Numerical simulations of quantum many-body systems with applications to superfluid-insulator and metal-insulator transitions

Miscellaneous · Fri Jan 01 00:00:00 EST 1993

OSTI ID:7232873

Niyaz, P

Quantum Monte Carlo techniques were used to study two quantum many-body systems, the one-dimensional extended boson-Hubbard Hamiltonian, a model of superfluid-insulator quantum phase transitions, and the two-dimensional Holstein Model, a model for electron-phonon interactions. For the extended boson-Hubbard model, the authors studied the ground state properties at commensurate filling (density = 1) and half-integer filling (density = 1/2). At commensurate filling, the system has two possible insulating phases for strong coupling. If the on-site repulsion dominates, the system freezes into an insulating phase where each site is singly occupied. If the intersite repulsion dominates, doubly occupied and empty sites alternate. At weak coupling, the system becomes a superfluid. The authors investigated the order of phase transitions between these different phases. At half-integer filling, the authors found one strong coupling insulating phase, where singly occupied and empty sites alternate, and a weak coupling superfluid phase. The authors also investigated the possibility of a supersolid phase and found no clear evidence of such a new phase. For the electron-phonon (Holstein) model, the authors focused on the finite temperature phase transition from a metallic state to an insulating charge density wave (CDW) state as the temperature is lowered. The authors present the first calculation of the spectral density from Monte Carlo data for this system. The authors also investigated the formation of a CDW state as a function of various parameters characterizing the electron-phonon interactions. Using these numerical results as benchmarks, the authors then investigated different levels of Migdal approximations. The authors found the solutions of a set of gapped Migdal-Eliashberg equations agreed qualitatively with the Monte Carlo results.

• Research Organization: California Univ., Davis, CA (United States)
• OSTI ID: 7232873
• Resource Relation: Other Information: Thesis (Ph.D.)
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
MANY-BODY PROBLEM
MONTE CARLO METHOD
SUPERFLUIDITY
ELECTRON-PHONON COUPLING
HUBBARD MODEL
ELECTRICAL INSULATORS
PHASE TRANSFORMATIONS
CALCULATION METHODS
COUPLING
CRYSTAL MODELS
ELECTRICAL EQUIPMENT
EQUIPMENT
MATHEMATICAL MODELS
665420* - Superfluidity- (1992-)