arXiv subjects

O. P. Sushkov

Publications and source records attributed to O. P. Sushkov.

At least 73 records · Page 4Linked to original sources

arXiv2004

Bose-Einstein condensation of magnons in TlCuCl$_3$

A quantitative study of the field-induced magnetic ordering in TlCuCl$_3$ in terms of a Bose-Einstein condensation (BEC) of magnons is presented. It is shown that the hitherto proposed simple BEC scenario is in quantitative and qualitative disagreement with experiment. It is further shown that even very small Dzyaloshinsky-Moriya interactions or a staggered $g$ tensor component of a certain type can change the BEC picture qualitatively. Such terms lead to a nonzero condensate density for all temperatures and a gapped quasiparticle spectrum. Including this type of interaction allows us to obtain good agreement with experimental data.

cond-mat.str-el↗

arXiv2004

Manifestations of nuclear anapole moments in solid state NMR

We suggest to use insulating garnets doped by rare earth ions for measurements of nuclear anapole moments. A parity violating shift of the NMR frequency arises due to the combined effect of the lattice crystal field and the anapole moment of the rare-earth nucleus. We show that there are two different observable effects related to frequency: 1) A shift of the NMR frequency in an external electric field applied to the solid. The value of the shift is about Δν_1 ~ 10^{-5} Hz with E = 10 kV/cm; 2) A splitting of the NMR line into two lines. The second effect is independent of the external electric field. The value of the splitting is about Δν_2 ~ 0.5 Hz and it depends on the orientation of the crystal with respect to magnetic field. Both estimates are presented for a magnetic field of about 10 tesla. We also discuss a radiofrequency electric field and a static macroscopic magnetization caused by the nuclear anapole moment.

physics.atom-ph↗

arXiv2003

Finite nuclear size effect on Lamb shift of s1/2, p1/2, and p3/2 atomic states

We consider one-loop self-energy and vacuum polarization radiative corrections to the shift of atomic energy level due to finite nuclear size. Analytic expressions for vacuum polarization corrections are derived. For the self-energy of p1/2 and p3/2 states in addition to already known terms we derive next-to-leading nonlogarithmic Zα-terms. Together with contributions obtained earlier the terms derived in the present work give explicit analytic expressions for s1/2 and p1/2 corrections which agree with results of previous numerical calculations up to Z=100 (Z is the nuclear charge number). We also show that the finite nuclear size radiative correction for a p3/2 state is not small compared to the similar correction for a p1/2 state at least for small Z.

physics.atom-ph↗

arXiv2003

Planar Cu and O hole densities in high-Tc cuprates determined with NMR

The electric hyperfine interaction observable in atomic spectroscopy for O and Cu ions in various configurations is used to analyze the quadrupole splitting of O and Cu nuclear magnetic resonance (NMR) in La2-xSrxCuO4 and YBa2Cu3O6+y and to determine the hole densities at both sites as a function of doping. It is found that in La2-xSrxCuO4 all doped holes (x) reside in the Cu-O plane but almost exclusively at O. For YBa2Cu3O6+y and y<0.6 doped holes are found at planar Cu as well as O. For y>0.6 further doping increases the hole content only for planar O. The phase diagram based on NMR data is presented. Further implications from the Cu A and B site in La2-xSrxCuO4 and the two planar O sites in YBa2Cu3O6+y and consequences for the phase diagram are discussed.

cond-mat.supr-con↗

arXiv2003

A closer look at symmetry breaking in the collinear phase of the $J_1-J_2$ Heisenberg Model

The large $J_2$ limit of the square-lattice $J_1-J_2$ Heisenberg antiferromagnet is a classic example of order by disorder where quantum fluctuations select a collinear ground state. Here, we use series expansion methods and a meanfield spin-wave theory to study the excitation spectra in this phase and look for a finite temperature Ising-like transition, corresponding to a broken symmetry of the square-lattice, as first proposed by Chandra et al. (Phys. Rev. Lett. 64, 88 (1990)). We find that the spectra reveal the symmetries of the ordered phase. However, we do not find any evidence for a finite temperature phase transition. Based on an effective field theory we argue that the Ising-like transition occurs only at zero temperature.

cond-mat.str-el↗

arXiv2003

Long Range Dynamics Related to Magnetic Impurity in the 2D Heisenberg Antiferromagnet

We consider a magnetic impurity in the two-dimensional Heisenberg antifferomagnet with long range antiferromagnetic order. At low temperature the impurity magnetic susceptibility has a Curie term ($\propto 1/T$) and a logarithmic correction ($\propto \ln(T)$). We calculate the correction and derive related Ward identity for the impurity-spin-wave vertex.

