Fractional Quantum Hall Effect in the N=2 Landau Level in Bilayer Graphene
Georgi Diankov1, Chi Te Liang1,2*, François Amet3,4, Patrick Gallagher1, Menyoung Lee1, Andrew J. Bestwick1, Kevin Tharratt1, William Coniglio5, Jan Jaroszynski5, Kenji Watanabe6, Takashi Taniguchi6, David Goldhaber-Gordon1
1Physics, Stanford University, Stanford, USA
2Physics, National Taiwan University, Taipei, Taiwan
3Physics, Duke University, Durham, USA
4Physics and Astronomy, Appalachian State University, Boone, USA
5National High Magnetic Field Laboratory, Tallahassee, USA
6Advanced Materials Laboratory, NIMS, Tuskuba, Japan
* presenting author:Chi-Te Liang,
The fractional quantum Hall (FQH) effect is a canonical example of electron-electron interactions producing new ground states in many-body systems. Most FQH studies have focused on the lowest Landau level (LL). Here we report transport measurements of FQH states in the N=2 LL (filling factors 4 < |ν| < 8) in bilayer graphene, a system with spin and valley degrees of freedom in all LLs, and an additional orbital degeneracy in the 8-fold degenerate N=0/N=1 LLs. In contrast with recent observations of particle-hole asymmetry in the N=0/N=1 LLs of bilayer graphene, the FQH states we observe in the N=2 LL form a complete sequence of particle-hole symmetric states whose relative strength is dependent on their denominators. The FQH states in the N=2 LL display energy gaps of a few Kelvin, comparable to and in some cases larger than those of fractional states in the N=0/N=1 LLs. The FQH states we observe form, to the best of our knowledge, the highest set of particle-hole symmetric pairs seen in any material system.

Keywords: Fractional quantum Hall effect, Bilayer graphene, High Landau level