Field-Induced Carrier Delocalization in the Strain-Induced Mott Insulating State of an Organic Superconductor

We report the influence of the field effect on the dc resistance and Hall coefficient in the strain-induced Mott insulating state of an organic superconductor κ-(BEDT-TTF)₂Cu[N(CN)₂]Br. Conductivity obeys the formula for an activated transport σ_=σ₀exp(-W/kBT), where σ₀ is a constant and W depends on the gate voltage. The gate-voltage dependence of the Hall coefficient shows that, unlike in conventional field-effect transistors, the effective mobility of dense hole carriers (~1.6×10¹⁴ cm^-2) is enhanced by a positive gate voltage. This implies that carrier doping involves delocalization of intrinsic carriers that were initially localized due to electron correlation.