8 research outputs found
Quantum Phase Transitions for Bosons in One Dimension
We study the ground state phase diagram and the critical properties of
interacting Bosons in one dimension by means of a quantum Monte Carlo
technique. The direct experimental realization is a chain of Josephson
junctions. For finite-range interactions we find a novel intermediate phase
which shows neither solid order nor superfluidity. We determine the location of
this phase and study the critical behaviour of the various transitions. For
on-site interaction only, we map out the phase diagram as a function of the
hopping strength and the chemical potential.Comment: 11 pages, revtex, 2 eps-figure
Correlations of conductance peaks and transmission phases in deformed quantum dots
We investigate the Coulomb blockade resonances and the phase of the
transmission amplitude of a deformed ballistic quantum dot weakly coupled to
leads. We show that preferred single--particle levels exist which stay close to
the Fermi energy for a wide range of values of the gate voltage. These states
give rise to sequences of Coulomb blockade resonances with correlated peak
heights and transmission phases. The correlation of the peak heights becomes
stronger with increasing temperature. The phase of the transmission amplitude
shows lapses by between the resonances. Implications for recent
experiments on ballistic quantum dots are discussed.Comment: 29 pages, 9 eps-figure
Correlations in the cotunneling regime of a quantum dot
Off-resonance conductance through weakly coupled quantum dots ("valley
conductance") is governed by cotunneling processes in which a large number of
dot states participate. Virtually the same states participate in the transport
at consecutive valleys, which leads to significant valley-valley conductance
correlations. These correlations are calculated within the constant interaction
model. Comparison with experiment shows that these correlations are less robust
in reality. Among the possible reasons for this is the breakdown of the
constant interaction model, accompanied by "scrambling" of the dot as the
particle number is varied.Comment: 10 pages, 4 eps-figures; reference adde
Quantum-Phase Transitions of Interacting Bosons and the Supersolid Phase
We investigate the properties of strongly interacting bosons in two
dimensions at zero temperature using mean-field theory, a variational Ansatz
for the ground state wave function, and Monte Carlo methods. With on-site and
short-range interactions a rich phase diagram is obtained. Apart from the
homogeneous superfluid and Mott-insulating phases, inhomogeneous charge-density
wave phases appear, that are stabilized by the finite-range interaction.
Furthermore, our analysis demonstrates the existence of a supersolid phase, in
which both long-range order (related to the charge-density wave) and
off-diagonal long-range order coexist. We also obtain the critical exponents
for the various phase transitions.Comment: RevTex, 20 pages, 10 PostScript figures include