Possible relationship between Cu-NQR frequencies and Cu valence states in CuO2-planes for high-T c superconductors

We report on⁶³Cu-NQR frequency ν_NQR measurements on various high-T _c superconductors. An empirical relationship betweenT _c and ν_NQR is presented. We attribute this finding to variations in the valence state of the in-plane Cu ions which, due to the unusual electric polarizability of the O^2? ions, depends sensitively on the Cu?O distance.     

Dilation-analyticity and decay properties of interactions

LetH=H ₀+V be a Schrödinger operator onL ²(? ⁿ ). We show that the more dilation analyticV is, the slower it must decay at infinity.     

Antiferromagnetic phase transition in garnet-type AgCa2Co2V3O12 and AgCa2Ni2V3O12

Antiferromagnetic phase transition in two vanadium garnets AgCa₂Co₂V₃O₁₂ and AgCa₂Ni₂V₃O₁₂ has been found and investigated extensively. The heat capacity exhibits sharp peak due to the antiferromagnetic order with the Néel temperature T_N=6.39 K for AgCa₂Co₂V₃O₁₂ and 7.21 K for AgCa₂Ni₂V₃O₁₂, respectively. The magnetic susceptibilities exhibit broad maximum, and these T_N correspond to the inflection points of the magnetic susceptibility χ a little lower than T(χ_max). The magnetic entropy changes from zero to 20 K per mol Co²⁺ and Ni²⁺ ions are 5.31 J K⁻¹ mol-Co²⁺-ion⁻¹ and 6.85 J K⁻¹ mol-Ni²⁺-ion⁻¹, indicating S=1/2 for Co²⁺ ion and S=1 for Ni²⁺ ion. The magnetic susceptibility of AgCa₂Ni₂V₃O₁₂ shows the Curie-Weiss behavior between 20 and 350 K with the effective magnetic moment μ_eff=3.23 μ_B Ni²⁺-ion⁻¹ and the Weiss constant θ=−16.4 K (antiferromagnetic sign). Nevertheless, the simple Curie-Weiss law cannot be applicable for AgCa₂Co₂V₃O₁₂. The complex temperature dependence of magnetic susceptibility has been interpreted within the framework of Tanabe-Sugano energy diagram, which is analyzed on the basis of crystalline electric field. The ground state is the spin doublet state ²E(t₂⁶e) and the first excited state is spin quartet state ⁴T₁(t₂⁵e²) which locates extremely close to the ground state. The low spin state S=1/2 for Co²⁺ ion is verified experimentally at least below 20 K which is in agreement with the result of the heat capacity.     

Nuclear orientation study of182Ta in 2H-TaS2

Quadrupole-interaction nuclear orientation experiments have been performed on¹⁸²Ta (j^π=3^?1; T_1/2=115d) in 2H-TaS₂. γ-anisotropies up to ～ 30 % have been observed at a temperature of ～ 8 mK, which, however, is only about half of the value expected taking into account known results of TDPAC measurements on¹⁸¹Ta in 2H-TaS₂. In principle, matrices of dichalcogenides could be well suited for nuclear quadrupole resonance on oriented nuclei (NQR-ON) experiments.     

Electron density of states and superconducting Tc in A15-compounds

We compare the superconductivity parameters of V₃Ga and V₃Ge by the method of McMillan with the help of new neutron diffraction data obtained by P. Schweiss. We consider the strongly varying density of states in V₃Ga at the Fermi energy, a complication suggested by Labbé, Barisic, and Friedel. We find that increased electronic density of states contributes about equally with lattice softening to the enhancement of T_c in V₃Ga as compared to V₃Ge, although the values of N(O)J² = Mλ〈ω²〉 are roughly consistent with those obtained for some other metals by McMillan. The reason N(O) is not more effective in raising T_c is the partial compensation obtained from averaging over the narrow density-of-states peak which gives N ? 0.6N(O).     

A note on the mean square deviation of the voltage of a resistively shunted Josephson junction in the running state

We show that a resistively shunted Josephson junction, in steady state, satisfies the relation 〈V²〉_T = IR〈V_T〉, where V is the voltage, I is the bias current, R is the junction resistance, and 〈 〉_T is a time average.     

Global Foliations of Vacuum Spacetimes withT2Isometry

We prove a global existence theorem (with respect to a geometrically defined time) for globally hyperbolic solutions of the vacuum Einstein equations which admit aT²isometry group with two-dimensional spacelike orbits, acting onT³spacelike surfaces.     

