36 research outputs found
Kosterlitz-Thouless signatures in the low-temperature phase of layered three-dimensional systems
We study the quasi-two-dimensional quantum O(2) model, a quantum
generalization of the Lawrence-Doniach model, within the nonperturbative
renormalization-group approach and propose a generic phase diagram for layered
three-dimensional systems with an O(2)-symmetric order parameter. Below the
transition temperature we identify a wide region of the phase diagram where the
renormalization-group flow is quasi-two-dimensional for length scales smaller
than a Josephson length , leading to signatures of Kosterlitz-Thouless
physics in the temperature dependence of physical observables. In particular
the order parameter varies as a power law of the interplane coupling with an
exponent which depends on the anomalous dimension (itself related to the
stiffness) of the strictly two-dimensional low-temperature Kosterlitz-Thouless
phase.Comment: v2) 11 pages, 9 figure
Tan's two-body contact in a planar Bose gas: experiment vs theory
We determine the two-body contact in a planar Bose gas confined by a
transverse harmonic potential, using the nonperturbative functional
renormalization group. We use the three-dimensional thermodynamic definition of
the contact where the latter is related to the derivation of the pressure of
the quasi-two-dimensional system with respect to the three-dimensional
scattering length of the bosons. Without any free parameter, we find a
remarkable agreement with the experimental data of Zou {\it et al.} [Nat. Comm.
{\bf 12}, 760 (2021)] from low to high temperatures, including the vicinity of
the Berezinskii-Kosterlitz-Thouless transition. We also show that the
short-distance behavior of the pair distribution function and the high-momentum
behavior of the momentum distribution are determined by two contacts: the
three-dimensional contact for length scales smaller than the characteristic
length of the harmonic potential and, for
length scales larger than , an effective two-dimensional contact,
related to the three-dimensional one by a geometric factor depending on
.Comment: v1) 6+10 pages, 2+1 figures; v2) 6+12 pages, 2+4 figures, published
versio
Dynamical many-body delocalization transition of a Tonks gas in a quasi-periodic driving potential
The quantum kicked rotor is well-known for displaying dynamical (Anderson)
localization. It has recently been shown that a periodically kicked Tonks gas
will always localize and converge to a finite energy steady-state. This
steady-state has been described as being effectively thermal with an effective
temperature that depends on the parameters of the kick. Here we study a
generalization to a quasi-periodic driving with three frequencies which,
without interactions, has a metal-insulator Anderson transition. We show that a
quasi-periodically kicked Tonks gas goes through a dynamical many-body
delocalization transition when the kick strength is increased. The localized
phase is still described by a low effective temperature, while the delocalized
phase corresponds to an infinite-temperature phase, with the temperature
increasing linearly in time. At the critical point, the momentum distribution
of the Tonks gas displays different scaling at small and large momenta
(contrary to the non-interacting case), signaling a breakdown of the
one-parameter scaling theory of localization.Comment: v1) 12 pages, 17 figures; v2) 12 pages, 16 figures, some references
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