arXiv subjects

P. Cosme

Publications and source records attributed to P. Cosme.

3 recordsLinked to original sources

arXiv2026

Subsonic terahertz plasmon instability in space-time plasmonic crystals

We investigate collective plasma-wave dynamics in a two-dimensional electron fluid subected to a travelling periodic modulation of the effective plasma velocity. Using a hydrodynamic description combined with Floquet-Bloch theory, we show that the travelling modulation acts as a moving plasmonic crystal whose band structure is governed by an effective drift velocity in the comoving frame. We demonstrate that the closure of the Bragg gap at the edge of the Brillouin zone gives rise to an exceptional point and triggers a Krein-type instability through the coupling of positive- and negative-energy modes. Analytical expressions are derived for the instability threshold and growth rate, revealing that self-amplification can occur even when the electron drift remains subsonic in the laboratory frame. Numerical simulations of the nonlinear hydrodynamic equations confirm the theoretical predictions and show the evolution towards a saturated regime dominated by a coherent Floquet-Bloch mode. These results identify travelling plasmonic crystals as a novel platform for wave amplification and non-Hermitian band dynamics in electronic fluids.

cond-mat.mes-hall↗

arXiv2025

Hydrodynamics in generalized electronic two-band systems

In this paper, we derive the Euler and Navier-Stokes equations for electronic two-band systems in arbitrary dimension and with generic power-law dispersion relations. We focus on the hydrodynamic transport regime, where such systems offer a unique tunability between a Fermi-liquid type regime at high doping and the inherent two-band physics of the low-density system close to the Dirac-type band-touching point. For a generic dispersion, the absence of Euclidean or Lorentzian invariance leads to novel types of hydrodynamic equations. We characterize these novel hydrodynamic regimes through dimensionless numbers, such as the Prandtl and Lorenz numbers, or the ratio between shear viscosity and entropy density. In all cases, we provide a derivation of the physics of the long-wavelength plasmonic modes.

cond-mat.str-el↗

arXiv2022

Topological waves in the continuum in magnetized graphene devices

We show that topological waves at the interface between two magnetic domains in a graphene device are possible. First, we consider the case of a linear relation between the applied gate voltage and local density in the channel and, secondly, we investigate the effect of non-local Coulomb interactions. We obtain two distinct edge modes for each interaction type: a Yanai mode with rotational flow and dispersion relation that extends to infinite wave-number, and a Kelvin mode with purely longitudinal flow and bound dispersion relation. The scattering matrix concept is applied to verify the infinite frequency regime of the spectrum, and the bulk-edge correspondence principle is satisfied if one takes into account the Kelvin modes that merge with an imaginary cut of the bulk band.

cond-mat.mes-hall↗