arXiv subjects

V. V. Flambaum

Publications and source records attributed to V. V. Flambaum.

At least 415 records · Page 23Linked to original sources

arXiv1999

Spin structure of impurity band of semiconductors in two and three-dimensional cases

The exchange interaction between electrons located at different randomly distributed impurities is studied for small density of impurities. The singlet-triplet splitting 2J(R) is calculated for two Coulomb centers at a distance R. Interpolated formulas are found which work for all distances R from zero to infinity. The data from atomic physics are used for the interpolation in three-dimensional case. For two-dimensional case the original calculations are performed to find asymptotic behavior of the splitting at large R, the splitting for the ``two-dimensional helium atom'' (R=0) and the splitting at $R=a_B$, where $a_B$ is the effective Bohr radius. The spin structure of impurity band is described by the Heisenberg Hamiltonian. The ground state of a system consists of localized singlets. The new results are obtained for the distribution of the singlet pairs in the ground state. These results are exact at low density. The problem is reduced to a non-trivial geometric problem which is solved in the mean field approximation and by computer modeling. The density of free electrons is found as a function of temperature and the distribution function of the singlet-triplet transitions energies is calculated. Both functions are given in an analytical form.

cond-mat.str-el↗

arXiv1999

Realistic model of correlated disorder and Anderson localization

A conducting 1D chain or 2D film inside (or on the surface of) an insulator is considered. Impurities displace the charges inside the insulator. This results in a long-range fluctuating electric field acting on the conducting line (plane). This field can be modeled by that of randomly distributed electric dipoles. This model provides a random correlated potential with \propto 1/k. In the 1D case such correlations may essentially influence the localization length but do not destroy Anderson localization.

cond-mat↗

arXiv1999

Quantum chaos in multicharged ions and statistical approach to the calculation of electron-ion resonant radiative recombination

We show that the spectrum and eigenstates of open-shell multicharged atomic ions near the ionization threshold are chaotic, as a result of extremely high level densities of multiply excited electron states ($10^3 eV^{-1}$ in Au^{24+}) and strong configuration mixing. This complexity enables one to use statistical methods to analyse the system. We examine the dependence of the orbital occupation numbers and single-particle energies on the excitation energy of the system, and show that the occupation numbers are described by the Fermi-Dirac distribution, and temperature and chemical potential can be introduced. The Fermi-Dirac temperature is close to the temperature defined through the canonical distribution. Using a statistical approach we estimate the contribution of multielectron resonant states to the radiative capture of low-energy electrons by Au^{25+} and demonstrate that this mechanism fully accounts for the 10^2 times enhancement of the recombination over the direct radiative recombination, in agreement with recent experimental observations.

physics.atom-ph↗

arXiv1999

Realistic model of correlated disorder and Anderson localization

A conducting 1D line or 2D plane inside (or on the surface of) an insulator is considered.Impurities displace the charges inside the insulator. This results in a long-range fluctuating electric field acting on the conducting line (plane). This field can be modeled by that of randomly distributed electric dipoles. This model provides a random correlated potential with decaying as 1/k . In the 1D case such correlations give essential corrections to the localization length but do not destroy Anderson localization.

cond-mat.dis-nn↗

arXiv1998

Excited Eigenstates and Strength Functions for Isolated Systems of Interacting Particles

Eigenstates in finite systems such as nuclei, atoms, atomic clusters and quantum dots with few excited particles are chaotic superpositions of shell model basis states. We study criterion for the equilibrium distribution of basis components (ergodicity, or Quantum Chaos), effects of level density variation and transition from the Breit-Wigner to the Gaussian shape of eigenstates and strength functions. In the model of $n$ interacting particles distributed over $m$ orbitals, the shape is given by the Breit-Wigner function with the width in the form of gaussian dependence on energy.

cond-mat.stat-mech↗

arXiv1998

Quantum Münchhausen effect in tunneling

It is demonstrated that radiative corrections increase tunneling probability of a charged particle.

nucl-th↗

arXiv1998

Enhancement factor for the electron electric dipole moment in francium and gold atoms

If electrons had an electric dipole moment (EDM) they would induce EDMs of atoms. The ratio of the atomic EDM to the electron EDM for a particular atom is called the enhancement factor, R. We calculate the enhancement factor for the francium and gold atoms, with the results 910 plus/minus 5% for Fr and 260 plus/minus 15% for Au. The large values of these enhancement factors make these atoms attractive for electron EDM measurements, and hence the search for time-reversal invariance violation.

