Negative Off-Diagonal Conductivities in a Weakly Coupled Quark Gluon Plasma

We calculate the conductivity matrix of a weakly coupled quark-gluon plasma at the leading-log order. By setting all quark chemical potentials to be identical, the diagonal conductivities become degenerate and positive, while the off-diagonal ones become degenerate but negative (or zero when the chemical potential vanishes). This means a potential gradient of a certain fermion flavor can drive backward currents of other flavors. A simple explanation is provided for this seemingly counter intuitive phenomenon. It is speculated that this phenomenon is generic and most easily measured in cold atom experiments.