Quantum capacitance measurements of electron-hole asymmetry and next-nearest-neighbor hopping in graphene

Abstract

The next-nearest-neighbor hopping term t′ determines a magnitude, and, hence, the importance of several phenomena in graphene that include self-doping due to broken bonds and the Klein tunneling, which in the presence of t′, is no longer perfect. Theoretical estimates for t′ vary widely, whereas a few existing measurements by using polarization-resolved magnetospectroscopy have found surprisingly large t ′, close to or even exceeding the highest theoretical values. Here, we report dedicated measurements of the density of states in graphene by using high-quality capacitance devices. The density of states exhibits a pronounced electron-hole asymmetry that increases linearly with energy. This behavior yields t′ ≈ -0.3 eV±15%, in agreement with the high end of theory estimates. We discuss the role of electron-electron interactions in determining t′ and overview phenomena, which can be influenced by such a large value of t′. © 2013 American Physical Society.