arXiv subjects

Michael Hinczewski

Publications and source records attributed to Michael Hinczewski.

57 records · Page 4Linked to original sources

arXiv2005

Multicritical Point Relations in Three Dual Pairs of Hierarchical-Lattice Ising Spin-Glasses

The Ising spin-glasses are investigated on three dual pairs of hierarchical lattices, using exact renormalization-group transformation of the quenched bond probability distribution. The goal is to investigate a recent conjecture which relates, on such pairs of dual lattices, the locations of the multicritical points, which occur on the Nishimori symmetry line. Towards this end we precisely determine the global phase diagrams for these six hierarchical spin-glasses, using up to 2.5 x 10^9 probability bins to represent the quenched distribution subjected to an exact renormalization-group transformation. We find in all three cases that the conjecture is realized to a very good approximation, even when the mutually dual models belong to different spatial dimensionalities d and have different phase diagram topologies at the multicritical points of the conjecture and even though the contributions to the conjecture from each lattice of the dual pair are strongly asymmetric. In all six phase diagrams, we find reentrance near the multicritical point. In the models with d=2 or 1.5, the spin-glass phase does not occur and the phase boundary between the ferromagnetic and paramagnetic phases is second order with a strong violation of universality. PACS numbers: 75.10.Nr, 64.60.Kw, 05.45.Df, 05.10.Cc

cond-mat.dis-nn↗

arXiv2005

Superfluid Weight, Free Carrier Density, and Specific Heat of the d=3 tJ Model at Finite Temperatures

The superfluid weight, free carrier density, and specific heat of the three-dimensional tJ model are calculated by renormalization-group theory. We find that optimal hole doping for superfluidity occurs in the electron density range of n_i approximately between 0.63 - 0.68, where the superfluid weight n_s/m* reaches a local maximum. This density range is within the novel tau phase, where the electron hopping strength renormalizes to infinity, the system remains partially filled at all length scales, and the electron-hopping expectation value remains distinctively non-zero at all length scales. The calculated superfluid weight drops off sharply in the overdoped region. Under hole doping, the calculated density of free carriers increases until optimal doping and remains approximately constant in the overdoped region, as seen experimentally in high-T_c materials. Furthermore, from calculation of the specific heat coefficient gamma, we see clear evidence of a gap in the excitation spectrum for the tau phase.

cond-mat.str-el↗

arXiv2005

Two Superconducting Phases in the d=3 Hubbard Model: Phase Diagram and Specific Heat from Renormalization-Group Calculations

The phase diagram of the d=3 Hubbard model is calculated as a function of temperature and electron density n_i, in the full range of densities between 0 and 2 electrons per site, using renormalization-group theory. An antiferromagnetic phase occurs at lower temperatures, at and near the half-filling density of = 1. The antiferromagnetic phase is unstable to hole or electron doping of at most 15%, yielding to two distinct "tau" phases: for large coupling U/t, one such phase occurs between 30-35% hole or electron doping, and for small to intermediate coupling U/t another such phase occurs between 10-18% doping. Both tau phases are distinguished by non-zero hole or electron hopping expectation values at all length scales. Under further doping, the tau phases yield to hole- or electron-rich disordered phases. We have calculated the specific heat over the entire phase diagram. The low-temperature specific heat of the weak-coupling tau phase shows a BCS-type exponential decay, indicating a gap in the excitation spectrum, and a cusp singularity at the phase boundary. The strong-coupling tau phase, on the other hand, has characteristics of BEC-type superconductivity, including a critical exponent alpha approximately equal to -1, and an additional peak in the specific heat above the transition temperature indicating pair formation. In the limit of large Coulomb repulsion, the phase diagram of the tJ model is recovered.

cond-mat.str-el↗