Masamichi Saitoh

Surface Majorana cone of the superfluid 3He B phase

The superfluid 3 He B phase, one of the oldest unconventional fermionic condensates experimentally realized, is recently predicted to support Majorana fermion surface states. Majorana fermion, which is characterized by the equivalence of particle and antiparticle, has a linear dispersion relation referred to as the Majorana cone. We measured the transverse acoustic impedance Z of the superfluid 3 He B phase changing its boundary condition and found a growth of peak in Z on a higher specularity wall. Our theoretical analysis indicates that the variation of Z is induced by the formation of the cone-like dispersion relation and thus confirms the important feature of the Majorana fermion in the specular limit.

Application of surface acoustic wave sensors for liquid helium-4 and helium-3

A surface acoustic wave (SAW) sensor can be used to determine the acoustic properties of liquid He. We applied this sensor for liquid 3He and liquid 4He. Two kinds of SAW were used in this experiment, Rayleigh-SAW and shear horizontal SAW. The damping of Rayleigh-SAW was measured in liquid 4He. The results agreed well with the reported values of the acoustic impedance, and the superfluid transition was clearly seen. The damping and the phase shift of shear horizontal SAW were measured in the normal liquid 3He. Temperature dependence of the damping and the phase shift was analyzed by the viscoelastic model, and the results were compared with the transverse acoustic impedance in the normal 3He.

Surface condition dependence of transverse acoustic impedance in superfluid 3He

The surface states in superfluid 3He were studied by measuring the transverse acoustic impedance. To reveal the boundary condition dependence of the surface state, the surface was coated with 4He. Evidence of modification of the surface density of states was determined from the temperature dependence of transverse acoustic impedance in both superfluid A phase and B phase.

Transverse acoustic impedance of normal liquid 3He with 4He coating

We measured the transverse acoustic impedance of the normal liquid 3He at 16 MHz and 10 bar with and without 4He layers plated on a wall in the temperature range of 500 to 3 mK. The real component of the impedance gradually increased with cooling in the high-temperature hydrodynamic region and saturated in the low-temperature collisionless region. In the crossover region around 20 mK, the real component had a steep increase and the imaginary component was minimum. Overall change in the temperature dependence became smaller by 4He coating and we can obtain the specularity parameter S of the wall by fitting the temperature dependence of the experimental impedance to the theory.

Pressure Dependence of the Transverse Acoustic Impedance of Superfluid 3He‐B

We measured the pressure dependence of the complex transverse acoustic impedance of superfluid 3HE‐B using an AC‐cut quartz transducer. The measurements were performed by a CW bridge method at the third harmonics of the fundamental resonance frequency 9.56 MHz. We obtained the real (Z′) and the imaginary (Z″) parts of the transverse acoustic impedance independently. Z′ and Z″ did not change from the normal state values at Tc, but Z′ started to increase at the pair breaking edge temperature Tpb upon cooling. The slope of the increase changed at a temperature defined as T* which was lower than Tpb. With further cooling, it reached a maximum and then decreased slowly. Z″ had a small peak at T* and decreased rapidly with decreasing temperature. These temperature dependences were possibly influenced by quasi‐particle density of states within the energy gap originating from the surface Andreev bound states. At lower pressure the maximum of Z′ and the small peak of Z″ moved to smaller T/Tc and became larger due ...

Observation of A-B Phase Transition of Superfluid 3He by Transverse Acoustic Response

By using an AC‐cut quartz transducer at the frequencies of 9.56 and 28.7 MHz, we observed discontinuity in the temperature dependence of transverse acoustic impedance of superfluid 3He at 24.9 bar. Though the transverse acoustic response of superfluid 3He is not well understood, we can conclude that the discontinuity occurred at the A‐B transition, from its temperature and frequency dependence. Since the density of states near the boundary within a coherence length dominates the momentum transfer between an oscillating wall and 3He quasi‐particles, the large difference in the transverse acoustic impedance between the A and B phases can be explained by a difference in the symmetry of the order parameters near the wall.