Pulsed Nuclear Magnetic Resonance on 3He Adsorbed on Bare and 4He Preplated MCM-41 Using DC SQUID Detection

We report low field DC SQUID NMR measurements down to 1.5 K of ³He adsorbed in the pores of the mesoporous molecular sieve MCM-41. In the first experiment measurements were made on ³He adsorbed onto the bare pore walls of MCM-41 with coverages ranging from $n_{^{3}\mathrm{He}}=0.86n_{1}$ to full pores at $n_{^{3}\mathrm{He}}=1.79n_{1}$ , where n ₁ is the coverage for monolayer completion. A second experiment was performed with low ³He coverages ( $n_{^{3}\mathrm{He}}\sim0.01n_{1}$ ) on ⁴He preplated pores, where a crossover to a quasi-1D state is expected to occur at temperatures sufficiently below 700 mK. In both experiments relaxation times T ₁ and T ₂ ^* were measured as a function of temperature and coverage at frequencies from 80 to 240 kHz. The frequency dependence of the linewidth in the pure ³He experiment is extremely weak therefore T ₂ ^* ≈T ₂. The 1.5 K isotherm shows a small minimum in T ₂ ^* at a coverage corresponding to monolayer completion. In the experiment with ⁴He preplating there was no significant change in T ₁ or T ₂ ^* when the ³He coverage was doubled from $n_{^{3}\mathrm{He}}=0.01n_{1}$ to 0.02n ₁ at a ⁴He preplating of $n_{^{4}\mathrm{He}}=1.05n_{1}$ . This suggests that the relaxation times are dominated by single particle effects in the low density regime.     

Self-consistent approximations in the theory of triplet pairing superfluidity in3He

Spin-lattice relaxation times of bcc solid ³ He with impurity concentrationsx of ⁴ He, 1.4×10 ^?3 <x<7 × 10 ^?3 , have been studied by NMR pulse techniques in the temperature range 0.27 K<T<1.2 K. In the lower part of the temperature range a temperature-independent relaxation process governed by the impurities is observed and its characteristic timeT _1D varies as a simple function ofx:T _1D> ∞x ^?3; the features of this process seem to be consistent with a diffusion mechanism to some clusters of ⁴ He impurities. In this plateau region a long relaxation time is also measured and found to be insensitive tox and strongly dependent on the temperature. A phenomenological model is suggested.     

Theory of ion mobility in liquid3He

An ion interacting with quasiparticles in liquid³He is treated theoretically by summing most divergent terms in perturbation series of the self-energy of the ion and the vertex part. The ion Green's function is renormalized by a factorZ(T), and the vertex part byZ(T) ^?1, where \({\text{Z(T)}} = {\text{(T/T}}_F {\text{)}}^{{\text{2V}}_{{\text{0}}^{\rho ^{\text{2}} } }^{\text{2}} } \) , forT ₀?T?T _F. Here,T ₀=(m/M)T _F, withm the³He mass andM the ion mass, and \({\text{V}}_{0^\rho } \) is the strength of the interaction. The factor explains the weak temperature dependence of the mobility around the minimum atT ₀; we also discuss its effect on the behavior of the mobility in³He-B nearT _c.     

NMR Studies of 3He Droplets in Dilute 3He-4He Solid Solutions

We have performed measurements of the temperature dependence of the nuclear spin-lattice relaxation times (T ₁) for a wide range of ³He concentrations for dilute mixtures of ³He in solid ⁴He. The temperatures for phase separation are determined for ³He concentrations 500<x ₃<2000 ppm for a molar volume V _M =20.7 cm³. We report the temperature dependence of the nuclear spin-lattice relaxation times for ³He in the droplets formed after phase separation at low temperatures. The temperature dependence suggests that the interface ³He atoms responsible for the relaxation are degenerate, not solid-like.     

3He Vapor Pressure near Its Critical Point

Between 0.65 K and 3.2 K, the temperature dependence of the vapor pressure P of ³He is defined by the International Temperature Scale of 1990 (ITS-90). However, the ITS-90 vapor pressure equation was not designed to be consistent with the scaling law required for the second temperature derivative of the vapor pressure in the vicinity of the liquid-vapor critical point. In this paper, two scaling-type equations are used to describe the ³He vapor pressure in the region near the critical point. The first scaling equation contains two unknown coefficients which are obtained by taking as reference the temperature $\bar{T}$ at which the product (T _c ?T)P presents a maximum ( $\bar{T}=2.56736$  K). The second scaling equation contains three unknown coefficients which are obtained by using as references $\bar{T}$ and T _up=3.2 K, the upper value of the ITS-90 interval. In both equations we take for the critical temperature and pressure the values T _c =3.31554 K and P _c =114?632.7 Pa. The proposed equations, specially the second one, are satisfactorily compared with experimental data for P and dP/dT within the temperature range (T _c ?T)/T _c ≤0.065 and with semiempirical data for d ² P/dT ² within the temperature range 0.0001≤(T _c ?T)/T _c ≤0.03.     

