23.10.14, 15:15-16:15, SR7


Many-body localization edge for disordered interacting spin chains

David Luitz, Toulouse

We present a large scale exact diagonalization study of the one dimensional spin Heisenberg model in a disordered magnetic field. In order to access properties at varying energy densities across the entire spectrum for system sizes up to L=22 spins, we use a spectral transformation which can be applied in a massively parallel fashion. Our results allow for an energy resolved interpretation of the many body localization transition and the resolution of a many-body mobility edge. The metallic (ergodic) phase is well characterized by GOE statistics, volume-law entanglement, and a full delocalization in the Fock space. Conversely, the localized (non-ergodic) regime displays Poisson statistics, area-law entanglement and multifractality in the Fock space where a true localization never occurs. Finite size scaling allows to extract the critical edge and an estimate for the exponent nu=0.8(3). D. J. Luitz, N. Laflorencie and F. Alet, preprint

23.10.14, 16:15-17:15, SR7


Efficient continuous-time quantum Monte Carlo algorithm for fermionic lattice models

M. Iazzi, ETHZ

Efficient continuous time quantum Monte Carlo (CT-QMC) algorithms that do not suffer from time discretization errors have become the state-of-the-art for most discrete quantum models. They have not been widely used yet for fermionic quantum lattice models, such as the Hubbard model, due to a suboptimal scaling with inverse temperature, compared to one of discrete time algorithms. I will present a CT-QMC algorithms for fermionic lattice models that matches the scaling of discrete-time methods but is faster and free of time discretization errors. This provides an efficient simulation scheme that is free from the systematic errors opening an avenue to more precise studies of large systems at low temperatures.