High pressure effect on the electrical properties of NiS2

A semiconductor-metal transition in the electrical resistance of NiS₂, which has been suggested to be a Mott transition, is observed with decreasing temperature under pressure up to 44 kbar. The transition temperature increases with pressure with a slope of $\text{dT}\text{dP}\text{= 6 ± 1 K/kbar}$. The activation energy in a semiconducting region is found to decrease with increasing pressure and to vanish at about 46 kbar. The critical pressure and temperature are predicted to be 46 ± 2 kbar and 350 ± 20 K.     

Pressure dependence of the magnetic transition fields of the quasi two-dimensional antiferromagnet (C2H5NH3)2 CuCℓ4

Using magnetic susceptibility measurements, we have studied the pressure dependence of the magnetic transition fields of powder samples of antiferromagnetic (C₂H₅NH₃)₂CuC?₄, for hydrostatic pressures up to P ～ 7 kbar. The spin-flop field H₁ decreases linearly with pressure $\text{(}\text{dH}{}_1\text{dP}\text{= ?(20±4)}\text{G}\text{kbar}\text{)}$, while the field corresponding to the paramagnetic transition H₂ shows an increase, ～ 70% for P～7 kbar, that is roughly quadratic with P.     

A note on the compression of cubic ZnS

Using X-ray diffraction the compression of cubic ZnS (sphalerite) has been measured to 9.4 GPa under hydrostatic pressure conditions. The results analysed using a two parameter Birch-Murnaghan equation may be presented by K₀ = 74.8 ± 3.2 GPa and K′₀ = 4.91 ± 1.2. These compare well with 3.76 ± 0.96 for K₀ = 76.5 GPa, the value calculated by Chang and Barsch from their wurzite data. $\text{Δa}\text{a}{}_{\mathrm{o}}$, the change in lattice parameter at 15 GPa in ZnS is $\text{0.255}\text{A}\text{?}\text{± 0.012}$ corresponding to a change of $\text{0.110}\text{A}\text{?}\text{± 0.005}$ in Zn-S distances at this transition to the metallic state.     

Pressure dependence of the superconducting transition temperature of Th4H15

Measurements of the superconducting transition temperature of Th₄H₁₅ under hydrostatic pressure up to 28 kbar are reported. The initial linear increase is found to be $\text{+42}\text{mK}\text{kbar}$.     

Pressure dependence of superconductivity in the pseudo-one-dimensional compound Tl2Mo6Se6

Measurements of the temperature and pressure dependences of the resistivity of the pseudo-one-dimensional ternary compound Tl₂Mo₆Se₆ are presented. We find that the conductivity parallel to the highly conducting c-axis is enhanced by pressure and the superconducting transition temperature T_c is suppressed by pressure at a rate $\text{?T}{}_{\mathrm{c}}\text{?P}\text{=?7.6×10}{}^{\mathrm{?5}}$ kbar^?1. These results are discussed in relation to the current models of transport in one-dimensional conductors.     

Magnetic ordering in uranium monophosphide

The magnetic ordering in uranium monophosphide (UP) has been studied by neutron diffraction from a single crystal in a magnetic field. UP orders at T_N ? 122 ± 0.1 K with the type-I antiferromagnetic structure (+-+-), the ordering taking place in a first-order transition. At T₀ = 22.5 K the ordered magnetic moment jumps from 1.7 μ_B to 1.9 μ_B. With a magnetic field H = 25 kOe applied along the [11&#x0304;10] direction, it is found that UP has the collinear single-$\text{K}$ type-I structure above T₀ and undergoes a first-order transition to the planar double-$\text{K}$ type-I structure, accompanied by a “moment jump” due to the change in the moment direction from <001> to <110>.     

Effect of temperature and pressure on the raman spectrum of As4S3

The Raman spectrum of crystalline As₄S₃ has been investigated as a function of temperature from 4 to 430 K at ambient pressure, and as a function of pressure to 70 kbar at ambient temperature. The external mode frequencies which appear clearly separated from the internal modes exhibit stronger pressure and temperature sensitivity compared to the latter modes. At the β-As₄S₃ to α-As₄S₃ phase transition near 410 K, the external modes change discontinuously indicating a first-order phase transition. The internal mode frequencies remain practically unaffected. The $\text{dv}\text{dP}$ and $\text{dv}\text{dT}$ data are analyzed using well established approaches. Application of non-hydrostatic pressure (>60 kbar) appears to destroy the crystallinity of As₄S₃.     

