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E. M. Chudnovsky

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

At least 73 records · Page 4Linked to original sources
arXiv2006

Two-phonon spin-lattice relaxation of rigid atomic clusters

Spin-phonon relaxation due to two-phonon processes of a spin cluster embedded in an elastic medium has been studied. For the case of uniaxial anisotropy, relaxation rates due to Raman processes and processes involving the emission of two phonons have been obtained. For a biaxial spin Hamiltonian, the rates of transitions between tunnel-split levels have been computed. By comparison with the rates of corresponding direct processes, we have established temperature ranges where the Raman mechanism dominates over the one-phonon decay mechanism.

cond-mat.stat-mech↗
arXiv2006

Phonon-induced relaxation of a two-state system in solids

We study phonon-induced relaxation of quantum states of a particle (e.g., electron or proton) in a rigid double-well potential in a solid. Relaxation rate due to Raman two-phonon processes have been computed. We show that in a two-state limit, symmetry arguments allow one to express these rates in terms of independently measurable parameters. In general, the two-phonon processes dominate relaxation at higher temperature. Due to parity effect in a biased two-state system, their rate can be controlled by the bias.

cond-mat.stat-mech↗
arXiv2005

Propagation of Avalanches in Mn$_{12}$-acetate: Magnetic Deflagration

Local time-resolved measurements of fast reversal of the magnetization of single crystals of Mn12-acetate indicate that the magnetization avalanche spreads as a narrow interface that propagates through the crystal at a constant velocity that is roughly two orders of magnitude smaller than the speed of sound. We argue that this phenomenon is closely analogous to the propagation of a flame front (deflagration) through a flammable chemical substance.

cond-mat.other↗
arXiv2005

Field Dependence of the Electron Spin Relaxation in Quantum Dots

Interaction of the electron spin with local elastic twists due to transverse phonons has been studied. 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. The theory contains no unknown parameters and it can be easily tested in experiment. At high magnetic field it provides parameter-free lower bound on the electron spin relaxation in quantum dots.

cond-mat.stat-mech↗
arXiv2005

Universal mechanism of spin relaxation in solids

We consider relaxation of a rigid spin cluster in an elastic medium in the presence of the magnetic field. Universal simple expression for spin-phonon matrix elements due to local rotations of the lattice is derived. The equivalence of the lattice frame and the laboratory frame approaches is established. For spin Hamiltonians with strong uniaxial anisotropy the field dependence of the transition rates due to rotations is analytically calculated and its universality is demonstrated. The role of time reversal symmetry in spin-phonon transitions has been elucidated. The theory provides lower bound on the decoherence of any spin-based solid-state qubit.

cond-mat.stat-mech↗
arXiv2005

Quantum dynamics of a nanomagnet in a rotating field

Quantum dynamics of a two-state spin system in a rotating magnetic field has been studied. Analytical and numerical results for the transition probability have been obtained along the lines of the Landau-Zener-Stueckelberg theory. The effect of various kinds of noise on the evolution of the system has been analyzed.

cond-mat.mes-hall↗
arXiv2004

Phonon superradiance and phonon laser effect in nanomagnets

We show that the theory of spin-phonon processes in paramagnetic solids must take into account the coherent generation of phonons by the magnetic centers. This effect should drastically enhance spin-phonon rates in nanoscale paramagnets and in crystals of molecular nanomagnets.

cond-mat.mes-hall↗
arXiv2004

Pulsed field studies of the magnetization reversal in molecular nanomagnets

We report experimental studies of crystals of Mn12 molecular magnetic clusters in pulsed magnetic fields with sweep rates up to 4x10^3 T/s. The steps in the magnetization curve are observed at fields that are shifted with respect to the resonant field values. The shift systematically increases as the rate of the field sweep goes up. These data are consistent with the theory of the collective dipolar relaxation in molecular magnets.

cond-mat.other↗
arXiv2003

Inertial mass of a superconducting vortex

We show that a large contribution to the inertial mass of a moving superconducting vortex comes from transversal displacements of the crystal lattice. The corresponding part of the mass per unit length of the vortex line is $M_{l} = ({\rm m}_e^2c^{2}/64πα^{2}μλ_{L}^{4})\ln(λ_{L}/ξ)$ , where ${\rm m}_{e}$ is the the bare electron mass, $c$ is the speed of light, $α=e^{2}/{\hbar}c {\approx} 1/137$ is the fine structure constant, $μ$ is the shear modulus of the solid, $λ_{L}$ is the London penetration length and $ξ$ is the coherence length. In conventional superconductors, this mass can be comparable to or even greater than the vortex core mass computed by Suhl.