physics.atom-ph↗

arXiv1998

Quantum chaos, statistical equilibrium and resonant radiative capture of electrons by multicharged ions: Au 24+

physics.atom-ph↗

arXiv1998

Calculations of the Relativistic Effects in Many-Electron Atoms and Space-Time Variation of Fundamental Constants

Theories unifying gravity and other interactions suggest the possibility of spatial and temporal variation of physical ``constants'' in the Universe. Detection of high-redshift absorption systems intersecting the sight lines towards distant quasars provide a powerful tool for measuring these variations. We have previously demonstrated that high sensitivity to the variation of the fine structure constant $α$ can be obtained by comparing spectra of heavy and light atoms (or molecules). Here we describe new calculations for a range of atoms and ions, most of which are commonly detected in quasar spectra: Fe II, Mg II, Mg I, C II, C IV, N~V, O I, Al III, Si II, Si IV, Ca I, Ca II, Cr II, Mn II, Zn II, Ge II (see the results in Table 3). The combination of Fe II and Mg II, for which accurate laboratory frequencies exist, have already been used to constrain $α$ variations. To use other atoms and ions, accurate laboratory values of frequencies of the strong E1-transitions from the ground states are required. We wish to draw the attention of atomic experimentalists to this important problem. We also discuss a mechanism which can lead to a greatly enhanced sensitivity for placing constraints on variation on fundamental constants. Calculations have been performed for Hg II, Yb II, Ca I and Sr II where there are optical transitions with the very small natural widths, and for hyperfine transition in Cs I and Hg II.

physics.atom-ph↗

arXiv1998

Dyons as a source of CP and time invariance violation: electric dipole moments and K-meson decays

We consider a mechanism by which dyons (electrically charged magnetic monopoles) can produce both a T- and P-odd (i.e. time reversal invariance and parity violating) mixed polarizability beta [defined by Delta E = -beta E.B, where Delta E is the energy change when electric (E) and magnetic (B) fields are applied to a system] and a T- and P-odd interaction between two particles: psi_1-bar gamma_5 psi_1 psi_2-bar psi_2, where the psi_i are electron and quark spinors. The latter can create atomic and neutron electric dipole moments (EDMs). From experimental bounds on these we find limits on the properties of dyons. Our best limit, using the experimental limit for the EDM of the Tl atom, is M |Q g (Q^2 - g^2)|^(-1/4) > 6 GeV, where M is the dyon mass and Q is the electric and g the magnetic charge of the dyons. The contribution of dyons to CP violation in K-meson decays is also estimated.

hep-ph↗

arXiv1998

Spin-spin interaction and magnetic state of 2-D Wigner crystal

It is demonstrated that there is anti-ferromagnetic spin-spin interaction between nearest electrons in the 2D Wigner crystal. This is also valid for the Wigner liquid - the state with destroyed long-range order but preserved short-range one. We calculate the value of the anti-ferromagnetic interaction (both analytically and numerically) and discuss a possible magnetic state of the Wigner crystal. This state can be strongly influenced by the spin-Peierls mechanism.

cond-mat.str-el↗

arXiv1998

Space-Time Variation of Physical Constants and Relativistic Corrections in Atoms

Detection of high-redshift absorption in the optical spectra of quasars have provided a powerful tool to measure spatial and temporal variations of physical ``constants'' in the Universe. It is demonstrated that high sensitivity to the variation of the fine structure constant alpha can be obtained from a comparison of the spectra of heavy and light atoms (or molecules). We have performed calculations for the pair FeII and MgII for which accurate quasar and laboratory spectra are available. A possibility of $10^5$ times enhanced effects of the fundamental constants variation suitable for laboratory measurements is also discussed.

physics.atom-ph↗

arXiv1998

Statistics of electromagnetic transitions as a signature of chaos in many-electron atoms

Using a configuration interaction approach we study statistics of the dipole matrix elements (E1 amplitudes) between the 14 lower odd states with J=4 and 21st to 100th even states with J=4 in the Ce atom (1120 lines). We show that the distribution of the matrix elements is close to Gaussian, although the width of the Gaussian distribution, i.e. the root-mean-square matrix element, changes with the excitation energy. The corresponding line strengths are distributed according to the Porter-Thomas law which describes statistics of transition strengths between chaotic states in compound nuclei. We also show how to use a statistical theory to calculate mean squared values of the matrix elements or transition amplitudes between chaotic many-body states. We draw some support for our conclusions from the analysis of the 228 experimental line strengths in Ce [J. Opt. Soc. Am. v. 8, p. 1545 (1991)], although direct comparison with the calculations is impeded by incompleteness of the experimental data. Nevertheless, the statistics observed evidence that highly excited many-electron states in atoms are indeed chaotic.

