Electronic states in externally modulated dilute magnetic semiconductor/superconductor hybrids

Attapon Amthong

Research output: ThesisDoctoral Thesis

Abstract

Dilute magnetic semiconductors (DMSs) are attractive. They are candidate materials for applications in novel spintronic devices. Because of the giant Zeemaneect in the paramagnetic state, a magnetic eld can be used to manipulate the spin and charge of carriers in DMSs. One possibility is to exploit the nonhomogeneous magnetic elds due to superconductors. In this thesis, the heterostructures of the planar DMS and superconductors in dierent geometries and superconducting states are investigated to understand the electronic structure of electrons in the DMS.
The combination of a superconducting disk in the Meissner state and the planar
DMS is studied using both simple and realistic models of the magnetic eld
associated with the disk. The giant Zeeman interaction is found to substantially
inuence the energies of magnetically conned states in the adjacent DMS. In the
simple model eld, the giant Zeeman energy acts as an extra conning potential
and results in spin dependent electron states exhibiting dierent spatial distributions, while the more realistic model eld results in conned states exhibiting a variety of mixed spin characters.
The hybrid of a superconducting lm in a superconducting vortex state and
the DMS is then explored. The concentrated magnetic eld due to an isolated
vortex is shown to trap strongly spin polarised electron states. In the case of
an Abrikosov lattice of vortices, interactions between vortex-bound states result
in a band structure which can be controlled by the magnitude of an external
uniform magnetic eld. It is found that the numerical band structures obtained
using a basis of Landau states dier from those previously reported, leading to
the development of a tight-binding theory to conrm their corrections. Another
hybrid investigated is a square superconductor above the DMS. In this case, the
arrangement of vortices is distorted by the boundary of the sample, leading to the possibility of multivortex state and/or giant vortex states. It is discovered that
the magnetic eld due to the former state induces \molecular" electron states
in the DMS, while that due to the latter state induces electron states with increased spatial distribution. Tight-binding theory is again used to describe the
observed energy levels and the interactions between electron states induced by
the magnetic elds due to separated vortices in the multivortex state.
LanguageEnglish
QualificationPh.D.
Awarding Institution
  • University of Bath
Supervisors/Advisors
  • Crampin, Simon, Supervisor
Award date30 Sep 2012
StatusUnpublished - 30 Sep 2012

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electron states
vortices
electronics
spatial distribution
theses
interactions
energy levels
traps
electronic structure
energy
geometry
electrons

Keywords

  • dilute magnetic semiconductor
  • superconductor
  • spintronics

Cite this

Electronic states in externally modulated dilute magnetic semiconductor/superconductor hybrids. / Amthong, Attapon.

2012. 176 p.

Research output: ThesisDoctoral Thesis

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title = "Electronic states in externally modulated dilute magnetic semiconductor/superconductor hybrids",
abstract = "Dilute magnetic semiconductors (DMSs) are attractive. They are candidate materials for applications in novel spintronic devices. Because of the giant Zeemaneect in the paramagnetic state, a magnetic eld can be used to manipulate the spin and charge of carriers in DMSs. One possibility is to exploit the nonhomogeneous magnetic elds due to superconductors. In this thesis, the heterostructures of the planar DMS and superconductors in dierent geometries and superconducting states are investigated to understand the electronic structure of electrons in the DMS.The combination of a superconducting disk in the Meissner state and the planarDMS is studied using both simple and realistic models of the magnetic eldassociated with the disk. The giant Zeeman interaction is found to substantiallyinuence the energies of magnetically conned states in the adjacent DMS. In thesimple model eld, the giant Zeeman energy acts as an extra conning potentialand results in spin dependent electron states exhibiting dierent spatial distributions, while the more realistic model eld results in conned states exhibiting a variety of mixed spin characters.The hybrid of a superconducting lm in a superconducting vortex state andthe DMS is then explored. The concentrated magnetic eld due to an isolatedvortex is shown to trap strongly spin polarised electron states. In the case ofan Abrikosov lattice of vortices, interactions between vortex-bound states resultin a band structure which can be controlled by the magnitude of an externaluniform magnetic eld. It is found that the numerical band structures obtainedusing a basis of Landau states dier from those previously reported, leading tothe development of a tight-binding theory to conrm their corrections. Anotherhybrid investigated is a square superconductor above the DMS. In this case, thearrangement of vortices is distorted by the boundary of the sample, leading to the possibility of multivortex state and/or giant vortex states. It is discovered thatthe magnetic eld due to the former state induces \molecular{"} electron statesin the DMS, while that due to the latter state induces electron states with increased spatial distribution. Tight-binding theory is again used to describe theobserved energy levels and the interactions between electron states induced bythe magnetic elds due to separated vortices in the multivortex state.",
keywords = "dilute magnetic semiconductor, superconductor, spintronics",
author = "Attapon Amthong",
year = "2012",
month = "9",
day = "30",
language = "English",
school = "University of Bath",

