Electronic Transport in Dual-Gated Bilayer Graphene at Large Displacement Fields

Abstract

We study the electronic transport properties of dual-gated bilayer graphene devices. We focus on the regime of low temperatures and high electric displacement fields, where we observe a clear exponential dependence of the resistance as a function of displacement field and density, accompanied by a strong non-linear behavior in the transport characteristics. The effective transport gap is typically two orders of magnitude smaller than the optical band gaps reported by infrared spectroscopy studies. Detailed temperature dependence measurements shed light on the different transport mechanisms in different temperature regimes.PACS numbers: 72.80. Vp, 73.20.Hb, 73.22.Pr The ability to electrostatically tune and deplete the charge density in two-dimensional electron gases enables the fabrication of basic mesoscopic devices, such as quantum point contacts or quantum dots, which enhance our understanding of electronic transport in nanostructures [1]. Creating such electrically tunable nanostructures in monolayer graphene, a novel two-dimensional system [2], is far more challenging due to its gapless nature. In this respect, Bernal-stacked bilayer graphene (BLG) is an interesting material, because of the possibility of opening a band gap by breaking the symmetry between the top and bottom graphene sheets [3][4][5].The low-energy band structure of free-standing BLG is gapless but in the presence of an on-site energy difference between the bottom and top layers a band gap develops. Different methods have been employed to induce a band gap including molecular doping, coupling to the substrate, and electric displacement field generated by gate electrodes [6][7][8][9][10][11][12]. However, the low-temperature (≤ 100 K) transport characteristics of dual-gated BLG devices do not exhibit the strong suppression of conductance expected given the large band gaps (up to 250 meV) measured by infrared spectroscopy [9][10][11][12]. In addition, only very weak non-linearities were found in the current versus source-drain voltage (I-V SD ) characteristics [9], in contrast with the strong non-linear behavior of typical semiconducting devices. A more complete study is needed to address the transport characteristics of gapped BLG devices as well as the role played by disorder.In this letter, we report on the electronic transport properties of dual-gated (back-gated (BG) and topgated (TG)) BLG devices. We focus on the regime of large transverse electric displacement fields, 0.8 V/nm < |D| < 2.5 V/nm, over 3 times larger than in previous low-temperature experiments [9]. Upon the application of a large displacement field, we observe an exponential dependence of the device resistance on |D| and density, which is accompanied by a strong non-linear behavior in the I-V SD characteristics. However, the size of the effective transport gap is on the order of a few meV, two orders of magnitude smaller than the optical band gaps at the same D [11,12], suggesting a strong role played by disorder. Temperature dependent measurements in the 300 mK to 10...

Microscopic polarization in bilayer graphene

“…However, band gaps determined from conventional electronic transport measurements are smaller than theoretically expected or extracted from the optical measurements by an order of magnitude or more 7,8,13,[22][23][24][25] . Recently, it has been suggested that disorder-induced localized states inside devices or along the edges can introduce additional conducting channels inside the gap, consequently reducing the effective gap seen in transport measurements [23][24][25] . Additionally, 3 many-body interactions in bilayer graphene, which can be sensitive to local electrostatic variations such as disorder potential fluctuations, are expected to open a gap even in zero applied field 11,17 .…”

Electronic spin transport in dual-gated bilayer graphene

“…Although infrared spectroscopy measurements yield large band gaps of up to 250 meV, 42 the strong role played by disorder limits the expected strong suppression of charge transport measurements and results in only a few meV as the effective transport gap. 43 Figure 5a shows the 2D plot of the local resistance as a function of V BG and V TG . Near the charge neutrality point, the device resistance increases approximately fivefold as the total displacement electric field is increased.…”

Quasiparticle energy and optical excitations of gated bilayer graphene

“…For instance, electrical conductance experiments [11][12][13] have confirmed the existence of a finite QP band gap but their measured value is disturbed by many extrinsic factors, e.g., the inevitable contact resistance between the electrodes and graphene sheet. While noncontacting optical measurements [8][9][10] have revealed a tunable band gap in GBLG, these results are indirect because the optical absorption peak (edge) is not conceptually equivalent to the QP band gap 14,15 .…”

“…One promising approach is to apply the gate electric field perpendicular to the AB (Bernal) stacked bilayer graphene (BLG) to break the inversion symmetry of sublattices 6,7,[9][10][11] . Such an induced band gap of GBLG can be tuned in a wide range by field strength 9,[11][12][13] , offering an important degree of freedom to optimize performance of graphene devices.…”