Microwave power absorption and nonresonant signals due to viscous fluxon motion

To account for low field microwave absorption in high-T _c superconducting cuprates situated in the electron spin resonance configuration, an elegant model based on viscous fluxon motion has been proposed by Portiset al. [11–13]. In view of this model, however, derivations of neither the explicit expression of the power absorption nor the signal had been addressed. In this publication, the stated expressions are derived by fusing the idea of Portiset al. [11–13] and that of Kessleret al. and Duliet al. [20,21].     

Observation of e2/h Conductance Steps in a Side-Gate Point Contact on In0.75Ga0.25As/In0.75Al0.25As Heterostructure

In 1996, it was suggested by K. J. Thomas et al. (Phys. Rev. Lett. 77, 135 (1996)) that 0.7(2e²/h) conductance structure in Quasi-1DEG (Q1DEG) at GaAs/AlGaAs heterostructure might be related to spin polarization at zero magnetic field. We have recently studied spontaneous spin-splitting in the 2DEGs formed at normal metamorphic In_0.75Ga_0.25As/In_0.75Al_0.25As heterojunctions grown on GaAs substrates and obtained the value of 10 meV as the zero-field splitting at Fermi level (Y. Sato et al., J. Appl. Phys. 89, 8017 (2001)). In this work, we attempted to observe spin-related phenomena in this heterojunction Q1DEGs at zero magnetic field. We observed e²/h conductance steps in low electron concentration side-gate point contact.     

Spin diffusion and spin echo in normal liquid3He

The problem of spin diffusion in normal liquid³He in the presence of precessional effects is reexamined taking into account the energy dependence of the quasiparticle relaxation time. This leads to a generalization of Leggett's relation for the successive height of the echoes in a φ-180°-180° experiment. Reanalyzing the experiment of Corruccini et al. (including finite-temperature corrections) leads to almost exact and model-independent values for F ₁ ^a and λ_D.     

Electrical Manipulation of Spin Injection into a Single InAs Quantum Dots

We demonstrate spin injection from a n-Zn_0.96Mn_0.04Se layer into individual InAs quantum dots (SQDs) in a p–i–n diode structure using cw polarization resolved magneto-micro photoluminescence spectroscopy. Interestingly, we find that the spin injection efficiency strongly varies from dot to dot. We obtain a single quantum dot circular polarization degree ranging from 2% to almost 50% (at B=4 T) at zero biasing and within the spectral range studied here, we found 2 maxima of the degree of the circular polarization at SQD energies separated by ∼33 meV. Importantly, we demonstrate that the spin injection efficiency can be manipulated by external forward biasing (U _ext).     

Infinite Spin Diffusion Length of Any Spin Polarization Along Direction Perpendicular to Effective Magnetic Field from Dresselhaus and Rashba Spin–Orbit Couplings with Identical Strengths in (001) GaAs Quantum Wells

In this note, we show that the latest spin grating measurement of spin helix by Koralek et al. (Nature 458:610, 2009) provides strong evidence of the infinite spin diffusion length of any spin polarization along the direction perpendicular to the effective magnetic field from the Dresselhaus and Rashba spin–orbit couplings with identical strengths in (001) GaAs quantum wells, predicted by Cheng et al. (Phys. Rev. B 75:205328, 2007).     

Effective Electron Correlation and Spin Density Fluctuation in Iron-Based Fluorides SrFe1?x Co x AsF (x=0,0.125)

Using first-principles calculation, we study effective electron correlation and spin density fluctuation in iron-based fluorides SrFe_1?x Co _x AsF (x=0, 0.125). We obtain the observed magnetic moment of Fe atom with a strongly attractive electron correction. Whereas, different from the parent compound, the density of state of superconducting SrFe_1?x Co _x AsF (x=0.125) near to the Fermi energy is reduced for both signs of effective electron correlation, and suggests strong instability there. In addition, spin density fluctuation resulted from the effective correlation exists in Co-doped compound, may propagate in the form of collective excitation and manifest as spin fluctuation with specific q-vector in momentum space.     

