Tunneling field effect transistors provide insight into graphene charges at high magnetic fields

Despite recent advances in graphene nanodevices, scientists have been limited in their ability to directly probe graphene’s electronic structure in high magnetic fields and explore the exotic electronic states that exist under these conditions. In a new paper, Davenport et al. demonstrate that graphene tunneling field effect transistors (TFETs) can be used to address this limitation.

The researchers used TFETs to directly probe the electronic properties of graphene charges at high magnetic fields. “Our work widens the vantage point of more conventional tip-based tunneling,” said author John Davenport.

Using the new approach, the researchers observed that graphene charges coalesce under high magnetic fields to form tightly packed cyclotron orbits, which manifest as Landau levels in graphene’s electronic structure. The researchers found that as the sample bias voltage and gate voltage are modulated, graphene’s charge density changes and its Landau levels shift away from their expected energies. By applying a shear transformation to the data, the resulting charge density changes and observed band structure features can be reconciled with existing theory.

“Landau levels in graphene are an interesting platform because they confine electrons in a state where their repulsion from other electrons gives rise to collective phenomena that are indescribable using simple theoretical tools,” Davenport said.

This work provides a path for studying Landau levels directly, and the researchers anticipate the TFETs will allow them to study the electronic structure of graphene and other two-dimensional materials at even higher magnetic fields. “Once a new tool is developed, there is always the excitement to try it out on different materials and under different conditions,” said author Jairo Velasco.

Source: “Probing the electronic structure of graphene near and far from the Fermi level via planar tunneling spectroscopy,” by John L. Davenport, Zhehao Ge, Junyan Liu, Carlos Nuñez-Lobato, Seongphill Moon, Zhengguang Lu, Eberth A. Quezada-Lopez, Kaitlin Hellier, Patrick G. LaBarre, Takashi Taniguchi, Kenji Watanabe, Sue Carter, Arthur P. Ramirez, Dmitry Smirnov, and Jairo Velasco Jr., Applied Physics Letters (2019). The article can be accessed at https://doi.org/10.1063/1.5118422 .