Transport determination of tunable band gap in bilayer graphene

Bernal stacked bilayer graphene is a unique two-dimensional material with a tunable band gap. A perpendicular electric field can break the inversion symmetry of the two graphene layers and open up a field-dependent band gap $\Delta $ (E) up to 0.25 eV. Although $\Delta $ (E) have been measured by optical spectroscopy [1], transport determination is hindered by stronger disorder in oxide- supported samples [2]. By using high-quality dual hexagonal boron nitride gated samples, we measure the temperature dependence of the charge neutrality point resistance, from which $\Delta $ (E) is determined. We find $\Delta $ (E) to increase approximately linearly with the applied displacement field D and reach $\sim$ 0.2 eV at D$=$1.6V/nm. The transport results are close to previous optical measurements but with much higher accuracy. Comparisons to theory and measurements in oxide-supported samples are made. An electric field tunable clean band gap in high quality bilayer graphene can be potentially useful in near and mid-infrared light detection.\\[4pt] [1] Y. Zhang, et. al., Nature 459, 820-823, (2009).\\[0pt] [2] K. Zou and J. Zhu, PRB 82, 081407 (R) (2010).