Theoretical predictions on the effective piezoelectric coefficients of 0–3 PZT/Polymer composites

Two explicit formulae for the effective piezoelectric coefficients (d ₃₁ and d ₃₃) of 0–3 composite have been derived by taking into account the interaction effects between the inclusions and are expressed directly in terms of the properties of the constituents. Predictions using these two formulae are compared with published experimental data of 0–3 composite systems having three different polarization states: only the inclusion phase is polarized; both phases are polarized in the same direction and the two phases are polarized in opposite directions. In addition, the predictions using Wong et al.’s scheme (Wong CK, Poon YM, Shin FG (2001) J Appl Phys 90:4690) and Furukawa et al.’s model (Furukawa T, Fujino K, Fukada E (1976) Jpn J Appl Phys 15:2119) are included for comparison. For the first two cases, the results show that both our model and Wong et al.’s scheme have comparable performance. However, for the last case, our model gives more favorable predictions than theirs.     

Impurity effects in D-wave superconductors

It is well documented that substitution of Cu in the Cu-O₂ plane by Zn has dramatic effects on the superconducting properties of high T_c cuprates. Assuming that Zn introduces nonmagnetic impurities in the unitarity limit, we study the electron density of states, static spin susceptibility and other properties systematically. In particular we find that our density of states describes quite well the one observed in Bi₂Sr₂CaCu₂O_x by Barbiellini et al. Further the knight shift in 1% and 2% Zn substituted YBa₂Cu₃O₇ observed by Ishida et al. is well described by the present model.     

Tilting Mode Relaxation and Oxygen Isotope Effect in La2?xSrxCuO4 Studied by Electron Paramagnetic Resonance

The electron paramegnetic resonance (EPR) of Mn²⁺ doped into La_2–x Sr _x CuO₄ was used to probe the copper spin relaxation via the bottleneck effect for oxygen isotope (¹⁶O and ¹⁸O)–substituted samples. It was found that the EPR linewidth is larger for the ¹⁸O isotope samples than for the ¹⁶O samples. For x = 0.03, the linewidth for the ¹⁸O sample is larger than for ¹⁶O sample by a factor of 2. The isotope effect is pronounced at low temperatures and decreases with increasing Sr concentration. This effect is quantitatively explained by the Cu²⁺ S = 1/2 spin relaxation to the lattice via Dzyaloshinski terms coupled linearly to the local Q ₄/Q ₅ tilting modes of the CuO₆ octahedra as proposed by Kochelaev et al. [1] The Q ₄/Q ₅ modes are coupled sterically to the Q ₂ Jahn–Teller modes considered to be relevant for the (bi)-polaron formation and thus for the high-temperature superconductivity (HTSC).     

Spin Dynamics in the Ferromagnetic Phase of Colossal Magnetoresistive Oxides

A review is given that focuses on the spin dynamics in the ferromagnetic regime of the magnetoresistive oxides. At small wave vectors the quadratic dispersion relation is remarkably isotropic throughout the composition range, with a gap that is too small to measure with conventional neutron scattering techniques. At larger wave vectors the spin waves are strongly damped in the ground state, in contrast to expectations based on a simple half-metallic band structure, while the temperature dependence of the damping and renormalization of the spin waves is anomalous. An unusual spin-diffusion component to the fluctuation spectrum develops as the Curie temperature is approached, which appears to be related to the formation of polarons in the system and the consequent charge localization. Near and above T_C the diffuse scattering from polarons is directly observed, as well as the correlations between the polarons.     

Electrical and magnetic properties of electro-oxidative polymerized poly(tris(thienylphenyl)amine)s

Electro-oxidative polymerized poly(tris(thienylphenyl)amine)s, which have the hyperbranched (dendritic) structure (PTPA) and linear type (PMeTPA), were investigated for their electrical and magnetic properties. The conductivity PTPA showed was almost one order higher than that of PMeTPA. From the solid state ESR measurements of the polymers, observation of ESR signal at g = 2.0027 and 2.0030 indicated the formation of a triphenylamine cation radical. The normalized magnetization plots (M/M_s) for PTPA and PMeTPA are close to the theoretical Brillouin curves for S = 1, indicating a magnetic interaction between the spin centers in PMeTPA. The spin concentrations determined by the M_s values of PTPA and PMeTPA were 7.3–7.4 and 1.3–1.4%, respectively. This large difference in the spin concentration of the polymers according to the structure resulted from a different spin conformation by the radical structure.     

