arXiv subjects

Philippe Curty

Publications and source records attributed to Philippe Curty.

6 recordsLinked to original sources

arXiv2007

An interaction model on random networks: from social to airports networks

Social movements, neurons in the brain or even industrial suppliers are best described by agents evolving on networks with basic interaction rules. In these real systems, the connectivity between agents corresponds to the a critical state of the system related to the noise of the system. The new idea is that connectivity adjusts itself because of two opposite tendencies: on the one hand informations percolation is better when the network connectivity is small but all agents have rapidely the same state and the dynamics stops. On the other hand, when agents have a large connectivity, the state of a node (opinion of a person, state of a neuron, ...) tends to freeze: agents find always a minority among their neighbours to support their state. The model introduced here captures this essential feature showing a clear transition between the two tendencies at some critical connectivity. Depending on the noise, the dynamics of the system can only take place at a precise critical connectivity since, away from this critical point, the system remains in a static phase. When the noise is very small, the critical connectivity becomes very large, and highly connected networks are obtained like the airports network and the Internet. This model may be used as a starting point for understanding the evolution of agents living on networks.

physics.soc-ph↗

arXiv2006

Pseudogap and Amplitude Fluctuations in High Temperature Superconductors

Amplitude fluctuations of the pairing field are responsible together with phase fluctuations for the pseudogap phenomena in high temperature superconductors. Here we present the more detailed theory of the amplitude and phase fluctuations approach in the framework of a fermionic pairing model. New experimental comparisons are presented for the specific heat of the curprate LSCO confirming the generality of this phenomenological approach. The strong decrease of amplitude fluctuations near optimal doping induces the illusion of a "quantum critical point", which in fact does not exist since the pseudogap energy scale is always different from zero even in the overdoped regime.

cond-mat.supr-con↗

arXiv2006

Phase coexistence in a forecasting game

Individual choices are either based on personal experience or on information provided by peers. The latter case, causes individuals to conform to the majority in their neighborhood. Such herding behavior may be very efficient in aggregating disperse private information, thereby revealing the optimal choice. However if the majority relies on herding, this mechanism may dramatically fail to aggregate correctly the information, causing the majority adopting the wrong choice. We address these issues in a simple model of interacting agents who aim at giving a correct forecast of a public variable, either seeking private information or resorting to herding. As the fraction of herders increases, the model features a phase transition beyond which a state where most agents make the correct forecast coexists with one where most of them are wrong. Simple strategic considerations suggest that indeed such a system of agents self-organizes deep in the coexistence region. There, agents tend to agree much more among themselves than with what they aim at forecasting, as found in recent empirical studies.

physics.soc-ph↗

arXiv2004

Thermodynamics and Phase Diagram of High Temperature Superconductors

Thermodynamic quantities are derived for superconducting and pseudogap regimes by taking into account both amplitude and phase fluctuations of the pairing field. In the normal (pseudogap) state of the underdoped cuprates, two domains have to be distinguished: near the superconducting region, phase correlations are important up to the temperature $T_ϕ$. Above $T_ϕ$, the pseudogap region is only determined by amplitudes, and phases are uncorrelated. Our calculations show excellent quantitative agreement with specific heat and magnetic susceptibility experiments on cuprates. We find that the mean field temperature $T_0$ has a similar doping dependence as the pseudogap temperature $T^*$, whereas the pseudogap energy scale is given by the average amplitude above $T_c$.

cond-mat.supr-con↗

arXiv2000

Simulations of the 3d Ginzburg-Landau Model with Soft Amplitudes

Using cluster Monte Carlo simulations, the 3d complex Ginzburg-Landau model reveals a first order transition when the amplitude of the complex field is sufficiently soft, i.e. adapts itself to the phase configurations of the field. This transition is driven by phase fluctuations in agreement with a previous analytical approach.

cond-mat.stat-mech↗

arXiv2000

First Order Transition in the Ginzburg-Landau Model

The d-dimensional complex Ginzburg-Landau (GL) model is solved according to a variational method by separating phase and amplitude. The GL transition becomes first order for high superfluid density because of effects of phase fluctuations. We discuss its origin with various arguments showing that, in particular for d = 3, the validity of our approach lies precisely in the first order domain.

cond-mat.stat-mech↗