Klaus Wiele - Academia.edu (original) (raw)
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Papers by Klaus Wiele
Physical Review B, 2004
As part of a study that investigates the dynamics of the s = 1 2 XXZ model in the planar regime |... more As part of a study that investigates the dynamics of the s = 1 2 XXZ model in the planar regime |∆| < 1, we discuss the singular nature of the Bethe ansatz equations for the case ∆ = 0 (XX model). We identify the general structure of the Bethe ansatz solutions for the entire XX spectrum, which include states with real and complex magnon momenta. We discuss the relation between the spinon or magnon quasiparticles (Bethe ansatz) and the lattice fermions (Jordan-Wigner representation). We present determinantal expressions for transition rates of spin fluctuation operators between Bethe wave functions and reduce them to product expressions. We apply the new formulas to two-spinon transition rates for chains with up to N = 4096 sites.
Journal of Physics A: Mathematical and General, 2006
Die Arbeit beginnt mit einer kurzen Einfuehrung in das anisotrope Heisenberg-Modell (XXZ-Modell).... more Die Arbeit beginnt mit einer kurzen Einfuehrung in das anisotrope Heisenberg-Modell (XXZ-Modell). Im Hauptteil werden als Spezialfaelle davon das XX-Modell und das Haldane-Shastry-Modell untersucht. Fuer das XX-Modell wird eine vollstaendige Beschreibung des Spektrums durch Spinonen (spezielle Quasiteilchen) gegeben. Die Beschreibung umfasst Teilchen-Wechselwirkung, Orbital-Wechselwirkung, Bethe-Ansatzgleichungen und eine alternative Herleitung der Thermodynamik fuer endliche Temperatur und endliches Magnetfeld. Ausserdem wird eine allgemeingueltige Darstellung des dynamischen Spin-Strukturfaktors gegeben und fuer verschiedene Faelle asymptotisch im thermodynamischen Limes und numerisch auf endlichen Systemen ausgewertet. Das Spektrum des Haldane-Shastry-Modell kann auch durch Spinonen parametrisiert werden. Die Arbeit gibt eine dezidierte Untersuchung eines einzelnen Orbitals und eine geschlossene Darstellung der Energie eines generischen Zustandes mit beliebig vielen Orbitalen. Fu...
Journal of Physics A: Mathematical and Theoretical, 2008
The mapping between the fermion and spinon compositions of eigenstates in the one-dimensional spi... more The mapping between the fermion and spinon compositions of eigenstates in the one-dimensional spin-1/2 XX model on a lattice with N sites is used to describe the spinon interaction from two different perspectives: (i) For finite N the energy of all eigenstates is expressed as a function of spinon momenta and spinon spins, which, in turn, are solutions of a set of Bethe ansatz equations. The latter are the basis of an exact thermodynamic analysis in the spinon representation of the XX model. (ii) For N → ∞ the energy per site of spinon configurations involving any number of spinon orbitals is expressed as a function of reduced variables representing momentum, filling, and magnetization of each orbital. The spins of spinons in a single orbital are found to be coupled in a manner well described by an Ising-like equivalent-neighbor interaction, switching from ferromagnetic to antiferromagnetic as the filling exceeds a critical level. Comparisons are made with results for the Haldane-Shastry model.
Journal of Physics A: Mathematical and General, 2006
The exact one-to-one mapping between (spinless) Jordan-Wigner lattice fermions and (spin-1/2) spi... more The exact one-to-one mapping between (spinless) Jordan-Wigner lattice fermions and (spin-1/2) spinons is established for all eigenstates of the one-dimensional s = 1/2 XX model on a lattice with an even or odd number N of lattice sites and periodic boundary conditions. Exact product formulas for the transition rates derived via Bethe ansatz are used to calculate asymptotic expressions of the 2-spinon and 4-spinon parts (for large even N ) as well as of the 1-spinon and 3-spinon parts (for large odd N ) of the dynamic spin structure factors. The observability of these spectral contributions is assessed for finite N and for N → ∞.
Physical Review B, 2004
As part of a study that investigates the dynamics of the s = 1 2 XXZ model in the planar regime |... more As part of a study that investigates the dynamics of the s = 1 2 XXZ model in the planar regime |∆| < 1, we discuss the singular nature of the Bethe ansatz equations for the case ∆ = 0 (XX model). We identify the general structure of the Bethe ansatz solutions for the entire XX spectrum, which include states with real and complex magnon momenta. We discuss the relation between the spinon or magnon quasiparticles (Bethe ansatz) and the lattice fermions (Jordan-Wigner representation). We present determinantal expressions for transition rates of spin fluctuation operators between Bethe wave functions and reduce them to product expressions. We apply the new formulas to two-spinon transition rates for chains with up to N = 4096 sites.