Magnetic excitations in iron chalcogenide superconductors

Abstract

Nuclear magnetic resonance and neutron scattering experiments in iron chalcogenide superconductors are reviewed to make a survey of the magnetic excitations in FeSe, FeSe_1?xTe_x and alkali-metal-doped A_xFe_2?ySe₂ (A = K, Rb, Cs, etc). In FeSe, the intimate relationship between the spin fluctuations and superconductivity can be seen universally for the variations in the off-stoichiometry, the Co-substitution and applied pressure. The isovalent compound FeTe has a magnetic ordering with different wave vector from that of other Fe-based magnetic materials. The transition temperature T_c of FeSe increases with Te substitution in FeSe_1?xTe_x with small x, and decreases in the vicinity of the end member FeTe. The spin fluctuations are drastically modified by the Te substitution. In the vicinity of the end member FeTe, the low-energy part of the spin fluctuation is dominated by the wave vector of the ordered phase of FeTe; however, the reduction of T_c shows that it does not support superconductivity. The presence of same wave vector as that of other Fe-based superconductors in FeSe_1?xTe_x and the observation of the resonance mode demonstrate that FeSe_1?xTe_x belongs to the same group as most of other Fe-based superconductors in the entire range of x, where superconductivity is mediated by the spin fluctuations whose wave vector is the same as the nesting vector between the hole pockets and the electron pockets. On the other hand, the spin fluctuations differ for alkali-metal-doped A_xFe_2?ySe₂ and FeSe or other Fe-based superconductors in their wave vector and strength in the low-energy part, most likely because of the different Fermi surfaces. The resonance mode with different wave vector suggests that A_xFe_2?ySe₂ has an exceptional superconducting symmetry among Fe-based superconductors.     

Electroforming in MIM structure of SiOx and SiOx/SnO composite dielectric thin films

Electroforming and related phenomena in SiO _x and SiO _x -SnO thin films incorporated in copper-oxide-copper metal-insulator-metal structures have been investigated. Both types of devices showed voltage-controlled negative resistance, voltage memory effects (thermal and threshold) and electron emission. The voltage-controlled negative resistance and voltage memory effects may be interpreted in terms of the filamentary model of Dearnaley et al. The electron emission phenomenon is attributed to the Dearnaley model as modified by Rakhshani et al. The a.c. conductance of the devices before and after forming was also studied and the results support the proposed filamentary model of the electroforming process.     

Magnetism of the LTT phase of Eu-doped La2-x Sr x CuO4

The ESR signal of Gd spin probes (0.5 at.%) as well as the static normal state susceptibility of Eu (J(Eu³⁺) = 0) doped La_2-x-ySr_xEu_yCuO₄ reveal pronounced changes of the Cu magnetism at the structural transition from the orthorhombic to the low-temperature tetragonal phase for all nonsuperconducting compositions. Both a jumplike decrease ofx as well as the ESR data show an increase of the in-plane magnetic correlation length in the LTT phase. From the Gd³⁺ ESR linewidth we find that for specific Eu and Sr concentrations in the LTT phase the correlation length increases up to more than 100 lattice constants and the fluctuation frequency of the CuO₂ spin system slows down to ~10¹⁰-10¹¹ s^-1 However, there is no static order above T~8 K in contrast to the LTT phase of Nd-doped La_{2-x}Sr_xCuO₄ with pinned stripe correlations.     

Suppression of spin fluctuations by alloying in UPt3

In order to investigate the normal state spin fluctuation behavior of UPt₃, we have measured the low temperature resistivity and specific heat C of U(Pt_0.8Pd_0.2)₃, which we find to be close to the phase stability boundary for the hexagonal UPt₃ structure. The evidence for spin fluctuations observed in UPt₃, aT ³ ln (T/T _SF) upturn inC/T below 10 K, is totally suppressed in U(Pt_0.8Pd_0.2)₃, and the value, proportional to the dressed density of states, is decreased by 50% compared to pure UPt₃. This extreme sensitivity to substitution by isoelectronic Pd for Pt indicates that the spin fluctuations in UPt₃ depend critically on the hybridization of the U electrons, U-U separation equal to 4.2 Å, with the electrons of the intervening atoms.     

