arXiv subjects
Publications and source records attributed to Sergei Sergeenkov.
We discuss the properties of the electronic viscosity of a Dirac fluid in deformed graphene by introducing a strain and velocity gradient as equivalent to a pseudo-magnetic and pseudo-electric field respectively into the Dirac equation. It is thereby analytically established that the dynamic shear viscosity coefficient substantially decreases with the applied strain.
By using an analogy with axionic like systems, we study light propagation in periodic photonic topological insulator (PTI). The main result of this paper is an explicit expression for the PTI band structure. More specifically, it was found that for nonzero values of the topological phase difference $γ=θ_2-θ_1$ a finite gap $δ\proptoγ^2$ opens in the spectrum which is equivalent to appearance of nonzero effective photon mass $m^{*}(δ)\propto \frac{\sqrtδ}{δ+2}$.
We discuss a possible origin of the experimentally observed nonlinear contribution to the shift $ΔT_{c}=T_c-T_{c}^{0}$ of the critical temperature $T_{c}$ in an atomic Bose-Einstein condensate (BEC) with respect to the critical temperature $T_{c}^{0}$ of an ideal gas. We found that accounting for a nonlinear (quadratic) Zeeman effect (with applied magnetic field closely matching a Feshbach resonance field $B_0$) in the mean-field approximation results in a rather significant renormalization of the field-free nonlinear contribution $b_{2}$, namely $ΔT_{c}/T_{c}^{0}\simeq b_{2}^{\ast }(a/λ_{T})^{2}$ (where $a$ is the s-wave scattering length, $λ_{T}$ is the thermal wavelength at $T_{c}^{0}$) with $b_{2}^{\ast }=γ^{2}b_{2}$ and $γ=γ(B_0)$. In particular, we predict $b_{2}^{\ast }\simeq 42.3$ for the $B_{0}\simeq 403G$ resonance observed in the $\ ^{39}K$ BEC.
To answer this question, we discuss the properties of electronic viscosity in deformed graphene by introducing strain and velocity gradient as pseudo-magnetic and pseudo-electric fields, respectively, into the Dirac model. We found that viscosity decreases with applied strain, simultaneously leading to a rather significant increase of the Reynolds number and enabling a real possibility for manifestation of noticeable turbulent effects in strained graphene.
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 $ΔT_{c}/T_{c}^{0}=b^{*}_0+b^{*}_1 (a/λ_{T}) + b^{*}_2 (a/λ_{T})^2$ 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 $λ_T$ 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 $^{39}K$ or other atomic condensates.
By introducing a realistic model of nanogranular superconductors (NGS) based on 2D arrays of Josephson nanocontacts (created by a network of twin-boundary dislocations with strain fields acting as insulating barriers between hole-rich domains), in this Chapter we present some novel phenomena related to mechanical, magnetic, electric and transport properties of NGS in underdoped single crystals. In particular, we consider chemically induced magnetoelectric effects and flux driven temperature oscillations of thermal expansion coefficient. We also predict a giant enhancement of the nonlinear thermal conductivity of NGS reaching up to 500% when the intrinsically induced chemoelectric field (created by the gradient of the chemical potential due to segregation of hole producing oxygen vacancies) closely matches the externally produced thermoelectric field. The estimates of the model parameters suggest quite an optimistic possibility to experimentally realize these promising and important for applications effects in non-stoichiometric NGS and artificially prepared arrays of Josephson nanocontacts.
By attributing a circulating Josephson current induced diamagnetic moment to a SQUID-type three-level qubit, a wireless connection between such qubits is proposed based only on dipole-dipole interaction between their moments. The estimates of the model parameters suggest quite an optimistic possibility to experimentally realize the suggested coupling scheme.
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.
A possible scenario for an ac Josephson effect initiated by the flow of dislocations through a mechanically loaded but electrically unbiased superconductor is proposed. The characteristic voltages due to the motion of dislocations in loaded (under the applied stress of 10^7N/m^2) YBCO crystals are estimated to be of the order of a few picovolts (which corresponds to the Josephson frequency of 10 kHz).