Vortex Diffusivity and Core Diameter of 2D Superfluid in 4He Films on Gold and H2 Substrates

The two-dimensional (2D) ⁴He fluid films show the Kosterlitz-Thouless (KT) transition where pairing and unpairing of the 2D vortices play an important role. However, the vortex properties (the diffusion constant D, the core diameter a ₀) have not been precisely obtained for various conditions. Here, we accurately determined the parameter D/a ₀ ² by the high frequency dependence of the superfluid onset up to 180 MHz for the submonolayer ⁴He fluid films adsorbed on gold and H₂ (3.3 layers) preplated on gold, respectively. The superfluid onset coverage changes from 1.6 (gold) to 0.5 layers (H₂), which clearly indicates the large difference of the adsorption potential. The parameter D/a ₀ ² , on the other hand, has the same value for the coverages with the same KT temperature T _KT. This suggests that the vortex diffusions on both substrates have the largest value D～?/m in the quantum limit. The core diameter a ₀ was estimated to be the same magnitude as the de Broglie wavelength at T _KT between 0.1 and 0.9 K.     

Superfluid Phases of 3He in a Periodic Confined Geometry

Predictions and discoveries of new phases of superfluid ³He in confined geometries, as well as novel topological excitations confined to surfaces and edges of near a bounding surface of ³He, are driving the fields of superfluid ³He infused into porous media, as well as the fabrication of sub-micron to nano-scale devices for controlled studies of quantum fluids. In this report we consider superfluid ³He confined in a periodic geometry, specifically a two-dimensional lattice of square, sub-micron-scale boundaries (“posts”) with translational invariance in the third dimension. The equilibrium phase(s) are inhomogeneous and depend on the microscopic boundary conditions imposed by a periodic array of posts. We present results for the order parameter and phase diagram based on strong pair breaking at the boundaries. The ordered phases are obtained by numerically minimizing the Ginzburg-Landau free energy functional. We report results for the weak-coupling limit, appropriate at ambient pressure, as a function of temperature T, lattice spacing L, and post edge dimension, d. For all d in which a superfluid transition occurs, we find a transition from the normal state to a periodic, inhomogeneous “polar” phase with $T_{c_{1}} < T_{c}$ for bulk superfluid ³He. For fixed lattice spacing, L, there is a critical post dimension, d _c , above which only the periodic polar phase is stable. For d<d _c we find a second, low-temperature phase onsetting at $T_{c_{2}} < T_{c_{1}}$ from the polar phase to a periodic “B-like” phase. The low temperature phase is inhomogeneous, anisotropic and preserves time-reversal symmetry, but unlike the bulk B-phase has only $\mathtt{D}_{\text{4h}}^{\text{L}+\text{S}}$ point symmetry.     

Effect of nonideality on the collisional recombination coefficient in an ultracold plasma

The effect of nonideality on the dependence of the collisional recombination coefficient α in an ultracold plasma on the temperature T _e and density n _e of electrons is discussed. It has been shown that the dependence of the recombination coefficient on the density and temperature α ? n _e ² T _e ^?9/2 characteristic of a weakly nonideal plasma is transformed to α ? n _e ^1.2 T _e ^?2 when the ratio of the potential energy to the kinetic energy of an electron (nonideality parameter) reaches unity. As the nonideality parameter increases, the temperature dependence disappears and the density dependence becomes n _e ^1/2 . The existing theoretical results for various physical models have been analyzed and compared to the experimental data.     

Possible Existence of Dense Superfluid 3He-4He Mixture in Aerogel

While studying superfluid ³He of 2.4 MPa in 97.5 %-porosity aerogel with NMR/MRI techniques, we find that the T _C is reduced when more than adequate amount of ⁴He, which covers the surface of silica strands, is introduced. For a sample, whose T _C is reduced to as low as 0.9 mK, we find that the spin diffusion coefficient in the normal phase is increased by a factor of 1.56 both in high temperature region, where ³He-³He scattering dominates, and in low temperature region, where ³He-aerogel scattering dominates. This enhancement is attributed to a modification of Landau parameter $F_{0}^{a}$ from ?0.757 to ?0.62, which is a change towards less ferromagnetic direction. The modification of microscopic quantity could be explained if small amount of ⁴He has homogeneously mixed into liquid ³He in the aerogel.     

