NMR study of the dynamics of ³He atoms in dilution ³He-⁴He solid solutions

Superfluidity is a fascinating emergent phenomenon not only because matters are transported without energy dissipation but fundamentally it is a macroscopic manifestation of the quantum state of microscopic particles. Superfluidity was discovered in quantum liquids like liquid helium and most recently in ultra cold atomic gas Bose condensate. However the experimental evidence of the existence of superfluid state in the crystalline solid (“supersolid”) has been elusive in spite of a theoretical prediction more than 40 years ago [1]. The discovery of Non Classical Rotational Inertial (NCRI) in the solid ⁴He with torsional oscillator (TO) technique [2] ignited renewed interest in solid helium. Further studies indicate multiple possible origins of NCRI. In this presentation, I will give a concise introduction about the progress in the search for “supersolid”. I will also discuss our NMR experiments on dilute solid solution of ³He in ⁴He. We observed isotopic phase separation in all the samples we studied. We detected a significant change in the spin lattice relaxation time (T₁) in the regime where NCRI was reported, which suggests an abnormal dynamics of ³He atoms near the Larmor frequency. A phenomenological model of thermally activated relaxation is proposed to describe this anomaly.

[1] A. F. Andreev and I. M. Lifshits, JEPT 29, 1107 (1969)

[2] E. Kim and M. H. W. Chan, Nature 427, 225 (2004); Science 305, 1941 (2004)