Observation of Even Denominator Fractional Quantum Hall Effect in Suspended Bilayer Graphene

Abstract

We investigate low-temperature magneto-transport in recently developed, high-quality multiterminal suspended bilayer graphene devices, enabling the independent measurement of the longitudinal and transverse resistance. We observe clear signatures of the fractional quantum Hall effect, with different states that are either fully developed, and exhibit a clear plateau in the transverse resistance with a concomitant dip in longitudinal resistance, or incipient, and exhibit only a longitudinal resistance minimum. All observed states scale as a function of filling factor ν, as expected. An unprecedented even-denominator fractional state is observed at ν = -1/2 on the hole side, exhibiting a clear plateau in Rxy quantized at the expected value of 2h/e 2 with a precision of ~0.5%. Many of our observations, together with a recent electronic compressibility

Topological Phases in the Zeroth Landau Level of Bilayer Graphene

“…In conclusion, we have presented a method to analyze the effect of screening and strong LL mixing in the zeroth LL of BG. We have identified several robust fractions with Abelian (ν = −1, − 4 3 , − 5 3 , − 8 5 ) and non-Abelian (ν = − 1 2 ) topological order, some of which have been observed in recent experiments [14]. Future work will address the microscopic characterization of the excitations in these states, and ways to further increase their gaps or perhaps stabilize new states using the potential tunability of the interactions in BG [16,17,44].…”

“…Very recently, an observation of robust FQHE in the zeroth LL of bilayer graphene (BG) was also reported [14]. Remarkably, both odd-denominator (filling factor ν = − 4 3 ) and even-denominator (ν = − 1 2 ) fractions were observed.…”

“…In this Letter, motivated by the experiment [14], we provide an insight into the nature of various topological phases arising in the zeroth Landau level of BG. In contrast to previous work [15][16][17][18][19], our study fully takes into account the realistic effects of screening of the Coulomb interaction in BG and the strong LL mixing effects between the degenerate sublevels.…”

“…In this case, the filling factor is simply defined asν = N/N Φ . Our convention forν below is such that the filling factor of states observed in BG [14] corresponds to ν ≡ −2 +ν. Generally, we note that in BG, owing to orbital degeneracy and asymmetry between 0 and 1, electron-hole symmetry is broken, and we expect it to be substituted by ν → ν + 2 symmetry.…”

Charge Inversion and Topological Phase Transition at a Twist Angle Induced van Hove Singularity of Bilayer Graphene

“…This represents to the best of our knowledge a record value for a twisted bilayer [20][21][22][23] and competes with state-of-the-art Bernal 6 stacked bilayer graphene samples. 17,[24][25][26] The top-and back-gate were unintentionally short circuited. Because the h-BN gate dielectric layers do not have the exact same layer thickness (approximately 6 and 9 nm for the hBN layer above and below the twisted bilayer, respectively), the application of a gate voltage may induce a small transverse electric field across the twisted graphene layers (for further information and an estimate of the size of the transverse electric field we refer to section S1 in the Supporting Information).…”