8 research outputs found
Mott Transition in Quasi-One-Dimensional Systems
We report the application of the density-matrix renormalization group method
to a spatially anisotropic two-dimensional Hubbard model at half-filling. We
find a deconfinement transition induced by the transverse hopping parameter
from an insulator to a metal. Therefore, if is fixed in the
metallic phase, increasing the interaction leads to a metal-to-insulator
transition at a finite critical . This is in contrast to the weak-coupling
Hartree-Fock theory which predicts a nesting induced antiferromagnetic
insulator for any .Comment: 4 pages, 3 figure
Quantum phase transitions, frustration, and the Fermi surface in the Kondo lattice model
The quantum phase transition from a spin-Peierls phase with a small Fermi
surface to a paramagnetic Luttinger-liquid phase with a large Fermi surface is
studied in the framework of a one-dimensional Kondo-Heisenberg model that
consists of an electron gas away from half filling, coupled to a spin-1/2 chain
by Kondo interactions. The Kondo spins are further coupled to each other with
isotropic nearest-neighbor and next-nearest-neighbor antiferromagnetic
Heisenberg interactions which are tuned to the Majumdar-Ghosh point. Focusing
on three-eighths filling and using the density-matrix renormalization-group
(DMRG) method, we show that the zero-temperature transition between the phases
with small and large Fermi momenta appears continuous, and involves a new
intermediate phase where the Fermi surface is not well defined. The
intermediate phase is spin gapped and has Kondo-spin correlations that show
incommensurate modulations. Our results appear incompatible with the local
picture for the quantum phase transition in heavy fermion compounds, which
predicts an abrupt change in the size of the Fermi momentum.Comment: 9 pages, 8 figure
Dynamical Mean Field Theory of the Bilayer Hubbard Model with Inchworm Monte Carlo
Dynamical mean-field theory allows access to the physics of strongly
correlated materials with nontrivial orbital structure, but relies on the
ability to solve auxiliary multi-orbital impurity problems. The most successful
approaches to date for solving these impurity problems are the various
continuous time quantum Monte Carlo algorithms. Here, we consider perhaps the
simplest realization of multi-orbital physics: the bilayer Hubbard model on an
infinite-coordination Bethe lattice. Despite its simplicity, the majority of
this model's phase diagram cannot be predicted by using traditional Monte Carlo
methods. We show that these limitations can be largely circumvented by recently
introduced Inchworm Monte Carlo techniques. We then explore the model's phase
diagram at a variety of interaction strengths, temperatures and filling ratios
Coherent control of correlated nanodevices: A hybrid time-dependent numerical renormalization-group approach to periodic switching
The time-dependent numerical renormalization-group approach (TD-NRG),
originally devised for tracking the real-time dynamics of quantum-impurity
systems following a single quantum quench, is extended to multiple switching
events. This generalization of the TD-NRG encompasses the possibility of
periodic switching, allowing for coherent control of strongly correlated
systems by an external time-dependent field. To this end, we have embedded the
TD-NRG in a hybrid framework that combines the outstanding capabilities of the
numerical renormalization group to systematically construct the effective
low-energy Hamiltonian of the system with the prowess of complementary
approaches for calculating the real-time dynamics derived from this
Hamiltonian. We demonstrate the power of our approach by hybridizing the TD-NRG
with the Chebyshev expansion technique in order to investigate periodic
switching in the interacting resonant-level model. Although the interacting
model shares the same low-energy fixed point as its noninteracting counterpart,
we surprisingly find the gradual emergence of damped oscillations as the
interaction strength is increased. Focusing on a single quantum quench and
using a strong-coupling analysis, we reveal the origin of these
interaction-induced oscillations and provide an analytical estimate for their
frequency. The latter agrees well with the numerical results.Comment: 20 pager, Revtex, 10 figures, submitted to Physical Review