Spin waves in anisotropic superfluid3He

Spin waves in the A phase of superfluid³He are studied theoretically. It is assumed that the condensate in the A phase consists of theP-wave triplet pairs of the type suggested by Anderson and Brinkman. We show that the spin wave mode with a finite energy gap exists throughout the A phase. In particular atT=0 K the dispersion of the spin wave is given by, forvq<Δ, $$\omega ^2 = \omega _0^2 + 2(1 - \bar I)A\Delta ^2 + \tfrac{1}{3}(1 - \bar I)v^2 q^2 $$ where θ is the spin wave energy, ω _T =[ω ₀ ² +2(1?ī)AΔ²]^1/2 is the nuclear magnetic resonance energy,v is the Fermi velocity,q is the wave vector of the spin wave, andī=IN(0)=?1/4Z ₀ is the Landau-Fermi liquid parameter.     

Reduction of U(VI) in laser liquids POCl3-SnCl4-235UO 2 2+ -Nd3+

U(IV) is irreversibly accumulated during synthesis of laser liquids POCl₃-SnCl₄-²³⁵UO ₂ ²⁺ -Nd³⁺ prepared from various initial Nd(III) and U(VI) compounds, irrespective of the way of their introduction. The rate of U(IV) accumulation in POCl₃-SnCl₄-²³⁵UO ₂ ²⁺ -Nd³⁺ solutions increases with increasing UO ₂ ²⁺ and Nd³⁺ concentrations; for laser liquids with the Nd³⁺ luminescence lifetime τ > 150 μs the observed rate constant of U(IV) accumulation by the second-order reaction k ₂[U⁴⁺] is equal to (3 ± 1) × 10^?5 1 mol^?1 s^?1 at T = 380 K. U(IV) is accumulated during storage of POCl₃-SnCl₄-²³⁵UO ₂ ²⁺ -Nd³⁺ solutions in hermetically sealed glass cells at room temperature and upon irradiation of solutions by xenon lamp light in the spectral region of UO ₂ ²⁺ absorption. The U(VI) reduction proceeds by chemical and photochemical activation of uranyl with formation of stable U⁴⁺ complexes with dichlorophosphate ions and also with Nd³⁺. Deactivation of the uranyl ion excitation with proton-and chlorine-containing impurities prevents U(VI) reduction.     

Sublimation study of BiBr3

Steady-state sublimation vapour pressures of anhydrous bismuth tribromide have been measured by the continuous gravimetric Knudsen-effusion method from 369.3 to 478.8 K. Additional effusion measurements have also been made from 435.4 to 478.6 K by the torsion—effusion method. Based on a correlation of Δ_sub H ₂₉₈ ⁰ and Δ_sub S ₂₉₈ ⁰ , a recommended p(T) equation has been obtained for BiBr₃(s) $$\alpha - {\rm B}i{\rm B}r_3 :log{\text{ }}p = - C\alpha /T - 12.294log{\text{ }}T + 5.79112 \times 10^{ - 3} {\text{ }}T + 47.173$$ with Cα=(Δ _subH ₂₉₈ ⁰ +20.6168)/1.9146×10^-2 $$\beta - {\rm B}i{\rm B}r_3 :log{\text{ }}p = - C\beta /T - 23.251log{\text{ }}T + 1.0492 \times 10^{ - 2} {\text{ }}T + 77.116$$ with Cβ=(Δ _subH ₂₉₈ ⁰ +46.2642)/1.9146×10^-2 where p is in Pa, T in Kelvin, Δ _sub H ₂₉₈ ⁰ in kJ mol^?1. Condensation coefficients and their temperature dependence have been derived from the effusion measurements.     

Probable Observation of Quantized Vortex Lines Through Solid He Under DC Rotation

