Soliton-Like Spin State in the A-Like Phase of 3He in Anisotropic Aerogel

We have found a new stable spin state in the A-like phase of superfluid ³He confined to intrinsically anisotropic aerogel. The state can be formed by radiofrequency excitation applied while cooling through the superfluid transition temperature and its NMR properties are different from the standard A-like phase obtained in the limit of very small excitation. It is possible that this new state is formed by textural domain walls pinned by aerogel.      

Spin Fluctuations in A-like Superfluid Phase of 3He in Aerogel

The frequency spectrum of the spin fluctuations δ S(t) superimposed on the coherently precessing spin modes in the A-like superfluid phase in aerogel is analysed. It is shown that the low amplitude spin fluctuations could be most easily observed in the case of an uni-axially deformed aerogel. It is demonstrated, in particular, that for axially stretched (radially squeezed) aerogel described by the U(1)LIM model the fourth order harmonic in δ S _z (t) is erased, in contrast with what is expected for the long range Leggett orbital configuration in the ³He-A (ABM state).     

NMR in Superfluid A-Like Phase of 3He Confined in?Globally Deformed Aerogel in?Tilted Magnetic Field

NMR spectra in superfluid A-like phases confined in axially deformed aerogel in the presence of a magnetic field inclined with respect to deformation axis is considered. The characteristic features of dipole frequency shift in axially compressed and axially stretched cases are compared. In particular, it is shown that in axially stretched aerogel environment the stability region of coherently spin-precessing mode is rather narrow due to the U(1) LIM effect. The spectrum of high-frequency spin fluctuations accompanying coherently precessing spin modes is constructed.     

Experiments on 3He–4He Mixtures in Aerogel

We describe experiments on ³ He- ⁴ He mixtures in 98% open aerogel grown by cold-deposition (T80mK) of ⁴ He followed by the deposition of ³ He or alternatively by cooling down a homogenous mixture. The two approaches led to different ⁴ He film morphologies. We will also describe the observation of migration of ⁴ He from or toward the cell below 100 mK. This migration can lead to the exclusion of ⁴ He (other than the localized surface layers) for ⁴ He concentrations between 4% and 11% in the cell.     

3He Correlation Energy in the Random Phase Approximation: the One-Ripplon-Exchange Potential in Thin 3He–4He Superfluid Films

A new approach to the calculation of correlation energies in the random phase approximation (RPA) is introduced. The method is applied to the system of adsorbed ³ He in thin ⁴ He superfluid films. The ³ He component interacts by means of the exchange of virtual surface interactions (ripplons) in addition to the usual atom-atom interaction. We report on a calculation of the RPA contribution to the ³ He ground-state energy of a previously introduced model for this effective interaction called the one-ripplon-exchange potential (OREP). V_OREP is manifestly frequency dependent and complex. In this paper we study the differences in the RPA contribution to the ground-state energy between the fully complex and frequency dependent V_OREP and V_OREP in the real, static limit.     

Acoustics of a “Dirty” Fermi Liquid: 3He in Aerogel

An acoustic cavity containing ³He in 98% porous silica aerogel was used to investigate the effects of impurity scattering in a Fermi liquid. The pressure and temperature dependence of the sound attenuation in the normal Fermi liquid was extracted from the cavity response. The attenuation of sound displays behavior very different from the bulk owing to strong elastic scattering of quasi-particles by the silica strands. Using a visco-elastic model of the Fermi liquid, we find a mean free path restricted to 340 nm. Information on the sound velocity is inferred from the pressure dependence of the oscillation period of the cavity response. The data can be accounted for by a Biot model of the ³He liquid in the porous aerogel.     

3He in Aerogel – an Inhomogeneously Disordered Unconventional Superfluid

We have examined the superfluidity of ³ He in 98.2% porous silica aerogel with up to 34% ⁴ He at 21.6 bar. The mixture is phase-separated for ⁴ He fractions between 11% and 34%. The ⁴ He-rich, phase preferentially occupies the regions of highest silica density in the aerogel, thus modifying the distribution of the correlated disorder seen by superftuid ³ He. The ³ He T _c increases slightly with ⁴ He content while the superfluid fraction decreases rapidly. This behavior is inconsistent with that of ³ He in a homogeneously scattering medium and is analogous to that of a granular superconductor.     

