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E. M. Chudnovsky

Publications and source records attributed to E. M. Chudnovsky.

At least 55 records · Page 3Linked to original sources
arXiv2010

Interaction of a Nanomagnet with a Weak Superconducting Link

We study electromagnetic interaction of a nanomagnet with a weak superconducting link. Equations that govern coupled dynamics of the two systems are derived and investigated numerically. We show that the presence of a small magnet in the proximity of a weak link may be detected through Shapiro-like steps caused by the precession of the magnetic moment. Despite very weak magnetic field generated by the weak link, a time-dependent bias voltage applied to the link can initiate a non-linear dynamics of the nanomagnet that leads to the reversal of its magnetic moment. We also consider quantum problem in which a nanomagnet interacting with a weak link is treated as a two-state spin system due to quantum tunneling between spin-up and spin-down states.

cond-mat.mes-hall↗
arXiv2010

Quantum Tunneling of Normal-Superconducting Interfaces in a Type-I Superconductor

Evidence of a non-thermal magnetic relaxation in the intermediate state of a type-I superconducor is presented. It is attributed to quantum tunneling of interfaces separating normal and superconducting regions. Tunneling barriers are estimated and temperature of the crossover from thermal to quantum regime is obtained from Caldeira-Leggett theory. Comparison between theory and experiment points to tunneling of interface segments of size comparable to the coherence length, by steps of order one nanometer.

cond-mat.supr-con↗
arXiv2009

Rotational States of Magnetic Molecules

We study a magnetic molecule that exhibits spin tunneling and is free to rotate about its anisotropy axis. Exact low-energy eigenstates of the molecule that are superpositions of spin and rotational states are obtained. We show that parameter $α= 2(\hbar S)^2/(IΔ)$ determines the ground state of the molecule. Here $\hbar S$ is the spin, $I$ is the moment of inertia, and $Δ$ is the tunnel splitting. The magnetic moment of the molecule is zero at $α< α_c = [1-1/(2S)^{2}]^{-1}$ and non-zero at $α> α_c$. At $α\to \infty$ the spin of the molecule localizes in one of the directions along the anisotropy axis.

cond-mat.mes-hall↗
arXiv2009

Intrinsic spin Hall effect in noncubic crystals

We study the dependence of the intrinsic spin Hall effect on the crystal symmetry and geometry of experiment. The spin current is obtained and the Hall voltage caused by the polarization of the electron spins is computed. The unique dependence of the effect on the crystal symmetry permits the choice of geometry in which the spin Hall effect can be unambiguously distinguished from the effects due to the orbital motion of charge carriers and due to the magnetic field generated by the transport current.

cond-mat.mes-hall↗
arXiv2009

Instanton Glass Generated by Noise in a Josephson-Junction Array

We compute correlation function of a superconducting order parameter in a continuous model of a two-dimensional Josephson-junction array in the presence of a weak Gaussian noise. When the Josephson coupling is large compared to the charging energy the correlations in the Euclidian space decay exponentially at low temperatures regardless of the strength of the noise. We interpret such a state as a collective Cooper-pair insulator and argue that it resembles properties of disordered superconducting films.

cond-mat.supr-con↗
arXiv2009

Self-organized patterns of macroscopic quantum tunneling in molecular magnets

We study low temperature resonant spin tunneling in molecular magnets induced by a field sweep with account of dipole-dipole interactions. Numerical simulations uncovered formation of self-organized patterns of the magnetization and of the ensuing dipolar field that provide resonant condition inside a finite volume of the crystal. This effect is robust with respect to disorder and should be relevant to the dynamics of the magnetization steps observed in molecular magnets.

cond-mat.stat-mech↗
arXiv2009

Magnetic Molecule on a Microcantilever: Quantum Magneto-mechanical Oscillations

We study the quantum dynamics of a system consisting of a magnetic molecule placed on a microcantilever. The amplitude and frequencies of the coupled magneto-mechanical oscillations are computed. Parameter-free theory shows that the existing experimental techniques permit observation of the driven coupled oscillations of the spin and the cantilever, as well as of the splitting of the mechanical modes of the cantilever caused by spin tunneling.

cond-mat.mtrl-sci↗
arXiv2008

Dynamics of Einstein - de Haas Effect: Application to Magnetic Cantilever

Local time-dependent theory of Einstein - de Haas effect is developed. We begin with microscopicinteractions and derive dynamical equations that couple elastic deformations with internal twists due to spins. The theory is applied to the description of the motion of a magnetic cantilever caused by the oscillation of the domain wall. Theoretical results are compared with a recent experiment on Einstein - de Haas effect in a microcantilever.

