Electrical transport in twisted bilayer graphene moirè devices at small twist angles
Experimentally, twisted bilayer graphene moirè superlattice can be realized by physically stacking two graphene layers together with a relative twist, as shown in the above schematics.
Longitudinal resistance, Rxx (color scale) vs n at various temperatures
The central resistance peak denotes the total charge neutrality point in which tBLG maintains charge neutral (total carrier density, n = 0). The two insulating peaks at n = 9.9 x 10^12 cm^-2 originate from the moirè superlattice induced gaps (~45 - 65 meV), which are absent in typical graphene.
Temperature dependence of resistivity for n from 2.2 to 7.2 x 10^12 cm^-2
Between the resistive peaks, tBLG exhibits metallic behavior where resistivity increases with increase in temperature. We found that the observed metallic behavior is strongly carrier density dependent (i.e. a different rate of change of resistivity), in contrast to that of monolayer and AB-bilayer graphene.
Fitted temperature exponent (b) vs n for devices at 2° and 5°
We discovered that the evolution of the temperature exponent b with n in Device A (with a twist angle of 2°) presents a W-shaped dependence, with minima of b ~0.9 near the VHS (n ~5 x 10^12 cm^-2) and maxima of b ~1.7 toward the superlattice induced gaps. Contrary to Device A, data from Device D (5°) do not show a strong dependence on n. The value of b is extracted by fitting the resistivity data (< ~150 K) to the following expression
