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We have studied the B⇌A phase transitions in a rotating container. The initial state contains the equilibrium number of vortices, and after the A-B interface has traversed the container, the vortex state was studied using NMR. We find that the A-phase state resulting from a B→A transition contains the equilibrium number of continuous vortices. Possible explanations are discussed.

The phase-shifted NMR absorption response of an array of vortices to a harmonic modulation of the rotation velocity is discussed. The measured phase lag between the rotation drive and its response can be explained by a torque, which acts on the nonaxisymmetric vortex core cross-section and derives contributions from both the vortex displacement and velocity. The result supports the earlier conclusion that the NMR absorption signal can be employed for studying vortex motion in rotating3He-B.

The sensitivity of continuous-wave NMR can be increased with a high- Q resonance tank circuit by using superconducting wire and a GaAs FET preamplifier operating at liquid helium temperatures. We discuss impedance matching to obtain an optimal signal-to-noise ratio for input circuits operating at ≈500 kHz, with Q ≈10 3 –10 4 at an impedance level of 1 Mω and a noise voltage of 1.3nV/√Hz. High rf compensation of 1:10 5 is achieved with orthogonally oriented transmitter coils and an astatically wound pick-up coil. The performance is evaluated on the basis of resolution that we achieved in the measurement of the NMR line in normal liquid 3 He; this is better than 1 part in 10 3 of the peak amplitude, while in the integrated intensity the standard deviation from the mean is better than 0.3%.

In rotating 3 He-B a large energy barrier leads to a well-defined critical rotation velocity ω c ( T, p ) for the nucleation of quantized vortex lines. We have observed with cw NMR techniques the signature from single vortex lines, which nucleate at the cylindrical side wall of the rotating container proportional to ω−ω c above the nucleation threshold. Well-resolved steps are seen in the NMR absorption, when vortices enter the NMR cell and modify the order parameter texture in the presence of vortex-free counterflow. The steps have been calibrated to correspond to the nucleation of either single or multiple vortex lines, both in terms of their distance as a function of ω as well as the step height.

The homogeneously precessing domain (HPD) is a coherent dynamic order parameter state of 3He-B, which originates from the stiffness of the spin part of the order parameter. We have investigated the HPD state in the presence of vortex-free counterflow as a function of the rotation velocity ω. The energy difference between the orbital textures across the domain boundary leads to a shift of the boundary, such that the precessing domain shrinks ∝ω2. In the equilibrium vortex state no such shift is observed. By monitoring the shift vs ω we have studied the B phase superfluid density anisotropy in a magnetic field, the nucleation of quantized vortex lines at the side wall of the rotating container, and the spatial distribution of counterflow and vortices, when the number of vortices is less than in equilibrium.

A unique property of 3 He-B is vortex-free rotation, due to a high nucleation threshold of the singular vortices. In contrast to other superfluids, rotational states consisting of a vortex cluster surrounded by vortex-free counterflow form spontaneously and can also be prepared with a fixed number of vortices. The clusters can be analyzed by means of NMR measurements with high precision. These techniques have been exploited to study rotational states in the presence of different phase boundaries.

Superfluid counterflow in rotating vortex-free 3 3He-B induces distinct changes in the homogeneously precessing resonance domain: its volume is reduced and the NMR absorption increased. Both effects disappear if the domain fills the whole experimental cell.

NMR absorption by vortices in the homogeneously precessing spin domain is discussed in terms of a torque, which arises from spin-orbit coupling between the coherently precessing spins and the nonuniformity in the orbital order parameter in the vortex core. A new soft mode of the nonaxisymmetric vortex core has been observed to contribute to spin relaxation.

The measurement of cw NMR absorption in a homogeneously precessing spin domain of 3 He-B is discussed. The absorption is divided into several contributions, based upon their different dependences on the domain length. Within our experimental accuracy, we found no contribution linear with domain size which would be caused by surface relaxation on the cell wall.

