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$$^4$$ He crystals usually sink to the bottom of the container in a superfluid and are deformed into a flat shape by gravity when their size is much larger than the capillary length of 1 mm. When gravity is reduced to zero, the capillary length diverges and the gravity-flattened crystals are expected to relax into an equilibrium crystal shape determined by the interfacial free energy at low enough temperatures where the relaxation time is very short. We performed a reduced gravity experiment on $$^4$$ He crystals at ultralow temperatures by developing a specially designed $$^3$$ He– $$^4$$ He dilution refrigerator compatible with the experimental restrictions in a small jet plane. $$^4$$ He crystals relaxed to the equilibrium crystal shape below 600 mK during a reduced gravity period of 20 s produced by a parabolic flight. The equilibrium crystal shape, however, was metastable in most cases, governed by the boundary conditions imposed by the wall. Utilizing acoustic radiation pressure, we deformed the crystal enough to allow it to escape from the metastable shape below 150 mK. After this large deformation, the crystal relaxed to a shape completely different from its initial shape, showing three types of facets, viz., c-, a-, and s-facets, which was concluded to be the lowest energy equilibrium shape.

Solid 4He shows unusual mechanical properties caused by interaction between dislocations and 3He impurities, both of which are highly mobile due to quantum nature of helium. Applying rotation to so...

To investigate the elastic properties of solid 4 He at low temperatures, the shear modulus of solid 4 He confined in a narrow gap, comparable to the length of the dislocation network of solid 4 He was measured. Two sets of parallel plate transducers were prepared. One set has a narrow gap of 11 μm and the other has a 290 μm gap as a reference of the bulk solid measurement. The temperature and strain dependences of the shear modulus were measured for solid 4 He in both cases. The increase of the shear modulus from 200 mK down to 14 mK was found to be smaller by 0.3 in the narrow-gap solid compared with the case of the bulk solid. By measuring the strain dependence of the shear modulus, the stress required to unbind 3 He in the narrow-gap solid was an order of magnitude larger than that in the bulk solid. These gap dependences can be related to the dislocation-network difference between two solids. The maximum length of the dislocation segment in the narrow-gap solid 4 He was found to be shorter than 6 μm, which was one order of magnitude smaller than that in the bulk. The difference of the network distribution is considered to originate in the difference of the crystal quality which is caused by the confinement effect in the slab geometry.

This paper presents a fully integrated SAR ADC for GSM/WCDMA/LTE triple-mode transceiver (RFIC) with non-binary DAC structure and digital correction techniques. All blocks including input buffer, ADC core, bias, references and ADC logics are implemented in a single chip with a small die area of 0.044 mm $^{2}$ /0.066 mm $^{2}$ for ADC core and ADC logic. The proposed ADC does not require off-chip decoupling capacitor for reference voltage by employing charge-sharing topology. Reconfigurable structure is used for multi-mode operation by adjusting ADC speed and noise, where SNDR of 67.0 dB in GSM and 58.2 dB in WCDMA/LTE are achieved at the sampling frequencies of 52 MS/s and 80 MS/s, respectively.

Crystal-superfluid interface of 4He in aerogel was shown to advance smoothly in a high temperature creep growth region above 0.6 K. In this report, we focused on the shape of the growing interface in the region and attempted to analyze the roughness of interfaces. The growth of rough interfaces is very common in nature and is known to often follow a scaling law; roughness usually increases with time and saturates in the later stage. We measured the roughness w(t) defined as the standard deviation of the interface height as a function of time t. It was found that w(t) in 98 % porosity aerogel initially increased with t and decreased after a particular time in the later stage. The abrupt reduction of roughness in the end of crystallization is unusual if it is intrinsic in the crystallization in aerogel.

4He crystals in a 96% porosity aerogel were grown by pressurization at 0.85 K; however, liquid pockets remained uncrystallized, even with application of a further overpressure, due to the absence o...

Topological superfluids and superconductors have been theoretically proposed, and it is now necessary to experimentally confirm their existence. Superfluid 3He should be the ideal test subject for topological theories because its bulk state is established to be that of a spin-triplet p-wave superfluid. Surface Andreev bound states of superfluid 3He were investigated by transverse acoustic impedance measurements and their linear dispersion was confirmed on a highly specular wall. The superfluid 3He B phase was found to be a topological superfluid showing bulk–edge correspondence and a surface Majorana cone was confirmed on the surface. Possible manifestations of the Majorana nature of the surface states are discussed.