Magneto-Absorption in the α Phase of Solid Oxygen at Megagauss Magnetic Fields

Optical absorption spectra of solid oxygen α phase and liquid oxygen were measured in high magnetic fields over 100 T using a single turn coil method. The absorption originates from the bimolecular transition was observed. The spectra strongly reflect the local magnetic interaction between two oxygen molecules. The shape of the absorption spectrum of the α oxygen changed dramatically with increasing magnetic fields, even though the absorption intensity of liquid oxygen simply declined. This difference cannot be explained by only the local magnetic interaction, and we speculate that the field induced lattice distortion plays an important role in the solid oxygen α phase.     

Preliminary Measurement of the Critical Casimir Effect near the Tricritical Point in 3He–4He Mixture Films

We report a preliminary measurement of the critical Casimir effect in ³ He- ⁴ He mixture films near the tricritical point. Whereas we had found that the pure ⁴ He film adsorbed on Cu substrates thins due to the critical Casimir force near the lambda transition, in our present experiments we find that the adsorbed mixture film thickens near the tricritical point. This difference in behavior most likely reflects the difference in the universality class of these two phase transitions and the difference in boundary conditions that the order parameter must satisfy at liquid-substrate and liquid-vapor interfaces.     

Sound Velocity Measurements in the Low and the High Field Phases of the Nuclear-Ordered bcc Solid 3He in Magnetic Fields

We have measured the temperature and magnetic-field dependences of the sound velocity for one longitudinal and two transverse waves in the low field phase (LFP) and the high field phase (HFP) of nuclear spin ordered bcc solid ³He crystals with a single magnetic domain along the melting curve. From sound velocity measurements for various crystal orientations as a function of the sound propagation direction, we determined the elastic stiffness constants, c _ij (T,B). In the LFP with tetragonal symmetry for the nuclear spin structure, we extracted six nuclear spin elastic stiffness constants Δc _ij ^ℓ (T,0.06 T) from the temperature dependence of the sound velocity at 0.06 T and Δc _ij ^ℓ (0.5 mK,B) from the magnetic-field dependence of sound velocity at 0.5 mK. In the HFP with cubic symmetry for the nuclear spin structure, we extracted three Δc _ij ^h (T,0.50 T) at 0.50 T and Δc _ij ^h (0.5 mK,B) at 0.5 mK. At the first-order magnetic phase transition from the LFP to the HFP at the lower critical field B _c1, large jumps in sound velocities were observed for various crystal directions and we extracted three . Using the thermodynamic relation between Δc _ij and the change in the internal energy for the exchange interaction in this system, ΔU _ex(T,B), Δc _ij are related to the generalized second-order Grüneisen constants Γ _ij ^X ≡∂ ²ln X/∂ ε _i ∂ ε _j as Δc _ij (T,B)=Γ _ij ^X ΔU _ex(T,B), where X represents some physical quantity which depends on the molar volume and ε _j is the j-th component of a strain tensor. In the LFP, the Δc _ij ^ℓ (T,0.06 T) were proportional to T ⁴, and Δc _ij ^ℓ (0.5 mK,B) were proportional to B ². We extracted for the spin wave velocity in the LFP, s ^ℓ , from Δc _ij ^ℓ (T,0.06 T) and for the inverse susceptibility, 1/χ ^ℓ from Δc _ij ^ℓ (0.5 mK,B). In the HFP, Δc _ij ^h (T,0.50 T) were proportional to T ⁴ and Δc _ij ^h (0.5 mK,ΔB) were proportional to ΔB(≡B−B _c1). We obtained for the spin wave velocity in the HFP, s ^h , from Δc _ij ^h (T,0.50 T) and for B _c1 from Δc _ij ^h (0.5 mK,ΔB). The values obtained for and were compared with the Multiple Spin Exchange model (MSE) with three parameters by using analytic expressions for s ^ℓ and χ ^ℓ . The three-parameter MSE does not agree with the observed Δc _ij in the LFP.      

Magnetic Field–Temperature Phase Diagram of Quasi-Two-Dimensional Organic Conductors Under Magnetic Fields

Under magnetic fields perpendicular to the conductive plane in quasi-two-dimensional organic conductors: -(BEDT-TTF)₂ MHg(SCN)₄ (M= K, Rb, and Tl), the experimentally reported H–T phase diagram has been explained partially. By the self-consistent numerical calculation including the quantum magnetic oscillation and the magnetic breakdown; in addition to the imperfectness of the SDW nesting, we try to completely understand the phase diagram.     

