Papers by Sergei Sergeenkov
This Chapter reviews some of the recently suggested novel effects which are expected to occur in ... more This Chapter reviews some of the recently suggested novel effects which are expected to occur in intrinsically granular non-stoichiometric material modeled by 2D JJAs which are created by a regular 2D network of twin-boundary (TB) dislocations with strain fields acting as an insulating barrier between hole-rich domains in underdoped crystals. In Section 2 we consider phase-related magnetization effects, including Josephson chemomagnetism (chemically induced magnetic moment in zero applied magnetic field) and its influence on a low-field magnetization (chemically induced PME), and magnetoconcentration effect (creation of extra oxygen vacancies in applied magnetic field) and its influence on a high-field magnetization (chemically induced analog of "fishtail" anomaly). Section 3 addresses charge-related phenomena which are actually dual to the chemomagnetic effects described in Section 2. More specifically, we discuss a possible existence of a non-zero electric polarization (...
We consider the response of a granular superconductor described by a random three-dimensional Jos... more We consider the response of a granular superconductor described by a random three-dimensional Josephson junction array model in the presence of a constant electric field E. The electric field couples to the phase of the superconducting grains and it induces the appearance of an electric field dependent magnetization M (E). This superconducting magneto-electric effect (MEE) is linear for small fields reaching a maximum at a characteristic field and then it decays for larger fields. A rough estimate indicates that this superconducting MEE is about three orders of magnitude smaller than the normal MEE but it may still be measurable in known high-Tc superconductors.
Despite the fact that Josephson Junction Arrays (JAA) have been actively studied for decades, the... more Despite the fact that Josephson Junction Arrays (JAA) have been actively studied for decades, they continue to contribute to the variety of intriguing and peculiar phenomena (both fundamental and important for potential applications) providing at the same time a useful tool for testing new theoretical ideas. To give just a few recent examples, it is sufficient to mention paramagnetic Meissner effect (PME) as well as the recently introduced thermophase and piezophase effects suggesting, respectively, a direct influence of a thermal gradient and an applied stress on phase difference between the adjacent grains. At the same time, an artificially prepared islands of superconducting grains, well-described by the various models of JJAs, proved useful in studying the charging effects in these systems, ranging from Coulomb blockade of Cooper pair tunneling and Bloch oscillations to propagation of quantum ballistic vortices. The present paper reviews some of the recently suggested novel effects which should manifest themselves either in weak-links-bearing superconductors or in artificially prepared JJAs. In Section 2 we consider the appearance of an electric-field induced magnetization (analog of the so-called magnetoelectric effect) in a model granular superconductor. The dual effect, that is an appearance of a magnetic field induced electric polarization is studied in Section 3. Finally, in Section 4 we discuss a possibility of two other interesting effects which are expected to occur in a granular material under mechanical loading. Specifically, we predict the existence of stress induced paramagnetic moment in zero applied magnetic field (Josephson piezomagnetism) and study its influence on a low-field magnetization (leading to a mechanically induced PME).
J Appl Phys, 2007
Some possible connection between spin and charge degrees of freedom in magnetoresistive manganite... more Some possible connection between spin and charge degrees of freedom in magnetoresistive manganites is investigated through a thorough experimental study of the magnetic [alternating current susceptibility and direct current (dc) magnetization] and transport (resistivity and thermal conductivity) properties. Measurements are reported in the case of well characterized polycrystalline La0.8Sr0.2MnO3 samples. The experimental results suggest rather strong field-induced polarization effects in our material, clearly indicating the presence of ordered ferromagnetic regions inside the semiconducting phase. Using an analytical expression which fits the spontaneous dc magnetization, the temperature and magnetic field dependences of both electrical resistivity and thermal conductivity data are found to be well reproduced through a universal scenario based on two mechanisms: (i) a magnetization dependent spin polaron hopping influenced by a Zeeman splitting effect and (ii) properly defined thermally excited polaron states which have to be taken into account in order to correctly describe the behavior of the less conducting region. Using the experimentally found values of the magnetic and electron localization temperatures, we obtain L =0.5 nm and mp=3.2me for estimates of the localization length (size of the spin polaron) and effective polaron mass, respectively.
Scaling behaviour of the relaxation function in a proton glass model
Ferroelectrics Lett Sect, 1988
Eur Phys J B, 1996
A method, using a Corbino disk sample geometry, is described and applied to study of resistive ta... more A method, using a Corbino disk sample geometry, is described and applied to study of resistive tails of sintered $YBCO$. When the transport current passes radially from the rim of the disk sample to its center, the two component potential drop signal is detected below $T_c$, which is due to (i) quasiparticles $W_q$ and (ii) vortex-core-motion related contribution $W_{\phi }$. When the contact pairs for $W$ are placed radially, $W_q(r)$ and $W_{\phi }(r)$ are found to follow the markedly distinctive functional dependences, providing a unique possibility to deconvolute the relative strengths of both contributions. The results obtained suggest that the mixed state dissipation of high-$T_c$ superconductors is strongly influenced by the quasiparticle excitations.
