Searcharxiv⌕ Search

arXiv subjects

L. A. Openov

Publications and source records attributed to L. A. Openov.

At least 37 records · Page 2Linked to original sources
arXiv2006

Formation of a "Cluster Molecule" (C20)2 and its thermal stability

The possible formation of a "cluster molecule" (C20)2 from two single C20 fullerenes is studied by the tight-binding method. Several (C20)2 isomers in which C20 fullerenes are bound by strong covalent forces and retain their identity are found; actually, these C20 fullerenes play the role of "atoms" in the "cluster molecule". The so-called open-[2+2] isomer has a minimum energy. Its formation path and thermal stability at T = 2000 - 4000 K are analyzed in detail. This isomer loses its molecular structure due to either the decay of one of C20 fullerenes or the coalescence of two C20 fullerenes into a C40 cluster. The energy barriers for the metastable open-[2+2] configuration are calculated to be U = 2 - 5 eV.

cond-mat.mes-hall↗
arXiv2006

Decay and fusion as two different mechanisms of stability loss for the (C_20)_2 cluster dimer

The thermal stability of the (C_20)_2 cluster dimer consisting of two C_20 fullerenes is examined using a tight-binding approach. Molecular dynamics simulations of the (C_20)_2 dimer at temperatures T = 2000 - 3500 K show that the finite lifetime τof this metastable system is determined by two fundamentally different processes, the decay of one of the C_20 fullerenes and the fusion of two C_20 fullerenes into the C_40 cluster. The activation energies for these processes Ea = 3.4 and 2.7 eV, respectively, as well as their frequency factors, have been determined by analyzing the dependence of τon T.

cond-mat.mes-hall↗
arXiv2006

Numerical simulation of the thermal fragmentation process in fullerene C60

The processes of defect formation and annealing in fullerene C60 at T=(4000-6000)K are studied by the molecular dynamics technique with a tight-binding potential. The cluster lifetime until fragmentation due to the loss of a C2 dimer has been calculated as a function of temperature. The activation energy and the frequency factor in the Arrhenius equation for the fragmentation rate have been found to be Ea = (9.2 +- 0.4) eV and A = (8 +- 1)10^{19} 1/s. It is shown that fragmentation can occur after the C60 cluster loses its spherical shape. This fact must be taken into account in theoretical calculations of Ea.

cond-mat.mes-hall↗
arXiv2005

Stone-Wales Transformation Paths in Fullerene C60

The mechanisms of formation of a metastable defect isomer of fullerene C60 due to the Stone-Wales transformation are theoretically studied. It is demonstrated that the paths of the "dynamic" Stone-Wales transformation at a high sufficient for overcoming potential barriers) temperature can differ from the two "adiabatic" transformation paths discussed in the literature. This behavior is due to the presence of a great near-flat segment of the potential-energy surface in the neighborhood of metastable states. Besides, the sequence of rupture and formation of interatomic bonds is other than that in the case of the adiabatictransformation.

cond-mat.other↗
arXiv2005

Anomalous Thermal Stability of Metastable C_20 Fullerene

The results of computer simulation of the dynamics of fullerene C_20 at different temperatures are presented. It is shown that, although it is metastable, this isomer is very stable with respect to the transition to a lower energy configuration and retains its chemical structure under heating to very high temperatures, T ~ 3000 K. Its decay activation energy is found to be E_a ~ 7 eV. Possible decay channels are studied, and the height of the minimum potential barrier to decay is determined to be U = 5.0 eV. The results obtained make it possible to understand the reasons for the anomalous stability of fullerene C_20 under normal conditions.

cond-mat.mes-hall↗
arXiv2005

Auxiliary-level-assisted operations with charge qubits in semiconductors

We present a new scheme for rotations of a charge qubit associated with a singly ionized pair of donor atoms in a semiconductor host. The logical states of such a qubit proposed recently by Hollenberg et al. are defined by the lowest two energy states of the remaining valence electron localized around one or another donor. We show that an electron located initially at one donor site can be transferred to another donor site via an auxiliary molecular level formed upon the hybridization of the excited states of two donors. The electron transfer is driven by a single resonant microwave pulse in the case that the energies of the lowest donor states coincide or two resonant pulses in the case that they differ from each other. Depending on the pulse parameters, various one-qubit operations, including the phase gate, the NOT gate, and the Hadamard gate, can be realized in short times. Decoherence of an electron due to the interaction with acoustic phonons is analyzed and shown to be weak enough for coherent qubit manipulation being possible, at least in the proof-of-principle experiments on one-qubit devices.

cond-mat.mes-hall↗
arXiv2004

Irradiation-induced suppression of the critical temperature in high-Tc superconductors: Pair breaking versus phase fluctuations

Experiments on the irradiation-induced suppression of the critical temperature in high-Tc superconductors are analyzed within the mean-field Abrikosov-Gor'kov-like approach. It is shown that the experimental data for YBa2Cu3O7 single crystals can be quantitatively explained by the pair breaking effects under the assumption of the combined effect of potential and spin-flip scattering on the critical temperature and with account for a non-pure d-wave superconducting order parameter.

cond-mat.supr-con↗
arXiv2004

Resonant-pulse operations on the buried donor charge qubits in semiconductors

A new scheme is proposed for rotations of a double-donor charge qubit whose logical states are defined by the two lowest energy states of a single electron localized around one or another donor. It is shown that making use of the microwave pulses tuned to the resonance with an auxiliary excited molecular level allows for implementation of various one-qubit operations in very short times. Decoherence effects are analyzed by the example of the P$_2^+$:Si system and shown to be weak enough for experimental realization of this scheme being possible.