Phase transitions in alloys of the Ni–Mo system

The structure of Ni–20 at.% Mo and Ni–25 at.% Mo alloys heat treated at different temperatures was studied by the method of transmission electron microscopy. X-ray photoelectron spectroscopy was used to detect the sign of the chemical interaction between Ni and Mo atoms at different temperatures. It is shown that at high temperatures the tendency toward phase separation takes place. The system of additional reflections at positions {1 ½ 0} on the electron diffraction patterns testifies that the precipitation of crystalline bcc Mo particles begins in the liquid solution. At 900 °C and below, the tendency toward ordering leads to the precipitation of the particles of the chemical compounds. A body-centered tetragonal phase Ni₄Mo (D1_a) is formed in the Ni–20 at.% Mo alloy. In the Ni–25 at.% Mo alloy, the formation of the Ni₃Mo (D0₂₂) chemical compound from the A1 solid solution has gone through the intervening stage of the Ni₄Mo (D1_a) and Ni₂Mo (Pt₂Mo) formation.     

Effect of High Magnetic Fields on the Charge–Density–Wave State in NbSe3

We present a systematic study on a large magnetoresistance in NbSe₃ as a function of temperature under various pressures. The large magnetoresistance below T _c2 is observed as long as the T _c2-CDW phase exists. However, when the T _c2-CDW phase is suppressed totally by high pressure and the superconducting phase is induced at the same time, no anomaly, including the large magnetoresistance, is induced by a magnetic field up to 12 T. The origin of the large magnetoresistance is discussed by considering normal carriers on the ungapped Fermi surface created on the CDW transition and comparing this magnetoresistance with the pressure-induced magnetoresistance that is newly observed above T _c2.     

Phase Relations in the Reduction of Solid Solutions in the Co–Mn–Ti–O System

The hydrogen reduction of spinel solid solutions in the Co–Mn–Ti–O system was investigated by a static method. Six phase regions were identified in which the gas phase is in equilibrium with various combinations of -Co, TiO₂ (rutile), and solid solutions of variable composition: Co _A Mn _B Ti_{3 – A – B} O₄ (spinel), Co _m Mn_{2 – m} TiO₄ (spinel), Co _N Mn_{1 – N} TiO₃ (ilmenite), and Co _n Mn_{1 – n} O (NaCl). The equilibrium compositions of the solid solutions and the corresponding oxygen partial pressures were determined, and the general trends of the reduction of spinel solid solutions in the Co–Mn–Ti–O system were established.     

Phase Transitions of Superfluid 3He in 0.8-μm Slab Geometry

We have studied superfluid ³ He in 0.8 m slab geometry by cw-NMR method. The static magnetic field for NMR was 22 mT and was perpendicularly applied to the surface. At pressures from 5 bar to 27 bar, we observed the negative shifts of NMR frequencies below the transition temperatures. Moreover we observed the fast order phase transition with the supercooling phenomena at lower temperatures, but NMR frequencies did not show a jump as they do at the A-B transition in the bulk liquid. Although the phase at low temperatures seemed to be B-phase, NMR frequencies still had the negative shifts.     

Transport in 3He–4He Mixtures in Restricted Geometry

The effect of wall scattering on transport in dilute degenerate ³He–⁴He mixtures in quasi-2D flow channels or films is discussed. The calculation of the quasiparticle mean free path combines particle–wall and particle–particle collisions including the interference between them. The spin polarization affects the wall-driven contribution by changing bulk mean free path and particle wavelength. The expressions for the wall contribution to transport coefficients are especially transparent in the limiting cases of large and small bulk mean free paths. The calculated temperature, concentration, and polarization dependences of the transport coefficients allow one to extract parameters of surface roughness from experimental data on transport.     

On the Existence of Ternary Magnetic Phases in the In–Cr–Te System

Phase relations along the In₂Te₃–Cr₃Te₄ join of the In–Cr–Te system were investigated by differential thermal analysis, x-ray diffraction, and microstructural analysis, and the 600°C section of the InTe–CrTe–Te phase diagram was mapped out. Under the conditions of this study, the compounds InCr₂Te₄, In₂CrTe₄, and InCrTe₃ were not obtained. The only ternary compound identified is In₂Cr₆Te₁₁.     

Thermodynamic Modeling of Phase Equilibria in the U–Zr–N System

Inorganic Materials - A thermodynamic model is proposed for condensed phases in the ternary system U–Zr–N in the range 298–2800 K. The model is based on previously reported models...