Searcharxiv⌕ Search

arXiv subjects

V. Fleurov

Publications and source records attributed to V. Fleurov.

At least 19 recordsLinked to original sources
arXiv2019

Sliding Luttinger liquid with alternating interwire couplings

We study a phase diagram for the sliding Luttinger liquid (SLL) of coupled one-dimensional quantum wires packed in a two-dimensional array in the absence of a magnetic field. We analyze whether nearest-neighbor inter-wire interactions, stabilize the SLL phase. We construct an analogue of a Su-Schriefer-Heeger (SSH) model (allowing alternating couplings between wires). Calculating the scaling dimensions of the two most relevant perturbations, charge-density wave, and superconducting inter-wire couplings, but excluding the inter-wire single-particle hybridization, we find a finite stability region for the SLL. It emerges due to the inter-wire forward scattering interaction, and remains stable up to a significant asymmetry between alternating couplings.

cond-mat.str-el↗
arXiv2015

Finite width of the sonic event horizon and grey body Hawking radiation

Finite width of the analog event horizon is determined by the nonlinearity length in the Kerr nonlinear optical system, which is discussed here, or by the healing length in Bose-Einstein condensates. The various eigen modes of fluctuations are found in the immediate vicinity of the event horizon and the scattering matrix due to the finite width horizon is calculated to within the leading order correction in the nonlinearity length. The Hawking radiation is found to be that of a grey body with the emissivity larger than one. A procedure of paraxial quantization of the fluctuation field is discussed and its connection to the conventional quantization of the electromagnetic field is demonstrated.

gr-qc↗
arXiv2013

Soliton in a Well. Dynamics and Tunneling

We derive the leading order radiation through tunneling of an oscillating soliton in a well. We use the hydrodynamic formulation with a rigorous control of the errors for finite times.

math-ph↗
arXiv2013

Nonlocality and fluctuations near the optical analog of a sonic horizon

We consider the behavior of fluctuations near the sonic horizon and the role of the nonlocality of interaction (nonlinearity) on their regularization. The nonlocality dominates if its characteristic length scale is larger than the regularization length. The influence of nonlocality may be important in the current experiments on the transonic flow in Kerr nonlinear media. Experimental conditions, under which the observation of straddled fluctuations can be observed, are discussed.

physics.optics↗
arXiv2011

Regularization of fluctuations near the sonic horizon due to the quantum potential and its influence on the Hawking radiation

We consider dynamics of fluctuations in transonically accelerating Bose-Einstein condensates and luminous liquids (coherent light propagating in a Kerr nonlinear medium) using the hydrodynamic approach. It is known that neglecting the quantum potential (QP) leads to a singular behavior of quantum and classical fluctuations in the vicinity of the Mach (sonic) horizon, which in turn gives rise to the Hawking radiation. The neglect of QP is well founded at not too small distances $|x| \gg l_h$ from the horizon, where $l_h$ is the healing length. Taking the QP into account we show that a second characteristic length $l_r > l_h$ exists, such that the linear fluctuation modes become regularized for $|x| \ll l_r$. At $|x| \gg l_r$ the modes keep their singular behavior, which however is influenced by the QP. As a result we find a deviation of the high frequency tail of the spectrum of Hawking radiation from Planck's black body radiation distribution. Similar results hold for the wave propagation in Kerr nonlinear media where the length $l_h$ and $l_r$ exist due to the nonlinearity.

cond-mat.quant-gas↗
arXiv2011

Cotunneling mechanism of single-electron shuttling

The problem of electron transport by means of a dumbbell shaped shuttle in strong Coulomb blockade regime is solved. The electrons may be shuttled only in the cotunneling regime during the time spans when both shoulders of the shuttle approach the metallic banks. The conventional Anderson-like tunneling model is generalized for this case and the tunneling conductance is calculated in the adiabatic regime of slow motion of the shuttle. Non-adiabatic corrections are briefly discussed.

