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Oded Agam

Publications and source records attributed to Oded Agam.

At least 37 records · Page 2Linked to original sources
arXiv2012

Manifestations of electron interactions in photogalvanic effect in chiral nanotubes

Carbon nanotubes provide one of the most accessible experimental realizations of one dimensional electron systems. In the experimentally relevant regime of low doping the Luttinger liquid formed by electrons may be approximated by a Wigner crystal. The crystal-like electronic order suggests that nanotubes exhibit effects similar to the Mössbauer effect where the momentum of an emitted photon is absorbed by the whole crystal. We show that the circular photovoltaic effect in chiral nanotubes is of the same nature. We obtain the frequency dependence of the photovoltage and characterize its singularities in a broad frequency range where the electron correlations are essential. Our predictions provide a basis for using the photogalvanic effect as a new experimental probe of electron correlations in nanotubes.

cond-mat.mes-hall↗
arXiv2011

Critical point correlations in random gaussian fields

We consider fluctuations in the distribution of critical points - saddle points, minima and maxima - of random gaussian fields. We calculate the asymptotic limits of the two point correlation function for various critical point densities, for both long and short range. We perform the calculation for any dimension of the field, provide explicit formulae for two and three dimensions, and verify our results with numerical calculations.

cond-mat.dis-nn↗
arXiv2010

Parametrically excited "Scars" in Bose-Einstein condensates

Parametric excitation of a Bose-Einstein condensate (BEC) can be realized by periodically changing the interaction strength between the atoms. Above some threshold strength, this excitation modulates the condensate density. We show that when the condensate is trapped in a potential well of irregular shape, density waves can be strongly concentrated ("scarred") along the shortest periodic orbits of a classical particle moving within the confining potential. While single-particle wave functions of systems whose classical counterpart is chaotic may exhibit rich scarring patterns, in BEC, we show that nonlinear effects select mainly those scars that are locally described by stripes. Typically, these are the scars associated with self retracing periodic orbits that do not cross themselves in real space. Dephasing enhances this behavior by reducing the nonlocal effect of interference.

cond-mat.other↗
arXiv2010

Localized Rayleigh Instability in Evaporation Fronts

A qualitatively different manifestation of the Rayleigh instability is demonstrated, where, instead of the usual extended undulations and breakup of the liquid into many droplets, the instability is localized, leading to an isolated narrowing of the liquid filament. The localized instability, caused by a nonuniform curvature of the liquid domain, plays a key role in the evaporation of thin liquid films off solid surfaces.

cond-mat.soft↗
arXiv2009

Viscous fingering in volatile thin films

A thin water film on a cleaved mica substrate undergoes a first order phase transition between two values of film thickness. By inducing a finite evaporation rate of the water, the interface between the two phases develops a fingering instability similar to that observed in the Saffman-Taylor problem. We draw the connection between the two problems, and construct solutions describing the dynamics of evaporation in this system.

cond-mat.soft↗
arXiv2008

Correlated tunneling and the instability of the fractional quantum Hall edge

We consider a class of interaction terms that describes correlated tunneling of composite fermions between effective Landau levels. Despite being generic and of similar strength to that of the usual density-density couplings, these terms are not included in the accepted theory of the edges of fractional quantum Hall systems. Here we show that they may lead to an instability of the edge towards a new reconstructed state with additional channels, and thereby demonstrate the incompleteness of the traditional edge theory.

cond-mat.mes-hall↗
arXiv2007

The contact conductance of a one-dimensional wire partly embedded in a superconductor

The conductance through a semi-infinite one-dimensional wire, partly embedded in a superconducting bulk electrode, is studied. When the electron-electron interactions within the wire are strongly repulsive, the wire effectively decouples from the superconductor. If they are moderately or weakly repulsive, the proximity of the superconductor induces superconducting order in the segment of the wire embedded in it. In this case it is shown that the conductance exhibits a crossover from conductive to insulating behavior as the temperature is lowered down. The characteristic crossover temperature of this transition has a stretched exponential dependence on the length of the part of the wire embedded in the superconductor. The amount of this stretch is determined by the nature of the electron interactions within the wire.

cond-mat.str-el↗
arXiv2007

Propagation of coherent waves in elastically scattering media

A general method for calculating statistical properties of speckle patterns of coherent waves propagating in disordered media is developed. It allows one to calculate speckle pattern correlations in space, as well as their sensitivity to external parameters. This method, which is similar to the Boltzmann-Langevin approach for the calculation of classical fluctuations, applies for a wide range of systems: From cases where the ray propagation is diffusive to the regime where the rays experience only small angle scattering. The latter case comprises the regime of directed waves where rays propagate ballistically in space while their directions diffuse. We demonstrate the applicability of the method by calculating the correlation function of the wave intensity and its sensitivity to the wave frequency and the angle of incidence of the incoming wave.

