Field-effect modulation of thermoelectric properties in multigated silicon nanowires.

Electric-field-induced charge carriers typically exhibit greater mobility over carriers contributed by chemical dopants and offer a powerful mechanism for thermoelectric power factor enhancement. We fabricate multigated silicon nanowires (Si NWs) and demonstrate significant modulation of electrical conductivity and the Seebeck coefficient with gate bias. Because of the higher mobility of field-effect charge carriers, we demonstrate that power factor for the gated Si NWs is similar to the highest values reported for n-type Si nanostructures despite charge transport only occurring at the NW surface. Field-effect doping is a promising strategy for optimizing power factor and may result in significant power factor enhancement in smaller diameter Si NWs where high average carrier densities can be obtained with induced surface charge.

Correlated insulating and superconducting states in twisted bilayer graphene below the magic angle.

The emergence of flat bands and correlated behaviors in "magic angle" twisted bilayer graphene (tBLG) has sparked tremendous interest, though its many aspects are under intense debate. Here we report observation of both superconductivity and the Mott-like insulating state in a tBLG device with a twist angle of ~0.93°, which is smaller than the magic angle by 15%. At an electron concentration of ±5 electrons/moiré unit cell, we observe a narrow resistance peak with an activation energy gap ~0.1 meV. This indicates additional correlated insulating state, and is consistent with theory predicting a high-energy flat band. At doping of ±12 electrons/moiré unit cell we observe resistance peaks arising from the Dirac points in the spectrum. Our results reveal that the "magic" range of tBLG is in fact larger than what is previously expected, and provide a wealth of new information to help decipher the strongly correlated phenomena observed in tBLG.