cond-mat.mes-hall↗
arXiv2004

Selective electron transfer between the quantum dots under the resonant pulse

The coherent quantum dynamics of an electron in the quantum-dot ring structure under the resonant electromagnetic pulse is studied theoretically. A possibility of the selective electron transfer between any two dots is demonstrated. The transfer probability as a function of the pulse and dot parameters is calculated. It is shown that this probability can be close to unity. The factors lowering the transfer probability in real systems are discussed. The results obtained may be used in the engineering of novel nanoelectronic devices for quantum bits processing.

cond-mat.mes-hall↗
arXiv2004

Charge qubit rotations in a double-dot nanostructure

Quantum operations with a charge solid-state qubit whose logical states are formed by two spatially separated localized states of an electron in the double-dot structure are studied theoretically. We show that it is possible to perform various one-qubit rotations making use of the microwave pulses tuned to the resonances between the localized states and the excited state delocalized over the nanostructure. Explicit analytic expression for the time-dependent electron state vector is derived, and the appropriate pulse parameters are determined.

cond-mat.mes-hall↗
arXiv2004

Comment on "Influence of Pair Breaking and Phase Fluctuations on Disordered High Tc Cuprate Superconductors"

It is shown that an account for combined effect of both nonmagnetic and magnetic scatterers on Tc and/or an assumption about a non-pure d-wave order parameter allows for a quantitative explanation of the experimental data on the electron irradiation-induced suppression of superconductivity in Y-123 single crystals within the AG-like pair breaking theory, without resorting to phase fluctuations effects.

cond-mat.supr-con↗
arXiv2004

Comment on "Universal Decoherence in Solids"

We discuss the formula for the decoherence rate proposed by Eugene M. Chudnovsky [Phys. Rev. Lett. 92, 120405 (2004)]. We show that it has a limited range of validity and is not applicable to evaluation of the width of a low-energy optical mode considered by Chudnovsky as an example. This is due to unjustified use of the Fermi golden rule for calculation of the relaxation rate. We present more general expression for the probability of the phonon-induced transition.

cond-mat.dis-nn↗
arXiv2004

On the momentum-space approach to calculation of one-electron energy spectra and wave functions of atomic clusters

Momentum-space approach to calculation of one-electron energies and wave functions proposed initially by Fock for a hydrogen atom and considered later by Shibuya, Wulfman, and Koga for diatomic molecules is applied to clusters composed of three and more atoms. The corresponding basis set in the coordinate space is of the Sturmian type since all the hydrogenlike orbitals in this set have a common exponent, i.e., correspond to the same energy (as opposed to one-electron atomic orbitals). By the examples of He$_4^{+7}$ and He$_6^{+11}$ cluster ions it is shown that increase in the number of orbitals in the set results in rapid convergence of eigenenergies and eigenfunctions of highly excited states. The momentum-space approach to the one-electron many-center problem may be used for various solid-state and quantum-chemical applications.

quant-ph↗
arXiv2002

Metastable spin-polarized carbon clusters C_8 and their ensembles

Results of tight-binding calculations on metastable spin-polarized carbon clusters C_8 (prismanes) are presented. It is shown that those clusters can form ensembles due to intercluster bonding. The binding energy of a given metastable configuration decreases monotonously with the total spin S, while the activation energy for the decay of a metastable state has distinct maxima as a function of S. For specific values of S, the dynamical stability of spin-polarized ensembles of prismanes appears to be higher than that of an isolated prismane, pointing to a possibility of existence of "cluster matter" composed of spin-polarized clusters C_8

cond-mat.mes-hall↗
arXiv2002

Metastable quasi-one-dimensional ensembles of nitrogen clusters N_8

By means of ab initio and tight-binding calculations it is shown that metastable nitrogen clusters N_8 (boats) can form quasi-one-dimensional ensembles in which the nearest clusters N_8 are bound to each other by covalent bonds. Those ensembles are characterized by rather high energy barriers (~ 0.3 eV) that prevent the fission of the ensembles into isolated N_8 clusters and/or N_2 molecules.

cond-mat.mes-hall↗
arXiv2001

Localized electron state in a T-shaped confinement potential

We consider a simple model of an electron moving in a T-shaped confinement potential. This model allows for an analytical solution that explicitly demonstrates the existence of laterally bound electron states in quantum wires obtained by the cleaved edge overgrowth technique.

cond-mat.mes-hall↗
arXiv2001

Isotope Effect in the Presence of Magnetic and Nonmagnetic Impurities

The effect of impurities on the isotope coefficient is studied theoretically in the framework of Abrikosov-Gor'kov approach generalized to account for both potential and spin-flip scattering in anisotropic superconductors. An expression for the isotope coefficient as a function of the critical temperature is obtained for a superconductor with an arbitrary contribution of spin-flip processes to the total scattering rate and an arbitrary degree of anisotropy of the superconducting order parameter, ranging from isotropic s-wave to d-wave and including anisotropic s-wave and mixed (s+d)-wave as particular cases. It is found that both magnetic and nonmagnetic impurities enhance the isotope coefficient, the enhancement due to magnetic impurities being generally greater than that due to nonmagnetic impurities. From the analysis of the experimental results on La-Sr-Cu-M-O high temperature superconductor, it is concluded that the symmetry of the pairing state in this system differs from a pure d-wave.

cond-mat.supr-con↗