Using a variable volume cell, we were able to crystallize 4He in aerogels at a constant temperature. The entire crystallization process was monitored visually owing to the transparency of the aerogel. Two different crystallization processes of 4He in aerogels were observed: creep at high temperatures and avalanche at low temperatures. In a 96 % porosity aerogel, we noticed that 4He remained liquid in some parts of the cell even though other parts of the aerogel were completely crystallized. Once such a situation was formed, the application of additional pressure did not further crystallize the liquid. This is presumably because a supply path of 4He atoms from the bulk crystal was blocked by the crystals in the aerogel. This leftover liquid, however, was found to begin to crystallize via avalanches when cooled below a particular temperature. If the crystallization pressure in aerogel is temperature independent at low temperatures as the bulk crystallization pressure, the crystallization by cooling is rather unusual. Possible explanations would be a decrease of the crystallization pressure in aerogel in the low temperature region, or the supersolidity of crystals in aerogel playing some role in mass transport.

Superfluid 4He was produced on a small jet plane for the first time using a small GM-refrigerator to condense the liquid and a scroll pump to get the superfluid by evaporation. The surface wave on superfluid under 0.5gE, 0.1gE and 0.05gE, together with 2gE and 1gE, was successfully examined by an optical method utilizing parabolic flight. Here, gE is the gravitational constant on the ground. Assuming that only the fundamental mode was excited as determined by the sample cell width, the resonance peak in the frequency domain was well reproduced by the gravity wave with corresponding gravity constant.

Surface Andreev bound states of superfluid 3He have been detected by transverse acoustic impedance measurement. In the diffusive limit of the quasiparticle scattering off a wall, a singularity in the temperature dependence of the acoustic impedance appears at a particular temperature. At this temperature, pair excitations of the surface Andreev bound state quasiparticle and the propagating Bogoliubov quasiparticle drastically change their nature due to a very sharp band edge of the surface Andreev bound states, resulting in the singularity of the acoustic impedance. This temperature dependence was well reproduced by a theory which properly takes into account the surface Andreev bound states. In a partially specular wall boundary condition achieved by coating the wall with thin 4He layers, the singularity shifted to a higher temperature since the bandwidth became broader as the specularity increased. The coating with 4He influences only the states in the vicinity of the wall and thus the shift is further evidence that the transverse acoustic impedance senses the surface Andreev bound states.

Crystallization of 4He in aerogels of 90 and 96% porosities shows a dynamical phase transition at around 600 mK due to the competition between thermal fluctuation and disorder: crystals grow via creep at high temperatures and via avalanche at low temperatures. In a very high porosity 99.5% aerogel, however, the transition had not been observed in our previous publication (Nomura et al. in Phys. Rev. Lett. 101:175703, 2008). We improved the spatial resolution of the video image and found that the 99.5% aerogel did have the transition at around 200 mK, which is much lower than those of the lower porosities. The avalanche size is significantly smaller in the 99.5% aerogel. The reduction in the transition temperature and avalanche size may be the consequence of weaker disorder for the crystallization in the very high porosity aerogel.

We measured transverse acoustic impedance Z of normal fluid 3He at 46.6 MHz on a surface coated with a thin 4He film. The real component of the impedance, Z′, in the coated samples deviates from Z′ in the pure 3He in the low temperature region. Z′ on the coated samples is almost identical with Z′ in the pure sample at high temperature and gradually deviates below a particular temperature T onset . T onset is possibly the superfluid onset temperature of the 4He film pressurized by the bulk liquid 3He. The gradual decrease in Z′ means that the superfluid component in 4He film increases gradually, which is expected from the dynamic KT transition at high frequency. The thicker is the film, the higher is the T onset . The range of T onset we observed was between 40 and 160 mK. This is much lower than that at the saturated vapor pressure. Suppression of T onset achieved by the applied pressure from bulk liquid 3He was presumably caused by the dissolved 3He in the film, thickening of the inert layers and/or by the strong correlation effect. The result shows that the specularity of 3He quasiparticle scattering is strongly affected by superfluidity of the 4He film.

