345 research outputs found
Study of the correlation effects in Yb^+ and implications for parity violation
Calculation of the energies, magnetic dipole hyperfine structure constants,
E1 transition amplitudes between the low-lying states, and nuclear
spin-dependent parity-nonconserving amplitudes for the ^2S_{1/2} -
^2D_{3/2,5/2} transitions in ^{171}Yb^+ ion is performed using two different
approaches. First, we carried out many-body perturbation theory calculation
considering Yb^+ as a monovalent system. Additional all-order calculations are
carried out for selected properties. Second, we carried out configuration
interaction calculation considering Yb as a 15-electron system and compared the
results obtained by two methods. The accuracy of different methods is
evaluated. We find that the monovalent description is inadequate for evaluation
of some atomic properties due to significant mixing of the one-particle and the
hole-two-particle configurations. Performing the calculation by such different
approaches allowed us to establish the importance of various correlation
effects for Yb^+ atomic properties for future improvement of theoretical
precision in this complicated system.Comment: 11 pages;v2: minor changes and one reference adde
Electric dipole moment enhancement factor of thallium
The goal of this work is to resolve the present controversy in the value of
the EDM enhancement factor of Tl. We have carried out several calculations by
different high-precision methods, studied previously omitted corrections, as
well as tested our methodology on other parity conserving quantities. We find
the EDM enhancement factor of Tl to be equal to -573(20). This value is 20%
larger than the recently published result of Nataraj et al. [Phys. Rev. Lett.
106, 200403 (2011)], but agrees very well with several earlier results.Comment: 5 pages; v2: link to supplemental material adde
Mobility-Dependence of the Critical Density in Two-Dimensional Systems: An Empirical Relation
For five different electron and hole systems in two dimensions (Si MOSFET's,
p-GaAs, p-SiGe, n-GaAs and n-AlAs), the critical density, that marks the
onset of strong localization is shown to be a single power-law function of the
scattering rate deduced from the maximum mobility. The resulting curve
defines the boundary separating a localized phase from a phase that exhibits
metallic behavior. The critical density in the limit of infinite
mobility.Comment: 2 pages, 1 figur
Calculation of P,T-odd electric dipole moments for diamagnetic atoms Xe, Yb, Hg, Rn, and Ra
Electric dipole moments of diamagnetic atoms of experimental interest are
calculated using the relativistic Hartree-Fock and random-phase approximation
methods, the many-body perturbation theory and configuration interaction
technique. We consider P,T-odd interactions which give rise to atomic electric
dipole moment in the second order of the perturbation theory. These include
nuclear Schiff moment, P,T-odd electron-nucleon interaction and electron
electric dipole moment. Interpretation of a new experimental constraint of a
permanent electric dipole moment of Hg [W. C. Griffith {\it et al.},
Phys. Rev. Lett. {\bf 102}, 101601 (2009)] is discussed.Comment: 9 page
Transition frequency shifts with fine structure constant variation for Fe II: Breit and core-valence correlation correction
Transition frequencies of Fe II ion are known to be very sensitive to
variation of the fine structure constant \alpha. The resonance absorption lines
of Fe II from objects at cosmological distances are used in a search for the
possible variation of \alpha in cause of cosmic time. In this paper we
calculated the dependence of the transition frequencies on \alpha^2 (q-factors)
for Fe II ion. We found corrections to these coefficients from valence-valence
and core-valence correlations and from the Breit interaction. Both the
core-valence correlation and Breit corrections to the q-factors appeared to be
larger than had been anticipated previously. Nevertheless our calculation
confirms that the Fe II absorption lines seen in quasar spectra have large
q-factors of both signs and thus the ion Fe II alone can be used in the search
for the \alpha-variation at different cosmological epochs.Comment: 7 pages, submitted to Phys. Rev.
Melting transition of an Ising glass driven by magnetic field
The quantum critical behavior of the Ising glass in a magnetic field is
investigated. We focus on the spin glass to paramagnet transition of the
transverse degrees of freedom in the presence of finite longitudinal field. We
use two complementary techniques, the Landau theory close to the T=0 transition
and the exact diagonalization method for finite systems. This allows us to
estimate the size of the critical region and characterize various crossover
regimes. An unexpectedly small energy scale on the disordered side of the
critical line is found, and its possible relevance to experiments on metallic
glasses is briefly discussed.Comment: 4 pages, 3 figure
Calculation of nuclear spin-dependent parity-nonconserving amplitude for (7s,F=4) --> (7s,F=5) transition in Fr
Many-body calculation of nuclear spin-dependent parity-nonconserving
amplitude for (7s,F=4) --> (7s,F=5) transition between hyperfine sublevels of
the ground state of Fr is carried out. The final result is <7s,F=5
||d_PNC|| 7s,F=4> = -0.49 10^{-10} i kappa a.u., where kappa is the
dimensionless coupling constant. This is approximately an order of magnitude
larger than similar amplitude in Cs. The dominant contribution to kappa is
associated with the anapole moment of the nucleus.Comment: 4 pages, submitted to Phys.Rev.
The metal-insulator transition in Si:X: Anomalous response to a magnetic field
The zero-temperature magnetoconductivity of just-metallic Si:P scales with
magnetic field, H, and dopant concentration, n, lying on a single universal
curve. We note that Si:P, Si:B, and Si:As all have unusually large magnetic
field crossover exponents near 2, and suggest that this anomalously weak
response to a magnetic field is a common feature of uncompensated doped
semiconductors.Comment: 4 pages (including figures
Hopping Conduction in Uniaxially Stressed Si:B near the Insulator-Metal Transition
Using uniaxial stress to tune the critical density near that of the sample,
we have studied in detail the low-temperature conductivity of p-type Si:B in
the insulating phase very near the metal-insulator transition. For all values
of temperature and stress, the conductivity collapses onto a single universal
scaling curve. For large values of the argument, the scaling function is well
fit by the exponentially activated form associated with variable range hopping
when electron-electron interactions cause a soft Coulomb gap in the density of
states at the Fermi energy. The temperature dependence of the prefactor,
corresponding to the T-dependence of the critical curve, has been determined
reliably for this system, and is proportional to the square-root of T. We show
explicitly that nevlecting the prefactor leads to substantial errors in the
determination of the scaling parameters and the critical exponents derived from
them. The conductivity is not consistent with Mott variable-range hopping in
the critical region nor does it obey this form for any range of the parameters.
Instead, for smaller argument of the scaling function, the conductivity of Si:B
is well fit by an exponential form with exponent 0.31 related to the critical
exponents of the system at the metal- insulator transition.Comment: 13 pages, 6 figure
Conductivity of Metallic Si:B near the Metal-Insulator Transition: Comparison between Unstressed and Uniaxially Stressed Samples
The low-temperature dc conductivities of barely metallic samples of p-type
Si:B are compared for a series of samples with different dopant concentrations,
n, in the absence of stress (cubic symmetry), and for a single sample driven
from the metallic into the insulating phase by uniaxial compression, S. For all
values of temperature and stress, the conductivity of the stressed sample
collapses onto a single universal scaling curve. The scaling fit indicates that
the conductivity of si:B is proportional to the square-root of T in the
critical range. Our data yield a critical conductivity exponent of 1.6,
considerably larger than the value reported in earlier experiments where the
transition was crossed by varying the dopant concentration. The larger exponent
is based on data in a narrow range of stress near the critical value within
which scaling holds. We show explicitly that the temperature dependences of the
conductivity of stressed and unstressed Si:B are different, suggesting that a
direct comparison of the critical behavior and critical exponents for stress-
tuned and concentration-tuned transitions may not be warranted
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