Solid State Communications, 1993
The behavior of the thermal conductivity ~; of twinned YBa2Cu307_ x and tweeded YBa2(Cu0.95Fe0.05... more The behavior of the thermal conductivity ~; of twinned YBa2Cu307_ x and tweeded YBa2(Cu0.95Fe0.05)307_x polycrystals in a magnetic field up to 5 T is presented. Data as a function of field are shown to depart from the usual linear behavior of thermal magnetoresistivity (TMR) n-l(B) for conventional superconductors. A set of stretched exponential laws, of the form n-l (B) -~;-I(0) = CBexp(-pB q) has been found to describe our data with q decreasing with temperature from 1 to 1 and from ~ to ¼ for pure and iron-doped samples, respectively/in contrast to'the unique interpolation formula (q = ¼) for TMR proposed recently by Richardson et al.
Eprint Arxiv Cond Mat 0509057, Sep 2, 2005
This paper reviews some of the recently suggested (by the author) novel effects expected to occur... more This paper reviews some of the recently suggested (by the author) novel effects expected to occur in intrinsically granular non-stoichiometric material modeled by 2D Josephson junction arrays which are created by a regular 2D network of twin-boundary dislocations with strain fields acting as an insulating barrier between hole-rich domains in underdoped crystals. In Section 2 we consider phase-related magnetization effects, including Josephson chemomagnetism (chemically induced magnetic moment in zero applied magnetic field) and its influence on a low-field magnetization (chemically induced PME), and magnetoconcentration effect (creation of extra oxygen vacancies in applied magnetic field) and its influence on a high-field magnetization (chemically induced analog of "fishtail" anomaly). Section 3 addresses charge-related phenomena which are actually dual to the chemomagnetic effects described in Section 2. More specifically, we discuss a possible existence of a non-zero electric polarization (chemomagnetoelectic effect) and the related change of the charge balance in intrinsically granular non-stoichiometric material under the influence of an applied magnetic field. In particular, we predict an anomalous low-field magnetic behavior of the effective junction charge and concomitant magnetocapacitance in paramagnetic Meissner phase and a charge analog of "fishtail" anomaly at high magnetic fields as well as field-dependent weakening of the chemically-induced Coulomb blockade.
A method, using a Corbino disk sample geometry, is described and applied to study of resistive ta... more A method, using a Corbino disk sample geometry, is described and applied to study of resistive tails of sintered $YBCO$. When the transport current passes radially from the rim of the disk sample to its center, the two component potential drop signal is detected below $T_c$, which is due to (i) quasiparticles $W_q$ and (ii) vortex-core-motion related contribution $W_{\phi }$. When the contact pairs for $W$ are placed radially, $W_q(r)$ and $W_{\phi }(r)$ are found to follow the markedly distinctive functional dependences, providing a unique possibility to deconvolute the relative strengths of both contributions. The results obtained suggest that the mixed state dissipation of high-$T_c$ superconductors is strongly influenced by the quasiparticle excitations.
Nonlinear s-models with noncompact symmetry group in the theory of a nearly ideal bose gas
Physica a, 1986
A unified approach for description of the anomalous critical current enhancement in dislocated, d... more A unified approach for description of the anomalous critical current enhancement in dislocated, deoxygenated, and particle irradiated superconductors is proposed based on a novel concept of "active pinning" (pinning via external fields modified intrinsic Josephson junctions) and existence of various competitive forces affecting a rather delicate balance between extended defects (dislocations) and point defects (oxygen vacancies) inside a crystal. The proposed scenario implies that practically any treatment of the superconducting sample (such as sintering, melt-texturing, silver coating, thermal and mechanical treatment, oxygenation/deoxygenation process, particle irradiation, application of high magnetic and electric fields) will inevitably result in a "self-organized" rearrangement of the pre-treated defect structure of the material to optimize its pinning ability.