We measured the complex transverse acoustic impedance in both superfluid 3He A1 and A2 phases. This impedance is sensitive to surface states. In our preliminary results, the temperature dependence of the impedance in the A1 phase is similar to that in A phase, and the imaginary part shows an anomaly in the A2 phase. These anomalies occurred at the temperature defined as T k , which is lower as the frequency gets higher. The similar frequency dependence of T k in each phase suggests that the anomaly is attributed to the same origin. The frequency dependence of the T k /T c indicates that the shape of the surface density of each spin pair state did not greatly change in the present experimental temperature range.

Dynamical transition of 4He crystals in aerogel was reported recently (Nomura et al. Phys. Rev. Lett. 101:175703, 2008). Bare aerogel, which was placed in the bulk 4He crystals, was used in the report. 4He crystals inside the aerogel grew via creep at high temperatures and via avalanche at low temperatures owing to the competition between thermal fluctuation and quenched disorder. Crystal-liquid interface advanced from the edge to inside of the aerogel. Crystal has a greater density than liquid so that the extra mass has to be transported in the crystallization process. It is not known how the mass is transported in the aerogel. To find a clue to this issue, we did an experiment with aerogel in a glass tube so that the aerogel had contact with the bulk on only one surface. In this case, a similar dynamical transition was observed at low temperatures. In the avalanche region, however, 4He crystals did not grow from the outer surface of the aerogel but nucleated at various sites inside the aerogel. This means that crystallization in aerogel does not occur by the forced invasion of 4He crystal but by a process of the bulk crystal once being melted and transported to increase the pressure of the liquid in the aerogel. Thus, a mass transport mechanisms for the crystallization has been revealed by this observation.

An enhancer trap-based GAL4-UAS system in zebrafish requires strong GAL4 activators with minimal adverse effects. However, the activity of yeast GAL4 is too low in zebrafish, while a fusion protein of the GAL4 DNA-binding domain and the VP16 activation domain is toxic to embryonic development, even when expressed at low levels. To alleviate this toxicity, we developed variant GAL4 activators by fusing either multimeric forms of the VP16 minimal activation domain or the NF-κB activation domain to the GAL4 DNA-binding domain. These variant GAL4 activators are sufficiently innocuous and yet highly effective transactivators in developing zebrafish. Enhancer-trap vectors containing these GAL4 activators downstream of an appropriate weak promoter were randomly inserted into the zebrafish genome using the Sleeping Beauty transposon system. By the combination of these genetic elements, we have successfully developed enhancer trap lines that activate UAS-dependent reporter genes in a tissue-specific fashion that reflects trapped enhancer activities. Developmental Dynamics 238:641–655, 2009. © 2009 Wiley-Liss, Inc.

In order to compare the bubble dynamics of various quantum liquids, we performed the visual observation of a sound-induced bubble in a normal liquid 4He, pure superfluid 4He, and superfluid 3He–4He liquid mixtures of saturated and unsaturated 3He concentrations. When an acoustic wave pulse was applied to these liquids under saturated vapour pressure, a macroscopic bubble was generated on the surface of a piezoelectric transducer. For all liquids, the size of the bubble increased, as a higher voltage was applied to the transducer at a fixed temperature. In the normal 4He we observed a primary bubble surrounded with many small bubbles which ascended upward together. In contrast to normal phase, only one bubble was generated in the superfluid 4He, and its shape proved to be highly irregular with an ill-defined surface. In the 3He saturated superfluid mixture, we also observed a solitary bubble but with a nearly perfect spherical shape. The bubble in this mixture expanded on the transducer surface, grew to a maximum size of the order of 1 mm and then started shrinking. As the bubble detached from the transducer with shrinking, we clearly detected an origination of the upward jet flow which penetrated the bubble. The jet velocity in the liquid mixture was approximately 102–103 times smaller than in water. At the final stage of the process we could sometimes observe a vortex ring generation. It is interesting that, though the bubble size and time scale of the phenomenon differ from those in water, the behaviour in the collapsing process had much in common with the simulation study of the vortex ring generation in water. In addition, for the mixture with the unsaturated 3He concentration of about 25% at 600 mK, the shape of the upward jet was observed distinctly, using more precise measurement with shadowgraph method.

