Spin Current Manipulation in Superfluid 3He A1 Phase
A. Yamaguchi, Y. Aoki and M. Kubota
The superfluid phases of liquid 3He appear below a pressure-dependent transition temperature Tc. In zero applied magnetic field two superfluid phases known as A and B phases appear. In applied magnetic fields, a new A1 phase emerges between the two transition temperatures TC1 and TC2 where TC2< TC< TC1 at all pressures. The A1 phase has been regarded as a “ferromagnetic” superfluid phase whose condensate involves spin polarized pairs with the energy gap Δ↑↑>0 but Δ↓↓≡0. Such a unique phase like A1 phase has not been observed in any other condensed-matter system yet. Therefore, it is quite interesting to investigate this magnetically ordered superfluid A1 phase from the aspect of fundametal physics. The unique hydrodynamics of the A1 phase originating in the broken relative spin-orbit-gauge symmetry allows spin superflow to be created either by magnetic field or pressure gradient; In the magnetic fountain effect (MFE), an applied magnetic field gradient across a superleak is accompanied by a pressure gradient, creating spin-flow through the superleak; In the mechano-spin effect (MSE), on the other hand, the mechanically applied pressure gradient and the superleak serving as spin filter enable us to directly create spin supercurrent and to boost spin polarization of 3He in a small chamber. Recently, we have extensively studied the spin fluid dynamics in the A1 phase using both the MFE and MSE techniques [1-5]. One very important issue in the spin fluid dynamics is the origin of the unexpected spin relaxation that we observed in MFE experiments [1]. Understanding this spin relaxation would yield important clues in designing a spin-pumping device for boosting the spin polarization to much greater level than feasible by available static magnetic fields.
We are currently developing a new 3He -hydraulic actuator for achieving greater enhancement of spin density. The actuator consists of two small liquid 3He chambers located at a 4.2 K plate and in the interior of the cell. The pressure in the 4.2 K chamber is heater-controlled and it transmits a force onto a flexible membrane in the cell. The motion of the membrane induces spin-polarized current through an array of superleak capillary tubes into an accumulation chamber. At the same time, a high field-3He-NMR detector is tested to detect the polarization increase directly.
The superfluidity of liquid 3He in the higher magnetic fields is one of the long-standing unexplored topics in the ultra-low temperature physics. It might open up a new technique for manipulating the spin super current and for studying A1 phase in much greater effective field than the maximum 15 T static field so far achieved.
References
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- A. Yamaguchi, S. Kobayashi, H. Ishimoto, and H. Kojima, J. Low Temp. Phys., 148, 513 (2007)
- A. Yamaguchi, Y. Aoki, K. Suzuki, H. Ishimoto, and H. Kojima, J. Phys.: Conf. Ser. 150, 032122 (2009).
- A. Yamaguchi, Y. Aoki, S. Murakawa, H Ishimoto, and H. Kojima, Phys. Rev. B 80, 052507 (2009)
- Y. Aoki, A. Yamaguchi, K. Suzuki, H. Ishimoto, and H. Kojima, Phys. Rev. B 82, 054527 (2010