Quantum geometric exciton drift velocity
Quantum geometric exciton drift velocity
复制标题
DOI：
10.1103/physrevb.103.115422
复制
发表时间：
2021-03-15
影响因子：
3.7
通讯作者：
Brey, Luis
中科院分区：
文献类型：
--
作者：
Cao, Jinlyu;Fertig, H. A.;Brey, Luis
在许多情况下，在绝缘基态之上的激子束缚的粒子-空穴对携带电偶极矩，允许它们通过耦合到电场来操纵。对于二维系统，我们证明了激子的这种性质是由其本征态的量子几何唯一确定的，并证明了它与我们称之为量子几何偶极子的量的密切联系。我们证明，这个量自然产生的激子在电场中的运动的半经典方程，增加了一个额外的项来自贝里的曲率的异常速度。在均匀电场中，这有助于激子的漂移速度，类似于激子在交叉电场和磁场中的预期速度，即使在没有真实的磁场的情况下。我们计算了几个有趣的例子，双层系统的弱层间隧穿和费米能的间隙，激子可以合理地描述为一个两体问题的半经典激子动力学相关的数量。这些量包括激子色散、其量子几何偶极子和其Berry曲率。对于一个简单的例子，两个缺口石墨烯层在一个消失的磁场，我们证明了有一个非零量子几何偶极子时，层是不同的，例如，具有不同的间隙，但是当层相同时消失。我们进一步分析的例子中存在的磁场，使我们能够检查涉及石墨烯的情况下，其中一个间隙是开放的朗道能级分裂。还考虑了涉及过渡金属二硫属化物材料的异质结构。在每种情况下，量子几何偶极和贝里曲率都以不同的方式发挥作用。在某些情况下，最低能量的激子状态被发现驻留在有限的动量，在这些系统中的玻色凝聚有趣的可能后果。此外，我们发现的情况下，量子几何偶极单调增加激子动量，这表明量子几何可以被利用来产生光电流从最初绑定激子与电场，而不需要通过隧穿或热激发克服有效的障碍。我们推测进一步可能的影响的半经典动力学的几何结构中的组成层受到相同或不同的电场。
In many situations, excitons-bound particle-hole pairs above an insulating ground state-carry an electric dipole moment, allowing them to be manipulated via coupling to an electric field. For two-dimensional systems, we demonstrate that this property of an exciton is uniquely determined by the quantum geometry of its eigenstates, and demonstrate its intimate connection with a quantity which we call the quantum geometric dipole. We demonstrate that this quantity arises naturally in the semiclassical equations of motion of an exciton in an electric field, adding a term additional to the anomalous velocity coming from Berry's curvature. In a uniform electric field, this contributes a drift velocity to the exciton akin to that expected for excitons in crossed electric and magnetic fields, even in the absence of a real magnetic field. We compute the quantities relevant to semiclassical exciton dynamics for several interesting examples of bilayer systems with weak interlayer tunneling and Fermi energy in a gap, where the exciton may be sensibly described as a two-body problem. These quantities include the exciton dispersion, its quantum geometric dipole, and its Berry's curvature. For a simple example of two gapped-graphene layers in a vanishing magnetic field, we demonstrate that there is a nonvanishing quantum geometric dipole when the layers are different, e.g., have different gaps, but vanishes when the layers are identical. We further analyze examples in the presence of magnetic fields, allowing us to examine cases involving graphene, in which a gap is opened by Landau level splitting. Heterostructures involving transition metal dichalcogenides materials are also considered. In each case, the quantum geometric dipole and Berry's curvatures play out in different ways. In some cases, the lowest energy exciton state is found to reside at finite momentum, with interesting possible consequences for Bose condensation in these systems. Additionally, we find situations in which the quantum geometric dipole increases monotonically with exciton momentum, suggesting that the quantum geometry can be exploited to produce photocurrents from initially bound excitons with electric fields, without the need to overcome an effective barrier via tunneling or thermal excitation. We speculate on further possible effects of the semiclassical dynamics in geometries where the constituent layers are subject to the same or different electric fields.