In higher vertebrates, the expression of Sox2, a group B1 Sox gene, is the hallmark of neural primordial cell state during the developmental processes from embryo to adult. Sox2 is regulated by the combined action of many enhancers with distinct spatio-temporal specificities. DNA sequences for these enhancers are conserved in a wide range of vertebrate species, corresponding to a majority of highly conserved non-coding sequences surrounding the Sox2 gene, corroborating the notion that the conservation of non-coding sequences mirrors their functional importance. Among the Sox2 enhancers, N-1 and N-2 are activated the earliest in embryogenesis and regulate Sox2 in posterior and anterior neural plates, respectively. These enhancers differ in their evolutionary history: the sequence and activity of enhancer N-2 is conserved in all vertebrate species, while enhancer N-1 is fully conserved only in amniotes. In teleost embryos, Sox19a/b play the major pan-neural role among the group B1 Sox paralogues, while strong Sox2 expression is limited to the anterior neural plate, reflecting the absence of posterior CNS-dedicated enhancers, including N-1. In Xenopus, neurally expressed SoxD is the orthologue of Sox19, but Sox3 appears to dominate other B1 paralogues. In amniotes, however, Sox19 has lost its group B1 Sox function and transforms into group G Sox15 (neofunctionalization), and Sox2 assumes the dominant position by gaining enhancer N-1 and other enhancers for posterior CNS. Thus, the gain and loss of specific enhancer elements during the evolutionary process reflects the change in functional assignment of particular paralogous genes, while overall regulatory functions attributed to the gene family are maintained.

Static behaviors of crystallization of 4He in porous materials, such as the increase of melting pressure, have been studied extensively, but nonequilibrium dynamics of the phase transition is hardly known. Our interest was in how 4He crystals grow in a 90.4% porosity aerogel. Aerogels are transparent and the dynamics in them can be studied visually. A Pomeranchuk-type variable-volume cell was used to study crystallization at a fixed temperature with a blocked capillary condition. By continuously compressing a chamber, the pressure rose above the bulk melting pressure and at a pressure 1.7 bar above the bulk melting pressure these crystals began to invade the aerogel. A clear crystal-superfluid interface was moved smoothly by the steady compression. No macroscopic facets were observed in the aerogel well below the bulk roughening transition temperature.

We measured the complex transverse acoustic impedance of superfluid 3He in the B phase by coating a surface with 4He to study the boundary condition dependence of the surface bound states. Observed features in the temperature dependence were similar to those without 4He coating. However, temperatures showing singularities became higher and variations in the dependence became smaller. The small variations indicated that a specular surface was realized by the 4He coating. Increase in the singularity temperature indicated that the bandwidth of the surface Andreev bound states became broader by the coating.

The hydrogen molecules embedded in superfluid helium as a gas jet are shown to form long thin filaments. These filaments survived under a helium transition to anormal phase demonstrating their conjugated entity. The concentration of an impurity in the core of the vortex may be the mechanism of the impurity coalescence providing a cotton-like structure of the condensate obtained by introducing an impurity-containing gas helium jet to He-II.

When an acoustic wave pulse of several msec was applied to superfluid 4He at melting pressure, 4He crystal was nucleated on the transducer and rapidly disappeared after the pulse. We measured thresholds of the acoustic wave power which induced a nucleation in the temperature range between 0.09 K and 1 K. The treshold of the nucleation exhibited no temperature dependence below 0.3 K. The nucleation was not induced above 0.6 K even if the injected acoustic pulse was strong. 0.6 K is close to the inversion temperature at which the direction of the force by acoustic wave was inverted on the solid-liquid interface of 4He [Phys. Rev. Lett. 90, 075301 (2003)]. Our observation indicates that the effect of acoustic radiation pressure contributes to the heterogeneous nucleation by acoustic waves.

