A Monte Carlo study of magnetic pairing mechanisms in high temperature superconductors
A Monte Carlo study of magnetic pairing mechanisms in high temperature superconductors
Using a semi-classical Monte Carlo simulation technique the t-t'-J model and the MMP model are studied. The models are based on a local real space interaction and a local k-space interaction respectively. These interactions couple the charge carriers in the cuprate high temperature superconductors. In both cases the coupling originates from antiferromagnetic effects in the CuO2 layers of the cuprates. The simulations are performed on a 2-dimensional k-space grid corresponding to a single layer. Both models have been proposed to explain the phenomenon of high temperature superconductivity.
In this work the reduced BCS pairing projections of each model are used to investigate and compare the properties of their superconducting phases. The symmetry and magnitude of the energy gap parameter at low temperatures, and its dependence on filling for a range of different band structures is reported. Both extended s-wave and d-wave superconducting order are found. D-wave ordering is shown to be strongly dependent on Van Hove singularities in the band structure. Orthorhombic distortions, which split the degeneracy of Van Hove singularities, are shown to result in a corresponding split of the peak of the d-wave energy gap parameter as a function of filling. These distortions are also shown to enhance the extended s-wave ordering, giving it a definite phase angle relation to the d-wave component. By varying the strength of the interactions in each model various mixed s/d states are observed. The effect of varying temperature on these superconducting states is examined for the t-t'-J model. The form, relative strength, and doping dependence, of the simulated superconducting phases, are in good qualitative agreement with experimentally determined superconducting phase diagrams.
Using a two band quasi-spin simulation the hole modulated hopping (HMH) model is investigated. The reduced BCS pairing projection of the model is used to examine the normal state of the high temperature superconductors. Previous quasi-spin studies have indicated that a non-superconducting gap opens up in the normal state of the model. This gap is compared with the experimentally observed pseudogap found above Tc in high temperature superconductors. In particular it is established whether an incoherent bound pair state exists in the normal state of the HMH model. Such a state has been invoked to explain the existence of the pseudogap. The simulated Tc vs hole doping diagram is found to be in reasonable qualitative and quantitative agreement with the experimental pseudogap phase diagram.
University of Southampton
Bromley, Stefan
f15d6ec7-c1b5-4a3d-b16e-6ed311839f23
1998
Bromley, Stefan
f15d6ec7-c1b5-4a3d-b16e-6ed311839f23
Bromley, Stefan
(1998)
A Monte Carlo study of magnetic pairing mechanisms in high temperature superconductors.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Using a semi-classical Monte Carlo simulation technique the t-t'-J model and the MMP model are studied. The models are based on a local real space interaction and a local k-space interaction respectively. These interactions couple the charge carriers in the cuprate high temperature superconductors. In both cases the coupling originates from antiferromagnetic effects in the CuO2 layers of the cuprates. The simulations are performed on a 2-dimensional k-space grid corresponding to a single layer. Both models have been proposed to explain the phenomenon of high temperature superconductivity.
In this work the reduced BCS pairing projections of each model are used to investigate and compare the properties of their superconducting phases. The symmetry and magnitude of the energy gap parameter at low temperatures, and its dependence on filling for a range of different band structures is reported. Both extended s-wave and d-wave superconducting order are found. D-wave ordering is shown to be strongly dependent on Van Hove singularities in the band structure. Orthorhombic distortions, which split the degeneracy of Van Hove singularities, are shown to result in a corresponding split of the peak of the d-wave energy gap parameter as a function of filling. These distortions are also shown to enhance the extended s-wave ordering, giving it a definite phase angle relation to the d-wave component. By varying the strength of the interactions in each model various mixed s/d states are observed. The effect of varying temperature on these superconducting states is examined for the t-t'-J model. The form, relative strength, and doping dependence, of the simulated superconducting phases, are in good qualitative agreement with experimentally determined superconducting phase diagrams.
Using a two band quasi-spin simulation the hole modulated hopping (HMH) model is investigated. The reduced BCS pairing projection of the model is used to examine the normal state of the high temperature superconductors. Previous quasi-spin studies have indicated that a non-superconducting gap opens up in the normal state of the model. This gap is compared with the experimentally observed pseudogap found above Tc in high temperature superconductors. In particular it is established whether an incoherent bound pair state exists in the normal state of the HMH model. Such a state has been invoked to explain the existence of the pseudogap. The simulated Tc vs hole doping diagram is found to be in reasonable qualitative and quantitative agreement with the experimental pseudogap phase diagram.
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Published date: 1998
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Local EPrints ID: 463382
URI: http://eprints.soton.ac.uk/id/eprint/463382
PURE UUID: e2aa9027-d02f-4b5b-8220-350925db09e6
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Date deposited: 04 Jul 2022 20:51
Last modified: 04 Jul 2022 20:51
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Author:
Stefan Bromley
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