Glass Model, Hubbard Model and High-Temperature Superconductivity

In this paper we revisit the glass model describing the macroscopic behavior of the High-Temperature superconductors. We link the glass model at the microscopic level to the striped phase phenomenon, recently discussed widely. The size of the striped phase domains is consistent with earlier predictions of the glass model when it was introduced for High-Temperature Superconductivity in 1987. In an additional step we use the Hubbard model to describe the microscopic mechanism for d-wave pairing within these finite size stripes. We discuss the implications for superconducting correlations of Hubbard model, which are much higher for stripes than for squares, for finite size scaling, and for the new view of the glass model picture.Comment: 7 pages, 7 figures (included), LaTex using Revtex, accepted by Int. J. Mod. Phys.

Spin-spin correlations in the tt'-Hubbard model

We present calculations of the tt'-Hubbard model using Quantum Monte Carlo techniques. The parameters are chosen so that the van Hove Singularity in the density of states and the Fermi level coincide. We study the behaviour of the system with increasing Hubbard interaction U. Special emphasis is on the spin-spin correlation (SSC). Unusual behaviour for large U is observed there and in the momentum distribution function ( n(q))

Crown Graphene Nanomeshes: Highly Stable Chelation-Doped Semiconducting Materials

Graphene nanomeshes (GNMs) formed by the creation of pore superlattices in graphene are a possible route to graphene-based electronics due to their semiconducting properties, including the emergence of fractional electronvolt band gaps. The utility of GNMs would be markedly increased if a scheme to stably and controllably dope them was developed. In this work, a chemically motivated approach to GNM doping based on selective pore-perimeter passivation and subsequent ion chelation is proposed. It is shown by first-principles calculations that ion chelation leads to stable doping of the passivated GNMsboth <i>n</i>- and <i>p</i>-doping are achieved within a rigid-band picture. Such chelated or “crown” GNM structures are stable, high mobility semiconducting materials possessing intrinsic doping-concentration control; these can serve as building blocks for edge-free graphene nanoelectronics including GNM-based complementary metal oxide semiconductor (CMOS)-type logic switches

Edge-state-mediated collective charging effects in a gate-controlled quantum dot array

[[abstract]]We report the observation of two distinct types of magnetoconductance oscillations in six coupled quantum dots (QDs) in the integer quantum Hall regime. By tuning the magnetic field and gate voltage, we find robust conductance peaks and dips on the plateau of one conductance quantum 2 e 2 / h . These features fall into two types associated with two different collective quantum states: for the first type, only dips and the crossing behaviors are found, and their traces show an anomalous temperature dependence, named “reversed Coulomb blockade oscillation”, whereas for the second type, the peak traces show both crossing and anticrossing behaviors with resonance-type temperature dependence. Notably, all peaks show clear Coulomb diamonds in their differential conductance. We argue that the observed features reveal the electron addition spectra in an edge-state-mediated QD network, manifesting intricate interdot and dot-edge Coulomb interactions. In the first-type regime, the dots are more isolated from each other and the electron transport is governed by the dot-edge interaction. Conversely, in the second-type regime, the QDs behave as a coupled dot array due to the presence of strong interdot interactions. Our results open a route by using the edge-state-mediated multi-QD system as a laboratory for exploring coherent many-body interactions.[[sponsorship]]MOST[[notice]]補正完

Evidence for electronic gap-driven metal-semiconductor transition in phase-change materials

Phase-change materials are functionally important materials that can be thermally interconverted between metallic (crystalline) and semiconducting (amorphous) phases on a very short time scale. Although the interconversion appears to involve a change in local atomic coordination numbers, the electronic basis for this process is still unclear. Here, we demonstrate that in a nearly vacancy-free binary GeSb system where we can drive the phase change both thermally and, as we discover, by pressure, the transformation into the amorphous phase is electronic in origin. Correlations between conductivity, total system energy, and local atomic coordination revealed by experiments and long time ab initio simulations show that the structural reorganization into the amorphous state is driven by opening of an energy gap in the electronic density of states. The electronic driving force behind the phase change has the potential to change the interconversion paradigm in this material class