Sökning: "spin Hamiltonians"

Visar resultat 1 - 5 av 6 avhandlingar innehållade orden spin Hamiltonians.

  1. 1. Theoretical Studies of Two-Dimensional Magnetism and Chemical Bonding

    Författare :Oleksiy Grechnyev; Olle Eriksson; Alexander Lichtenstein; Uppsala universitet; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Physics; spin Hamiltonians; quantized spin models; Heisenberg model; spin waves; self-consistent spin-wave theory; dipolar interaction; density functional theory; chemical bonding; overlap population; MAX phases; metal hydrides; Fysik; Physics; Fysik;

    Sammanfattning : This thesis is divided into two parts. In the first part we study thermodynamics of the two-dimensional Heisenberg ferromagnet with dipolar interaction. This interaction breaks the conditions of the Mermin-Wagner theorem, resulting in a finite transition temperature. LÄS MER

  3. 2. Quantum mechanical models of nanomagnetism in transition metal clusters and diluted magnetic semiconductors

    Författare :Olof Strandberg; Matematisk fysik; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; diluted magnetic semiconductors; Mn As; Ga; transition metal clusters; magnetic anisotropy; Nanomagnetism; quantum geometric phases; Chern numbers; effective spin Hamiltonians; dimers;

    Sammanfattning : This dissertation investigates nanomagnetism in small transition metal clusters and the diluted magnetic semiconductor (Ga,Mn)As. We derive quantum mechanical models aimed at a realistic description of the low energy physics in these systems. LÄS MER

  4. 3. Elastic and inelastic scattering effects in conductance measurements at the nanoscale : A theoretical treatise

    Författare :Peter Berggren; Jonas Fransson; Wolfgang Belzig; Uppsala universitet; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Scattering theory; Scanning tunneling microscopy; tunnel junctions; molecular graphene; paramagnetic molecules; spin interaction; nano electromechanical system; Josephson junction; superconductivity; chaos; Physics with spec. in Atomic; Molecular and Condensed Matter Physics; Fysik med inriktning mot atom- molekyl- och kondenserande materiens fysik;

    Sammanfattning : Elastic and inelastic interactions are studied in tunnel junctions of a superconducting nanoelectromechanical setup and in response to resent experimental superconducting scanning tunneling microscope findings on a paramagnetic molecule. In addition, the electron density of molecular graphene is modeled by a scattering theory approach in very good agreement with experiment. LÄS MER

  5. 4. The one-dimensional Kondo Lattice in the Majorana Fermion representation

    Författare :Matteo Bazzanella; Göteborgs universitet; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Majorana fermions; kondo lattice; path integral; spin-selective kondo insulator;

    Sammanfattning : This thesis analyses the possibilities offered by the representation of quantum mechanical operators in terms of Majorana fermions. These objects can be imagined as algebraic constituents of the fermionic degrees of freedom, allowing for a different representation of many Hamiltonians. LÄS MER

  7. 5. Molecular Electronics : A Theoretical Study of Electronic Structure of Bulk and Interfaces

    Författare :Mikael Unge; Sven Stafström; Mads Brandbyge; Linköpings universitet; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; molecular electronics; electron transport; disorder; localization; long-range correlation; organometallic magnets; interface dipole; Computational physics; Beräkningsfysik;

    Sammanfattning : This thesis deals with theoretical studies of the electronic structure of molecules used in the context of molecular electronics. Both studies with model Hamiltonians and first principle calculations have been performed. LÄS MER