cond-mat.dis-nn↗
arXiv2006

Singular limit of Hele-Shaw flow and dispersive regularization of shock waves

We study a family of solutions to the Saffman-Taylor problem with zero surface tension at a critical regime. In this regime, the interface develops a thin singular finger. The flow of an isolated finger is given by the Whitham equations for the KdV integrable hierarchy. We show that the flow describing bubble break-off is identical to the Gurevich-Pitaevsky solution for regularization of shock waves in dispersive media. The method provides a scheme for the continuation of the flow through singularites.

nlin.SI↗
arXiv2006

Statistics of speckle patterns

We develop a general method for calculating statistical properties of the speckle pattern of coherent waves propagating in disordered media. In some aspects this method is similar to the Boltzmann-Langevin approach for the calculation of classical fluctuations. We apply the method to the case where the incident wave experiences many small angle scattering events during propagation, but the total angle change remains small. In many aspects our results for this case are different from results previously known in the literature. The correlation function of the wave intensity at two points separated by a distance $r$, has a long range character. It decays as a power of $r$ and changes sign. We also consider sensitivities of the speckles to changes of external parameters, such as the wave frequency and the incidence angle.

cond-mat.mes-hall↗
arXiv2005

Non-ohmicity and energy relaxation in diffusive 2D metals

We analyze current-voltage characteristics taken on Au-doped indium-oxide films. By fitting a scaling function to the data, we extract the electron-phonon scattering rate as function of temperature, which yields a quadratic dependence of the electron-phonon scattering rate on temperature from 1K down to 0.28K. The origin of this enhanced electron-phonon scattering rate is ascribed to the mechanism proposed by Sergeev and Mitin.

cond-mat.dis-nn↗
arXiv2002

Viscous fingering and a shape of an electronic droplet in the Quantum Hall regime

We show that the semiclassical dynamics of an electronic droplet confined in the plane in a quantizing inhomogeneous magnetic field in the regime when the electrostatic interaction is negligible is similar to viscous (Saffman-Taylor) fingering on the interface between two fluids with different viscosities confined in a Hele-Shaw cell. Both phenomena are described by the same equations with scales differing by a factor of up to $10^{-9}$. We also report the quasiclassical wave function of the droplet in an inhomogeneous magnetic field.

cond-mat↗
arXiv2001

Projecting the Kondo Effect: Theory of the Quantum Mirage

A microscopic theory is developed for the projection (quantum mirage) of the Kondo resonance from one focus of an elliptic quantum corral to the other focus. The quantum mirage is shown to be independent of the size and the shape of the ellipse, and experiences λ_F/4 oscillations (λ_F is the surface-band Fermi wavelength) with an increasing semimajor axis length. We predict an oscillatory behavior of the mirage as a function of a weak magnetic field applied perpendicular to the sample.

cond-mat↗
arXiv2000

Weak localization in disordered systems at the ballistic limit

The weak localization (WL) contribution to the two-level correlation function is calculated for two-dimensional disordered conductors. Our analysis extends to the nondiffusive (ballistic) regime, where the elastic mean path is of order of the size of the system. In this regime the structure factor (the Fourier transform of the two-point correlator) exhibits a singular behavior consisting of dips superimposed on a smooth positive background. The strongest dips appear at periods of the periodic orbits of the underlying clean system. Somewhat weaker singularities appear at times which are sums of periods of two such orbits. The results elucidate various aspects of the weak localization physics of ballistic chaotic systems.

cond-mat.mes-hall↗
arXiv2000

Shot noise in chaotic systems: "classical" to quantum crossover

This paper is devoted to study of the classical-to-quantum crossover of the shot noise value in chaotic systems. This crossover is determined by the ratio of the particle dwell time in the system, $τ_d$, to the characteristic time for diffraction $t_E \simeq λ^{-1} |\ln \hbar|$, where $λ$ is the Lyapunov exponent. The shot noise vanishes in the limit $t_E \gg τ_d $, while reaches its universal quantum value in the opposite limit. Thus, the Lyapunov exponent of chaotic mesoscopic systems may be found by the shot noise measurements.

cond-mat.mes-hall↗
arXiv2000

The leading Ruelle resonances of chaotic maps

The leading Ruelle resonances of typical chaotic maps, the perturbed cat map and the standard map, are calculated by variation. It is found that, excluding the resonance associated with the invariant density, the next subleading resonances are, approximately, the roots of the equation $z^4=γ$, where $γ$ is a positive number which characterizes the amount of stochasticity of the map. The results are verified by numerical computations, and the implications to the form factor of the corresponding quantum maps are discussed.

nlin.CD↗
arXiv2000

"Scars" in parametrically excited surface waves

We consider the Faraday surface waves of a fluid in a container with a non-integrable boundary shape. We show that, at sufficiently low frequencies, the wave patterns are ``scars'' selected by the instability of the corresponding periodic orbits, the dissipation at the container side walls, and interaction effects which reflect the nonlinear nature of the Faraday waves. The results explain the observation of a limited number of scars with anomalous strengths in recent experiments by Kudrolli, Abraham and Gollub.

cond-mat↗