Correlation between the electric-field effect and weak-link type in YBa2Cu3−x Oy and YBa2Cu3−x Oy /Agx high-T c superconducting ceramics

An experimental study is reported of the effect of an electric field E⩽120 MV/m and of temperature T on the critical current I _c and I-V characteristics of yttrium-based high-T _c superconducting ceramics. The materials studied were copper-deficient ceramics, YBa₂Cu_3−x O_y (D samples), and YBa₂Cu_3−x O_y/Ag_x ceramics [S samples with silver present in amounts equal to the copper deficiency (0⩽x⩽0.4)]. It has been established that in D samples at 77 K, the electric field increases I _c and reduces substantially R for I>I _c, whereas in S samples no field effect is observed. Measurements of the I _c(T) dependence near the critical temperature showed that they can be described for all samples by a relation of the type I _c =const(1−T/T _c )^α, where α≈1 for the D samples, and α≈2 for the S samples. The results obtained suggest that the electric-field effect correlates with the existence in the ceramic of SIS-type weak links at grain boundaries. Fiz. Tverd. Tela (St. Petersburg) 40, 1195–1198 (July 1998)     

Effect of γ irradiation on the low-temperature electrical conductivity and dielectric properties of TlGaSe2 crystals

Electrical conductivity and dielectric properties of single-crystal TlGaSe₂ have been studied as a function of γ irradiation dose in the 100–280 K range including the existence of an incommensurate phase. Anomalies in the form of maxima have been observed in the σ=f(T), tan δ=f(T), and ɛ=f(T) curves at the points of transition from the paraphase to incommensurate (IC) phase, T _i, and from the IC to commensurate phase, T _c. The increase in the quantities σ, tan δ, and ɛ observed initially with increasing irradiation dose is followed by their strong decrease and disappearance of the anomalies. It has been established that γ irradiation does not affect the phase transition temperatures T _i and T _c. Fiz. Tverd. Tela (St. Petersburg) 40, 1328–1331 (July 1998)     

Zero differential resistance in a double quantum well at high filling factors

The differential resistance r _xx in a GaAs double quantum well with two occupied size-quantization subbands have been studied at temperatures T = 1.6–4.2 K in magnetic fields B < 0.5 T. It has been found that differential resistance r _xx vanishes at the maxima of magneto-intersubband oscillations with an increase in the direct current I _dc. It has been shown that the discovered r _xx ≈ 0 state appears under the condition 2R _c E _H/ħω_c < 1/2, where R _c is the cyclotron radius of electrons at the Fermi level, E _H is the Hall electric field induced by the current I _dc, and ω_c is the cyclotron frequency.     

Quenching of photoconductivity by a strong electric field in tin δ-doped GaAs structures

The conductivity of GaAs structures δ-doped with tin on the vicinal and singular faces was investigated in strong electric fields up to E=10⁴ V/cm and temperatures in the range 4.2 K <T<300 K. The measurements were performed in the dark and under illumination with visible light. Long-time photoconductivity of 2D electrons with threshold T _c ≈240 K was observed in samples which were δ-doped with tin on the vicinal face. A strong electric field not only quenches photoconductivity, but also increases the resistance of the structures at temperatures T<T _c by several orders of magnitude with respect to the dark resistance. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 5, 326–330 (10 March 1996)     

Electron transport in hybrid superconductor heterostructures with manganite interlayers

Hybrid herostructures comprising an YBa₂Cu₃O _x (YBCO) high-temperature superconductor (HTS) layer and Nb/Au low-temperature superconductor (LTS) bilayer (with critical HTS and LTS temperatures T _c and T′_c, respectively), separated by a thin (d _M = 5–20 nm) interlayer of LaMnO₃, La_0.7Ca_0.3MnO₃, or La_0.7Sr_0.3MnO₃ manganite have been studied. The electric resistance and magnetic properties of individual (evaporated directly onto the substrate) manganite films and related hybrid herostructures have been measured. Based on quasi-classical equations, analytical expressions for the conductivity of herostructures at T ≤ T′_c are obtained in the case of a low-transparency superconductor/manganite interface. It is established that the conductivity of heterostructures is determined by the proximity effect (related to the penetration of a condensate wavefunction from the Nb/Au bilayer to manganite) and depends strongly on interface transparency. At low temperatures (T ≪ T _c′), the conductivity peaks are found at voltages determined by the exchange field of the manganite interlayer. At T _c′ < T < T _c, conductivity features at nearly zero bias voltages are observed, which are related to the superconductivity of the YBCO electrode.     