}

TY - THES

T1 - Electronic states in externally modulated dilute magnetic semiconductor/superconductor hybrids

AU - Amthong,Attapon

PY - 2012/9/30

Y1 - 2012/9/30

N2 - Dilute magnetic semiconductors (DMSs) are attractive. They are candidate materials for applications in novel spintronic devices. Because of the giant Zeemaneect in the paramagnetic state, a magnetic eld can be used to manipulate the spin and charge of carriers in DMSs. One possibility is to exploit the nonhomogeneous magnetic elds due to superconductors. In this thesis, the heterostructures of the planar DMS and superconductors in dierent geometries and superconducting states are investigated to understand the electronic structure of electrons in the DMS.The combination of a superconducting disk in the Meissner state and the planarDMS is studied using both simple and realistic models of the magnetic eldassociated with the disk. The giant Zeeman interaction is found to substantiallyinuence the energies of magnetically conned states in the adjacent DMS. In thesimple model eld, the giant Zeeman energy acts as an extra conning potentialand results in spin dependent electron states exhibiting dierent spatial distributions, while the more realistic model eld results in conned states exhibiting a variety of mixed spin characters.The hybrid of a superconducting lm in a superconducting vortex state andthe DMS is then explored. The concentrated magnetic eld due to an isolatedvortex is shown to trap strongly spin polarised electron states. In the case ofan Abrikosov lattice of vortices, interactions between vortex-bound states resultin a band structure which can be controlled by the magnitude of an externaluniform magnetic eld. It is found that the numerical band structures obtainedusing a basis of Landau states dier from those previously reported, leading tothe development of a tight-binding theory to conrm their corrections. Anotherhybrid investigated is a square superconductor above the DMS. In this case, thearrangement of vortices is distorted by the boundary of the sample, leading to the possibility of multivortex state and/or giant vortex states. It is discovered thatthe magnetic eld due to the former state induces \molecular" electron statesin the DMS, while that due to the latter state induces electron states with increased spatial distribution. Tight-binding theory is again used to describe theobserved energy levels and the interactions between electron states induced bythe magnetic elds due to separated vortices in the multivortex state.

AB - Dilute magnetic semiconductors (DMSs) are attractive. They are candidate materials for applications in novel spintronic devices. Because of the giant Zeemaneect in the paramagnetic state, a magnetic eld can be used to manipulate the spin and charge of carriers in DMSs. One possibility is to exploit the nonhomogeneous magnetic elds due to superconductors. In this thesis, the heterostructures of the planar DMS and superconductors in dierent geometries and superconducting states are investigated to understand the electronic structure of electrons in the DMS.The combination of a superconducting disk in the Meissner state and the planarDMS is studied using both simple and realistic models of the magnetic eldassociated with the disk. The giant Zeeman interaction is found to substantiallyinuence the energies of magnetically conned states in the adjacent DMS. In thesimple model eld, the giant Zeeman energy acts as an extra conning potentialand results in spin dependent electron states exhibiting dierent spatial distributions, while the more realistic model eld results in conned states exhibiting a variety of mixed spin characters.The hybrid of a superconducting lm in a superconducting vortex state andthe DMS is then explored. The concentrated magnetic eld due to an isolatedvortex is shown to trap strongly spin polarised electron states. In the case ofan Abrikosov lattice of vortices, interactions between vortex-bound states resultin a band structure which can be controlled by the magnitude of an externaluniform magnetic eld. It is found that the numerical band structures obtainedusing a basis of Landau states dier from those previously reported, leading tothe development of a tight-binding theory to conrm their corrections. Anotherhybrid investigated is a square superconductor above the DMS. In this case, thearrangement of vortices is distorted by the boundary of the sample, leading to the possibility of multivortex state and/or giant vortex states. It is discovered thatthe magnetic eld due to the former state induces \molecular" electron statesin the DMS, while that due to the latter state induces electron states with increased spatial distribution. Tight-binding theory is again used to describe theobserved energy levels and the interactions between electron states induced bythe magnetic elds due to separated vortices in the multivortex state.

KW - dilute magnetic semiconductor

KW - superconductor

KW - spintronics

M3 - Doctoral Thesis

ER -