Keola Wierschem

Phase diagram and magnetic excitations of anisotropic spin-one magnets

We use a generalized spin-wave approach and large-scale quantum Monte Carlo (QMC) simulations to study the quantum phase diagram and quasiparticle excitations of the S = 1 Heisenberg model with an easy-plane single-ion anisotropy in dimensions d = 2 and 3. We consider two alternative approximations for describing the quantum paramagnetic state: the standard Holstein-Primakoff approximation and a modified treatment in which the local constraint (finite dimension of the local Hilbert space) is enforced by introducing a Lagrange multiplier. While both approximations produce qualitatively similar results, the latter approach is the only one that is in good quantitative agreement with the quantum phase diagram and the quasiparticle dispersions obtained with QMC. This result is very important for low-temperature studies of quantum paramagnets in magnetic fields because it shows that a simple modification of the standard analytical approach should produce much better quantitative agreement between theory and experiment.

Simulation of melting of two-dimensional Lennard-Jones solids

We study the nature of melting of a two-dimensional (2D) Lennard-Jones solid using large-scale Monte Carlo simulation. We use systems of up to 102 400 particles to capture the decay of the correlation functions associated with translational order (TO) as well as the bond-orientational (BO) order. We study the role of dislocations and disclinations and their distribution functions. We computed the temperature dependence of the second moment of the TO parameter (

Magnetic and nematic orderings in spin-1 antiferromagnets with single-ion anisotropy

{\ensuremath{\Psi}}_{G}

Columnar antiferromagnetic order and spin supersolid phase on the extended Shastry-Sutherland lattice.

) as well as of the order parameter

Origin of modulated phases and magnetic hysteresis in TmB4

{\ensuremath{\Psi}}_{6}

Detection of symmetry-protected topological order in AKLT states by exact evaluation of the strange correlator

associated with BO order. By applying finite-size scaling of these second moments, we determined the anomalous dimension critical exponents

Strange correlations in spin-1 Heisenberg antiferromagnets

\ensuremath{\eta}(T)

Magnetic phases in the S=1 Shastry-Sutherland model with uniaxial anisotropy

and

Characterizing the Haldane phase in quasi-one-dimensional spin-1 Heisenberg antiferromagnets

{\ensuremath{\eta}}_{6}(T)

Dimensional crossover in spin-1 Heisenberg antiferromagnets: a quantum Monte Carlo study

associated with power-law decay of the