Attention : désormais les séminaires auront lieu tous les lundis à 11h00 en salle  523 du LPTMC - Tour 12-13 

Pierfrancesco Urbani
(IPhT, CEA, Saclay.)

Critical exponents of the jamming transition

Jammed packings of hard spheres are well known marginally stable systems. They are isostatic and display power laws in the distributions of contact forces and of spheres in quasi-contact. I will discuss the solution of the hard sphere model in the limit of infinte dimensions from which we can derive analytically both the power laws and the values of the corresponding exponents. Close to jamming a new transition, the Gardner transition, is found. The high pressure phase is characterized by a new free energy landscape whose features are deeply related with the marginal stability properties of jammed packings. Remarkably, this new free energy landscape is very close to what is found in the solution of the Sherrington-Kirkpatrick spin glass model. The values of the exponents are compatible with both a recently proposed scaling theory of the jamming transition and numerical simulations in finite dimensions. Finally, I will discuss a perturbative renormalization group analysis of the Gardner transition in finite dimensions.


Kirone Mallick

"The Asymmetric Simple Exclusion Process, a Review"

The asymmetric simple exclusion process plays the role of a
paradigm to study various aspects of non-equilibrium statistical physics.
It is a minimal model of interacting particles with transport,
that displays interesting collective behaviour and breaks time-reversal
symmetry. This system appears as a building block in 
more realistic descriptions of low-dimensional transport with constraints. 

During the last twenty years, a large number of exact results
have been derived for the exclusion process. The aim of this talk
is to review the main techniques used to study this system
and some of the important results that have been obtained. 

Pedro Ribeiro
Centro de Física das Interações Fundamentais, Instituto Superior Técnico, Universidade de Lisboa

Non-equilibrium-induced pattern formation in strongly interacting electronic systems in one dimension.

Quantum phases of matter are typically defined for systems in thermal equilibrium. Strong non-equilibrium conditions eventually drive a system away from its linear response regime, strongly affecting the properties of the underlying equilibrium phase. A well known example arising in classical fluid mechanics is Rayleigh-Bernard convection, where a fluid placed between two plates at different temperatures develops an instability towards the formation of convection rolls of a specific wave-length.
In this talk I will report on recent results regarding the effects of large bias voltages applied across an half-filled Hubbard chain. At equilibrium this system shows a charge gap and strong antiferromagnetic correlations. I will show that out of equilibrium the wave-vector maximizing the spin-susceptibility shifts from it equilibrium value $q=\pi$, as a function of the applied voltage and of temperature. I will describe the rich mean-field diagram obtained upon increasing the electron-electron interaction term. Some of phases found here are examples of non-equilibrium-induced spacial pattern formation. I will briefly comment on the properties and stability of these phases. Finally I will proceed to argue that, although no symmetry breaking arises in the 1D Hubbard model, these results suggest a modulation of the charge gap that may be observed experimentally by STM on engineered atomic chains and nano-wires.

François Crépin

Appariement impair en fréquence d'électrons dans les canaux de bord d'isolants topologiques.

Les liquides hélicaux sont des gaz uni-dimensionnels d'électrons ayant la particularité d'une forte corrélation entre la valeur du spin et le sens de propagation. Ils émergent naturellement aux bords de certains semi-conducteurs communément appelés isolants topologiques [1]. En plus d'une certaine robustesse face aux impuretés non-magnétiques, ces nouveaux états électroniques présentent de nombreuses propriétés remarquables, notamment lorsqu'on les place à proximité d'un supraconducteur [2]. Dans ce séminaire, je propose tout d'abord de passer en revue plusieurs phénomènes directement causés par l'hélicité et caractéristiques d'une supraconductivité non-conventionnelle, comme des effets Josephson fractionnaires ou l'apparition d'états-liés exotiques. Dans une deuxième partie, je présenterai une analyse détaillée des symétries d'appariement dans des jonctions hybrides supraconducteur/isolant topologique [3]. En particulier, nous discuterons d'un appariement exotique, dit impair en fréquence, et de ses signatures possibles dans des mesures non-locales de la conductance de ces jonctions.

[1] M. Z. Hasan and C. L. Kane, Rev. Mod. Phys. 82, 3045 (2010)
[2] Liang Fu and C. L. Kane, Phys. Rev. Lett. 100, 096407 (2008)
[3] François Crépin, Pablo Burset, and Björn Trauzettel, Phys. Rev. B 92, 100507(R) (2015)