Sound velocity measurements of nuclear-ordered solid 3He along the melting curve

We have measured the temperature dependence of the 10.98 MHz longitudinal sound velocity of solid 3He in the nuclear-ordered U2D2 phase and in the paramagnetic phase along the melting curve. The temperature dependence of the sound was attributed to the contributions from the nuclear spin system and the molar volume change along the melting curve. The sound velocity increased with temperature as T4 in the U2D2 phase and the sound anisotropy due to the exchange interaction was found to be about 10% among single-domain crystals investigated. The average value of the Gruneisen constant of the spin wave velocity in the ordered phase was gamma(c) = 16 and is compared to the calculated value of the multiple-exchange model.     

High nuclear polarization in3He and3He-4He gas mixtures by optical pumping with a laser diode

New diode lasers delivering 50 mW output power at 1083 nm are shown to be efficient sources for optical pumping of helium. They can polarize nuclei in a³He gas up toM = 50% over the pressure range 0.4–1.6 torr. Larger nuclear polarizationsM of³He nuclei, of order 80%, can be obtained in³He-⁴He mixtures when the laser frequency is tuned to a⁴He line. A standard optical measurement of nuclear polarizationM has been extended to the case of³He-⁴He mixtures. The effect of various parameters on the steady-state polarizationM and on the pumping timeT _p is discussed.Laboratoire associé au Centre National de la Recherche Scientifique et à l'Université P. M. Curie     

Depression of the 3He melting curve by adsorptive solidification on carbon substrates

The depression of the ³He melting curve by up to one bar lower than the bulk melting curve for temperatures varying from the mK range up to 0.5 K was observed. Adsorptive solidification isotherms at several different temperatures were studied.     

Self-cooling of weak solutions of 3He in 4He during adiabatic melting

A new method of pressure regularization in the measuring cell is proposed for experiments on self-cooling of weak solutions. Preliminary results are presented for solutions with concentrations of 2% and 7%. Cooling by a factor of 1.5–2 was observed in the starting-temperature range 40–140 mK. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 3, 263–267 (10 February 1997)     

3D偏振演示实验

剖析了3D立体效果的形成原理,设计了3D演示实验装置.通过光偏振技术、透镜成像规律以及视觉暂留现象的运用,演示了3D立体效果形成过程.     

The polarization energy of normal liquid 3He

We present new quantum Monte Carlo calculations of the ground-state energy of liquid ³He using backflow and 3-body wavefunctions and twist-averaged boundary conditions. We estimate the effects of the 3-body potential and compare to experimental measurements of the unpolarized equation of state and the magnetic susceptibility. There is still a large discrepancy with respect to the magnetic susceptibility, requiring either improved nodal surfaces or going beyond the fixed-node method.     

T-violation neutron experiment and polarized3He

An experimental scheme of the spin detailed balance in polarized neutron transmission through a polarized nuclear target is discussed for the T-violation test. The value of the spin detailed balance is estimated by using the data of the scattering amplitudes. The nuclear polarizations of proton,³He and¹³⁹La are discussed for the T-violation experiment.     

Thermal studies of the spin liquid state and analog to the He melting curve in a geometrically frustrated magnet

Gadolinium gallium garnet, Gd₃Ga₅O₁₂ (GGG) has an extraordinary low-temperature phase diagram. Although the Curie–Weiss temperature of GGG is −2 K, GGG shows no long-range order down to T0.4 K. At low temperatures GGG has a spin glass phase at low fields (0.1 T), a field-induced long-range ordered antiferromagnetic state at fields of between 0.7 and 1.3 T, and, at intermediate fields, an apparent spin-liquid state without long-range order. We have characterized the intermediate field (IF) state through heat capacity, thermal conductivity, and magnetocaloric measurements. Our results show a sharp high-field phase boundary of the thermal irreversibility of the spin glass phase of GGG implying that the intermediate field phase is distinct from the spin glass. The lower field boundary of the AFM phase is shown to have distinct minimum at T0.2 K, in analogy to the minimum in the melting curve of ⁴He. The existence of such a minimum is confirmed by measurements of the latent heat of the transition below that temperature.     

Sound velocity measurement of nuclear-ordered U2D2 solid He along the melting curve

The sound velocity of a single-domain ³He crystal was measured in the nuclear-ordered low-field phase and the paramagnetic phase along the melting curve, using 10.98 MHz longitudinal sound. The temperature dependence of the sound velocity along the melting curve was explained by a nuclear spin contribution and the molar volume change along the melting curve. By comparing the measured velocity with thermodynamic quantities, we extracted the Grüneizen constant for the exchange energy. The anisotropy of the velocity in the ordered phase was investigated for three samples and was found to be smaller than 2×10⁻⁵ in Δv/v. The attenuation coefficient of the sound was much smaller than 0.2 cm⁻¹.     

The equilibrium polarization of an optically pumped3He target

The nuclear polarization of an optically pumped³He target can be determined by optical methods if one makes some assumptions on the kinetics of the pumping process. Experiments and calculations have been carried out to examine whether these postulates are permissible. A good agreement between experiments and theory confirms the correctness of the assumptions and consequently justify the determination of the nuclear polarization by optical methods.     

Theoretical study of a melting curve for tin

The melting curve of Sn has been calculated using the dislocation-mediated melting model with the `zone-linking method'. The results are in good agreement with the experimental data. According to our calculation, the melting temperature of γ -Sn at zero pressure is about 436~K obtained by the extrapolation of the method from the triple point of Sn. The results show that this calculation method is better than other theoretical methods for predicting the melting curve of polymorphic material Sn.     

Detection of 3He spins with ultra-low field nuclear magnetic resonance employing SQUIDs for application to a neutron electric dipole moment experiment

The precession of ³He spins is detected with ultra-low field NMR. The absolute strength of the NMR signal is accurately measured and agrees closely with theoretical calculations. The sensitivity is analyzed for applications to a neutron electric dipole moment (nEDM) fundamental symmetry experiment under development.