Graphene's quantum behavior reveals surprising asymmetry in magnetic fields
Researchers found that epitaxial graphene exhibits unusual, contradictory electrical behavior near its charge neutrality point when exposed to strong magnetic fields—a phenomenon tied to substrate-induced asymmetries. The discovery could inform efforts to build graphene-based electronics and quantum devices, where controlling such effects is critical for device performance.
Originaltitel: Magnetic field driven ambipolar quantum Hall effect in epitaxial graphene close to the charge neutrality point
<p>We have investigated the disorder of epitaxial graphene close to the charge neutrality point (CNP) by various methods: (i) at room temperature, by analyzing the dependence of the resistivity on the Hall coefficient; (ii) by fitting the temperature dependence of the Hall coefficient down to liquid helium temperature; (iii) by fitting the magnetoresistances at low temperature. All methods converge to give a disorder amplitude of (20 +/- 10) meV. Because of this relatively low disorder, close to the CNP, at low temperature, the sample resistivity does not exhibit the standard value similar or equal to h/4e(2) but diverges. Moreover, themagnetoresistance curves have a unique ambipolar behavior, which has been systematically observed for all studied samples. This is a signature of both asymmetry in the density of states and in-plane charge transfer. Themicroscopic origin of this behavior cannot be unambiguously determined. However, we propose a model in which the SiC substrate steps qualitatively explain the ambipolar behavior.</p>