In this paper, we report on different phenomena related to the magnetic properties of artificially prepared highly ordered (periodic) two-dimensional Josephson junction arrays (2D-JJA) of both shunted and unshunted Nb-AlOx-Nb tunnel junctions. By employing mutual-inductance measurements 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 2D-JJA. We also demonstrate the use of the scanning SQUID microscope for imaging the local flux distribution within our unshunted arrays.
Using a single-plaquette approximation, novel magnetoinductance effects in Josephson junction arrays (JJAs) are predicted, including the appearance of steps in the temperature behavior of magnetic susceptibility. The number of steps (as well as their size) is controlled by the kinetic inductance of the plaquette whose field dependence is governed by the Abrikosov vortices penetrating superconducting regions of the array. The experimental conditions under which the predicted effects should manifest themselves in artificially prepared JJAs are discussed.
Using a 2D model of capacitively coupled Josephson junction arrays (created by a network of twin boundary dislocations with strain fields acting as an insulating barrier between hole-rich domains in underdoped crystals), we study the influence of chemical pressure on nonlinear thermal conductivity (NLTC) of an intrinsically granular superconductor. Quite a substantial enhancement of NLTC is predicted when intrinsic chemoelectric field closely matches the externally produced thermoelectric field. The estimates of the model parameters suggest a realistic possibility to experimentally monitor this effect in non-stoichiometric superconductors.
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.
Based on the previously suggested model of nanoscale dislocations induced Josephson junctions and their arrays, we study the magnetic field induced electric polarization effects in intrinsically granular superconductors. In addition to a new phenomenon of chemomagnetoelectricity, the model predicts also a few other interesting effects, including charge analogues of Meissner paramagnetism (at low fields) and "fishtail" anomaly (at high fields). The conditions under which these effects can be experimentally measured in non-stoichiometric high-T_c superconductors are discussed.
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.
Within a 2D model of Josephson junction arrays (created by 2D network of twin boundary dislocations with strain fields acting as insulating barrier between hole-rich domains in underdoped crystals), a few novel effects expected to occur in intrinsically granular material are predicted including: (i) Josephson chemomagnetism (chemically induced magnetic moment in zero applied magnetic field) and its influence on a low-field magnetization (chemically induced paramagnetic Meissner effect), and (ii) magnetoconcentration effect (creation of oxygen vacancies in applied magnetic field) and its influence on a high-field magnetization (chemically induced analog of "fishtail" anomaly). The conditions under which these effects can be experimentally measured in non-stoichiometric high-T_c superconductors are discussed.
The temperature and electric field dependence of electronic contribution to the thermal conductivity (TC) of a granular superconductor is considered within a 3D model of inductive Josephson junction arrays. In addition to a low-temperature maximum of zero-field TC K(T,0) (controlled by mutual inductance L_0 and normal state resistivity R_n), the model predicts two major effects in applied electric field: (i) decrease of the linear TC, and (ii) giant enhancement of the nonlinear (i.e., grad T-dependent) TC with [K(T,E)-K(T,0)]/K(T,0) reaching 500% for parallel electric fields E=E_T (E_T=S_0|grad T| is an "intrinsic" thermoelectric field). A possiblity of experimental observation of the predicted effects in granular superconductors is discussed.
Based upon the recently introduced thermophase and piezophase mesoscopic quantum effects in Josephson junctions, several novel phenomena in a twisted superconductor (containing a small annular SIS-type contact) under influence of thermal gradient and applied magnetic field are predicted. Namely, we consider a torsional analog of Josephson piezomagnetism (and related magnetomechanical effect) as well as a possible generation of a heat flux induced magnetic moment in a weakly-coupled superconductor under a torsional deformation (analog of Zavaritskii effect) along with the concomitant phenomena of piezothermopower and piezothermal conductivity. The conditions under which the predicted effects can be experimentally measured in conventional superconductors and nanostructured materials with implanted Josephson contacts are discussed.