K. Obata | Searcharxiv

arXiv2009

Evidence for a Self-Bound Liquid State and the Commensurate-Incommensurate Coexistence in 2D $^3$He on Graphite

We made heat-capacity measurements of two dimensional (2D) $^3$He adsorbed on graphite preplated with monolayer $^4$He in a wide temperature range (0.1 $\leq T \leq$ 80 mK) at densities higher than that for the 4/7 phase (= 6.8 nm$^{-2}$). In the density range of 6.8 $\leq ρ\leq$ 8.1 nm$^{-2}$, the 4/7 phase is stable against additional $^3$He atoms up to 20% and they are promoted into the third layer. We found evidence that such promoted atoms form a self-bound 2D Fermi liquid with an approximate density of 1 nm$^{-2}$ from the measured density dependence of the $γ$-coefficient of heat capacity. We also show evidence for the first-order transition between the commensurate 4/7 phase and the ferromagnetic incommensurate phase in the second layer in the density range of 8.1 $\leq ρ\leq$ 9.5 nm$^{-2}$.

cond-mat.other↗

arXiv2008

Spin-Echo Measurements for an Anomalous Quantum Phase of 2D Helium-3

Previous heat-capacity measurements of our group had shown the possible existence of an anomalous quantum phase containing the zero-point vacancies (ZPVs) in 2D $^{3}$He. The system is monolayer $^{3}$He adsorbed on graphite preplated with monolayer $^{4}$He at densities ($ρ$) just below the 4/7 commensurate phase ($0.8\leq ρ/ρ_{4/7}\leq 1$). We carried out pulsed-NMR measurements in order to examine the microscopic and dynamical nature of this phase. The measured decay of spin echo signals shows the non-exponential behaviour. The decay curve can be fitted with the double exponential function, but the relative intensity of the component with a longer time constant is small (5%) and does not depend on density and temperature, which contradicts the macroscopic fluid and 4/7 phase coexistence model. This slowdown is likely due to the mosaic angle spread of Grafoil substrate and the anisotropic spin-spin relaxation time $T_{2}$ in 2D systems with respect to the magnetic field direction. The inverse $T_2$ value deduced from the major echo signal with a shorter time constant, which obeys the single exponential function, decreases linearly with decreasing density from $n=1$, supporting the ZPV model.

cond-mat.str-el↗