Determination of the electron-phonon coupling constants from the experimental temperature dependences of superconducting gaps in MgB2

Experimental temperature dependences Δ_{σ, π}(T) of the energy of superconducting gaps for MgB₂ samples with the critical temperatures 22 K < T _c < 41 K have been fitted by selecting the renormalized electron-phonon coupling constants λ _ij with the use of the Moskalenko-Shul system of equations, the expression for the frequency of collective plasma oscillations obtained by Leggett for two-gap superconductors, and two fitting parameters. We previously obtained the dependences Δ_{σ, π}(T) by the multiple Andreev reflection spectroscopy of superconductor-constriction-superconductor junctions based on MgB₂ with various degree of disorder of the crystal structure. It has been shown that the intraband pairing constants are decisive for the superconductivity mechanism in MgB₂; in this case, √V _σσ V _ππ/V _σπ = 8–22 and the ratio of the interband constants α can range from 3 to 11. The set of the Eliashberg coupling constants λ _ij ⁰ has been qualitatively determined for relatively pure MgB₂ with maximum values T _c ≈ 40 K. The leading constant is 0.7 < λ _σσ ⁰ ≈ λ _eff ⁰ < 0.9 and depends on the choice of the upper integration limit in the Bardeen-Cooper-Schrieffer (BCS) model and the effective Coulomb repulsion μ _iff ^* . The characteristic ratio for the gap in the σ band is 2Δ_σ/k _B T _c = 5.0–6.5.     

Li- and V-NMR study of LiVS2

⁷Li- and ⁵¹V-NMR have been measured to make clear the electronic state in a two-dimensional triangular lattice LiVS₂. Knight shift of both ⁷Li- and ⁵¹V-NMR is almost independent of temperature below the phase transition temperature T_c of about 310 K from the paramagnetic state to non-magnetic state. The ⁵¹V- spin-lattice relaxation rate 1/T₁ reveals an exponential temperature dependence below T_c, indicating a gap structure of electronic state. These results are consistent with a non-magnetic state with a trimer singlet of V³⁺ spins below T_c.     

Excitation of inner hole states in heavy nuclei with the (τ, α) reaction at 205 MeV

Energy spectra have been measured for the (τ, α) reaction at 205 MeV on⁹⁰Zr, ^118,124Sn and ²⁰⁸Pb. Results on the valence neutron shells and on the inner 1f_7/2 shell in ⁹⁰Zr, 1g_9/2 subshell in ^118,124Sn (T_< and T_> components) and 1h_11/2 subshell in ²⁰⁸Pb are presented.     

Antiferromagnetic phase transition in garnet-type AgCa2Mn2V3O12 and NaPb2Mn2V3O12

Ferrimagnetism has been extensively studied in garnets, whereas it is rare to find the antiferromagnet. Present work will demonstrate antiferromagnetism in the two Mn–V-garnets. Antiferromagnetic phase transition in AgCa₂Mn₂V₃O₁₂ and NaPb₂Mn₂V₃O₁₂ has been found, where the magnetic Mn²⁺ ions locate only on octahedral A site. The heat capacity shows sharp peak due to antiferromagnetic order with the Néel temperature T_N=23.8 K for AgCa₂Mn₂V₃O₁₂ and T_N=14.2 K for NaPb₂Mn₂V₃O₁₂. The magnetic entropy change over a temperature range 0–50 K is 13.9 J K^?1 mol-Mn²⁺-ions^?1 for AgCa₂Mn₂V₃O₁₂ and 13.6 J K^?1 mol-Mn²⁺-ions^?1 for NaPb₂Mn₂V₃O₁₂, which are in good agreement with calculated value of Mn²⁺ ion with spin S=5/2. The magnetic susceptibility shows the Curie–Weiss behavior over the range 29–350 K. The effective magnetic moment μ_eff and the Weiss constant θ are μ_eff=6.20 μ_B Mn²⁺-ion^?1 and θ=?34.1 K (antiferromagnetic sign) for AgCa₂Mn₂V₃O₁₂ and μ_eff=6.02 μ_B Mn²⁺-ion^?1 and θ=?20.8 K for NaPb₂Mn₂V₃O₁₂.     

