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Spin Dynamics of Superfluid 3 He in Aerogel

Spin Dynamics of Superfluid 3 He in Aerogel. Osamu Ishikawa Osaka City University. Collaborator. H. Nakagawa, R. Kado, K. Obara, H. Yano, T. Hata H. Yokogawa, M. Yokoyama. Outline of talk. Aerogel properties and temporary phase diagram of superfluid 3 He in 97.5 % porosity

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Spin Dynamics of Superfluid 3 He in Aerogel

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  1. Spin Dynamics of Superfluid 3He in Aerogel Osamu Ishikawa Osaka City University

  2. Collaborator H. Nakagawa, R. Kado, K. Obara, H. Yano, T. Hata H. Yokogawa, M. Yokoyama

  3. Outline of talk • Aerogel properties and temporary phase diagram of superfluid 3He in 97.5 % porosity • coexistence phenomena of A-like and B-like phases • Spin Dynamics in A-like phase and B-like phase by pulsed NMR experiments • Suppresion of Tc

  4. empty aerogel Aerogel properties Aerogel in cylindrical glass for NMR cell aerogel is directly grown inside glass tube to avoid any space between glass and aerogel NMR coils are wound on outside surface of glass

  5. Surface to volume ratio about 50 [m2/cc]estimated by the B.E.T surface measurements and ~1000 [m2/g] with aerogel mass ~ 6 [m2] surface area for aerogel in sample • Pre-coating of 4He film 2.5 layers of 4He film on silica strand in aerogel are controlled with large surface area in a heat exchanger in the sample cell of 660 [m2].

  6. density [g/cc] 97.5% porosity concentration of silica [%]

  7. Evidence of weak periodicity in aerogel • Characteristic distance between strands by neutron scattering experiment

  8. small-angle X-ray scattering • silica beads with diameter of 8.4 nm • smooth surface of silica beads • （DS = 2.0） • Fractal dimension is 1.8

  9. Temporary phase diagram of superfluid 3He in 97.5 % porosity B-like phase A-like phase

  10. NMR experiments showed two phases in superfluid 3He in aerogel; A-like phase and B-like phase. (1) in A-like phase • an absorption spectrum being a narrow peak, shifted as a whole from the Larmor freq., showing a positive or negative shift depending on aerogels • the magnetization is the same as in normal state (2) in B-like phase • an absorption spectrum widely spread due to a “texture” depending on aerogels • the magnetization decreased as decreasing temperatures

  11. Continuous phase conversion from A-like to B-like phase Region A Coexisting signals on cooling from normal state 3.2MPa +4He film

  12. Warming up from coexisting temperature (from Region A)

  13. One peak signal in on cooling from normal state and on warming from below region A Region B Turn around experiment (1) 3.2 MPa with 4He film

  14. Turn around experiment (2) 2.35 MPa with 4He film Different spectra at 1.3 mK with cooling

  15. coexistence phenomena without 4He film Rapid spin exchange mechanism between liquid and solid covers coexisting phenomena 3He at 3.2MPa

  16. 3He at 2.1MPa Frequencies changed continuously with cooling liquid This is an evidence of coexisting phases

  17. on cooling on warming on cooling on warming D f [Hz] D f [Hz] D f [Hz] Temperature [mK] Temperature [mK] Tipping angle [deg] Spin dynamics by pulsed NMR (A-like phase) 2.4 MPa with 4He film

  18. D f [Hz] D f [Hz] D f [Hz] Tipping angle [deg] Temperature [mK] Temperature [mK] 1.55 mK 3.2 MPa with 4He film

  19. pure 3He 2.5 layers 4He film Magnetization [a.u.] Magnetization [a.u.] Temperature [mK] Temperature [mK] pure 3He Magnetization [a.u.] Temperature [mK] Magnetization measurement At 3.2 MPa, surface solid 3He shows Curie-Weiss magnetism on 2.5 layers of 4He film

  20. 2.5 layers 4He films with 2.5 layers 4He film Magnetization [a.u.] pure 3He Temperature [mK] Magnetization [a.u.] Temperature [mK] At 2.4 MPa, Curie-Weiss behavior almost disappears

  21. D f [Hz] Tipping angle [deg] Tipping angle [deg] Tipping angle dependent frequency shift is attributed to superfluidity But they are different from those in bulk liquid

  22. A rubust phase A rubust phase proposed by I.A. Fomin explains FID frequencies M.Miura and K.Nagai (Hiroshima univ.)

  23. Full Width at Half Maximum [Hz] Temperature [mK]

  24. Flare out texture in cylindrical cell Large peak at Larmor freq. And having a tail to higher freq. by cw NMR . Spin dynamics by pulsed NMR (B-like phase)

  25. 2.35 MPa  [ a.u.] D f [Hz] Different from flare out texture Similar to absorption of bulk liquid confined in slab geometry where magnetic field parallel to surface

  26. 104˚ An evidence showing that B-like phase is B phase V.V.Dmitriev et al., JETP Letters 76 312-317 (2002) 5.3 mm diameter 5.6 mm height 98 % aerogel Confirmation of the order parameter of B-like phase as that of B phase in bulk liquid “n-vector”

  27. D f [kHz] BS-mode Tipping angle [deg]

  28. Tcaero / Tcpure Suppression of Tc • Inhomogeneous Impurity Scattering Model includes a length L as a parameter. • L=16.0 mm for pure 3He, • L=16.5 mm for 3He+ 4He • with Radius R=4.6L. Thuneberg et al.

  29. Summary • Aerogel has average periodicity • Adding a small amount 4He helped us to observe coexisting phenomena by reducing solid contribution to NMR signal • Boundaries between phases are probably pinned at inhomogeneous parts • Tipping angle dependent frequency shifts were observed in A-like phase and in B-like phase. • A-like phase seems to be a robust phase by Fomin • B-lile phase seems to be BW state as in bulk liquid

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