A phenomenological investigation of ππ → KK partial-wave amplitudes from hyperbolic dispersion relations

We calculate the $\text{ππ →}\text{K}\text{K}$ partial-wave amplitude g_J^(+-), J = 0, 1, 2, 3, in the unphysical region below the $\text{K}\text{K}$ threshold using partial-wave relations derived from hyperbolic dispersion relations. For g₁^(?) the results are in agreement with earlier calculations and we confirm the current low-energy predictions. For g_o⁽⁺⁾ we favour a down-type solution with a large positive $\text{K}\text{K}\text{→}\text{K}\text{K}$ s-wave scattering length.     

High pressure investigations of MoS2

MoS₂ has been studied to pressures of 50 kb (10 kb = 1 GPa) at ambient temperature. Electrical resistance measurements were made to 50 kb, and the effect of pressure on the energy gap E, was found to agree well with previous work. The variations in $\text{dE}\text{dP}$ reported in the literature were found to be an apparent result of sample orientation. Volume compression studies were made to 30kb, and X-ray structural studies to 42 kb. The compressibility data agreed well with the theoretical values derived from a model which assumed bond-stretching forces only. None of the experimental studies showed evidence of a phase transformation near 20 kb as reported by Bridgman.     

Semiconductor-metal transition in doped (CH)x: Thermoelectric power

Thermoelectric power studies of polyacetylene have been carried out as a function of dopant concentration and temperature. The thermopower of pure trans-(CH)_x is large $\text{(S =}\text{+850 μ V}\text{°K}\text{)}$ and positive consistent with p-type material. With iodine doping, (CHI_y)_x, the thermopower remains positive over the full range of concentration 0 < y < 0.22. The semiconductor-metal transition is clearly observed at n_c ? 3 mole %; S falls dramatically from $\text{S =}\text{+850 μ V}\text{°K}$ at y = 0.003 to $\text{S =}\text{+30 μ V}\text{°K}$ at y = 0.03. At higher concentrations, S remains nearly constant saturating at $\text{+18 μ V}\text{°K}$ in the heavily doped metallic polymer. Temperature dependences are consistent with metallic behavior at the highest dopant concentrations and hopping transport in the undoped and lightly doped polymer.     

Rotational analyses and vibrational assignments of the 463- and 474-nm bands of NO2

The excitation spectrum of NO₂ was investigated in the blue region by using a Nd:YAG laser-pumped dye laser. The 463- and 474-nm bands of the ²B₂-²A₁ system were identified and analyzed using the simplification that occurs if the excitation spectrum is monitored at particular wavelengths. Band origins and rotational constants were obtained. Vibrational assignments have been given to these bands by comparing the Franck-Condon Factors calculated for the ²B₂-²A₁ system with the fluorescence intensities of bands going to different vibrational levels of the ground state. The vibrational assignments and molecular constants obtained in this work are (v′₁, v′₂, v′₃) = (3, 11, 0)ν₀(K′ = 0) = 21584.1, $\text{B}\text{= 0.405}$, and $\text{∥}\text{?}\text{′∥ = 0.05}\text{cm}{}^{\mathrm{?1}}$ for the 463-nm band; and (v′₁, v′₂, v′₃) = (2, 12, 0), ν₀(K′ = 1) = 21104.9, $\text{B}\text{= 0.408}$, and $\text{∥}\text{?}\text{′∥ = 0.03}\text{cm}{}^{\mathrm{?1}}$ for the 474-nm band.     

Soft phonon mode at the martensitic phase transformation of AuCuZn2

The lattice dynamical property of AuCuZn₂ has been investigated by means of inelastic neutron scattering technique in connection with its martensitic phase transformation. The temperature dependent soft phonon was observed transformation. The temperature dependent soft phonon was observed around $\text{q =}\text{2}\text{3}\text{[110]}$ of TA₂ phonon branch. We have also found a premartensitic metastable phase, in which new satellite reflections at (H± $\text{2}\text{3}$, K ? $\text{2}\text{3}$, 0) have been observed around fundamental reflections with H + K = 4n. The atomic displacements of the soft phonon mode correspond to the atomic arrangement of the premartensitic phase.     

Influence of pressure on the inhomogeneous mixed-valent state in Eu3S4

The 21.7-keV nuclear gamma resonance of ¹⁵¹Eu was used for studying the inhomogeneous mixed-valent compound Eu₃S₄ in the presence range 0 to 15 kbar. At room temperature the activation energy for electron hopping between the crystallographically equivalent divalent and trivalent Eu sites was found to decrease with pressure by dE_a/dP = -1.8 ± 0.3 meV/kbar. No change of the mean valence of Eu with pressure was observed.     

