Properties of Two-dimensional 3He in 3He - 4He Mixture Films
Robert B. Hallock
Laboratory for Low Temperature Physics, University of Massachusetts, Amherst, MA, 01003, U.S.A.
3He atoms on a superfluid 4He film provide a unique example of an interacting two-dimensional Fermi system. NMR and specific heat experiments on this system reveal a number of its detailed properties and these will be described. For low 3He coverage, changes in the 4He substrate coverage allow the 3He energetics to be determined and a localization transition is seen. As the 3He coverage is increased, the two-dimensional system evolves from a very dilute Fermi fluid to an interacting two-dimensional Fermi liquid. A combination of NMR and specific heat measurements results in a determination of the two lowest order Landau Fermi liquid parameters F0A and F1S. Further increases in 3He coverage result in the occupation of a second two-dimensional quantum state. The subject will be surveyed with an emphasis on recent work.
2D 3He : from a pure spin-liquid phase to ferromagnetic clusters
E. Collin, R. Harakaly, C. Bäuerle, Yu. M. Bunkov, H. Godfrin
CNRS-CRTBT BP166, 38042 Grenoble Cedex 9, France
Using 4He and the "pushing gas" technique we have been able to tune the exchange constants of a solid 3He film (in the second layer of helium adsorbed on graphite) and to investigate this system by NMR techniques in a large temperature range, down to 100 microkelvins. We show that Dirac multi-spin exchange gives rise at low densities to a very stable gapped spin-liquid phase due to quantum frustration. As the 4He spreading pressure is increased we observe an evolution towards the well known ferromagnetic phase of 2D 3He, modified here by the nanometric size of the 3He two-dimensional clusters. This behavior is in agreement with recent theoretical calculations.
Evidence for Ferromagnetic Ordering of 3He Films on Graphite
H.M. Bozler, Jinshan Zhang, C.M. Gould
University of Southern California, Dept. of Physics and Astronomy, Los Angeles, CA 90089-0484, USA
Recent experiments at USC have shown that two-dimensional films of 3He on graphite order ferromagnetically at finite temperatures (T > 0) for densities above 20 atoms/nm2. These results, obtained by measuring NMR on these films in the zero field limit, appear to contradict several studies which concluded that there is no spontaneous order by measuring magnetic susceptibility through conventional NMR in finite magnetic fields, and heat capacity in zero field. The low field limit is important in understanding these two-dimensional magnetic systems. At higher temperatures and/or fields, these films have been described in terms of the multiple spin exchange model. However, two-dimensional systems are extremely sensitive to anisotropies such as nuclear dipole interactions, even when they are several orders of magnitude less than the dominant exchange mechanism. Supported by the NSF DMR-9973255.
Phonon velocity of 4He Bose fluids formed in one-dimensional 18Å-pores
Junko Taniguchia, Hiroki Ikegamib, Nobuo Wadac
aInstitute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
bRIKEN (Institute of Physical and Chemical Research), Wako, Saitama 351-0198, Japan
cDepartment of Physics, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan
We have studied 4He adsorbed on straight pores of 18Å in diameter by heat capacity and vapor pressure measurements. The second layer atoms adsorbed on the first solid layer become the Bose fluid that forms a tube of the diameter about 11Å. T-linear heat capacity of the fluid below about 0.2K is attributed to one-dimensional (1D) phonon excitations along the tube. Since the motion in the cross section is believed to be in the ground state, the 4He fluid is a true 1D Bose fluid. The phonon velocity vC derived from the phonon heat capacity almost agrees with vP deduced from the coverage dependence of the vapor pressure. The velocities indicate correlations in the 1D 4He Bose fluid.