19 March 2018

Switchable transmission of quantum Hall edge states in bilayer graphene

 Left: The variable coupling of edge states between two lateral quantum Hall states (blue regions). Right: R34 vs tunnel barrier gate voltage, which controls the barrier height. Left: The variable coupling of edge states between two lateral quantum Hall states (blue regions). Right: R34 vs tunnel barrier gate voltage, which controls the barrier height.

In the 14 years since its discovery, graphene has amazed scientists around the world with both the ground-breaking physics and technological potential it displays. Recently, scientists from Penn State University added to graphene's gallery of impressive scientific achievements and constructed a map that will aid future exploration of this material. This work is emblematic of the large number of university-based materials research efforts that use the MagLab to explore the frontiers of science.

What did scientists discover?

THE TOOLS THEY USED

This research was conducted in the SCM2 18-tesla superconducting magnet and the He-3 cryostat at the DC Field Facility.

Overcoming lithographic challenges, scientists working at the MagLab fabricated dual split gated bilayer graphene devices in which the height of the tunneling barrier between the edge states of two quantum Hall systems is controlled electrically by a gate voltage. This allows researchers to continuously tune the transmission rate of edge states to examine the entire regime of 0 ≤ a ≤ 1. Users observed experimental evidence of the sequential pinch-off of individual edge states, as a function of the barrier height.

Why is this important?

Bilayer graphene exhibits even-denominator fractional quantum Hall states, whose collective excitations follow unusual quantum statistics and could be used as a basis for topological quantum computation. Experimental examination of the collective excitations requires an electron interferometer. Gate-controlled manipulation of the edge states within the quantum Hall effect is the first step towards realizing the interferometer.

Who did the research?

Jing Li,1 Hua Wen,1 Kenji Watanabe,2 Takashi Taniguchi,2 and Jun Zhu1

1Penn State University; 2National Institute for Material Science, Japan

Why did they need the MagLab?

SCM2 provides both a high magnetic field up to 18 teslas, to fully develop the quantum Hall edge states, and a low-noise measurement environment, necessary to perform precision measurements needed for this study.

Details for scientists

Funding

This research was funded by the following grants: G.S. Boebinger (NSF DMR-1157490); Li, Wen, Zhu (NSF DMR-1506212); Watanabe and Taniguchi (JSPS KAKENHI Grant No. JP15K21722)


For more information, contact Tim Murphy.

Details

  • Research Area: 2D,Graphene, Topological Matter
  • Research Initiatives: Materials
  • Facility / Program: DC Field
  • Year: 2018
Last modified on 23 March 2018