Diffusion Control of Homogeneous Crystallization in Nanoconfined Domains of Block Copolymers

Abstract

Confined crystallization in a poly(oxyethylene)‐b‐poly(oxybutylene)/poly(oxybutylene) blend (E₁₁₅B₁₀₃/B₂₈, φ_E = 0.14) with bcc morphology and in a polystyrene‐b‐poly (oxyethylene)‐b‐polystyrene (S‐E‐S) triblock copolymer (S₄₀E₁₃₆S₄₀, φ_E = 0.407) with lamellar morphology was studied using differential scanning calorimetry (DSC). Two types of confined crystallization with different characteristic Avrami exponents were identified in both systems. At higher crystallization temperature (T _c), the Avrami exponent is 1.0 and the overall crystallization rate is controlled by the homogeneous nucleation rate. At lower T _c, the Avrami exponent is 0.5, which is attributed to diffusion‐controlled confined crystallization. This shows that diffusion has a great influence on the overall crystallization rate when chain mobility is reduced, which can be caused either by lower T _c or by constrained microstructure.     

Response of the capacitance of a planar La0.67Ca0.33MnO3/SrTiO3/La0.67Ca0.33MnO3 heterostructure to an electric field

Manganite film electrodes were integrated with a spacer layer of strontium titanate to produce an epitaxial La_0.67Ca_0.33MnO₃/(1000 nm)SrTiO₃/La_0.67Ca_0.33MnO₃ (LCMO/STO/LCMO) heterostructure by laser ablation. At T = 300 K, the mechanical stresses in the STO layer relaxed to a considerable extent, while the LCMO electrodes were found to be under biaxial lateral tensile strain, with the lattice unit cell of the top electrode distorted considerably stronger (a _∥/a _⊥ ≈ 1.026) than that of the bottom electrode (≈1.008) (a _∥ and a _⊥ are the unit cell parameters in the substrate plane and along the normal to its surface, respectively). The reciprocal of the capacitance C of the plane-parallel LCMO/STO/LCMO film capacitors thus formed increased almost linearly with increasing temperature T in the range 50–250 K. At T < 100 K, the capacitance C decreased by approximately 50% in an electric field E = 40 kV/cm. After the electric field E was varied as 0 → + 100 kV/cm → 0, the capacitance C decreased by approximately 3% and the maximum in the C(E, T > 200 K) dependence shifted by approximately 9 kV/cm with respect to the point E = 0.     

The paleoinformation value of natural remanent magnetization of several traps in Yakutia

Research was carried out to estimate the possibility of determining the direction and strength of the ancient geomagnetic field (H _an ) by natural remanent magnetization (I _n ) of nine oriented samples from traps of the Minor Botuoba Region (Yakutia) aged 260 Ma. Five samples (Pi-10, K-4, K-6, 315–13, and Ki-2) are characterized by negative polarity of In, while four samples (nos. 334-5, 331–2, 315–11, 299–2) have positive polarity as does the recent geomagnetic field in this region. The ferrimagnetic constituent of the samples with reverse I _n polarity appears to be quite variable: samples K-4 and K-5 are characterized by low Curie points (T _c ≈ 200°C) of the ferrimagnetic phase, sample Ki-2 contains single-phase oxidized titanomagnetite with T _c ≈ 310°C, and the T _c of the Pi-10 ferrimagnetic phase is 540°C. Hence, it may be concluded that the primary remanent magnetization of the first two samples was formed in a reverse polarity field. These samples also may be used to determine the paleostrength of the geomagnetic field. The properties of traps containing single-phase oxidized (sample Ki-2) and disintegrated (sample Pi-10) titanomagnetite require additional investigation. Samples with positive In polarities are characterized by the self-reversal phenomenon upon thermal demagnetization of the natural remanent magnetization, which was most likely caused by the occurrence of titanomagnetite exsolution textures in ferrimagnetic grains. The paleoinformation value of the I _n of these samples is doubtful.     