cond-mat.supr-con↗
arXiv2002

Decoherence of a Superposition of Macroscopic Current States in a SQUID

We show that fundamental conservation laws mandate parameter-free mechanisms of decoherence of quantum oscillations of the superconducting current between opposite directions in a SQUID -- emission of phonons and photons at the oscillation frequency. The corresponding rates are computed and compared with experimental findings. The decohering effects of external mechanical and magnetic noise are investigated.

cond-mat.mes-hall↗
arXiv2002

Quantum dynamics of crystals of molecular nanomagnets inside a resonant cavity

It is shown that crystals of molecular nanomagnets exhibit enhanced magnetic relaxation when placed inside a resonant cavity. Strong dependence of the magnetization curve on the geometry of the cavity has been observed, providing evidence of the coherent microwave radiation by the crystals. A similar dependence has been found for a crystal placed between Fabry-Perot superconducting mirrors. These observations open the possibility of building a nanomagnetic microwave laser pumped by the magnetic field.

cond-mat.mtrl-sci↗
arXiv2002

Reflectivity and Microwave Absorption in Crystals with Alternating Intrinsic Josephson Junctions

We compute the frequency and magnetic field dependencies of the reflectivity $R(ω)$ in layered superconductors with two alternating intrinsic Josephson junctions with different critical current densities and quasiparticle conductivities for the electric field polarized along the c-axis. The parameter $α$ describing the electronic compressibility of the layers and the charge coupling of neighboring junctions was extracted for the SmLa$_{1-x}$Sr$_{x}$CuO$_{4-δ}$ superconductor from two independent optical measurements, the fit of the loss function $L(ω)$ at zero magnetic field and the magnetic field dependence of the peak positions in $L(ω)$. The experiments are consistent with a free electron value for $α$ near the Josephson plasma frequencies.

cond-mat.supr-con↗
arXiv2002

Superradiance from crystals of molecular nanomagnets

We show that crystals of molecular nanomagnets can exhibit giant magnetic relaxation due to the Dicke superradiance of electromagnetic waves. Rigorous treatment of the superradiance induced by a field pulse is presented.

cond-mat.stat-mech↗
arXiv2002

Tunneling and EPR linewidths due to dislocations in Mn-12 acetate

We compute the width and shape of the EPR and tunneling resonances due to dislocations in Mn-12 acetate crystals. Uncorrelated dislocations produce the Gaussian shape of resonances while dislocations bound in pairs produce the Lorentzian shape. We stress that the uniaxial spin Hamiltonian together with crystal defects can explain the totality of experimental data on Mn-12.

cond-mat.stat-mech↗
arXiv2002

Tunneling with dissipation and decoherence for a large spin

We present rigorous solution of problems of tunneling with dissipation and decoherence for a spin of an atom or a molecule in an isotropic solid matrix. Our approach is based upon switching to a rotating coordinate system coupled to the local crystal field. We show that the spin of a molecule can be used in a qubit only if the molecule is strongly coupled with its atomic environment. This condition is a consequence of the conservation of the total angular momentum (spin + matrix), that has been largely ignored in previous studies of spin tunneling.

cond-mat.mtrl-sci↗
arXiv2001

Dislocation-induced spin tunneling in Mn-12 acetate

Comprehensive theory of quantum spin relaxation in Mn-12 acetate crystals is developed, that takes into account imperfections of the crystal structure and is based upon the generalization of the Landau-Zener effect for incoherent tunneling from excited energy levels. It is shown that linear dislocations at plausible concentrations provide the transverse anisotropy which is the main source of tunneling in Mn-12. Local rotations of the easy axis due to dislocations result in a transverse magnetic field generated by the field applied along the c-axis of the crystal, which explains the presence of odd tunneling resonances. Long-range deformations due to dislocations produce a broad distribution of tunnel splittings. The theory predicts that at subkelvin temperatures the relaxation curves for different tunneling resonances can be scaled onto a single master curve. The magnetic relaxation in the thermally activated regime follows the stretched-exponential law with the exponent depending on the field, temperature, and concentration of defects.

cond-mat.stat-mech↗