arXiv subjects

R. M. Fye

Publications and source records attributed to R. M. Fye.

4 recordsLinked to original sources

arXiv2014

Determinant Quantum Monte Carlo Study of d-wave pairing in the Plaquette Hubbard Hamiltonian

Determinant Quantum Monte Carlo (DQMC) is used to determine the pairing and magnetic response for a Hubbard model built up from four-site clusters -a two-dimensional square lattice consisting of elemental 2x2 plaquettes with hopping $t$ and on-site repulsion $U$ coupled by an inter-plaquette hopping $t' \leq t$. Superconductivity in this geometry has previously been studied by a variety of analytic and numeric methods, with differing conclusions concerning whether the pairing correlations and transition temperature are raised near half-filling by the inhomogeneous hopping or not. For $U/t=4$, DQMC indicates an optimal $t'/t \approx 0.4$ at which the pairing vertex is most attractive. The optimal $t'/t$ increases with $U/t$. We then contrast our results for this plaquette model with a Hamiltonian which instead involves a regular pattern of site energies whose large site energy limit is the three band CuO$_2$ model; we show that there the inhomogeneity rapidly, and monotonically, suppresses pairing.

cond-mat.str-el↗

arXiv2004

Hole-pair symmetry and excitations in the strong-coupling extended t-Jz model: competition between d-wave and p-wave

We analytically calculate the ground state pairing symmetry and excitation spectra of two holes doped into the half-filled t-t'-t"-Jz model in the strong-coupling limit (Jz>>|t|,|t'|,|t"|). In leading order, this reduces to the t'-t"-Jz model, where there are regions of d-wave, s-wave, and (degenerate) p-wave symmetry. We find that the t-Jz model maps in lowest order onto the t'-t"-Jz model on the boundary between d and p symmetry, with a flat lower band in the pair excitation spectrum. In higher order, d-wave symmetry is selected from the lower pair band. However, we observe that the addition of the appropriate t'<0 and/or t''>0, the signs of t' and t" found in the hole-doped cuprates, could drive the hole-pair symmetry to p-wave, implying the possibility of competition between p-wave and d-wave pair ground states. (An added t'>0 and/or t" <0 generally tend to promote d-wave symmetry.) We perturbatively construct an extended quasi-pair for the t-Jz model. In leading order, there are contributions from sites at a distance of sqrt{2} lattice spacings apart; however, contributions from sites 2 lattice spacings apart, also of the same order, vanish identically. Finally, we compare our approach with analytic calculations for a 2x2 plaquette and with existing numerical work, and discuss possible relevance to the physical parameter regime.

cond-mat.str-el↗

arXiv1999

Study of a generalized Metropolis decision rule in auxiliary field quantum Monte Carlo

We consider a generalization of the standard Metropolis algorithm acceptance/rejection decision rule and numerically explore its properties using auxiliary field quantum Monte Carlo. The generalization involves a free parameter which, given a criterion for proposing attempted moves, can be used to tune the average acceptance rate in a particular way. Such tuning can also potentially change Monte Carlo autocorrelation times, and the combination of the changing acceptance rate and autocorrelation times raises the possibility of more efficient simulations. We explore these issues using primarily massively parallel quantum Monte Carlo runs of the ``test case'' two-dimensional Hubbard model, and discuss results and applications.

cond-mat.str-el↗

arXiv1997

Hole-pair symmetry and excitations in the strong-coupling extended t-J_z model

We analytically calculate the ground state pairing symmetry and excitation spectra of two holes doped into the half-filled t-t'-t''-J_z model in the strong-coupling limit (J_z >> |t|, |t'|, |t''|). For the t'-t''-J_z model, there are regions of d-wave, s-wave, and p-wave symmetry. We find that the t-J_z model maps in lowest order onto the t'-t''-J_z model on the boundary between d and p symmetry, with a flat lower branch of the pair excitation spectrum. In higher order d-wave symmetry is selected; however, we predict that the addition of the appropriate t' and/or t'' should drive the hole-pair symmetry to p-wave. We perturbatively construct an extended quasi-pair for the t-J_z model. We compare with analytic calculations for a 2x2 plaquette and numerical work, and discuss implications for the experimentally relevant parameter regime.

cond-mat.str-el↗