Enhancement of Magnetization in Liquid 3He at Aerogel Interface

A novel feature of condensate state in liquid ³He is predicted theoretically, which consists of spin triplet s-wave Cooper pairs (Higashitani et al. in J. Low. Temp. Phys. 155:83–97, 2009). Such a spin triplet s-wave state will appear inside aerogel near the surface boundary contacting with superfluid ³He-B, and the enhancement of magnetization due to s-wave state is theoretically expected (Nagato et al. in J. Phys. Soc. Jpn. 78:123603, 2009; Higashitani et al. in Phys. Rev. B 85:024524, 2012). In order to detect this proximity effect, we made the interface in columnar glass tube which coated with 2.5 layer ⁴He, and set a saddle shape NMR coil very near the interface. At 7 bar, we found that superfluidity in liquid ³He inside aerogel never occurred, even at considerably low temperatures. At 24 bar below T/T _c =0.392, we observed no decrease of magnetization with decreasing temperatures. This phenomenon might be due to spin triplet s-wave Cooper pairs.     

Computation of phonon dynamics of Mg<Subscript>70</Subscript>Zn<Subscript>30</Subscript> metallic glass

In the present paper, the computation of the phonon dynamics of binary Mg₇₀Zn₃₀ metallic glass is reported using the well-recognized model potential of Gajjar et al. The present study includes the phonon dispersion curves (PDC), elastic and thermodynamic properties such as longitudinal sound velocity υ_L, transverse sound velocity υ_T, Debye temperature θ_D, isothermal bulk modulus B _T, modulus of rigidity G, Poisson’s ratio σ and Young’s modulus Y and specific heat capacity C _V of the glass. Three theoretical models given by Hubbard–Beeby (HB), Takeno–Goda (TG) and Bhatia–Singh (BS) are used to compute the PDC. Five local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru–Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) are employed for the first time to study the effect of exchange and correlation in the aforesaid properties. The pseudo-alloy-atom (PAA) model is applied for the first time instead of Vegard’s Law.     

Spin Hall Effect in Symmetric Wells with Two Subbands

We investigate the spin Hall conductivity σ _xy ^z of a clean 2D electron gas formed in a two-subband well. We determine σ _xy ^z as arising from the inter-subband induced spin–orbit (SO) coupling η (Calsaverini et al., Phys. Rev. B 78:155313, 2008) via a linear-response approach due to Rashba. By self-consistently calculating η for realistic wells, we find that σ _xy ^z presents a non-monotonic (and non-universal) behavior and a sign change as the Fermi energy varies between the subband edges. Although our σ _xy ^z is very small (i.e., ≪`` e/4π″), it is non-zero as opposed to linear-in-k SO models.     

New Equation for Vapor Pressures of Difluoromethane (HFC-32)

Critically evaluated experimental vapor-pressure data sets supplemented with calculated data for low-temperature region were used in the development of vapor-pressure equations. The optimum number of terms, coefficients, and exponents of the Wagner-type equation were derived by means of the Setzmann–Wagner program OPTIM based on the combination of the stepwise regression analysis and evolutionary optimization method. Equations were checked by the reduced enthalpy of vaporization criterion derived from the Clausius–Clapeyron equation and specific volume of ideal gas. An equation developed using 261 experimental data points and low-temperature data calculated by Lüddecke and Magee gives an RMS deviation of 0.102%; a second equation based on the same experimental data and low-temperature data calculated by Tillner-Roth gives an RMS deviation of 0.101% from experimental points. The triple-point pressure extrapolated to the measured temperature T _tp = 136.34 K is discussed. Comparisons with vapor pressure equations by Outcalt and McLinden, Duarte-Garza and Magee. and Kubota et al. are also given.     

Characterization of spin polarized dilute3He-4He solutions below 500 mK

We have prepared a large sample of spin polarized liquid ³ He- ⁴ He at 500 mK. Polarization is obtained by laser optical pumping, and studied by pulsed NMR. We have observed a nuclear magnetization lifetime T ₁ longer than 1 hour, and an anomalously long, non linear decay of tranverse magnetization.Unité de recherche de l'Ecole Normale Supérieure et de l'Université Pierre et Marie Curie, associé au CNRS (URA 18).