Search results for "density of state"
showing 10 items of 187 documents
Fourth-order perturbation theory for the half-filled Hubbard model in infinite dimensions
2003
We calculate the zero-temperature self-energy to fourth-order perturbation theory in the Hubbard interaction $U$ for the half-filled Hubbard model in infinite dimensions. For the Bethe lattice with bare bandwidth $W$, we compare our perturbative results for the self-energy, the single-particle density of states, and the momentum distribution to those from approximate analytical and numerical studies of the model. Results for the density of states from perturbation theory at $U/W=0.4$ agree very well with those from the Dynamical Mean-Field Theory treated with the Fixed-Energy Exact Diagonalization and with the Dynamical Density-Matrix Renormalization Group. In contrast, our results reveal t…
Exact solution of the 1D Hubbard model in the atomic limit with inter-site magnetic coupling
2012
In this paper we present for the first time the exact solution in the narrow-band limit of the 1D extended Hubbard model with nearest-neighbour spin-spin interactions described by an exchange constant J. An external magnetic field h is also taken into account. This result has been obtained in the framework of the Green's functions formalism, using the Composite Operator Method. By means of this theoretical background, we have studied some relevant features such as double occupancy, magnetization, spin-spin and charge-charge correlation functions and derived a phase diagram for both ferro (J>0) and anti-ferro (J<0) coupling in the limit of zero temperature. We also report a study on de…
Cooper-pair resonances and subgap Coulomb blockade in a superconducting single-electron transistor
2003
We have fabricated and measured superconducting single-electron transistors with Al leads and Nb islands. At bias voltages below the gap of Nb we observe clear signatures of resonant tunneling of Cooper pairs, and of Coulomb blockade of the subgap currents due to linewidth broadening of the energy levels in the superconducting density of states of Nb. The experimental results are in good agreement with numerical simulations.
Observation of thermally excited charge transport modes in a superconducting single-electron transistor
1997
Experiments on a superconducting single-electron transistor are reported. A new structure in the current-voltage characteristics at subgap voltages was observed when temperature was not too low as compared to the superconducting transition temperature Tc of the sample. The strength of the anomalies increases exponentially with temperature. The dominating features arise from matching of singularities in the density of states on two sides of a tunnel junction, and from the Josephson-quasiparticle cycle. Thermal excitations are essential for the former process, and they also make the latter process possible at low voltages.
Microscopic model for multiple flux transitions in mesoscopic superconducting loops
2006
A microscopic model is constructed which is able to describe multiple magnetic flux transitions as observed in recent ultra-low temperature tunnel experiments on an aluminum superconducting ring with normal metal - insulator - superconductor junctions [Phys. Rev. B \textbf{70}, 064514 (2004)]. The unusual multiple flux quantum transitions are explained by the formation of metastable states with large vorticity. Essential in our description is the modification of the pairing potential and the superconducting density of states by a sub-critical value of the persistent current which modulates the measured tunnel current. We also speculate on the importance of the injected non-equilibrium quasi…
Element-specific magnetic moments and spin-resolved density of states in CoFeMnZ(Z=Al, Ga; Si, Ge)
2011
Using circular dichroism in x-ray-absorption spectroscopy (XAS/XMCD), we determined element-specific magnetic moments and spin-resolved unoccupied densities of states (DOS) for Co, Fe, and Mn in the quaternary Heusler compounds CoFeMn$Z$ ($Z=\text{Al}$, Ga; Si, Ge). These compounds belong to a class of highly spin-polarized materials with cubic LiMgPdSn-type structure. Different structure models for the sublattice occupation leading to similar average magnetization values can be distinguished by comparison of element-specific moments with theory. We find that the compounds form similar structures, where Co, Fe, Mn, and $Z$ occupy the $X$, ${X}^{\ensuremath{'}}$, $Y$, and $Z$ sublattice of t…
Asymmetric Conductivity of Strongly Correlated Compounds
2014
In this chapter, we show that the FC solutions for distribution function \(n_0(\mathbf{p})\) generate NFL behavior, and violate the particle-hole symmetry inherent in LFL. This, in turn, yields dramatic changes in transport properties of HF metals, particularly, the differential conductivity becomes asymmetric. As it is demonstrated in Sect. 3.1, Fermi quasiparticles can behave as Bose one. Such a state is viewed as possessing the supersymmetry (SUSY) that interchanges bosons and fermions eliminating the difference between them. In the case of asymmetrical conductivity it is the emerging SUSY that violates the time invariance symmetry. Thus, restoring one important symmetry, the FC state vi…
Reply to “Comment to ‘Dynamics of supercooled confined water measured by deep inelastic neutron scattering’ by Y. Finkelstein and R. Moreh”
2019
We reply to the comment [Front. Phys. 14(5), 53605 (2019)] by Y. Finkelstein and R. Moreh on our article Front. Phys. 13(1), 138205 (2018). We agree with some of their criticisms about our calculation of the temperature effect on the kinetic energy of hydrogen atoms of supercooled confined water; we also agree with their statement that, in view of the current sensitivity of the technique, possible effects of the liquid-liquid water transition are hardly detected with deep inelastic neutron scattering (DINS). However, we disagree with their use of the translational mass ratio of a single water molecule and, in general, with their underestimation of collective effects.
Transport Properties of Correlated Electrons in High Dimensions
2003
We develop a new general algorithm for finding a regular tight-binding lattice Hamiltonian in infinite dimensions for an arbitrary given shape of the density of states (DOS). The availability of such an algorithm is essential for the investigation of broken-symmetry phases of interacting electron systems and for the computation of transport properties within the dynamical mean-field theory (DMFT). The algorithm enables us to calculate the optical conductivity fully consistently on a regular lattice, e.g., for the semi-elliptical (Bethe) DOS. We discuss the relevant f-sum rule and present numerical results obtained using quantum Monte Carlo techniques.
Level-spacing distribution in the tight-binding model of fcc clusters.
1993
A lattice-gas Monte Carlo method is used to simulate metallic fcc clusters at finite temperatures. A tight-binding model including s and p electrons has been derived for reproducing the free-electron-like energy band for the bulk metal and this model is used for calculating the electronic structures of the fcc cluster. The resulting level-spacing distribution at the Fermi energy is a Wigner distribution. The width of the distribution in small clusters is smaller than that calculated from the bulk density of states. In the lattice gas clusters the energy gaps related to the electronic magic numbers do not show up at the Fermi level. The energy between the last occupied and the first unoccupi…