Superfluid Helium-3
Superfluid Helium-3
Liquid helium-3 at ultra-low temperatures exhibits various properties,
which are unimaginable for normal fluids, as a Fermi liquid with a strong interaction.
Amongst these unique properties, the P-wave superfluid phase,
which has a transition at an ultra-low temperature of 1-2 mK,
results in a number of interesting physical phenomena.
Our research aims to develop a deeper understanding of superfluid helium-3 from novel viewpoints such as from the surface or boundary of superfluid helium-3. Hence, our research began by asking simple questions. What is the state of the surface of superfluid helium-3? When the wall immersed in superfluid is vibrated along the wall plane, how does the motion of this vibration translate into superfluid?
In the anisotropic BCS state of a non S-wave superfluid, quasi-particle bounf state (Surface Andreev Bound State, SABS) emerge in the vicinity of a scattering body such as a surface. In addition, the Surface Density of State (SDOS) of quasi-particles changes from that of bulk. These behavior are a manifestation of the interference caused by a change in polarity of the pair potential that the quasi-particles experience. A surface bound state of quasi-particles is expected to realize in the B-phase of superfluid helium-3.
The figure below shows the density of states for the surface states. The B-phase of superfluid helium-3 has isotropic gaps opened on the Fermi surface, but the theory has indicated that in the vicinity of the wall, quasiparticle states exist in the gap.
In our resent studies, we have vibrated the wall as a shear mode motion, and have precisely measured its acoustic impedance and successfully captured the existence of the particular SABS, as shown in the figure. We have clearly shown that the motion of the wall propagates to the superfluid body through collisions of the quasiparticles generated as a result of the pair-breaking near the wall.
The parameter s in the figure represents the degree of specularity. The elastic scattering of the quasiparticles, which is like a reflection of light on a mirror, is called the specular limit, and is given by s=1. On the other hand, s=0 represents a diffusive limit, which means isotropic scattering in all directions. A normal solid wall is considered to be in a diffusive state represented by s=0. Our experiments have in fact confirmed this assumption.
What is interesting about helium-3 is that coating superfluid helium-4 on the wall can control the s-parameter. Hence, our laboratory is currently conducting these experiments, and it is becoming apparent that the states of the wall significantly affect the surface states.
Our research aims to develop a deeper understanding of superfluid helium-3 from novel viewpoints such as from the surface or boundary of superfluid helium-3. Hence, our research began by asking simple questions. What is the state of the surface of superfluid helium-3? When the wall immersed in superfluid is vibrated along the wall plane, how does the motion of this vibration translate into superfluid?
In the anisotropic BCS state of a non S-wave superfluid, quasi-particle bounf state (Surface Andreev Bound State, SABS) emerge in the vicinity of a scattering body such as a surface. In addition, the Surface Density of State (SDOS) of quasi-particles changes from that of bulk. These behavior are a manifestation of the interference caused by a change in polarity of the pair potential that the quasi-particles experience. A surface bound state of quasi-particles is expected to realize in the B-phase of superfluid helium-3.
The figure below shows the density of states for the surface states. The B-phase of superfluid helium-3 has isotropic gaps opened on the Fermi surface, but the theory has indicated that in the vicinity of the wall, quasiparticle states exist in the gap.
In our resent studies, we have vibrated the wall as a shear mode motion, and have precisely measured its acoustic impedance and successfully captured the existence of the particular SABS, as shown in the figure. We have clearly shown that the motion of the wall propagates to the superfluid body through collisions of the quasiparticles generated as a result of the pair-breaking near the wall.
The parameter s in the figure represents the degree of specularity. The elastic scattering of the quasiparticles, which is like a reflection of light on a mirror, is called the specular limit, and is given by s=1. On the other hand, s=0 represents a diffusive limit, which means isotropic scattering in all directions. A normal solid wall is considered to be in a diffusive state represented by s=0. Our experiments have in fact confirmed this assumption.
What is interesting about helium-3 is that coating superfluid helium-4 on the wall can control the s-parameter. Hence, our laboratory is currently conducting these experiments, and it is becoming apparent that the states of the wall significantly affect the surface states.
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