Superfluid Transition Of 3He Research Articles

Magnetic Field Dependence of the A-like to B-like Transition of Superfluid 3He in Aerogel

Longitudinal ultrasound attenuation of superfluid 3He in 98% aerogel has been measured at 33 bar and 6.22 MHz in the presence of magnetic fields up to 4.44 kG. The A-like to B-like (A-B like) phase transition in aerogel was identified by a rounded jump in attenuation while sweeping the temperature at a fixed magnetic field perpendicular to the direction of sound propagation. The suppression of the B-like phase was monitored as the magnetic field increased until the A-like phase region extended below our lowest attainable temperature (0.2 mK) at the highest field. In addition, the attenuation in the metastable A-like phase that appears when cooling in zero magnetic field was almost identical to the values observed in the A-like phase in high magnetic field.

A-B Phase Conversion and Coexistence of Superfluid 3He in Aerogel

We have studied phase transition of superfluid 3He at 2.4 MPa in cylindrical aerogel by NMR method. When the liquid is cooled down from the normal state, the A-like phase appears below superfluid transition temperature T which is suppressed in comparison with the transition temperature of the bulk liquid. With further cooling below the certain temperature T , , the A-like phase is converted into the B-like phase gradually. Both phases stably coexist within about 90 μK. When you keep the temperature constant in which both phases coexist, the A-B phase conversion stops. With furthermore cooling, the whole liquid becomes the B-like phase. The cwNMR spectra at the coexistence state suggest that the B-like phase is not uniformly distributed in the A-like phase like a large number of small bubbles in a liquid, but separated as a whole from the A-like phase. By applying a field gradient which changes as a function of square of radius, we found that the A-like phase is in the edge part with a cylindrical shape and the B-like phase is in the central part with a columnar shape.

Phase Transition of Superfluid 3He in Aerogel

We have studied phase transition of superfluid 3He in 97.5% porosity aerogel by NMR method. Above 1.0 MPa, superfluid phase transition has been observed. The transition temperature Tca is strongly suppressed from its bulk value. The Pressure-Temperature diagram suggests that superfluid phase will not appear below near 0.8 MPa. The A-B phase transition has been observed above 1.3 MPa, below which a state of superfluid phases remains to be identified. The temperature dependence of NMR frequency shifts Δf in the A-like and the B-like phases are almost linear at pressures below 2.4 MPa. We obtained the differential coefficient of NMR frequency shifts ∂(Δf)/∂(T/Tca) at 0.9Tca as a function of pressure, and it suggests that superfluid phase will not appear below near 0.8 MPa which is the same pressure estimated by P-T diagram.

Phase diagram of the A and B phases of superfluid 3He in aerogel.

We report the first measurements of the A-B phase transition of superfluid 3He confined within 98% silica aerogel in high magnetic fields and low temperatures. A disk of aerogel is attached to a vibrating wire resonator. The resonant frequency yields a measure of the superfluid fraction rho(s)/rho of the 3He within the aerogel. The inferred rho(s)/rho value increases substantially at the A-to- B transition of the confined superfluid, allowing us to map the A-B phase diagram as a function of field and temperature. At 4.8 bars, the B-T transition curve looks very similar to that in bulk with a simple reduction factor of order 0.45 for both transition field and temperature.

A–B transition of superfluid 3He in a slab with rough surfaces

We discuss the A–B transition of superfluid 3He in a slab with rough surfaces using the quasi-classical theory in the weak coupling approximation. The superfluid transition temperature is presented as a function of the slab width for various roughness parameters. The surface roughness suppresses the A phase order parameter parallel to the surfaces, and thus favors the B phase. This agrees with the results of a Ginzburg–Landau theory by Li and Ho.

Vortex core size in 3He– 4He films with monolayer superfluid 4He

The superfluid transition of 3He– 4He mixture films adsorbed on alumina powder is studied, with a 4He superfluid coverage near one layer. With up to 1.3 layers of 3He added, the transition becomes strongly broadened, indicating a linear increase in the vortex core size for 3He coverages below one layer. Annealing of the sample mixture at 4.2 K is found to be critically important in ensuring a homogeneous film across the porous substrate.

Scaling of the superfluid fraction and T(c) of 3He in aerogel

We have investigated the superfluid transition of 3He in different samples of silica aerogel. By comparing new measurements on a 99.5% sample with previous observations on the behavior of 3He in 98% porous aerogel, we have found evidence for a scaling of the transition temperature and superfluid density of 3He to the correlation length of the aerogel.

Scaling Properties of Superfluid 3He in Aerogel

We have investigated the superfluid transition of 3 He in different samples of silica aerogel. Several of these samples have been characterized using x-ray imaging, yielding information about the microstructure of the aerogel. In comparing new measurements on a 99.5% sample with previous observations on the behavior of 3 He in 98% porous aerogel we have found evidence for a scaling of the superfluid transition temperature to the correlation length of the aerogel. Furthermore, the superfluid density exhibits a similar universal behaviour over a range of values of reduced temperature. We discuss these new results in the context of superfluid pairing in the presence of a correlated disorder, specifically focussing on the fractal nature of the aerogel.