cond-mat.mes-hall↗
arXiv2011

Jet-like tunneling from a trapped vortex

We analyze the tunneling of vortex states from elliptically shaped traps. Using the hydrodynamic representation of the Gross-Pitaevskii (Nonlinear Schrödinger) equation, we derive analytically and demonstrate numerically a novel type of quantum fluid flow: a jet-like singularity formed by the interaction between the vortex and the nonhomogenous field. For strongly elongated traps, the ellipticity overwhelms the circular rotation, resulting in the ejection of field in narrow, well-defined directions. These jets can also be understood as a formation of caustics since they correspond to a convergence of trajectories starting from the top of the potential barrier and meeting at a certain point on the exit line. They will appear in any coherent wave system with angular momentum and non-circular symmetry, such as superfluids, Bose-Einstein condensates, and light.

cond-mat.quant-gas↗
arXiv2010

Green-function method for calculation of adsorption of organic molecules on noble metal nanoparticles

A numerical method for calculation electronic structure of a nanosystem composed of a pseudoisocyanine (PIC) molecule assembled on a silver nanoparticle is developed. The electronic structure of the silver nanoparticle containing 125 atoms is calculated within the local density version of the density functional method. A model of an Ag atom embedded in the center of a spherical jellium cluster is used. The host electron Green function is calculated by means of the spherically symmetric expansion. The principal theoretical tool is the scattering theory using the Green function method. The molecule -- silver nanoparticle interaction is studied using the approach similar to that of the Anderson model for transition metal impurities in solids. Localized levels are shown to split off from the top of the band of the nanosystem. The electronic structure calculations yield information on the character of chemical bonding in the PIC molecule --- silver particle nanosystem.

cond-mat.mes-hall↗
arXiv2010

Dynamics of fluctuations in an optical analog of the Laval nozzle

Using the analogy between the description of coherent light propagation in a medium with Kerr nonlinearity by means of nonlinear Schrödinger equation and that of a dissipationless liquid we propose an optical analogue of the Laval nozzle. The optical Laval nozzle will allow one to form a transonic flow in which one can observe and study a very unusual dynamics of classical and quantum fluctuations including analogue of the Hawking radiation of real black holes. Theoretical analysis of this dynamics is supported by numerical calculations and estimates for a possible experimental setup are presented.

physics.optics↗
arXiv2009

Dynamics of Macroscopic Tunneling in Elongated BEC

We investigate macroscopic tunneling from an elongated quasi 1-d trap, forming a 'cigar shaped' BEC. Using recently developed formalism we get the leading analytical approximation for the right hand side of the potential wall, i.e. outside the trap, and a formalism based on Wigner functions, for the left side of the potential wall, i.e. inside the BEC. We then present accomplished results of numerical calculations, which show a 'blip' in the particle density traveling with an asymptotic shock velocity, as resulted from previous works on a dot-like trap, but with significant differences from the latter. Inside the BEC a pattern of a traveling dispersive shock wave is revealed. In the attractive case, we find trains of bright solitons frozen near the boundary.

cond-mat.quant-gas↗
arXiv2009

Time-dependent single electron tunneling through a shuttling nano-island

We offer a general approach to calculation of single-electron tunneling spectra and conductance of a shuttle oscillating between two half-metallic leads with fully spin polarized carriers. In this case the spin-flip processes are completely suppressed and the problem may be solved by means of canonical transformation, where the adiabatic component of the tunnel transparency is found exactly, whereas the non-adiabatic corrections can be taken into account perturbatively. Time-dependent corrections to the tunnel conductance of moving shuttle become noticeable at finite bias in the vicinity of the even/odd occupation boundary at the Coulomb diamond diagram.

cond-mat.mes-hall↗
arXiv2009

Location- and observation time-dependent quantum-tunneling

We investigate quantum tunneling in a translation invariant chain of particles. The particles interact harmonically with their nearest neighbors, except for one bond, which is anharmonic. It is described by a symmetric double well potential. In the first step, we show how the anharmonic coordinate can be separated from the normal modes. This yields a Lagrangian which has been used to study quantum dissipation. Elimination of the normal modes leads to a nonlocal action of Caldeira-Leggett type. If the anharmonic bond defect is in the bulk, one arrives at Ohmic damping, i.e. there is a transition of a delocalized bond state to a localized one if the elastic constant exceeds a critical value $C_{crit}$. The latter depends on the masses of the bond defect. Superohmic damping occurs if the bond defect is in the site $M$ at a finite distance from one of the chain ends. If the observation time $T$ is smaller than a characteristic time $τ_M \sim M$, depending on the location M of the defect, the behavior is similar to the bulk situation. However, for $T \gg τ_M$ tunneling is never suppressed.