Step algebras of semi-simple subalgebras of Lie algebras

For each pair (G,K) where G is a complex finite-dimensional Lie algebra and K a semi-simple subalgebra of G, we construct an associative algebra (step algebra) $\text{Y}$ (G,K) and a homomorphism i_*: $\text{Y}$ (G,K)→E(G) is the enveloping algebra of G. $\text{Y}$ (G,K) has the following properties: (1) If V is any G-module and x ? V a K-maximal vector, then sx = i_* (s)x is K-maximal for any s ? $\text{Y}$ (G,K); (2) If V is irreducible and a certain simple criteria is fulfilled, then any K-maximal vector can be written in the form sx_m, s ? $\text{Y}$ (G,K), where x_m is some fixed K-maximal vector. Because of these properties $\text{Y}$ (G,K) has great practical value when constructing irreducible representations of Lie algebras in a form which makes the reduction with respect to a semi-simple subalgebra explicit.     

The EPR and LMR spectra of the DO2 radical: Determination of ground-state parameters

The detection of lines in both the gas phase EPR spectrum at 9 GHz and the far-infrared LMR spectrum of the DO₂ radical is reported. The measurements are fitted with an appropriate Hamiltonian and several parameters for the molecule in the $\text{X}\text{?}{}^2\text{A″}$ state are determined. The majority of the transitions in the EPR spectrum are K-type doubling transitions and involve the a-component of the electric dipole moment. However the observation of one b-type transition (5₀₅-4₁₄) permits the determination of the off-diagonal component of the spin-rotation tensor, ?_ab, and an estimate of the relative magnitudes of the a- and b-components of the dipole moment. A combination of the parameters for HO₂ with those for DO₂ leads to a better understanding of the properties of the molecule. In particular, the r₀ molecular geometry has been determined more reliably than previously to be $\text{r}{}_0\text{(OH) = 0.9774}\text{A}\text{?}$, $\text{r}{}_0\text{(OO) = 1.3339}\text{A}\text{?}$, ∠HOO = 104.15°.     

Charge-density wave instability and nonlinear transport in Tl0.3MoO3 a new blue molybdenum oxide bronze

Single crystals of Tl_0.3MoO₃ blue bronze were grown by the temperature gradient flux technique for the first time. Tl_0.3MoO₃ crystalizes with monoclinic symmetry, space group C2, C2/m or Cm, $\text{a = 18.486(1)}\text{A}\text{?}$, $\text{b = 7.5474(6)}\text{A}\text{?}$, $\text{c = 10.0347(7)}\text{A}\text{?}$, β = 118.377(6)° and appears to be isostructural with the K_0.3MoO₃ blue bronze. The physical properties of Tl_0.3MoO₃ are similar to those of the K₃MoO₃ and Rb₃MoO₃ phases. The resistivity of Tl_0.3MoO₃ is highly anisotropic and its temperature susceptibility (4.2–300K) decreases sharply with decreasing temperature near the transition seen in the resistivity. The onset of another transition <60K is also indicated by the susceptibility data. Non-linear current-voltage (I–V) characteristics observed at ～70K above applied threshold voltages of the order of ～300mV/cm suggest the sliding of charge density condensate.     

A comparison of πππ, Kππ, πKKKK system produced in the reactions meson +p→3 mesons + p

A comparison is made of the low-mass three-meson systems (πππ), (Kππ), $\text{(π}\text{K}\text{K}\text{)}$ and $\text{(}\text{K}\text{K}\text{K}\text{)}$ diffractively produced in the reaction meson + proton → three mesons + proton. Several striking similarities and a few important differences are observed: (i) the reactions are consistent with the assumption that the three mesons decay entirely into a 0^? meson and a 0⁺, 1^? or 2⁺ resonance; (ii) the three-meson mass spectra have a peak ≈ 250 MeV above the effective threshold M_eff of the dominant decay mode and then fall off approximately as (mass)^?3;(iii) the average spin 〈J〉 = 0.55 + 1.1 Q_eff, where Q_eff = M - M_eff; (iv) the average orbital angular momentum 〈l〉 increases according to 〈l〉 = 0.75 Q_eff; (v) the three-meson states are produced dominantly in unnatural spin-parity states and no evidence for their being resonant is found; (vi) the only natural spin-parity states found are the well-established 2⁺ resonances A₂ and K¹ (1420); they have similar properties to the non-resonant unnatural parity states except for a dip at t = 0 in the dσ/dt distributions; (vii) both the unnatural and natural spin-parity states are produced mostly by an exchange of natural parity; (viii) there is evidence for two types of production mechanism with different polarization properties, one approximately conserving helicity in the t-channel and the other in the s-channel.