Yuichiro Wada

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.

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.

Acoustic properties of liquid measured by Rayleigh-SAW

Abstract Damping and velocity of Rayleigh surface acoustic waves (SAW) were measured in liquid 4 He . A Rayleigh-SAW propagates along the substrate surface by emitting compressional waves into the liquid and thus the damping of the Rayleigh-SAW is determined by the acoustic impedance of the surrounding liquid 4 He . Temperature dependence agreed well with the reported values of the impedance and the superfluid transition in 4 He was clearly seen. We also set up a reflection plate 1.5 mm above the SAW device which reflected the emission waves. They were converted back into the SAW and used to measure the velocity and damping of ultrasound in liquid 4 He separately.

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 ...