We have developed a new technique to study the transverse acoustic properties of superfluid 3He, employing a shear horizontal surface acoustic wave (SH-SAW) sensor. The transverse acoustic impedance can be obtained from the velocity and damping of SH-SAW which acoustically couples with liquid 3He all the interface. Since ultrasonic measurements provide the information about superfluid order-parameter through the excitation of collective modes, the SH-SAW sensor is expected to be a useful tool to study the boundary effect of superfluid 3He. Preliminary measurements were carried out at pressures of 17 and 23 bar, by the pulse transmission method at a frequency of 70 MHz. At 17 bar, imaginary squashing mode was observed as the sharp drop of the imaginary part of acoustic impedance. At 23 bar, the supercooled A-B phase transition was observed, as a jump of the real part of acoustic impedance, which was not observed in the warming process.

Both nucleation of a 4He crystal in superfluid and that of a 4He superfluid droplet in crystal were found to be induced by a heat pulse at the melting pressure. The time evolutions of nucleation on a heater were directly recorded by a high-speed camera. Duration of the heat pulse was usually 2 msec in this report. The nucleated crystal grew with facets for 4 msec and melted with an irregular shape in 40 msec at 500 mK. The nucleated superfluid droplet in crystal also grew with facets, which was a so-called negative crystal, and disappeared in 10 msec. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Melting of solid 4 He in a superfluid was observed when sound pulses were applied to the surface. Amount of melting was measured by changing the sound power and pulse numbers. It is not proportional to the power but to the square root of it. Both power and pulse number dependences are explained consistently if the melting coefficient is about 10% larger than that of the growth coefficient.

A 4He quantum crystal can be grown from a superfluid liquid extremely quickly owing to the high crystallization rate at sufficiently low temperatures. Such crystals are readily deformed by an appli...

Liquefaction dynamics of 4He in a silica aerogel with porosity of 90% was studied optically at 2.4 K. At low condensation rate of gas into a sample cell the aerogel became opaque during the condensation and then finally cleared up. Liquid outside of the aerogel appeared after the liquefaction in the aerogel was completed. At high condensation rate liquid appeared outside of the aerogel first and filled the lower part of the sample cell. When the surface of the liquid reached the bottom of the aerogel, the aerogel sucked up the liquid and made a visible interface in the aerogel. The height of the interface was proportional to the square root of time. This behaviour was consistent with the Washburn model and the effective pore radius obtained was 9.4 nm.

Transverse acoustic response in the B-phase of superfluid 3 He was measured by using an AC-cut quartz transducer at a pressure of 17.0 bar. The measurements were performed by a CW bridge method at a frequency of about 9.6 MHz utilizing a quadrature hybrid and a high-frequency lock-in amplifier. By sweeping frequency around the resonance frequency of the transducer, in-phase and quadrature responses of the resonance were obtained from the output of the high-frequency lock-in amplifier. The change of the Δ Q −1 and the resonance frequency Δ f 0 which were proportional to the real and the imaginary part of the transverse acoustic impedance of superfluid 3 He were obtained separately.

A Joule-Thomson (JT) expansion refrigerator with a Gifford-McMahon (GM) precooler which had magnetic regenerator was installed in a dilution refrigerator for use in long-term experiments without the necessity of helium transfer. A helium circulation system was constructed in which the boiled-off gas was precooled by the GM refrigerator with strong cooling power and liquefied by a JT loop heat exchanger. The dilution refrigerator was operated for two months without liquid helium transfer. The cooling power of the JT refrigerator with magnetic regenerator material Er0·7Ho0·3Ni was about 3.5W and was about 17% larger than that with lead. Then, the performance and stability of the system was much improved with magnetic regenerator material compared with Pb because of the increase in cooling power. The system was able to have some margin for extra boil-off using magnetic regenerator material. The only maintenance needed was supplying of liquid nitrogen to the trap and cleaning it every four days. An automatic refilling system was made for liquid nitrogen trap. A vibration isolation system effectively reduced heat leakage caused by vibration of the GM refrigerator. Nuclear demagnetization was possible with this system and the nuclear stage was cooled down to sub mK temperature. This system is applicable to various low temperature apparatus as well as dilution refrigerator because of little modification of the cryostat.

