Attention : désormais les séminaires ont lieu tous les lundis à 10h45 en salle 523 du LPTMC - Tour 12-13
Jordan Horowitz (University of Michigan)
Nonequilibrium thermodynamic limits to fluctuations and response
(Egalement par zoom
Meeting ID: 870 2843 9751
Thermodynamics is a remarkably successful theoretical framework, with wide ranging applications across the natural sciences. Unfortunately, thermodynamics is limited to equilibrium or near-equilibrium situations, whereas most of the natural world, especially life, operates very far from thermodynamic equilibrium. Research in nonequilibrium statistical thermodynamics is beginning to shed light on this domain. In this talk, I will present a collection of such predictions, namely a series of equalities and inequalities---akin to the Fluctuation-Dissipation theorem but valid arbitrarily far from equilibrium---that link a system’s response to the strength of nonequilibrium driving. These results open new avenues for experimentally characterizing nonequilibrium response and suggest design-principles for high-sensitivity, low-noise devices. I will also discuss how they rationalize known energetic requirements of some common biochemical motifs and provide new limits to others. Finally, I will demonstrate how they can be used to derive Green-Kubo relations for the transport coefficients of homogenous active fluids in terms of steady-state current fluctuations.
Julian Legendre (CPHT, École Polytechnique)
Two topological models on the kagome lattice: tuning the quantum anomalous Hall phase with ferromagnetism and a Z2 topological insulator with spin-orbit coupling
(Egalement par zoom
Meeting ID: 825 2118 0172
Topological phases, contrarily to many other phases of matter, cannot be understood in terms of local order parameters. Depending on the symmetries and the dimension of the system under consideration, an appropriate topological invariant describes the topological phase. For instance, the (first) Chern number characterizes the quantum anomalous Hall (QAH) phase associated to the Haldane model. With "two copies" of the Haldane model, we can restore time-reversal symmetry; the system is then characterized by a Z2 topological invariant. In this talk, we explore two topological phases, respectively associated to non zero Chern number and Z2 invariant, for two examples of kagome lattice physical systems.
First, we are interested by the kagome magnet Co3Sn2S2. It shows an impressive behavior of the QAH conductivity driven by the interplay between ferromagnetism in the z direction and antiferromagnetism in the xy plane. Motivated by these facts, we show how such a tuning of the QAH conductivity via the external tuning of the magnetic order can be described.
Then, we investigate the topological phases of a spin-orbit coupled tight-binding model with flux on the kagome lattice. This model is time-reversal invariant and shows Z2 topological insulating phases. We show the stability of the topological phase towards spin-flip processes and different types of on-site potentials. To describe the topological properties of the system we use a numerical approach based on the twisted boundary conditions and we develop an analytical approach related to smooth fields in the Brillouin Zone.