Low-temperature resistivity of YBa2Cu3O6+x single crystals in the normal state

A scan of the superconductor-nonsuperconductor transformation in single crystals of YBa₂Cu₃O_6+x (x≈0.37) is done in two alternative ways, namely, by applying a magnetic field and by reducing the hole concentration through oxygen rearrangement. The in-plane normal-state resistivity ρ_ab obtained in the two cases is quite similar; its temperature dependence can be fitted by a logarithmic law in a temperature range of almost two decades. However, an alternative representation of the temperature dependence of σ_ab=1/ ρ _ab by a power law, typical for a 3D material near a metal-insulator transition, is also plausible. The vertical conductivity σ_c=1/ρ_c followed a power law, and neither σ_c(T), nor ρ_c(T) could be fitted by log T. It follows from the ρ_c measurements that the transformation at T=0 is split into two transitions: superconductor-normal-metal and normal-metal-insulator. In our samples, they are separated in oxygen content by Δx≈0.025. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 11, 834–839 (10 June 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

High-sensitivity read-write volume holographic storage in reduced KNbO3 crystals

Reduced KNbO₃ is a photoconductive ferroelectric in which holograms can be recorded by the photorefractive effect. Read-write volume hologram storage and erase sensitivities ofS ⁻¹=100 J/cm² andS ⁻¹=84 J/cm² (S=d(Δn)/d(I₀t)‖_t=0) have been measured at zero applied electric field, where the charge transport is shown to be due to diffusion of photoexcited electrons. By applying an electric field along thec-axis, the migration length of the photoexcited electrons becomes comparable to the holographic grating spacing. This leads to storage sensitivities comparable to high-resolution photographic plates. Experimental data on storage and erase sensitivity as a function of the grating spacing, applied electric field, writing light intensity and temperature are reported and interpreted on the basis of the theoretical results of Young et al. and Amodei. Changes of the intensity ratio of the writing beams by self diffraction (beam coupling), reflections from surfaces and the residual dark conductivity are assumed to cause experimental results which deviate from the theoretical models. It is shown, that in reduced KNbO₃ and other ferroelectric photoconductors having photocarrier transport lengths much larger than the unit cell dimension, photovoltaic currents do not contribute significantly to the build-up of space-charges leading to the photorefractive effect.     

The effect of bias field on the value and temperature dependence of the piezoelectric coefficient d 31 in (1 ? x )Pb(Mg1/3Nb2/3)O3? x PbTiO3 ( x = 0.06, 0.13) single crystals

It is established that, as a result of application of even a small (∼0.5 kV cm⁻¹) bias field E, the maximum of the piezoelectric coefficient d ₃₁ in (1 − x)Pb(Mg_1/3Nb_2/3)O₃ − xPbTiO₃(x = 0.06, 0.13) crystals shifts from the Vogel-Fulcher temperature to the critical point in the E-T phase diagram of a given composition. The field dependence of the d ₃₁(T) peak magnitude has a maximum near the E values corresponding to the critical point. Original Russian Text ? A.S. Emelyanov, S.I. Raevskaya, F.I. Savenko, I.P. Raevski, M.A. Malitskaya, E.I. Sitalo, 2009, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2009, Vol. 73, No. 1, pp. 132–133.     

