520 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
Metal-insulator transition and glassy behavior in two-dimensional electron systems
Studies of low-frequency resistance noise demonstrate that glassy freezing
occurs in a two-dimensional electron system in silicon in the vicinity of the
metal-insulator transition (MIT). The width of the metallic glass phase, which
separates the 2D metal and the (glassy) insulator, depends strongly on
disorder, becoming extremely small in high-mobility (low-disorder) samples. The
glass transition is manifested by a sudden and dramatic slowing down of the
electron dynamics, and by a very abrupt change to the sort of statistics
characteristic of complicated multistate systems. In particular, the behavior
of the second spectrum, an important fourth-order noise statistic, indicates
the presence of long-range correlations between fluctuators in the glassy
phase, consistent with the hierarchical picture of glassy dynamics.Comment: Contribution to conference on "Noise as a tool for studying
materials" (SPIE), Santa Fe, New Mexico, June 2003; 15 pages, 12 figs.
(includes some low-quality figs; send e-mail to get high-quality figs.
Transition frequency shifts with fine-structure constant variation for Yb II
In this paper we report calculations of the relativistic corrections to
transition frequencies (q factors) of Yb II for the transitions from the
odd-parity states to the metastable state 4f^{13}6s^2 ^2F_{7/2}^o. These
transitions are of particular interest experimentally since they possess some
of the largest q factors calculated to date and the state can be
prepared with high efficiency. This makes Yb II a very attractive candidate for
the laboratory search for variation of the fine-structure constant alpha.Comment: 5 page
Magnetotransport in the low carrier density ferromagnet EuB_6
We present a magnetotransport study of the low--carrier density ferromagnet
EuB_6. This semimetallic compound, which undergoes two ferromagnetic
transitions at T_l = 15.3 K and T_c = 12.5 K, exhibits close to T_l a colossal
magnetoresistivity (CMR). We quantitatively compare our data to recent
theoretical work, which however fails to explain our observations. We attribute
this disagreement with theory to the unique type of magnetic polaron formation
in EuB_6.Comment: Conference contribution MMM'99, San Jos
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
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
On the issue of assessing the safety of adjunction on roads
The principal aim of this article is to meticulously investigate and enhance the standards of highway safety and the accompanying infrastructural elements. The article scrutinizes data pertaining to vehicular mishaps over the preceding years, pinpointing crucial elements that precipitate the incidents. Among these contributing factors are the condition of the paved roadway, the clarity of view, the magnitude of vehicular flow, illumination, amongst others. The authors devote considerable attention to the utilization of engineering management strategies, alongside risk management systems, to bolster the safety measures on highways. The discourse proposes the implementation of fuzzy logic allied with the FisPro system, as means to dissect and prognosticate traffic scenarios. The employment of these methodologies enables the consideration of the intricate and multidimensional nature of the issue of highway safety, taking into account the myriad of intertwined parameters. The article underscores the necessity for a holistic approach to effectively amplify the safety standards of highways, encompassing all factors that exert influence on the prevailing traffic conditions. Such a comprehensive methodology permits not merely the response to budding issues, but also the anticipation of potential risks, consequently enabling the timely implementation of preventative measures to avert them
The atomic electric dipole moment induced by the nuclear electric dipole moment; the magnetic moment effect
We have considered a mechanism for inducing a time-reversal violating
electric dipole moment (EDM) in atoms through the interaction of a nuclear EDM
(d_N) with the hyperfine interaction, the "magnetic moment effect". We have
derived the operator for this interaction and presented analytical formulas for
the matrix elements between atomic states. Induced EDMs in the diamagnetic
atoms 129Xe, 171Yb, 199Hg, 211Rn, and 225Ra have been calculated numerically.
From the experimental limits on the atomic EDMs of 129Xe and 199Hg, we have
placed the following constraints on the nuclear EDMs, |d_N(129Xe)|< 1.1 *
10^{-21} |e|cm and |d_N(199Hg)|< 2.8 * 10^{-24} |e|cm.Comment: 8 pages 1) Some typos are corrected. 2) A comparison of contributions
to the atomic EDM due to the nuclear EDM and the nuclear Schiff moment is
adde
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.
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
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