In this Chapter we review our latest results on magnetic (AC susceptibility) and transport (resis... more In this Chapter we review our latest results on magnetic (AC susceptibility) and transport (resistivity) properties of Pr1.85Ce0.15CuO4 (PCCO) and Sm1.85Ce0.15CuO4 (SCCO) thin films grown by pulsed laser deposition technique. Three main topics of our studies will be covered. We start with a thorough discussion of the pairing symmetry mechanisms in optimally-doped SCCO thin films based on the extracted with high accuracy temperature profiles of penetration depth. In particular, we found that above and below a crossover temperature T*=0.22T_C, our films are best-fitted by a linear and quadratic dependencies, respectively, with physically reasonable values of d-wave node gap parameter and paramagnetic impurity scattering rate. Our next topic is related to the flux distribution in our films. More precisely, we present a comparative study on their pinning ability at low magnetic fields extracted from their AC susceptibilities. Depending on the level of homogeneity of our films, two different types of the irreversibility line have been found. The obtained results are described via the critical-state model taking into account the low-field grain-boundary pinning. And finally, we demonstrate our recent results on the normal state temperature behavior of resistivity R(T) for the high-quality optimally-doped SCCO thin films. In addition to the expected contributions from the electron-phonon and electron-electron scattering processes, we also observed an unusual step-like behavior of R(T) around T=87K which we attributed the to the manifestation of thermal excitations due to spin fluctuations induced by Sm3+ moments through Cu2+-Sm3+ interaction.
Physics of Particles and Nuclei Letters
ABSTRACT
Physics Letters A
ABSTRACT
JETP Letters, 2015
We discuss a possible origin of the experimentally observed nonlinear contribution to the shift ∆... more We discuss a possible origin of the experimentally observed nonlinear contribution to the shift ∆Tc = Tc − T 0 c of the critical temperature Tc in an atomic Bose-Einstein condensate (BEC) with respect to the critical temperature T 0 c of an ideal gas. We found that accounting for a nonlinear (quadratic) Zeeman effect (with applied magnetic field closely matching a Feshbach resonance field B0) in the mean-field approximation results in a rather significant renormalization of the field-free nonlinear contribution b2, namely ∆Tc/T 0 c ≃ b * 2 (a/λT ) 2 (where a is the s-wave scattering length, λT is the thermal wavelength at T 0 c ) with b * 2 = γ 2 b2 and γ = γ(B0). In particular, we predict b * 2 ≃ 42.3 for the B0 ≃ 403G resonance observed in the 39 K BEC. PACS: 67.85.Hj, 67.85.Jk Studies of Bose-Einstein condensates (BECs) continue to be an important subject in modern physics (see, e.g., Refs.[1, 2, 3, 4] and further references therein). Atomic BECs are produced in the laboratory in lasercooled, magnetically-trapped ultra-cold bosonic clouds of different atomic species (including 87 Rb [5, 9], 7 Li [6], 23 N a [7], 1 H [8], 4 He [10], 41 K [11], 133 Cs [12], 174 Y b [13] and 52 Cr [14], among others). Also, a discussion of a relativistic BEC has appeared in Ref.[15] and BECs of photons are most recently under investigation [16]. In addition, BECs are successfully utilized in cosmology and astrophysics [17] as they have been shown to constrain quantum gravity models [18].
By employing mutual-inductance technique and using a high-sensitive bridge, we have thoroughly in... more By employing mutual-inductance technique and using a high-sensitive bridge, we have thoroughly investigated (both experimentally and theoretically) the temperature and magnetic field dependence of complex AC susceptibility of artificially prepared highly ordered (periodic) two-dimensional Josephson junction arrays (2D-JJA) of both shunted and unshunted Nb-based tunnel junctions as well as disordered three-dimensional arrays (3D-JJA). This paper reviews some of our latest results regarding the influence of non-uniform critical current density profile on magnetic field behavior of AC susceptibility in 2D-JJA, and the origin of remanent magnetization in disordered 3D-JJAs.
We discuss the effect of interatomic interactions on the condensation temperature $T_c$ of a labo... more We discuss the effect of interatomic interactions on the condensation temperature $T_c$ of a laboratory atomic Bose-Einstein condensate under the influence of an external trapping magnetic field. We predict that accounting for hyperfine interactions mediated Zeeman term in the mean-field approximation produces, in the case of the $403 \, G$ Feshbach resonance in the $|F,m_F> = |1,1>$ hyperfine state of a $^{39}K$ condensate, with $F$ the total spin of the atom, an experimentally observed (and not yet explained) shift in the condensation temperature $\Delta T_{c}/T_{c}^{0}=b^{*}_0+b^{*}_1 (a/\lambda_{T}) + b^{*}_2 (a/\lambda_{T})^2$ with $b^{*}_0 \simeq 0.0002$, $b^{*}_1 \simeq -3.4$ and $b^{*}_2 \simeq 47$, where $a$ is the s-wave scattering length, and $\lambda_T$ is the thermal wavelength at $T_{c}^{0}$. Generic expressions for the coefficients $b^*_0$, $b^*_1$ and $b^*_2$ are also obtained, which can be used to predict the temperature shift for other Feshbach resonances of ...
Physical review. B, Condensed matter, 1993
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Papers by Sergei Sergeenkov