We have performed NMR measurements on the flare-out texture of superfluid3He-B in a cylindrical container of 5 mm diameter in axial magnetic fields of 28.4 and 56.9 mT. The transverse cw NMR spectra have been analyzed both with respect to their overall shape and the spin-wave absorption peaks close to the Larmor frequency. Our analysis of the stationary state spectra, based on texture computations, yields the longitudinal resonance frequency v L (T), the magnetic healing length ξ H (T), and the dipolar length ξ D (T), which we report for pressures below 29 bar. A lattice of quantized vortex lines appears in the rotating state, and two additional textural free energy terms have to be included in the analysis. One of the terms is linear in the applied magnetic field and arises from the spontaneous magnetization of the vortex cores. The second term is quadratic in magnetic field; it is generated both by the superflow field v s (r) about the vortex core and the difference in the induced magnetizations of the vortex-core and the bulk superfluids. The rotational orienting effects have been studied for rotation speedsβ up to 2red/sec.

The thermal accommodation of H-gas atoms on a saturated superfluid-/sup 4/He-film-covered surface has been measured in the temperature range 0.18--0.4 K. A straightforward stationary-state measuring technique is employed whereby we determine the heat flux conducted by H-gas atoms from a superfluid-/sup 4/He-film-covered bolometer, biased above ambient temperature. The results agree with recent calculations of the thermal-accommodation properties dominated by sticking-evaporation collisions mediated by ripplon creation.

NMR measurements are reported on rotating3He-A in a long cylindrical geometry of 5 mm diameter at a liquid pressure of 29.3 bar and in axial magnetic fields of 14.2, 28.4, and 56.9 mT. At 28.4 mT, NMR studies are also reported in fields inclined by 25° and 90° from the axis of rotation. The frequency shift, the width, and the intensity of the spin wave modes localized on the soft vortex cores, as well as the additional broadening of the main NMR line during rotation, were measured as a function of temperature, angular velocity Ω, magnetic field intensity, and its inclination angle. Also observed were a critical angular velocity of vortex formation, hysteretic behavior in the number of vortices when comparing accelerating rotation to decelerating, and metastable vortex densities, presumably a vortex tangle after rapid oscillatory acceleration. The results can be understood in terms of the continuous 4π vortices first proposed by Seppala and Volovik.

The results from a series of transverse cw NMR measurements on the 3He superfluids in the rotating state are reviewed. The implications of these experiments on the structure of the quantized vortices in the A and B phases are discussed in the light of recent theoretical work on the order parameter distribution in the vortex lattice.

The low-temperature magnetic susceptibility of normal and superfluid 3He confined between mylar foils spaced 4.0 mu m apart shows a large and field-dependent enhancement over the bulk Fermi liquid magnitude. The excess susceptibility disappears when the liquid is doped with 0.5% 4He. The reason for the excess is unknown. The authors also studied the proton resonance of the mylar substrate and obtained spin polarizations large enough to permit the direct observation of double spin-flip RF absorption., späterer Zeitschr.titel. Journal of Physics C, Condensed matter

Magnetic anisotropy effects have been studied in 3He B with transverse NMR on liquid confined into 0.4 mm wide slits between flat parallel foils. The results have been fitted to recent theories on orientational effects in dynamic magnetism.

The phase diagram of quantized vortices in $^{3}\mathrm{He}$-$B$ has been obtained with two techniques. Our NMR measurements show that magnetization displays a pressure-dependent first-order phase change at ${T}_{V}(P)$. Our gyroscopic experiments reveal a transition curve ${T}_{G}(P)$ which marks an abrupt change in the critical velocity. Both curves show a weak magnetic field dependence, run similarly in the ($P$, $T$) plane, and seem to mark the same vortex-core transition.

