Oleg Derzhko

Universal low-temperature behavior of frustrated quantum antiferromagnets in the vicinity of the saturation field

Abstract. We study the low-temperature thermodynamic properties of a number of frustrated quantum antiferromagnets which support localized magnon states in the vicinity of the saturation field. For this purpose we use (1) a mapping of the low-energy degrees of freedom of spin systems onto the hard-core object lattice gases and (2) an exact diagonalization of finite spin systems of up to N=30 sites. The considered spin systems exhibit universal behavior which is determined by a specific hard-core object lattice gas representing the independent localized magnon states. We test the lattice gas description by comparing its predictions with the numerical results for low-lying energy states of finite spin systems. For all frustrated spin systems considered we find a strong variation of the low-temperature specific heat passing the saturation field and a maximum in the isothermal entropy at saturation field resulting in an enhanced magnetocaloric effect.

Numerical study of magnetization plateaux in the spin-1/2 kagome Heisenberg antiferromagnet

Institut fur Theoretische Physik, Otto-von-Guericke-Universit¨at Magdeburg, P.O. Box 4120, D-39016 Magdeburg, Germany(Dated: July 3, 2013; revised September 9, 2013)We clarify the existence of several magnetization plateaux for the kagome S = 1=2antiferromagnetic Heisen-berg model in a magnetic field. Using approximate or exact localized magnon eigenstates, we are able to de-scribe in a similar manner the plateaux states that occur for magnetization per site m = 1=3, 5=9, and 7=9 ofthe saturation value. These results are confirmed using large-scale Exact Diagonalization on lattices up to 63sites.

Magnetic-field induced spin-Peierls instability in strongly frustrated quantum spin lattices.

For a class of frustrated antiferromagnetic spin lattices (in particular, the square-kagomé and kagomé lattices) we discuss the impact of recently discovered exact eigenstates on the stability of the lattice against distortions. These eigenstates consist of independent localized magnons embedded in a ferromagnetic environment and become ground states in high magnetic fields. For appropriate lattice distortions fitting to the structure of the localized magnons the lowering of magnetic energy can be calculated exactly and is proportional to the displacement of atoms leading to a spin-Peierls lattice instability. Since these localized states are present only for high magnetic fields, this instability might be driven by magnetic-field. The hysteresis of the spin-Peierls transition is also discussed.

Dynamic probes of quantum spin chains with the Dzyaloshinskii-Moriya interaction

We consider the spin-

Finite-temperature order-disorder phase transition in a frustrated bilayer quantum Heisenberg antiferromagnet in strong magnetic fields

\frac{1}{2}

Emergent Ising degrees of freedom in frustrated two-leg ladder and bilayer s = 1/2 Heisenberg antiferromagnets

anisotropic

Low-temperature thermodynamics for a flat-band ferromagnet : Rigorous versus numerical results

XY

Thermodynamic properties of the periodic nonuniform spin-12 isotropic XY chains in a transverse field

chain in a transverse

SOLVABLE MODEL OF A RANDOM SPIN-1/2 XY CHAIN

(z)

Frustrated quantum Heisenberg antiferromagnets at high magnetic fields: Beyond the flat-band scenario

field with the Dzyaloshinskii-Moriya interaction directed along the