We report an observation of the amplitude-dependent velocity increase of first sound in superfluid $^{4}\mathrm{He}$. We performed a precise sound-velocity measurement at a frequency of 430 MHz in superfluid $^{4}\mathrm{He}$ as a function of sound amplitude. In the pressure region higher than 18 atm, we found that the velocity of sound begins to increase as the sound amplitude is raised above the threshold power of 0.5 W/${\mathrm{m}}^{2}$. The effect becomes more conspicuous with increasing pressure and input power density, and at 22.5 atm, \ensuremath{\delta}c/c reaches as much as 3\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ at the input power density of 50 W/${\mathrm{m}}^{2}$. In the low-pressure region less than 18 atm, the velocity change is weak and in the opposite direction. This amplitude-dependent velocity change is not explained by the third-order nonlinear effect derived from Navier-Stokes equations. Despite this strong pressure dependence, the threshold power of the velocity change is almost constant throughout the pressure range, and is close to the onset power of vortex line growth, which suggests the phenomenon is related to the turbulence.

We have investigated a nonlinear phenomenon which appears in a focused sound in superfluid4He under pressure higher than 18 atm. Wave front distortion of the focused ultrasound by nonlinear effect was obtained by the Fourier transform of the transducer output as a function of the defocusing length. The wave was found to suffer discontinuous wave front distortion for the input power above a certain value. This distortion is well represented by the picture that a second wave whose phase is shifted by approx. π develops, and interferes with the original wave. The amplitude of this second wave decreases suddenly as the pressure is lowered below 18 atm and the nonlinear wave front distortion also disappears. The possible mechanism of this second wave generation are discussed.

Longitudinal sound velocity in unidirectional hybrid composites or high-strength fiber-reinforced plastics (FRPs) was measured along the fiber axis over a wide temperature range (from 77 K to 420 K). We investigated two kinds of high-strength crystalline polymer fibers, polyethylene (Dyneema) and polybenzobisoxazole (Zylon), which are known to have negative thermal expansion coefficients and high thermal conductivities along the fiber axis. Both FRPs had very high sound velocities of about 9000 m/s at low temperatures and their temperature dependences were very strong. Sound velocity monotonically decreased with increasing temperature. The temperature dependence of sound velocity was much stronger in Dyneema-FRP than in Zylon-FRP.

Superfluid (3)He is an intensively investigated and well characterized p-wave superfluid. In the bulk Balian-Werthamer state, which is commonly called the (3)He B phase, the superfluid gap is opened isotropically but near a flat boundary such as a wall of a container it can harbor interesting quasi-particle states inside the gap. These states are called surface Andreev bound states, and have not been experimentally explored in detail. Transverse acoustic impedance measurement has revealed their existence and provided spectroscopic details of the dispersion of the bound states. Recent theoretical arguments claim that the surface Andreev bound states of the superfluid (3)He B phase can be recognized as the edge states of the topological superfluid and be regarded as a Majorana fermion, a fancy particle which has not been confirmed in elementary particle physics. In this review, we present up-to-date knowledge on the surface Andreev bound states of the (3)He B phase revealed by acoustic spectroscopy and the possible realization of a Majorana fermion, along with related studies on this topic.

The response of ${}^{4}$He crystals to the rapid reduction of gravity down to practically zero in a superfluid was investigated visually, utilizing the parabolic flight of a jet plane. At a high temperature of 1.6 K, the shape of ${}^{4}$He crystals in the bcc phase did not change with a reduction of gravity during a parabolic period of 20 s, due to the low crystallization rate. At lower temperatures, such as 0.63 K, where the crystallization rate is sufficiently high, the shape of ${}^{4}$He crystals in the hcp phase changed significantly, relaxing to a quasiequilibrium shape under zero gravity, where the $c$ facet became enlarged and the $a$ facet emerged on the surface. The crystal did not detach from the sample cell wall at any time because the adhesive force manifested as partial wetting to the wall was sufficiently strong. Some crystals removed from the wall by an acoustic wave pulse were found to float and drift in the superfluid for approximately 4.2 s under zero gravity, although most of them were quickly reattached to the wall.

We have found that the surface specularity for $^{3}\mathrm{He}$ quasiparticle scattering is closely related to the superfluidity and the Kosterlitz-Thouless (KT) transition of $^{4}\mathrm{He}$ film adsorbed on the surface. The specularity is determined by measurements of the transverse acoustic impedance of bulk liquid $^{3}\mathrm{He}$. The unique point of our system is that we can control the correlation among $^{4}\mathrm{He}$ atoms in the film by changing the pressure of the bulk $^{3}\mathrm{He}$. The observed KT transition temperature is significantly suppressed by increasing the pressure, which suggests a strong correlation effect on KT transition.