A-B transition of superfluid 3He with a film geometry

We have performedcwNMR experiments on superfluid3He confined to a parallel-plate geometry with a μm scale spacing for a wide pressure range. A static field was applied parallel or perpendicular to the plate surface. The spectra of two absorption signals, a main and a satellite, have been observed below the superfluid transition temperature in a parallel field. As the temperature decreased, the main signal decreased with shifts to higher frequencies, and the satellite grew with shifts to much higher frequencies. From the temperature dependence of these signals and the result in the perpendicular field, it is confirmed that the main signal and the satellite correspond to the A phase signal (ABM state) and the B phase signal (BW state), respectively. The temperature dependence of the two signals indicates that a phase transition from the A phase to the B phase occurs with decreasing temperature. By analyzing these signals, we determine A–B transition temperatures experimentaly. TheA–Btransition temperature normalized by the superfluid transition temperature is 0.95 at 20 bar, and decreased further to 0.70 at 0 bar for a thickness of 0.88 μm for pure3He. The values of TAB/TCwere slightly elevated when covering the surface with 4.5 layers of4He film, which suggests that this transition is also influenced by the surface condition.

3He in 99.5% Porous Aerogel at the Normal-Superfluid Transition

We have used a torsional oscillator to measure the superfluid density and dissipation near the superfluid transition of 3 He in aerogel of 99.5% porosity. We used a new cell (constructed at Penn State) for which the aerogel was grown in the pores of a ∼100 μm silver sinter. The cell was tested with 4 He and showed no signs of the second-sound resonances that have interfered with previous torsional oscillator measurements. The measurements with 3 He, presented here, were taken at pressures of 1.34 and 4.13 bars. We observed values of ρ s /ρ in the T→ 0 limit of 0.05 and 0.14 respectively. Our measurements show an increase in the dissipation on warming through T c . This series of measurements is ongoing and temperature sweeps at various pressures are planned.

Cooling of3He-4He dilute solution down to 97 ?K. Thermal boundary resistance between dilute solution and metal powder

We have cooled a3He-4He dilute solution down to 97 μK, which is the lowest temperature ever been achieved in a dilute mixture. However, there is no sign of the superfluid transition of3He quasiparticles in the solution. In the sub-millikelvin region, we have measured the thermal boundary resistance between the solutions and sintered metal powder as a function of temperature T. We find that the thermal boundary resistence is proportional to T−2 below 1 mK and that the resistance shows a strong dependence on magnetic fields below 0.1 T. These results suggest that the magnetic coupling is dominant in this temperature region. We have also estimated the heat leak into the dilute solution. It is found that the heat leak is proportional to the power of one third of inverse time, and the main source of the heat leak is ascribed to the viscous movement of3He quasiparticles.

Magnetization differences at the A-B transition of superfluid 3He

We report results from a new SQUID-based measurement of the total magnetization change of superfluid 3He at the A-B phase transition, ΔM AB total. We used a simple first-principles calibration technique. At low fields ∼0.03 T, our data agree with past measurements, verifying the long-standing discrepancy between ΔM AB total and ΔM AB nuclear, the magnetization change which is measured by NMR. Use of a self-shielded solenoid allowed the first measurement of ΔM AB total over the full range of magnetic field. We found the magnetization discrepancy to persist through the whole phase diagram.

Quasiclassical Green's function in slab geometry: Application to A-B transition of superfluid3He in a slab

We show that the quasiclassical Green's function method can be used in slab geometries when the separation is much longer than the Fermi wavelength; consequently, quantum interference effects due to the double walls can be averaged out. We apply the quasiclassical method to the A-B transition of superfluid3He in a slab with specular walls at arbitrary temperature. We consider the phase transition between the planar state and the BW state within the weak coupling theory. The phase transition is shown to be of second kind at all temperatures. We obtain the critical size at which the B phase becomes unstable as a function of temperature. AtT=0 K and at SVP, the critical size is estimated to be 0.78 µm.

A-B Phase Transition of Superfluid 3He Confined in Pore Geometry

A-B Phase Transition of Superfluid 3He Confined in Pore Geometry

Small heat exchanger using silver powder

A simple heat exchanger using silver powder for cooling pure liquid 3He is described. The temperature difference across the heat exchanger was less than 5μK at the superfluid transition of 3He with a thermal flux of 0.06 nW.

A-B Transition of Superfluid 3He under Magnetic Field at Low Pressures

Etude par l'approximation de couplage faible. Calcul de l'energie libre de la phase B et comparaison a l'etat planaire; bon accord du diagramme d'etat calcule avec les resultats experimentaux disponibles. Mise en evidence d'une transition d'ordre 1 au-dessous et d'ordre 2 au-dessus du point tricritique qui depend du parametre de Landau