We report how one can detect quantized vortices in superfluids contained in cylindrical vessels in well-designed torsional oscillator (TO) experiments under DC rotation. We show the case of an artificial 3D superfluid (Fukuda et al. in Phys. Rev. B 71:212502, 2005) which is made of Kosterlits-Thouless 2D He film condensed on a porous glass substrate with a 3D connected surface of well-controlled pore size. We understand the TO experimental results with an extra energy dissipation peak under DC rotation by considering the circular quantized superflow around each of the vortex lines and interaction with thermally excited 2D vortices as discussed in Fukuda et al. (Phys. Rev. B 71:212502, 2005) and in Nemirovskii and Sonin (Phys. Rev. B 76: 224507, 2007). We discuss here the case of hcp solid ⁴He (see for ex. Balibar and Caupin in J. Phys., Condens. Matter 20:173201-1-19, 2008) and show the evidence of observation of the vortex lines penetration below a supersolid transition temperature (Kubota et al. in J. Low Temp. Phys. 158:572, 2010), T _c , where macroscopic phase coherence is realized. It is found at exactly the same temperature T _c , below which the hysteresis occurrs (Shimizu et ail. in arXiv:0903.1326, 2009). For hcp solid ⁴He we have reported the vortex fluid (VF) state onset temperature (Penzev et al. in Phys. Rev. Lett. 101:065301, 2008) T _o =??500 mK, by detailed drive velocity, V _ac dependence study using TO technique. The TO response of the hcp ⁴He is characterized by the energy dissipation peaked at T _p near 100 mK similar to the behavior in a KT transition. The real supersolid (SS) state occurs at T _c below T _p and much lower than T _o . Our observation of the evidence of vortex lines penetration just below T _c together with the VF state properties gives support for the idea that hcp ⁴He shares some features with the ??new type of superconductors??, where the vortex state, involving the VF as well as various vortex solid states, has been commonly discussed (Fisher et al. in Phys. Rev. B 43(1):130, 1991; Leggett in Quantum Liquids, Oxford University Press, London, 2006).     

Generalized Rotational Susceptibility Studies of Solid 4He

Using a novel SQUID-based torsional oscillator (TO) technique to achieve increased sensitivity and dynamic range, we studied TO’s containing solid ⁴He. Below ～250?mK, the TO resonance frequency f increases and its dissipation D passes through a maximum as first reported by Kim and Chan. To achieve unbiased analysis of such ⁴He rotational dynamics, we implemented a new approach based upon the generalized rotational susceptibility $\chi_{{}^{4}\mathrm{He}}^{ - 1}(\omega,T)$ . Upon cooling, we found that equilibration times within f(T) and D(T) exhibit a complex synchronized ultraslow evolution toward equilibrium indicative of glassy freezing of crystal disorder conformations which strongly influence the rotational dynamics. We explored a more specific $\chi_{{}^{4}\mathrm{He}}^{ -1}(\omega,\tau(T))$ with τ(T) representing a relaxation rate for inertially active microscopic excitations. In such models, the characteristic temperature T ^? at which df/dT and D pass simultaneously through a maximum occurs when the TO angular frequency ω and the relaxation rate are matched: ωτ(T ^?)=1. Then, by introducing the free inertial decay (FID) technique to solid ⁴He TO studies, we carried out a comprehensive map of f(T,V) and D(T,V) where V is the maximum TO rim velocity. These data indicated that the same microscopic excitations controlling the TO motions are generated independently by thermal and mechanical stimulation of the crystal. Moreover, a measure for their relaxation times τ(T,V) diverges smoothly everywhere without exhibiting a critical temperature or velocity, as expected in ωτ=1?models. Finally, following the observations of Day and Beamish, we showed that the combined temperature-velocity dependence of the TO response is indistinguishable from the combined temperature-strain dependence of the ⁴He shear modulus. Together, these observations imply that ultra-slow equilibration of crystal disorder conformations controls the rotational dynamics and, for any given disorder conformation, the anomalous rotational responses of solid ⁴He are associated with generation of the same microscopic excitations as those produced by direct shear strain.     

The Annealing Process in Solid 4He

We have used a torsional oscillator with square cross section and a resonance frequency of 185 Hz to confirm the nonclassical rotational inertia (NCRI) discovered by Kim and Chan (Nature 427:225, 2004; Science 305:1941, 2004). We have also found a strong correlation between the NCRI signal and a high dissipation Q ^?1 of 4×10^?6 of the oscillation above the transition temperature. Here, we present preliminary results of the annealing process in ⁴He at a pressure of 26 bar. When holding the temperature constant above 1 K we have observed a immediate rise in the period and a slow decay of the dissipation. The equilibrium value of Q ^?1 decreases with increasing temperature.     

Refinement of data on the volatility of octavalent plutonium in the form of tetraoxide PuO4

The previous determinations [1–5] of the enthalpy of adsorption of PuO₄ on the quartz surface, which was calculated with an error of ±6 kJ mol^?1, are insufficiently accurate. Gas thermochromatographic experiments aimed to refine the temperature of PuO₄ deposition under definite temperature and gas-dynamic conditions were performed. The carrier gas was an He-O₂ mixture (1: 1). From the data obtained, more correct value of ?δH _a ⁰ was calculated: 43 ± 4 kJ mol^?1. The standard enthalpy of sublimation δH _{298, subl} ⁰ of PuO₄ was estimated at 35 ± 10 kJ mol^?1 using the linear correlation between the enthalpies of adsorption and sublimation of transition metal oxides.     