We report transverse cw NMR measurements on the superfluid phases of3He at temperatures between 3 and 0.7 mK. Nuclear demagnetization of copper was used for refrigeration. For thermometry we employed pulsed NMR on platinum powder immersed in the liquid. The measurements on3He were carried out in two NMR coil assemblies in which the liquid was confined between parallel Mylar foils with separations of 0.37 mm and 4 µm. The transition temperatureT c was measured at pressures between 32 bars and the saturated vapor pressure; a pressure-independent increase of ∼11% was observed inT c with respect to earlier data obtained with the same apparatus. We found that our temperature scale is not proportional to that used in La Jolla. In the 4-µm stack we observe a reduction in the B → A transition temperature. In our measurements on the orientational anisotropy of the B phase we found qualitative agreement with the theory of Brinkman et al. We also measured the longitudinal resonance frequencies of the A and B phases between 32 bars and the polycritical point. In the 4-µm stack we found a negative NMR shift in the A phase when the field was oriented perpendicular to the Mylar plates, in agreement with the prediction of Takagi. The static susceptibility XB of the B phase was measured as a function of temperature at 18.7 and 29 bars; its low-temperature limiting value was observed to be (0.33±0.02)XN , independent of pressure. We use our data to estimate the strong coupling corrections to the size of the energy gap. The initial slope of the reduced gap in the A phase, ΔA/T c , was found to increase by ∼25% when the pressure increased from 21.1 bars to the melting curve, whereas in the low-temperature limit ΔB(0)/T c was found to be independent of pressure and close to its weak coupling value.

Rotating superfluid $^{3}\mathrm{He}$-$B$ is found to possess a new contribution to the NMR frequency shift, which changes sign on reversal of either the angular velocity of rotation or the magnetic field. For $p=29.3$ bars this gyromagnetic effect shows a discontinuity in magnitude at the first-order phase-transition temperature $\frac{T}{{T}_{c}}=0.6$, at which a change in the vortex-core structure takes place. These observations support the conclusion that the vortex core possesses a spontaneous intrinsic magnetization.

By doping bismuth with tellurium to increase the charge carrier density and thus speed up the slow nuclear spin-lattice relaxation the nuclear quadrupole heat capacity becomes measurable in contrast to pure bismuth. The quadrupole heat capacity is greatly influenced by doping, increasing by 64% over the pure bismuth value on the addition of 0.23 at. % of tellurium. This results from a local asymmetric distortion of the valence electron states of the bismuth ions around the impurity site.

The nuclear heat capacity of praseodymium in fields from 0 to 18.6 kOe has been measured from 16 to 300 mK. In zero field the metal was found to be ordered with average magnetic moments of 0.62μB and 0.05μB on the two inequivalent lattice sites. Above 10 kOe the Van Vleck behavior dominates and an induced moment appears on both sites. The corresponding induced hyperfine field has been employed for nuclear cooling.

The specific heats of the Rare Earth metals Eu and Er have been measured in the temperature range 0.03 to 0.8K. The measurements yield magnetic hyperfine parameters of 13.2 mK, 5.85 mK, and 42.3 mK for 151 Eu, 153 Eu, and 167 Er, respectively, corresponding to magnetic hyperfine fields of 0.26 and 7.2 MOe for Eu and Er. The nuclear quadrupole coupling constants were found to be −0.06 mK, −0.16 mK, and −2.7 mK for 151 Eu, 153 Eu and 167 Er.

Results from cw NMR measurements on superfluid 3He‐B in rotation are discussed. The measurements have been performed with the magnetic field oriented at different angles with respect to the rotation axis. The results illustrate the effect of rotation on different order parameter textures in a cylindrical container. In particular, they allow the textural vortex free energy to be determined. The influence of boundary conditions on different textures has been investigated.

MACHe3 (MAtrix of Cells of superfluid He3) is a project of a new detector for direct Dark Matter (DM) search, using superfluid as a sensitive medium. An experiment on a prototype cell has been performed and the first results reported here are encouraging to develop of a multicell prototype. In order to investigate the discovery potential of MACHe3, and its complementarity with other DM detectors, a phenomenological study done with the DarkSUSY code is shown., Comment: 6 pages, 3 figures, Proceedings of the 4th International Workshop on the Identification of Dark Matter (York, UK, 09/02/2002-09/06/2002)

The static susceptibility and the longitudinal resonance frequency of superfluid 3 He B have been measured at 18.7 bar from T c to 0.27 T c using continuous wave transverse NMR.

Cw transverse NMR measurements on the A phase of liquid 3He confined in 4 μm wide plane parallel slabs are reported. The negative shift predicted by Takagi is observed when the static field is oriented perpendicular to the confining surfaces.