Physical Review B, 2004
As part of a study that investigates the dynamics of the s = 1 2 XXZ model in the planar regime |... more As part of a study that investigates the dynamics of the s = 1 2 XXZ model in the planar regime |∆| < 1, we discuss the singular nature of the Bethe ansatz equations for the case ∆ = 0 (XX model). We identify the general structure of the Bethe ansatz solutions for the entire XX spectrum, which include states with real and complex magnon momenta. We discuss the relation between the spinon or magnon quasiparticles (Bethe ansatz) and the lattice fermions (Jordan-Wigner representation). We present determinantal expressions for transition rates of spin fluctuation operators between Bethe wave functions and reduce them to product expressions. We apply the new formulas to two-spinon transition rates for chains with up to N = 4096 sites.
Journal of Physics A: Mathematical and General, 2006
Die Arbeit beginnt mit einer kurzen Einfuehrung in das anisotrope Heisenberg-Modell (XXZ-Modell).... more Die Arbeit beginnt mit einer kurzen Einfuehrung in das anisotrope Heisenberg-Modell (XXZ-Modell). Im Hauptteil werden als Spezialfaelle davon das XX-Modell und das Haldane-Shastry-Modell untersucht. Fuer das XX-Modell wird eine vollstaendige Beschreibung des Spektrums durch Spinonen (spezielle Quasiteilchen) gegeben. Die Beschreibung umfasst Teilchen-Wechselwirkung, Orbital-Wechselwirkung, Bethe-Ansatzgleichungen und eine alternative Herleitung der Thermodynamik fuer endliche Temperatur und endliches Magnetfeld. Ausserdem wird eine allgemeingueltige Darstellung des dynamischen Spin-Strukturfaktors gegeben und fuer verschiedene Faelle asymptotisch im thermodynamischen Limes und numerisch auf endlichen Systemen ausgewertet. Das Spektrum des Haldane-Shastry-Modell kann auch durch Spinonen parametrisiert werden. Die Arbeit gibt eine dezidierte Untersuchung eines einzelnen Orbitals und eine geschlossene Darstellung der Energie eines generischen Zustandes mit beliebig vielen Orbitalen. Fu...
Journal of Physics A: Mathematical and Theoretical, 2008
The mapping between the fermion and spinon compositions of eigenstates in the one-dimensional spi... more The mapping between the fermion and spinon compositions of eigenstates in the one-dimensional spin-1/2 XX model on a lattice with N sites is used to describe the spinon interaction from two different perspectives: (i) For finite N the energy of all eigenstates is expressed as a function of spinon momenta and spinon spins, which, in turn, are solutions of a set of Bethe ansatz equations. The latter are the basis of an exact thermodynamic analysis in the spinon representation of the XX model. (ii) For N → ∞ the energy per site of spinon configurations involving any number of spinon orbitals is expressed as a function of reduced variables representing momentum, filling, and magnetization of each orbital. The spins of spinons in a single orbital are found to be coupled in a manner well described by an Ising-like equivalent-neighbor interaction, switching from ferromagnetic to antiferromagnetic as the filling exceeds a critical level. Comparisons are made with results for the Haldane-Shastry model.
Journal of Physics A: Mathematical and General, 2006
The exact one-to-one mapping between (spinless) Jordan-Wigner lattice fermions and (spin-1/2) spi... more The exact one-to-one mapping between (spinless) Jordan-Wigner lattice fermions and (spin-1/2) spinons is established for all eigenstates of the one-dimensional s = 1/2 XX model on a lattice with an even or odd number N of lattice sites and periodic boundary conditions. Exact product formulas for the transition rates derived via Bethe ansatz are used to calculate asymptotic expressions of the 2-spinon and 4-spinon parts (for large even N ) as well as of the 1-spinon and 3-spinon parts (for large odd N ) of the dynamic spin structure factors. The observability of these spectral contributions is assessed for finite N and for N → ∞.
Physical Review B, 2004
As part of a study that investigates the dynamics of the s = 1 2 XXZ model in the planar regime |... more As part of a study that investigates the dynamics of the s = 1 2 XXZ model in the planar regime |∆| < 1, we discuss the singular nature of the Bethe ansatz equations for the case ∆ = 0 (XX model). We identify the general structure of the Bethe ansatz solutions for the entire XX spectrum, which include states with real and complex magnon momenta. We discuss the relation between the spinon or magnon quasiparticles (Bethe ansatz) and the lattice fermions (Jordan-Wigner representation). We present determinantal expressions for transition rates of spin fluctuation operators between Bethe wave functions and reduce them to product expressions. We apply the new formulas to two-spinon transition rates for chains with up to N = 4096 sites.