cond-mat.str-el↗

arXiv2003

Enhancement of the electron electric dipole moment in gadolinium garnets

Effects caused by the electron electric dipole moment (EDM) in gadolinium garnets are considered. Experimental studies of these effects could improve current upper limit on the electron EDM by several orders of magnitude. We suggest a consistent theoretical model and perform calculations of observable effects in gadolinium gallium garnet and gadolinium iron garnet. Our calculation accounts for both direct and exchange diagrams.

cond-mat↗

arXiv2002

Calculation of radiative corrections to the effect of parity nonconservation in heavy atoms

We calculate the self-energy and the vertex radiative corrections to the effect of parity nonconservation in heavy atoms. The sum of the corrections is of the form ${\cal A}\ln(λ_C/r_0)+{\calB}$, where ${\cal A}$ and ${\cal B}$ are functions of $Zα$, and $λ_C$ and $r_0$ are the Compton wavelength and the nuclear radius, respectively. The function ${\cal A}$ is calculated exactly in $Zα$ and the function ${\cal B}$ is calculated in the leading order. In the leading order ${\cal A}\propto α(Zα)^2$ and ${\cal B}\propto α(Zα)$. The sum of the corrections is -0.85% for Cs and -1.48% for Tl. Using these results we have performed analysis of the experimental data on atomic parity nonconservation. The values obtained for the nuclear weak charge, $Q_W=-72.81(28)_{exp}(36)_{theor}$ for Cs and $Q_W=-116.8(1.2)_{exp}(3.4)_{theor}$ for Tl, agree with predictions of the standard model within $0.6σ$. As an application of our approach we have also calculated dependence of the Lamb shift on the finite nuclear size.

hep-ph↗

arXiv2002

Finite nuclear size and Lamb shift of p-wave atomic states

We consider corrections to the Lamb shift of p-wave atomic states due to the finite nuclear size (FNS). In other words, these are radiative corrections to the atomic isotop shift related to FNS. It is shown that the structure of the corrections is qualitatively different from that for s-wave states. The perturbation theory expansion for the relative correction for a $p_{1/2}$-state starts from $α\ln(1/Zα)$-term, while for $s_{1/2}$-states it starts from $Zα^2$ term. Here $α$ is the fine structure constant and $Z$ is the nuclear charge. In the present work we calculate the $α$-terms for $2p$-states, the result for $2p_{1/2}$-state reads $(8α/9π)[\ln(1/(Zα)^2)+0.710]$. Even more interesting are $p_{3/2}$-states. In this case the ``correction'' is by several orders of magnitude larger than the ``leading'' FNS shift.

physics.atom-ph↗

arXiv2002

Restricted and unrestricted Hartree-Fock calculations of conductance for a quantum point contact

Very short quantum wires (quantum contacts) exhibit a conductance structure at a value of conductance close to $0.7 \times 2e^2/h$. It is believed that the structure arises due to the electron-electron interaction, and it is also related to electron spin. However details of the mechanism of the structure are not quite clear. Previously we approached the problem within the restricted Hartree-Fock approximation. This calculation demonstrated a structure similar to that observed experimentally. In the present work we perform restricted and unrestricted Hartree-Fock calculations to analyze the validity of the approximations. We also consider dependence of the effect on the electron density in leads. The unrestricted Hartree-Fock method allows us to analyze trapping of the single electron within the contact. Such trapping would result in the Kondo model for the ``0.7 structure''. The present calculation confirms the spin-dependent bound state picture and does not confirm the Kondo model scenario.

cond-mat.mes-hall↗

arXiv2002

Radiative corrections and parity nonconservation in heavy atoms

The self-energy and the vertex radiative corrections to the effect of parity nonconservation in heavy atoms are calculated analytically in orders Z alpha^2 and Z^2 alpha^3 ln(lambda_C/r_0), where lambda_C and r_0 being the Compton wavelength and the nuclear radius, respectively. The value of the radiative correction is -0.85% for Cs and -1.41% for Tl. Using these results we have performed analysis of the experimental data on atomic parity nonconservation. The obtained values of the nuclear weak charge, Q_W=-72.90(28)_{exp}(35)_{theor} for Cs, and Q_W=-116.7(1.2)_{exp}(3.4)_{theor} for Tl, agree with predictions of the standard model. As an application of our approach we have also calculated analytically dependence of the Lamb shift on the finite nuclear size.

hep-ph↗

arXiv2002

Energy levels and lifetimes of Gd IV and enhancement of the electron dipole moment

We have calculated energy levels and lifetimes of 4f7 and 4f6 5d configurations of Gd IV using Hartree-Fock and configuration interaction methods. This allows us to reduce significantly the uncertainty of the theoretical determination of the electron electric dipole moment (EDM) enhancement factor in this ion and, correspondingly, in gadolinium-containing garnets for which such measurements were recently proposed. Our new value for the EDM enhancement factor of Gd+3 is -2.2 +- 0.5. Calculations of energy levels and lifetimes for Eu~III are used to control the accuracy.

