Researchers at the Center for Theoretical Physics of Complex Systems (PCS), within the Institute for Basic Science (IBS, South Korea), and colleagues have reported a novel phenomenon, called Valley Acoustoelectric Effect, which takes place in 2-D materials, similar to graphene. This research is published in Physical Review Letters and brings new insights to the study of valleytronics.

In acoustoelectronics, surface acoustic waves (SAWs) are employed to generate electric currents. In this study, the team of theoretical physicists modelled the propagation of SAWs in emerging 2-D materials, such as single-layer molybdenum disulfide (MoS₂). SAWs drag MoS₂ electrons (and holes), creating an electric current with conventional and unconventional components. The latter consists of two contributions: a warping-based current and a Hall current. The first is direction-dependent, is related to the so-called valleys—electrons’ local energy minima—and resembles one of the mechanisms that explains photovoltaic effects of 2-D materials exposed to light. The second is due to a specific effect (Berry phase) that affects the velocity of these electrons travelling as a group and resulting in intriguing phenomena, such as anomalous and quantum Hall effects.

The team analyzed the properties of the acoustoelectric current, suggesting a way to run and measure the conventional, warping, and Hall currents independently. This allows the simultaneous use of both optical and acoustic techniques to control the propagation of charge carriers in novel 2-D materials, creating new logical devices.

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