10 research outputs found

    A Maximum Entropy Method of Obtaining Thermodynamic Properties from Quantum Monte Carlo Simulations

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    We describe a novel method to obtain thermodynamic properties of quantum systems using Baysian Inference -- Maximum Entropy techniques. The method is applicable to energy values sampled at a discrete set of temperatures from Quantum Monte Carlo Simulations. The internal energy and the specific heat of the system are easily obtained as are errorbars on these quantities. The entropy and the free energy are also obtainable. No assumptions as to the specific functional form of the energy are made. The use of a priori information, such as a sum rule on the entropy, is built into the method. As a non-trivial example of the method, we obtain the specific heat of the three-dimensional Periodic Anderson Model.Comment: 8 pages, 3 figure

    Quantum critical point in a periodic Anderson model

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    We investigate the symmetric periodic Anderson model ͑PAM͒ on a three-dimensional cubic lattice with nearest-neighbor hopping and hybridization matrix elements. Using Gutzwiller's variational method and the Hubbard-III approximation ͑which corresponds to an exact solution of the appropriate Falicov-Kimball model in infinite dimensions͒ we demonstrate the existence of a quantum critical point at zero temperature. Below a critical value V c of the hybridization ͑or above a critical interaction U c ) the system is an insulator in Gutzwiller's and a semimetal in Hubbard's approach, whereas above V c ͑below U c ) it behaves like a metal in both approximations. These predictions are compared with the density of states of the d and f bands calculated from quantum Monte Carlo and numerical renormalization group calculations. Our conclusion is that the half-filled symmetric PAM contains a metal-semimetal transition, not a metal-insulator transition as has been suggested previously

    Quantum critical point in a periodic Anderson model

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    We investigate the symmetric Periodic Anderson Model (PAM) on a three-dimensional cubic lattice with nearest-neighbor hopping and hybridization matrix elements. Using Gutzwiller's variational method and the Hubbard-III approximation (which corresponds to the exact solution of an appropriate Falicov-Kimball model in infinite dimensions) we demonstrate the existence of a quantum critical point at zero temperature. Below a critical value VcV_c of the hybridization (or above a critical interaction UcU_c) the system is an {\em insulator} in Gutzwiller's and a {\em semi-metal} in Hubbard's approach, whereas above VcV_c (below UcU_c) it behaves like a metal in both approximations. These predictions are compared with the density of states of the dd- and ff-bands calculated from Quantum Monte Carlo and NRG calculations. Our conclusion is that the half-filled symmetric PAM contains a {\em metal-semimetal transition}, not a metal-insulator transition as has been suggested previously.Comment: ReVteX, 10 pages, 2 EPS figures. Minor corrections made in the text and in the figure captions from the first version. More references added. Accepted for publication in Physical Review

    Doping-dependent study of the periodic Anderson model in three dimensions

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    We study a simple model for ff-electron systems, the three-dimensional periodic Anderson model, in which localized ff states hybridize with neighboring dd states. The ff states have a strong on-site repulsion which suppresses the double occupancy and can lead to the formation of a Mott-Hubbard insulator. When the hybridization between the ff and dd states increases, the effects of these strong electron correlations gradually diminish, giving rise to interesting phenomena on the way. We use the exact quantum Monte-Carlo, approximate diagrammatic fluctuation-exchange approximation, and mean-field Hartree-Fock methods to calculate the local moment, entropy, antiferromagnetic structure factor, singlet-correlator, and internal energy as a function of the f−df-d hybridization for various dopings. Finally, we discuss the relevance of this work to the volume-collapse phenomenon experimentally observed in f-electron systems.Comment: 12 pages, 8 figure

    Signatures of Spin and Charge Energy Scales in the Local Moment and Specific Heat of the Two-Dimensional Hubbard Model

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    Local moment formation driven by the on--site repulsion UU is one of the most fundamental features in the Hubbard model. At the simplest level, the temperature dependence of the local moment is expected to have a single structure at T∌UT \sim U, reflecting the suppression of the double occupancy. In this paper we show new low temperature Quantum Monte Carlo data which emphasize that the local moment also has a signature at a lower energy scale which previously had been thought to characterize only the temperatures below which moments on {\it different} sites begin to correlate locally. We discuss implications of these results for the structure of the specific heat, and connections to quasiparticle resonance and pseudogap formation in the density of states.Comment: 13 pages, 19 figure

    Evolution of the Density of States Gap in a Disordered Superconductor

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    It has only recently been possible to study the superconducting state in the attractive Hubbard Hamiltonian via a direct observation of the formation of a gap in the density of states N(w). Here we determine the effect of random chemical potentials on N(w) and show that at weak coupling, disorder closes the gap concurrently with the destruction of superconductivity. At larger, but still intermediate coupling, a pseudo-gap in N(w) remains even well beyond the point at which off-diagonal long range order vanishes. This change in the elementary excitations of the insulating phase corresponds to a crossover between Fermi- and Bose-Insulators. These calculations represent the first computation of the density of states in a finite dimensional disordered fermion model via the Quantum Monte Carlo and maximum entropy methods.Comment: 4 pages, 4 figure

    Progress in Canadian Geomorphology and Hydrology 1996–2000

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    List of publications on the economic and social history of Great Britain and Ireland published in 2018

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