physics.atom-ph↗

arXiv1997

New Limits on the Possible Variation of Physical Constants

Recent detections of high-redshift absorption by both atomic hydrogen and molecular gas in the radio spectra of quasars have provided a powerful tool to measure possible temporal and spatial variations of physical `constants' in the Universe. We have compared the frequency of high-redshift Hydrogen 21 cm absorption with that of associated molecular absorption in two quasars to place new (1 sigma) upper limits on any variation in y = g_p.alpha^2 (where alpha is the fine structure constant and g_p is the proton g-factor) of |Delta(y)/y| < 5.10^{-6} at redshifts z=0.25 and z=0.68. These quasars are separated by a comoving distance of 3000 Mpc (H_0=75 km/s/Mpc and q_0=0). We also derive limits on the time rates of change of |(d.g_p/d.t)/g_p| < 10^{-15}/y and |(d.alpha/d.t)/α| < 5.10^{-16}/y between the present epoch and z=0.68. These limits are more than an order of magnitude smaller than previous results derived from high-redshift measurements.

astro-ph↗

arXiv1997

Interaction-Driven Equilibrium and Statistical Laws in Small Systems. The Cerium Atom

It is shown that statistical mechanics is applicable to isolated quantum systems with finite numbers of particles, such as complex atoms, atomic clusters, or quantum dots in solids, where the residual two-body interaction is sufficiently strong. This interaction mixes the unperturbed shell-model (Hartree-Fock) basis states and produces chaotic many-body eigenstates. As a result, an interaction-induced statistical equilibrium emerges in the system. This equilibrium is due to the off-diagonal matrix elements of the Hamiltonian. We show that it can be described by means of temperature introduced through the canonical-type distribution. However, the interaction between the particles can lead to prominent deviations of the equilibrium distribution of the occupation numbers from the Fermi-Dirac shape. Besides that, the off-diagonal part of the Hamiltonian gives rise to the increase of the effective temperature of the system (statistical effect of the interaction). For example, this takes place in the cerium atom which has four valence electrons and which is used in our work to compare the theory with realistic numerical calculations.

cond-mat.stat-mech↗

arXiv1997

Can We Apply Statistical Laws to Small Systems? the Cerium Atom

It is shown that statistical mechanics is applicable to quantum systems with finite numbers of particles, such as complex atoms, atomic clusters, etc., where the residual two-body interaction is sufficiently strong. This interaction mixes the unperturbed shell-model basis states and produces ``chaotic'' many-body eigenstates. As a result, an interaction-induced equilibrium emerges in the system, and temperature can be introduced. However, the interaction between the particles and their finite number can lead to prominent deviations of the equilibrium occupation numbers distribution from the Fermi-Dirac shape. For example, this takes place in the cerium atom with four valence electrons, which was used to compare the theory with realistic numerical calculations.

cond-mat.stat-mech↗

arXiv1997

Limits on the Variability of Physical Constants

We have compared the frequency of high-redshift Hydrogen HI 21 cm absorption with that of associated molecular absorption in two quasars to place new (1 sigma) upper limits on any variation in y = g_p.alpha^2 (where alpha is the fine structure constant and g_p is the proton g-factor) of |Delta(y)/y| < 5.10^{-6} at redshifts z=0.25 and z=0.68.

astro-ph↗

arXiv1997

Polarizabilities and parity non-conservation in the Cs atom and limits on the deviation from the standard electroweak model

A semi-empirical calculation of the 6s - 7s Stark amplitude $α$ in Cs has been performed using the most accurate measurements and calculations of the electromagnetic amplitudes available. This is then used to extract the parameters of the electroweak theory from experimental data. The results are: $α= 269.0 (1.3) a_0^3$, weak charge of Cs $Q_W = -72.41(25)_{exp} (80)_{theor}$, deviation from the Standard model $S = -1.0(.3)_{exp} (1.0)_{theor}$ and limit on the mass of the extra Z-boson in SO(10) model $M_{Z_x} > 550 GeV$.

hep-ph↗