaction the superconducting condensation always produces a hexagonal vortex lattice.

cond-mat.supr-con↗