arXiv subjects

Sergio Rica

Publications and source records attributed to Sergio Rica.

25 records · Page 2Linked to original sources

arXiv2011

Non Classical Rotational Inertia Fraction in a One Dimensional Model of Supersolid

We study the rotational inertia of a model of supersolid in the frame of the mean field Gross-Pitaevskii theory in one space dimension. We discuss the ground state of the model and the existence of a non classical inertia (NCRI) under rotation that models an annular geometry. An explicit formula for the NCRI is deduced. It depends on the density profil of the ground state, in full agreement with former theories. We compare the NCRI computed through this theory with direct numerical simulations of rotating 1D systems.

cond-mat.quant-gas↗

arXiv2009

Induced interaction and crystallization of self-localized impurity fields in a Bose-Einstein condensate

We model the behavior of N classical impurity fields immersed in a larger Bose-Einstein condensate by N+1 coupled nonlinear Schrodinger equations in 1, 2, and 3 space dimensions. We discuss the stability of the uniform miscible system and show the importance of surface tension for self localization of the impurity fields. We derive analytically the attractive tail of impurity-impurity interaction due to mediation by the underlying condensate. Assuming all impurity fields interact with the same strength, we explore the resulting phase diagram, which contains four phases: {\it I}) all fields are miscible; {\it II}) the impurity fields are miscible with each other but phase separate from the condensate as a single bubble; {\it III}) the localized impurity fields stay miscible with the condensate, but not with each other; and {\it IV}) the impurity fields phase separate from the condensate and each other, forming a crystalline structure within a bubble. Thus, we show that a crystal can be constructed solely from superfluid components. Finally, we argue that the crystalline phases maintain their superfluid behavior, i.e. they possess a nonclassical rotational inertia, which, combined with lattice order, is a characteristic of supersolidity.

cond-mat.quant-gas↗

arXiv2008

Impurity crystal in a Bose-Einstein condensate

We investigate the behavior of impurity fields immersed in a larger condensate field in 1, 2, and 3 dimensions. We discuss the localization of a single impurity field within a condensate and note the effects of surface energy. We derive the functional form of the attractive interaction between two impurities due to mediation from the condensate. Generalizing the analysis to $N$ impurity fields, we show that within various parameter regimes a crystal of impurity fields can form spontaneously in the condensate. Finally, the system of condensate and crystallized impurity structure is shown to have nonclassical rotational inertia, which is characteristic of superfluidity, i.e. the system can be seen to exhibit supersolid behavior.

cond-mat.stat-mech↗

arXiv2006

Coexisting ordinary elasticity and superfluidity in a model of defect-free supersolid

We present the mechanics of a model of supersolid in the frame of the Gross-Pitaevskii equation at $T=0K$ that do not require defects nor vacancies. A set of coupled nonlinear partial differential equations plus boundary conditions is derived. The mechanical equilibrium is studied under external constrains as steady rotation or external stress. Our model displays a paradoxical behavior: the existence of a non classical rotational inertia fraction in the limit of small rotation speed and no superflow under small (but finite) stress nor external force. The only matter flow for finite stress is due to plasticity.

cond-mat.other↗

arXiv2005

Can we hear Kolmogorov spectra?

We study the long-time evolution of waves of a thin elastic plate in the limit of small deformation so that modes of oscillations interact weakly. According to the theory of weak turbulence a nonlinear wave system evolves in long-time creating a slow transfer of energy from one mode to another. We derive this kinetic equation for the spectral transfer in terms of the second order moment. We show explicitly that such a non-equilibrium theory describes the approach to an equilibrium wave spectrum, and describes also an energy cascade, often called the Kolmogorov-Zakharov spectrum. We perform numerical simulations confirming this scenario.

cond-mat.stat-mech↗

arXiv2005

Condensation of classical nonlinear waves

We study the formation of a large-scale coherent structure (a condensate) in classical wave equations by considering the defocusing nonlinear Schrödinger equation as a representative model. We formulate a thermodynamic description of the condensation process by using a wave turbulence theory with ultraviolet cut-off. In 3 dimensions the equilibrium state undergoes a phase transition for sufficiently low energy density, while no transition occurs in 2 dimensions, in analogy with standard Bose-Einstein condensation in quantum systems. Numerical simulations show that the thermodynamic limit is reached for systems with $16^3$ computational modes and greater. On the basis of a modified wave turbulence theory, we show that the nonlinear interaction makes the transition to condensation subcritical. The theory is in quantitative agreement with the simulations.

cond-mat.stat-mech↗

arXiv1998

Spontaneous Curvature-induced pearling instability

We investigate the instability of a tubular fluid membranes made of a water soluble surfactant. The tubules are obtained at high salinities. The instability is due to the introduction within the vesicle multilayer of an alkane. We measure the wavelength of this instability versus the unperturbed radius of the tubules. To interpretthis dependance we use a model that includes not only the surface tension in the elastic energy but the spontaneous curvature as well. The spontaneous curvature is induced by the presenceof the oil in the bilayer of the membrane and give a selection of a non-zero wavelength.

cond-mat.soft↗