NMR measurements of 2D ³He adsorbed on ZYX exfoliated graphite

We describe first successful usage of ZYX exfoliated graphite to cool adsorbed two dimensional (2D) ³He to ultra low temperatures (ULT). ZYX has much better characteristics as an adsorption substrate such as larger crystallite (platelet) size and smaller mosaic angle than Grafoil, a widely used exfoliated graphite in ULT experiments. In spite of the relatively small surface area of ZYX, we could perform a nuclear magnetization measurement of paramagnetic 2D solid ³He with continuous wave NMR below 10 mK. The data follow nicely the Curie law down to 200 μK. This indicates that ZYX can be used in experiments to study detailed density dependences of low temperature properties of 2D ³He including possible BCS transitions. We also show a preliminary result of pulsed NMR measurements of high density 2D fluid ³He adsorbed on ZYX preplated with a ⁴He monolayer.