Quantum Transport and Field-Induced Insulating States in Bilayer Graphene pnp Junctions

Abstract

We perform transport measurements in high quality bilayer graphene pnp junctions with suspended top gates. At a magnetic field B=0, we demonstrate band gap opening by an applied perpendicular electric field, with an On/Off ratio up to 20,000 at 260mK. Within the band gap, the conductance decreases exponentially by 3 orders of magnitude with increasing electric field, and can be accounted for by variable range hopping with a gate-tunable density of states, effective mass, and localization length. At large B, we observe quantum Hall conductance with fractional values, which arise from equilibration of edge states between differentially-doped regions, and the presence of an insulating state at filling factor ν=0. Our work underscores the importance of bilayer graphene for both fundamental interest and technological applications.

The electronic properties of bilayer graphene

“…Since then, the majority of experiments probing the band gap have used single or dual gate devices based on exfoliated bilayer graphene flakes [19,20]. The band gap has now been observed in a number of different experiments including photoemission [16], magnetotransport [20], infrared spectroscopy [55, 78-80, 129, 130], electronic compressibility [131,132], scanning tunnelling spectroscopy [133], and transport [19,31,[134][135][136][137][138][139].…”

Quantum transport in double-gated graphene devices

“…This unusual behavior of BLG pnp junction arises from opening of a band gap in the BLG energy spectrum [8,[11][12][13][14][15][16][17][18][19][20]. What sets dual-gated BLG from their SLG counterparts is that application of voltages to the two gates not only controls densities n 1 and n 2 , but also an electric field E 2 applied across bilayer in the top-gated region.…”

Transport measurements on ultra-clean dual-gated suspended bilayer graphene

“…This has been explicitly verified in optical studies [12]. In transport experiments [32][33][34][35] using BLG on SiO 2 substrates, exponential decrease in conductance with E  has been observed, though disorder and charged impurities obscure the gap and give rise to variable range hopping. Thus, the behavior of sample 1 can be accounted for by E  -induced band gap opening.…”