Temporal correlations and persistence in the kinetic Ising model: the role of temperature

We study the statistical properties of the sum S _t = dt'σ _t', that is the difference of time spent positive or negative by the spin σ _t, located at a given site of a D-dimensional Ising model evolving under Glauber dynamics from a random initial configuration. We investigate the distribution of S_t and the first-passage statistics (persistence) of this quantity. We discuss successively the three regimes of high temperature ( T > T _c), criticality ( T = T _c), and low temperature ( T < T _c). We discuss in particular the question of the temperature dependence of the persistence exponent , as well as that of the spectrum of exponents (x), in the low temperature phase. The probability that the temporal mean S _t/t was always larger than the equilibrium magnetization is found to decay as t ^{- - ?}. This yields a numerical determination of the persistence exponent in the whole low temperature phase, in two dimensions, and above the roughening transition, in the low-temperature phase of the three-dimensional Ising model. Received 4 December 2000     

Electric field dependence of the thermal conductivity of a granular superconductor: Giant field-induced effects predicted

The temperature and electric-field dependence of the electronic contribution to the thermal conductivity (TO) 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 κ(T, 0) (controlled by mutual inductance L ₀ and normal state resistivity R _n), the model predicts the two major effects in the applied electric field: (i) the decrease in the linear TC and (ii) the giant enhancement of the nonlinear (i.e. ∇T-dependent) TC with Δκ(T, E)/κ(T, 0), reaching 500% for parallel electric fields E≃ E _T(E _T=S ₀|∇T| is an “intrinsic” thermoelectric field). The possibility of experimentally observing the predicted effects in granular superconductors is discussed.     

Nuclear spin lattice relaxation and electric field gradient in liquid indium

We have measured the nuclear spin lattice relaxation time in liquid indium from 130°C to 300°C to be: 1/T ₁=(1.98 × 0.0082T) × 10³ sec^-1. The relaxation rate consists of two significant parts: (1/T ₁) _K from the nuclear magnetic hyperfine interaction, and (1/T ₁) _Q from the nuclear quadrupole interaction. We calculate (1/T ₁) _K from the the modified Korringa relation using a correction factor of order unity for electron-electron interactions. The hyperfine term is linear in T and accounts for the second term in 1/T ₁. Within experimental error the remaining rate, (1/T ₁) _Q , is temperature independent, and theoretically varies as the product of the square of the electric field gradient, q, and τ_c, a typical time between field gradient fluctuations. Making use of the x-ray RDF, we construct a simple model for liquid indium and calculate the ionic and electronic contributions, q _I and q _E, to the electric field gradient, to be q _I=1.4 × 10²⁴/cm³ and q _E=8.5 × 10²⁴/cm³. The calculation of q _E assumes covalent bonding between nearest neighbours. Taking q _I and q _E to be of opposite sign, we find that the correlation time τ_c is 1.6 × 10^-13 sec. When we further identify τ _c with the correlation time for diffusion in a three-dimensional random walk, we are able to calculate the r.m.s. jump distance, Δr _D, involved in self-diffusion, Δr _D=0.38 Å. This value is consistent with the x-ray peak width of 0.38 Å which we used earlier to calculate the electric field gradient.     

X-ray dosimetric characteristics of CdIn2S4〈Cu〉 single crystals

The effect of doping CdIn₂S₄ single crystals by copper (3 mol %) on their X-ray dosimetric characteristics is investigated. It is found that the characteristic X-ray conductivity of CdIn₂S₄〈Cu〉 single crystals increases 3–16 times compared with undoped CdIn₂S₄ at effective radiation hardness V _a = 25−50 keV and dose rate E = 0.75−78.05 R/min. Moreover, the persistence of the crystal characteristics completely disappears and the supply voltage of a CdIn₂S₄〈Cu〉 X-ray detector decreases fivefold. The dependence of the steady X-ray-induced current in CdIn₂S₄〈Cu〉 on the X-ray dose is described as ΔI _{E, 0} ∝ E ^α, where 0.6 ≤ α ≤ 1.8.     