cond-mat.other↗
arXiv2008

Nonlinear Dynamic Phenomena in Macroscopic Tunneling

Numerical simulations of the NLSE (or GPE) are presented demonstrating emission of short pulses of the matter (light) density formed in the course of tunneling in wave-guided light and/or trapped BEC. The phenomenon is observed under various conditions, for nonlinearities of different signs, zero nonlinearity included. We study, both numerically and analytically, pulsations of matter (light) remaining within the trap and use the results in order to induce emission of sequential pulses by properly narrowing the trap. This allows us to propose a mechanism for a realization of Atom Pulse Laser.

cond-mat.other↗
arXiv2008

Electronic structure of noble metal impurities in semiconductors: Cu in GaP

A numerical method for calculation of the electronic structure of transition metal impurities in semiconductors based on the Green function technique is developed. The electronic structure of 3d impurity is calculated within the LDA+U version of density functional method, whereas the host electron Green function is calculated by using the linearized augmented plane wave expansion. The method is applied to the Cu impurity in GaP. The results of calculations are compared with those obtained within the supercell LDA procedure. It is shown that in the Green function approach Cu impurity has an unfilled 3d shell. This result paves a way to explanation of the magnetic order in dilute Ga_{1-x}Cu_xP alloys.

cond-mat.other↗
arXiv2008

Collective excitations in a magnetically doped quantized Hall ferromagnet

A theory of collective states in a magnetically quantized two-dimensional electron gas (2DEG) with half-filled Landau level (quantized Hall ferromagnet) in the presence of magnetic 3d impurities is developed. The spectrum of bound and delocalized spin-excitons as well as the renormalization of Zeeman splitting of the impurity 3d levels due to the indirect exchange interaction with the 2DEG are studied for the specific case of n-type GaAs doped with Mn where the Lande` g-factors of impurity and 2DEG have opposite signs. If the sign of the 2DEG g-factor is changed due to external influences, then impurity related transitions to new ground state phases, presenting various spin-flip and skyrmion-like textures, are possible. Conditions for existence of these phases are discussed. PACS: 73.43.Lp, 73.21.Fg, 72.15.Rn

cond-mat.mes-hall↗
arXiv2006

Temporal dynamics of tunneling. Hydrodynamic approach

We use the hydrodynamic representation of the Gross -Pitaevskii/Nonlinear Schroedinger equation in order to analyze the dynamics of macroscopic tunneling process. We observe a tendency to a wave breaking and shock formation during the early stages of the tunneling process. A blip in the density distribution appears in the outskirts of the barrier and under proper conditions it may transform into a bright soliton. Our approach, based on the theory of shock formation in solutions of Burgers equation, allows us to find the parameters of the ejected blip (or soliton if formed) including the velocity of its propagation. The blip in the density is formed regardless of the value and sign of the nonlinearity parameter. However a soliton may be formed only if this parameter is negative (attraction) and large enough. A criterion is proposed. An ejection of a soliton is also observed numerically. We demonstrate, theoretically and numerically, controlled formation of soliton through tunneling. The mass of the ejected soliton is controlled by the initial state.

cond-mat.other↗
arXiv2006

Superexchange in Dilute Magnetic Dielectrics: Application to (Ti,Co)O_2

We extend the model of ferromagnetic superexchange in dilute magnetic semiconductors to the ferromagnetically ordered highly insulating compounds (dilute magnetic dielectrics). The intrinsic ferromagnetism without free carriers is observed in oxygen-deficient films of anatase TiO_2 doped with transition metal impurities in cation sublattice. We suppose that ferromagnetic order arises due to superexchange between complexes [oxygen vacancies + magnetic impurities], which are stabilized by charge transfer from vacancies to impurities. The Hund rule controls the superexchange via empty vacancy related levels so that it becomes possible only for the parallel orientation of impurity magnetic moments. The percolation threshold for magnetic ordering is determined by the radius of vacancy levels, but the exchange mechanism does not require free carriers. The crucial role of the non-stoichiometry in formation of the ferromagnetism makes the Curie temperatures extremely sensitive to the methods of sample preparation.

cond-mat.mtrl-sci↗