A study of electrical enhancement of polycrystalline MgZnO/ZnO bi-layer thin film transistors dependence on the thickness of ZnO layer

A polycrystalline MgZnO/ZnO bi-layer was deposited by using a RF co-magnetron sputtering method and the MgZnO/ZnO bi-layer TFTs were fabricated on the thermally oxidized silicon substrate. The performances with varying the thickness of ZnO layer were investigated. In this result, the MgZnO/ZnO bi-layer TFTs which the content of Mg is about 2.5 at % have shown the enhancement characteristics of high mobility (6.77–7.56 cm² V⁻¹ s⁻¹) and low sub-threshold swing (0.57–0.69 V decade⁻¹) compare of the ZnO single layer TFT (μ_FE = 5.38 cm² V⁻¹ s⁻¹; S.S. = 0.86 V decade⁻¹). Moreover, in the results of the positive bias stress, the ΔV_on shift (4.8 V) of MgZnO/ZnO bi-layer is the 2 V lower than ZnO single layer TFT (ΔV_on = 6.1 V). It reveals that the stability of the MgZnO/ZnO bi-layer TFT enhanced compared to that of the ZnO single layer TFT.     

Non-perturbative gravitational corrections in a class of N = 2 string duals

We investigate the non-perturbative equivalence of some heterotic/type II dual pairs with N = 2 supersymmetry. The perturbative heterotic scalar manifolds are respectively SU(1, 1)/U(1) × SO(2,2+N_V)/SO(2) × SO(2+N_V) and SO(4,4+N_H)/SO(4) × SO(4+N_H) for moduli in the vector multiplets and hypermultiplets. The models under consideration correspond, on the type II side, to self-mirror Calabi-Yau threefolds with Hodge numbers h^1,1 = N_V + 3 = h^2,1 = N_H + 3, which are K3 fibrations. We consider three classes of dual pairs, with N_V = N_H = 8, 4 and 2. The models with h^1,1 = 7 and 5 provide new constructions, while the h^1,1 = 11, already studied in the literature, is reconsidered here. Perturbative R²-like corrections are computed on the heterotic side by using a universal operator whose amplitude has no singularities in the (T, U) space, and can therefore be compared with the type II side result. We point out several properties connecting K3 fibrations and spontaneous breaking of the N = 4 supersymmetry to N = 2. As a consequence of the reduced S- and T- duality symmetries, the instanton numbers in these three classes are restricted to integers, which are multiples of 2, 2 and 4, for N_V = 8, 4 and 2, respectively.     

InGaAs/InP heterojunction-channel tunneling field-effect transistor for ultra-low operating and standby power application below supply voltage of 0.5 V

An In_0.53Ga_0.47As/InP heterojunction-channel tunneling field-effect transistor (TFET) with enhanced subthreshold swing (S) and on/off current ratio (I_on/I_off) is studied. The proposed TFET achieves remarkable characteristics including S of 16.5 mV/dec, on-state current (I_on) of 421 μA/μm, I_on/I_off of 1.2 × 10¹² by design optimization in doping type of In_0.53Ga_0.47As channel at low gate (V_GS) and drain voltages (V_DS) of 0.5 V. Comparable performances are maintained at V_DS below 0.5 V. Moreover, an extremely fast switching below 100 fs is accomplished by the device. It is confirmed that the proposed TFET has strong potentials for the ultra-low operating power and high-speed electron device.     

Highly mobile Einstein spaces in the large

We consider an Einstein spaceV of the Petrov type II or III admitting a group of motionsG of high order. First we calculate the composition law and topological structure ofG. ThenV (or its submanifolds of transitivity) is represented as the homogeneous spaceG/H ofG,H being a subgroup ofG, and the actionG onV and the topology ofV are determined. The topologies of the spacesV are as follows: ⁴ (spaceT*₂), ⁴ of ³ T¹ (spaceT ₂), ⁴ (spaceT*₃), ³ (submanifolds of transitivity in spaceT ₃).In two cases (spacesT ₂ andT ₃) we have obtained metrics free of singularities.     