physics.atom-ph↗

arXiv2002

Searches for violation of fundamental time reversal and space reflection symmetries in solid state experiments

The electric dipole moment (EDM) of a particle violates both time reversal (T) and space reflection (P) symmetries. There have been recent suggestions for searches of the electron EDM using solid state experiments [1,2]. These experiments could improve the sensitivity compared to present atomic and molecular experiments by several orders of magnitude. In the present paper we calculate the expected effect. We also suggest that this kind of experiment is sensitive to T,P-violation in nuclear forces and calculate effects caused by the nuclear Schiff moment. The compounds under consideration contain magnetic Gd$^{3+}$ ions and oxygen O$^{2-}$ ions. We demonstrate that the main mechanism for the T,P-odd effects is related to the penetration of the Oxygen 2p-electrons to the Gd core. All the effects are related to the deformation of the crystal lattice.

cond-mat.str-el↗

arXiv2002

Enhancement of the electron electric dipole moment in gadolinium 3+

There have been recent suggestions for searching for the electron electric dipole moment, using solid state experiments with compounds containing Gd 3+ ions. These experiments could improve the sensitivity compared to present atomic and molecular experiments by several orders of magnitude. The analysis of the problem requires a calculation of the enhancement coefficient K for the electron electric dipole moment in the Gd 3+ ion. In this work we perform this calculation. The result is K = -4.9 +- 1.6. Limitations of the accuracy of the calculation are mainly due to the lack of data on Gd 3+ excitation spectra. We formulate which quantities have to be measured and/or calculated to improve the accuracy.

physics.atom-ph↗

arXiv2001

Critical dynamics of singlet and triplet excitations in strongly frustrated spin systems

New data for the two-dimensional J1-J2 model shows that the critical points for singlet and triplet excitations near J2/J1=0.38 are very close together, or coincident. We propose that this is a more general result: in strongly frustrated spin systems the critical dynamics of singlet and triplet excitations are closely related. An effective field theory for such a critical point, or points, is developed, and its implications discussed. The analysis suggests the existance of gapless or almost gapless singlet excitations in the magnetically disordered phase.

cond-mat.str-el↗

arXiv2001

Parity nonconservation in heavy atoms: The radiative correction enhanced by the strong electric field of the nucleus

Parity nonconservation due to the nuclear weak charge is considered. We demonstrate that the radiative corrections to this effect due to the vacuum fluctuations of the characteristic size larger than the nuclear radius $r_0$ and smaller than the electron Compton wave-length $λ_C$ are enhanced because of the strong electric field of the nucleus. The parameter that allows one to classify the corrections is the large logarithm $\ln(λ_C/r_0)$. The vacuum polarization contribution is enhanced by the second power of the logarithm. Although the self-energy and the vertex corrections do not vanish, they contain only the first power of the logarithm. The value of the radiative correction is 0.4% for Cs and 0.9% for Tl, Pb, and Bi. We discuss also how the correction affects the interpretation of the experimental data on parity nonconservation in atoms.

hep-ph↗

arXiv2001

Conductance structure in a one-dimensional quantum contact: dependence on the longitudinal magnetic field

Very short quantum wires (quantum contacts) exhibit a conductance structure at the value of conductance close to 0.7 x 2e^2/h. The structure was discovered by Thomas et al (Phys. Rev. Lett. {\bf 77}, 135 (1996)). Dependence of the structure on the longitudinal magnetic field was studied in the same experiment. This dependence has clearly demonstrated that the effect is related to the electron spin. In the recent work (Sushkov, Phys. Rev. B {\bf 64}, (2001)) it was suggested that the effect is caused by the development of the charge density wave within the contact. The many-body Hartree-Fock calculation has confirmed the picture. The exchange electron-electron interaction is crucial for this calculation, so in agreement with experiment the effect is intrinsically related to the spin. However the dependence on the magnetic field has not been calculated yet. In the present paper the many-body Hartree-Fock calculation of conductance in the presence of the longitudinal magnetic field is performed.

cond-mat.mes-hall↗

arXiv2001

Two-dimensional randomly-frustrated spin 1/2 Heisenberg model

We investigate the properties of S=1/2 Heisenberg clusters with random frustration using exact diagonalizations. This is a model for a quantum spin glass. We show that the average ground state spin is $S \propto \sqrt{N}$, where N is the number of sites. We also calculate the magnetic susceptibility and the spin stiffness and low-energy excitations, and discuss these in terms of a semiclassical picture.

cond-mat.str-el↗