cond-mat.mtrl-sci↗
arXiv2008

Dipolar Ordering and Quantum Dynamics of Domain Walls in Mn-12 Acetate

We find that dipolar interactions favor ferromagnetic ordering of elongated crystals of Mn12 Acetate below 0.8 K. Ordered crystals must possess domain walls. Motion of the wall corresponds to a moving front of Landau-Zener transitions between quantum spin levels. Structure and mobility of the wall are computed. The effect is robust with respect to inhomogeneous broadening and decoherence.

cond-mat.stat-mech↗
arXiv2008

Voltage from mechanical stress in type-II superconductors: Depinning of the magnetic flux by moving dislocations

Mechanical stress causes motion of defects in solids. We show that in a type-II superconductor a moving dislocation generates a pattern of current that exerts the depinning force on the surrounding vortex lattice. Concentration of dislocations and the mechanical stress needed to produce critical depinning currents are shown to be within practical range. When external magnetic field and transport current are present this effect generates voltage across the superconductor. Thus a superconductor can serve as an electrical sensor of the mechanical stress.

cond-mat.supr-con↗
arXiv2008

Origin of Spin Hall Effect (Reply to Comment)

Conceptual framework behind the intrinsic spin Hall effect in three-dimensional conductors is discussed. Theory suggests how the spin Hall current should depend on symmetry and orientation of the crystal.

cond-mat.mes-hall↗
arXiv2007

Ignition of superconducting vortices by acoustic standing waves

Nucleation of vortices in a superconductor below the first critical field can be assisted by transverse sound in the GHz frequency range. Vortices will enter and exist the superconductor at the frequency of the sound. We compute the threshold parameters of the sound and show that this effect is within experimental reach.

cond-mat.supr-con↗
arXiv2007

Magneto-elastic waves in crystals of magnetic molecules

We study magneto-elastic effects in crystals of magnetic molecules. Coupled equations of motion for spins and sound are derived and the possibility of strong resonant magneto-acoustic coupling is demonstrated. Dispersion laws for interacting linear sound and spin excitations are obtained for bulk and surface acoustic waves. We show that ultrasound can generate inverse population of spin levels. Alternatively, the decay of the inverse population of spin levels can generate ultrasound. Possibility of solitary waves of the magnetization accompanied by the elastic twists is demonstrated.

cond-mat.stat-mech↗
arXiv2007

Theory of magnetic deflagration

Theory of magnetic deflagration (avalanches) in crystals of molecular magnets has been developed. The phenomenon resembles the burning of a chemical substance, with the Zeeman energy playing the role of the chemical energy. Non-destructive reversible character of magnetic deflagration, as well as the possibility to continuously tune the flammability of the crystal by changing the magnetic field, makes molecular magnets an attractive toy system for a detailed study of the burning process. Besides simplicity, new features, as compared to the chemical burning, include possibility of quantum decay of metastable spin states and strong temperature dependence of the heat capacity and thermal conductivity. We obtain analytical and numerical solutions for criteria of the ignition of magnetic deflagration, and compute the ignition rate and the speed of the developed deflagration front.

cond-mat.stat-mech↗
arXiv2007

Rabi oscillations from ultrasound in spin systems

It is shown that ultrasound in the GHz range can generate space-time Rabi oscillations between spin states of molecular magnets. We compute dynamics of the magnetization generated by surface acoustic waves and discuss conditions under which this novel quantum effect can be observed.

cond-mat.other↗
arXiv2006

Electromagnetic radiation from vortex flow in type-II superconductors

We show that a moving vortex lattice, as it comes to a crystal edge, radiates into a free space the harmonics of the washboard frequency, $ω_0=2πv/a$, up to a superconducting gap, $Δ/\hbar$. Here $v$ is the velocity of the vortex lattice and $a$ is the intervortex spacing. We compute radiation power and show that this effect can be used for generation of terahertz radiation and for characterization of moving vortex lattices.

cond-mat.supr-con↗
arXiv2006

Relaxation of the Electron Spin in Quantum Dots Via One- and Two-Phonon Processes

We have studied direct and Raman processes of the decay of electron spin states in a quantum dot via radiation of phonons corresponding to elastic twists. Universal dependence of the spin relaxation rate on the strength and direction of the magnetic field has been obtained in terms of the electron gyromagnetic tensor and macroscopic elastic constants of the solid.

cond-mat.other↗