On Flow of He II in Channels with Ends Blocked by Superleaks

We report an experimental investigation of a flow of the superfluid phase of ⁴He–He II—thermally induced by a fountain pump through vertical channels of square cross-section with ends blocked by sintered silver superleaks and its decay. We confirm the existence of a weakly temperature dependent critical velocity v _cr ^I of order 1 cm/s, which does not scale with the channel size and is therefore an intrinsic property of the self-sustained vortex tangle of vortex line density L, measured by second sound attenuation. In addition to the previously reported turbulent A-state characterized by L ^1/2=γ(T)(v?v _cr ^I ), where v is the mean superflow velocity through the channel, we have discovered a new B-state characterized by L=β(v?v _cr ^II ), where β seems only weakly temperature dependent. It poses an important question why, at higher flow velocities, the quadratic generation mechanism, so well established in thermal counterflow, ceases to work. We offer a phenomenological model assuming that in the B-state the coarse-grained superflow profile matches the classical parabolic profile, with a finite, temperature dependent slip velocity v _cr ^II of order few cm/s and that a confined viscous normal fluid flow of toroidal form is induced inside the channel due to the mutual friction force. When the fountain pump is switched off, after an initial decay, a confined quasi-viscous flow of a single-component fluid with an effective kinematic viscosity ν _eff(T) establishes, giving rise to the observed exponential decay. The values of ν _eff(T), calculated using our model from the measured decay times, are in agreement with those deduced from other experiments on decaying He II turbulence.     

On the Presence of 1D-Like Stripes in Superconducting Epitaxial La2 -x Sr x CuO4 thin Films

A large positive magnetoresistance (up to tens of percents) is observed in both underdoped (x?<?0.15) and overdoped superconducting La_{2? x}Sr_xCuO₄ (LSCO) epitaxial thin films, at temperatures far above the superconducting critical temperature T _c . In the underdoped regime, this magnetoresistance cannot be described by the Kohler rule and is due to the influence of superconducting fluctuations. On the other hand, in the overdoped regime, the Kohler rule does not seem to be violated. ?The strong magnetoresistance above T _c can be related to the preformed superconducting pairs existing well above T _c but forming a phase coherent superconducting state below T _c . The observations support the idea of a close relation between the pseudogap and the superconducting gap and provide evidence for the presence of pre-pairs above T _c . Both the observed fluctuations and the observed magnetoresistance are in accordance with the existence of 1D-like stripes. These results are further supported by recent high magnetic field measurements (up to 55 T) of the transverse magnetoconductivity σ _xy, which goes to zero for T→0 K.     

Measurements of the relaxation of quasiparticle branch imbalance in superconductors

An imbalanceQ in the quasiparticle populations of thek>k _F andk _F branches of a superconductor may be generated by the injection of a current through a tunnel barrier. This imbalance relaxes with a characteristic timeτ _Q . The steady-state value ofQ gives rise to a quasiparticle potentialV that differs from the pair chemical potential, and which may be measured by a second tunnel junction. Tinkham's theory of these effects is briefly reviewed. Detailed experimental results are presented for tin. Most of the data are for injection voltages much greater than the energy gapΔ(T). Close to the transition temperatureT _c ,Q relaxes by inelastic phonon scattering, andτ _Q ^ph =(1.0±0.2)×10^?10 Δ(0)/Δ(T) sec. This time is about one-half that estimated by Tinkham. At temperatures somewhat belowT _c, elastic scattering also contributes to theQ relaxation, provided the superconducting energy gap is anisotropic. With a size-effect-limited mean free path of about 2800 Å, we findτ _Q ^el ≈1.4×10^?10 sec forT/T _c <0.6, a value that is also in good agreement with Tinkham's theory. In a sample with a mean free path of 420 Å, and a greatly reduced anisotropy,τ _Q ^el was increased to about 10^?9 sec. Data were also taken for injection voltages close toΔ(T)/e. The degree of imbalance per unit injection current was greatly reduced, as predicted by the theory. Preliminary measurements were made on lead. At 4.2K (T/T _c =0.58) the characteristic time was about 3×10^?12 sec. The quasiparticle potential apparently increased steadily as the temperature was lowered, probably indicating that the characteristic time also increased. This result is not well understood. However, it is possible that recombination processes play a role in theQ relaxation in lead.