Simulations of 2-D spin systems with applications to the solid, superfluid, and supersolid phases of Bose films

Thesis/Dissertation · Tue Jan 01 04:00:00 EST 1985

OSTI ID:5797331

Loh, Jr, E Y

Two-dimensional spin models form a useful representation of adsorbed quantum gases. Here, simulations of various such models are used to explore phases which correspond to solids (Ising order), superfluids (Kosterlitz-Thouless order), and supersolids (both) in hard core Bose films. The first model studied, the classical XXZ spin Hamiltonian, is shown to exhibit solid (absolute value of lambda > 1) and superfluid (absolute value of lambda < 1) phases. The transition temperatures are found to drop off to zero at the isotropic point lambda = 1 even more abruptly than -1/log absolute value of lambda-1, as proposed by renormalization-group arguments. Next, the same Hamiltonian is simulated for quantum spins. The XY model (lambda = 0) has a Kosterlitz-Thouless phase transition at T/sub KT/ = 0.45 +/- 0.05, slightly above which the specific heat has a finite peak. The vortex density has a non-zero value in the low-temperature limit, probably due to quantum fluctuations. The critical temperature remains near the lambda = 0 value at least until lambda approx. = -0.8. Finally, simple arguments are formulated for the classical model to suggest terms that one might add to the Hamiltonian in order to get both phases concurrently. It is concluded that such a term should be quartic in spin operators.

• Research Organization: California Univ., Santa Barbara (USA)
• OSTI ID: 5797331
• Country of Publication: United States
• Language: English

Related Subjects

640450* -- Fluid Physics-- Superfluidity
656000 -- Condensed Matter Physics
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
BOSE-EINSTEIN GAS
CRITICAL TEMPERATURE
FERMI GAS
FLUIDS
GASES
PHYSICAL PROPERTIES
QUANTUM FLUIDS
RENORMALIZATION
SUPERFLUIDITY
THERMODYNAMIC PROPERTIES
TRANSITION TEMPERATURE