黑磷在超强磁场中的电输运性质研究

Two-dimensional (2D) crystals have emerged as a new class of materials with diverse physical properties. This is best exemplified by graphene, and more recently by transition metal dichalcogenide MoS2. These two 2D materials, however, are limited either by the lack of bandgap (in graphene) or the low carrier mobility (in MoS2). Our group, in collaboration with Prof. Xian Hui Chen group at USTC, has recently discovered that a novel 2D material, black phosphorus (BP), overcomes both limitations with a direct bandgap while retaining high carrier mobility. We found that a new 2D electron system (2DES) can be induced at the interface between BP and boron nitride by a back gate, and the mobility of the 2DEG was found to be on the order of 1000 cm2/Vs at low temperatures. Such a high quality 2DEG sets the stage for further exploration of the quantum transport phenomena in this new material. However, as a newly discovered material, the study of BP is still at the early stage and many interesting quantum transport phenomena are still needed to be explored. In this project, we will investigate the quantum phenomena in ultrahigh magnetic field. Our current results indicate that exotic even-denominator fractional quantum Hall states may emerge in higher magnetic fields. BP 2DES may therefore provide a new venue for exploring exotic many-body physics that are potentially relevant for topological quantum computation.

二维单晶是一类有丰富物性的新材料，例如石墨烯和二硫化钼。其中，石墨烯有极高的电子迁移率，但缺乏能隙；二硫化钼有大的能隙，却受限于低的电子迁移率。申请人所在的课题组和中国科技大学陈仙辉课题组合作发现的新型二维半导体材料黑磷则克服了石墨烯和二硫化钼的缺点：它既有能隙也有较高的电子迁移率。进一步研究发现，栅极电压在黑磷与氮化硼的界面处会产生新型的二维电子气系统。这个二维电子气在低温有几千的电子迁移率并且载流子浓度可以通过局部栅极电压系统调节。高质量的二维电子气为研究这个体系的量子输运现象奠定了基础。而作为一个新发现的材料，黑磷的研究还处于起步阶段，缺乏对相关量子输运效应的探索与研究。申请人针对这一重大挑战，致力于研究黑磷在超强磁场中的量子输运现象，完善对黑磷电子结构的理解。目前的结果显示黑磷可能在超强磁场中出现新的量子霍尔态，这不仅为多体物理的研究提供新的平台，而且可能直接应用于拓扑量子计算。

在项目执行的过去一年里，我们成功达到了项目的目标，原创性的成果好于预期。具体来说，我们的主要成果有：1）在国际上首次观测到新型二维半导体材料黑磷的压阻效应,并确定其物理机制是连续机械应变引起的黑磷能隙大小的改变。基于此效应，我们成功将黑磷制备成高精度应变传感器，并得到了优异的器件性能参数。这为今后制备基于黑磷的机电传感器提供了可能性。2）我们第一次在黑磷二维系统中观测到两极量子霍尔效应。我们发现黑磷较大的有效质量增强了二维电子气中的交换相互作用。3）我们首次在强磁场中观察到具有分数填充因子的强关联基态。这个效应和黑磷的各向异性有密切的关系。我们以上的这些成果为进一步在更高迁移率黑磷电子气中发现更多新的强关联基态奠定了基础。