Coherent magnetic vortex motion in optically formed channels for easy flow in YBa2Cu3O7−x superconducting thin films

We report our results of investigation of electric and magnetic properties of partially oxygen-depleted channels for easy vortex motion in YBa₂Cu₃O_7?x (YBCO) superconducting, 50-μm-wide, and 100-μm-long microbridges at temperatures below the onset of the superconducting state critical temperature T _c ^on . The channels were produced by means of a laser-writing technique. The writing was performed using a 0.1–0.3 W power, continuous-wave laser radiation focused down to a ~ 5 μm spot on the surface of a superconducting film in a nitrogen gas atmosphere, and resulted in perpendicular stripes (channels) with partial (x ~ 0.2) reduction of the oxygen content in the YBCO stripe. The oxygen-depleted channels exhibit a depressed T _c and lower both the critical current density and the first critical magnetic field, as compared with the laser-untreated areas. The bias current applied to the bridge self-produced a magnetic flux that penetrated the channels in a form of Abrikosov magnetic vortices that, subsequently, moved coherently (a quasi-Josephson effect) along the channels in the narrow temperature range of 0.943 T _c ^on –0.98 T _c ^on and manifested themselves as steps on the current–voltage characteristics of our microbridges. Our results demonstrate that laser-induced formation of artificial channels of the flux flow can be used for a precise control of vortex nucleation and their coherent motion in pre-assigned regions of thin-film YBCO devices.     

Ground states of a modified symmetric Anderson lattice in one dimension

Based on a previous exact solution of a one-dimensional symmetric Anderson lattice the energy distributions of pseudo-densities of states and the energies of localized and conduction electrons in singlet ground states are calculated. The Kondo-lattice temperature T_KL is obtained as T_KL ≈ (1/2 πUV²)^1/2exp(-/U/2V²) +1/4 πUV².     

Nuclear magnetic resonance studies of CePd2In and LaPd2In at low temperatures

We report on In nuclear magnetic resonance (NMR) and nuclear quadrupolar resonance (NQR) measurements on the new heavy-electron compound CePdZIn over a wide temperature range, from 45 mK up to 30 K. CePd₂In undergoes an antiferromagnetic (AF) phase transition at T _N = 1.23 K involving small localised Ce moments of 0.11 μ_B. In zero field, the spin-lattice relaxation rate T ₁ ^?1 (T) shows remarkable changes in its temperature dependence. Above 3 K, T ₁ ^?1 is constant and 850 sec^?1. Between T _N and 2T _N, (T ₁ T)^?1 = 330 (Ksec)^?1, but rapidly decreases below T _N. A Korringatype relaxation, characteristic for simple metals at low temperatures, with (T ₂ T)^?1 = 17(Ksec)¹ is resumed below 0.6 K. This value is an order of magnitude larger than (T ₁ T)^?1 for LaPd₂In and therefore is associated with low-energy excitations of the itinerant charge carriers with 4f symmetry. The T ₁ ^?1 data at various non-zero magnetic fields fall on a single curve when plotted as a function of (T/H) if H exceeds 3.5 T. Thus the AF ordering, the 4f moment fluctuations and the Kondo screening are drastically suppressed by the application of fields H of the order of 3.5 T.     

Magnetic behaviour in the semiconducting and superconducting regions of57Fe-doped La2−xSrxCuO4−σ

From Mössbauer and resistivity measurements on⁵⁷Fe-doped La_2?xSr_xCuO_4?σ samples, we have determined the phase diagram of the system for 0<x<0.35 and 1.5 K<T<295 K. Forx<~0.15, a magnetic ordering is detected at low temperature within the Cu sublattice within both the semiconducting and the superconducting phases. Forx>0.15, a Fe-induced spin-glass state is observed. Recent data on oriented powder samples are discussed.     

Mechanism of formation and decay of the compound nuclei150Gd produced by two entrance channels (16O+134Ba) and (40Ar+110Pd)

Excitation functions have been drawn for evaporation residues issued from¹⁵⁰Gd, a compound nucleus produced either by¹⁶O ions on¹³⁴Ba, or by⁴⁰Ar on¹¹⁰Pd. Absolute cross sections were measured for^145–147Gd,^145–147Eu,^141m Sm,^143m Sm,^140m Pm and^139m Nd. Complete fusion cross sections have been obtained and compared to calculated estimations based, at low energies, on the simple expressionσ _CF=πR _Fuss ² (1?V _Fus/E) whereR _Fus andV _Fus are respectively the distance and the potential for fusion atdV/dr=0. For high energies σ_CF=πR _cr ² (1?V_cr/E) with the model of critical distanceR _cr and critical potentialV _cr. Thresholds energies have been determined with a particular care. The analysis of the shape and the width of excitation functions, particularly for the emission of 4 and 5 neutrons, has been carried out and compared to calculated values. The difference between argon and oxygen induced reactions has been attributed to the difference inl population in the entrance channel.