In the realm of energy research, scientists are continually exploring innovative ways to harness and control energy at a fundamental level. Among these researchers are Yuncheng Mao and Claudio Attaccalite, affiliated with the University of California, Berkeley, and the Italian Institute of Technology, respectively. Their recent study, published in the journal Physical Review Letters, delves into the intriguing behavior of Bernal bilayer graphene under magnetic fields and its potential implications for energy harvesting technologies.
The study focuses on the bulk photovoltaic effect (BPVE), a phenomenon where certain materials generate electric current in response to light, without the need for a built-in electric field. This effect is highly sensitive to the material’s symmetry and can be influenced by magnetic fields, which break time-reversal symmetry (TRS).
Mao and Attaccalite investigated two types of currents within AB-stacked Bernal bilayer graphene: shift current (SC) and magnetic ballistic current (MBC). They found that SC responds only mildly to weak magnetic fields, maintaining an almost even function of field strength. In contrast, MBC is directly activated by the breaking of TRS and grows linearly with weak fields at selected photon energies.
The researchers then examined the behavior of SC and MBC in AB-bilayer graphene ribbons under both weak and strong vertical magnetic fields. They discovered that edge states play strikingly opposite roles in the SC response. Under weak fields, these highly localized edge modes are essentially inactive, or “dark.” However, under strong fields, when Landau levels dominate, the same edge states expand in spatial extent and become significant contributors to the SC response, or “bright.”
The practical applications of this research for the energy sector are still in the exploratory phase. However, understanding and controlling the BPVE in graphene could potentially lead to the development of more efficient photovoltaic devices. Graphene’s unique properties, such as its high electron mobility and flexibility, make it an attractive candidate for next-generation energy technologies. The insights gained from this study could contribute to the design of graphene-based photovoltaic cells or other energy-harvesting devices that leverage the BPVE.
This article is based on research available at arXiv.