Two-Dimensional Quantum Properties of Monolayer Helium Three Adsorbed on ZYX Graphite

我们通过测量物理吸附在石墨表面的^4He单层的热容和磁化强度，研究了二维费米子系统中的强关联效应。结果表明，该体系具有复杂的相图，在低密度区（Ⅰ区），准粒子有效质量比裸质量提高了10倍，可以用费米流体理论很好地描述其低温性质.在将密度增加到<-2>与底层相当的4/7相的密度（6.9nm2）时，热容和磁化强度的行为偏离费米流体理论，并显示出异常的自旋-质量分离倾向（区域II）。这一区域应该是一种新的量子流体，为此我们提出了4/7相（Mott局域相）掺杂零点空位（空穴）的假设。随着密度的进一步增加，出现了另一个区域，其中热容和磁化强度都没有明显变化（区域III）。然后在8.3nm以上，<-2>系统经历在区域III和铁磁相之间的两相共存区域（区域IV）。区域III也将是一种新的量子流体，其性质与区域II不同。在不久的将来，我们希望弄清楚它的流动性是来自于被提升到覆盖层的液相还是来自于掺杂了过量粒子的4/7相，我们验证了我们以前关于4/7相磁基态的无带隙量子自旋液体的说法。重要的是，在我们研究的整个密度范围内，在低至0.07 mK的温度下没有观察到带隙行为。这与三角晶格上哈伯德模型的路径积分重整化群计算是一致的，并且是具有阻挫的强关联费米子的一般性质。

We investigated strong correlation effects in two-dimensional Fermion systems by measuring hear capacities and magnetization of monolayer ^3He physisorbed on ^4He preplated graphite surfaces. Four distinct regions including so far unknown new quantum fluid phases were observed as a function of areal density, which indicates a rather complicated phase diagram for this system.At low densities (Region-I), the low temperature properties can be described well by the Fermi fluid theory where the quasi-particle effective mass is enhanced by ten times of the bare mass. Upon increasing density towards that (6.9 nm^<-2>) for the 4/7 phase which is commensurate against the underlayer, the behavior of heat capacity and magnetization deviates from the Fermi fluid theory and shows anomalous spin-mass separation like tendency (Region-II). This region should be a new quantum fluid, for which we proposed a hypothesis of the 4/7 phase (Mott localized phase) doped with the zero-point vacancies (holes). With further increasing density, there appears another region where both heat capacity and magnetization do not change appreciably (Region-III). And then above 8.3 nm^<-2> the system undergoes a two-phase coexistence region (Region-IV) between the Region-III and a ferromagnetic phase. Region-III would be also a new quantum fluid with different properties from those of Region-II. It is desired to clarify whether its fluidity comes from the liquid phase promoted to the overlayer or from the 4/7 phase doped with excess particles in the near future.We verified our previous claim of the gapless quantum spin-liquid for the magnetic ground state of the 4/7 phase. Importantly, no gapped behavior was observed at temperatures down to 0.07 mK in the whole density range we studied. This is consistent with the path integral renormalization group calculation for the Hubbard model on a triangular lattice, and would be a general property of the strongly correlated fermions with frustration.