Superconductor (Bi, Pb)2Sr2Ca2Cu3Oy samples were prepared in a single-phase polycrystalline form by adding a small amount of B2O3 as a flux. The samples prepared were examined by X-ray diffraction, magnetic susceptibility and electrical resistivity. The results of the experiment revealed that the addition of a small amount of B2O3 was very effective in forming the single high-Tc phase superconductor. Furthermore, the superconducting characteristic of the sample was enhanced by annealing under a low oxygen pressure of 1 13 atm.

The longitudinal sound velocity of the single crystalline La 1.88 Sr 0.12 CuO 4 was measured in order to examine the vortex dynamics in the mixed state. The sample was grown by the flux method in a platinum crucible. A longitudinal wave with a frequency of 200 MHz was propagated along both the c -axis and the a -axis under a magnetic field up to 14 T. For the perpendicular arrangement ( k ‖ the c -axis and B ‖ the Cu-O plane), the sound velocity enhancement due to the motion of pinned flux lines was below T c . The enhancement is in good agreement with the empirical Arrhenius form. The enhancement was also observed for the parallel arrangement ( k ‖ the a -axis and B ‖ the Cu-O plane), although the flux lines are not expected to couple with the longitudinal sound wave in a simple model.

The static magnetization of 3He film adsorbed on sintered silver powder has been measured for coverages from 0.10 to 0.54 atoms/»2 in steps of 0.02 atoms/»2 and at a coverage of 4.5 atoms/»2. Below 0.20 atoms/»2 the magnetization well obeys the Curie law, while above that coverage a ferromagnetic tendency appears. The coverage dependence of the magnetization greatly differs from that for graphite. At 0.23 atoms/»2 the magnetization has apeak like that for graphite; however, the magnitude of the peak is not so large. Furthermore, a multipeak structure is found in the isotherm of the magnetization at 0.2 mK. It has two prominent peaks at 0.23 and 0.29 atoms/»2, and two other peaks are found at 0.35 and 0.41 atoms/»2. These appear periodically with an interval of 0.06 atoms/»2, which is nearly equal to the coverage of one liquid layer.

We measured the transverse acoustic impedance of superfluid $^{3}\mathrm{He}\mathrm{\text{\ensuremath{-}}}\mathrm{B}$ with a wall coated by several layers of $^{4}\mathrm{He}$. The coating is known to enhance the specularity in quasiparticle scattering by the wall. We found a new anomaly, a bump and a peak, in the temperature dependence of the transverse acoustic impedance. This agrees with a theoretical calculation using a partially specular wall boundary condition. The new anomaly is shown to arise from a change in the surface density of states by coating and the scattering of thermally occupied surface bound states to other states. The change is towards the density of states of Majorana cone in the specular limit.

We have studied the propagation properties of a focused acoustic beam in superfluid 4 He at 300 mK under several pressures and observed new nonlinear phenomena under pressures higher than 18 atm. Under these high pressures (normal dispersion region), the received power is increased in proportion to the power input for the low-power region, but it is depleted rapidly after the saturation for higher power input. It exhibits several sharp dips for further increased power. This nonlinear phenomenon is a completely new one, so there is as yet no explanatory theory. We propose a possible mechanism to explain it which consists of two nonlinear processes.

The dynamical transition in the crystallization of 4 He in aerogel has been investigated by direct visualization and dynamical phase diagrams have been determined. The crystal-superfluid interface in aerogel advances via creep at high temperatures and avalanches at low temperatures. The transition temperature is higher at a higher interface velocity and lower in higher porosity aerogels. The transition is due to competition between thermal fluctuations and disorder for the crystallization process.

The dynamical transition in the crystallization of 4He in aerogel has been investigated by direct visualization and dynamical phase diagrams have been determined. The crystal-superfluid interface in aerogel advances via creep at high temperatures and avalanches at low temperatures. The transition temperature is higher at a higher interface velocity and lower in higher porosity aerogels. The transition is due to competition between thermal fluctuations and disorder for the crystallization process.