On the influence of a square-root van Hove singularity on the critical temperature of high-T c superconductors

It is shown that the square-root van Hove singularity appearing in the density of states ν (E _F )∼(E _F −E ₀)^−1/2 as a result of extended saddle-point singularities in the electron spectrum of high-T _c superconductors based on hole-type cuprate metal-oxide compounds gives a nonmonotonic dependence of the critical temperature T _c on the position of the Fermi level E _F relative to the bottom E ₀ of the saddle. Because the divergence of ν(E _F ) is canceled in the electron-electron interaction constant renormalized by strong-coupling effects, T _c approaches zero as E _F →E ₀, in contrast to the weak-coupling approximation, where in this limit T _c approaches a finite (close to maximum) value. The dependence obtained for T _c as a function of the doped hole density in the strong-coupling approximation agrees qualitatively with the experimental data for overdoped cuprate metal oxides. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 7, 473–477 (10 April 1998)     

Temperature dependence of gamma-ray-induced luminescence of xylene-based liquid scintillator between 200 and 242 K

The luminescence response of xylene-based liquid scintillator (scintillation grade), xylene + 1 g/l PPO + 0.1 g/l BBOT, has been studied as a function of temperature in the range 200 to 242 K. It has been observed that under gamma-ray excitation the light output increases with the decrease of temperature. The data are well described by the Arrhenius relation,I _low−I=I ₀ exp(−E/kT), whereI is the count rate at temperatureT.I _low is a constant equal to 5600 counts per min, theI ₀ factor is 3.3 × 10⁶ counts/min,k is the Boltzmann constant. The activation energyE was found to be equal to 0.20 eV. It is typical for thermally activated diffusion controlled process.     

Improvement on the breakdown voltage for silicon-on-insulator devices based on epitaxy-separation by implantation oxygen by a partial buried n+-layer

A novel silicon-on-insulator (SOI) high-voltage device based on epitaxy-separation by implantation oxygen (SIMOX) with a partial buried n⁺-layer silicon-on-insulator (PBN SOI) is proposed in this paper. Based on the proposed expressions of the vertical interface electric field, the high concentration interface charges which are accumulated on the interface between top silicon layer and buried oxide layer (BOX) effectively enhance the electric field of the BOX (E_I), resulting in a high breakdown voltage (BV) for the device. For the same thicknesses of top silicon layer (10 μm) and BOX (0.375 upmum), the E_I and BV of PBN SOI are improved by 186.5% and 45.4% in comparison with those of the conventional SOI, respectively.     

Short-Range Order of the Rotational Degree of Freedom of the Glycine Molecule in Triglycine Sulfate Glass State

The unit cell of triglycine sulfate (TGS) contains the following glycine ions: dimers (GIISHBGIII)⁺ with a short hydrogen bond (SHB) and a monomer (SO₄LHBGI)⁺ with a long hydrogen bond (LHB) to the SO₄ ²⁻ anion. The spontaneous polarization results from a statistical charge distribution and the Coulomb interaction between SO₄ ²⁻ and fast rotating –NH₃ ⁺ groups. In the lamellar model, chains of –SO₄–(GIISHBGIII)–SO₄–(GIISHBGIII)–SO₄ lying along the polar b-axis are linked perpendicularly to this axis by SO₄LHBGI⁺ units. Tilting the LHBGI⁺ ion around the axis in the mirror plane decides on the direction of the charge displacement from this symmetry plane. The reversal of the spontaneous polarization, i.e., −P _S↔ +P _S, is related to the rotation of the NH₃ group. If this rotation becomes slowed down at low temperature and/or under high pressure, the coercive field increases dramatically. Application of an external electric field E _⊥ perpendicular to the b-axis leads to a hysteresis loop of the polarity P(E), and finally to its disappearance. This phenomenon comes from an ordering of protons in hydrogen bonds perpendicular to the polar axis. This is the first study of the E _⊥ effect by nuclear magnetic resonance. Authors' address: Jan Stankowski, Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, Poznań 60-179, Poland     

2D-Electron Heating in Electric and Magnetic Crossed Fields

2D-electron heating in a potential well of a single n-(AlAs) _x (GaAs)_1–x /i-GaAs (x = 0.28) heterojunction is studied for the cases of a classical (weak) magnetic field B and constant and pulsed electric fields at fixed temperatures 77 and 4.2 K. It is shown that the heating of two-dimensional electrons is similar to that of the bulk ones. The magnetic field cools electrons, and this is manifested in the shifts of the characteristic critical electric fields E _{c 1} and E _{c 2} and in the regions of nonlinearity of voltage-current characteristics. The dependence of the effective electron temperature on the electric field T _e(E)_B is determined.