5 research outputs found
Force--induced depinning of directed polymers
We present an approach to studying directed polymers in interaction with a
defect line and subject to a force, which pulls them away from the line. We
consider in particular the case of inhomogeneous interactions. We first give a
formula relating the free energy of these models to the free energy of the
corresponding ones in which the force is switched off. We then show how to
detect the presence of a re-entrant transition without fully solving the model.
We discuss some models in detail and show that inhomogeneous interaction, e.g.
disordered interactions, may induce the re-entrance phenomenon.Comment: 15 pages, 2 figure
Smoothening of Depinning Transitions for Directed Polymers with Quenched Disorder
We consider disordered models of pinning of directed polymers on a defect
line, including (1+1)-dimensional interface wetting models, disordered
Poland--Scheraga models of DNA denaturation and other (1+d)-dimensional
polymers in interaction with columnar defects. We consider also random
copolymers at a selective interface. These models are known to have a
(de)pinning transition at some critical line in the phase diagram. In this work
we prove that, as soon as disorder is present, the transition is at least of
second order: the free energy is differentiable at the critical line, and the
order parameter (contact fraction) vanishes continuously at the transition. On
the other hand, it is known that the corresponding non-disordered models can
have a first order (de)pinning transition, with a jump in the order parameter.
Our results confirm predictions based on the Harris criterion.Comment: 4 pages, 1 figure. Version 2: references added, minor changes made.
To appear on Phys. Rev. Let
Delocalization transition of the selective interface model: distribution of pseudo-critical temperatures
According to recent progress in the finite size scaling theory of critical
disordered systems, the nature of the phase transition is reflected in the
distribution of pseudo-critical temperatures over the ensemble of
samples of size . In this paper, we apply this analysis to the
delocalization transition of an heteropolymeric chain at a selective
fluid-fluid interface. The width and the shift
are found to decay with the same exponent
, where . The distribution of
pseudo-critical temperatures is clearly asymmetric, and is well
fitted by a generalized Gumbel distribution of parameter . We also
consider the free energy distribution, which can also be fitted by a
generalized Gumbel distribution with a temperature dependent parameter, of
order in the critical region. Finally, the disorder averaged
number of contacts with the interface scales at like with
.Comment: 9 pages,6 figure