Electron doping in the honeycomb bilayer superconductors (Zr, Hf)NCl

Based on a virtual crystal treatment, we show that alkali doping introduces electron carriers into a single light mass ( m * = 0.6), low density of states band in Li x ZrNCl and Na x HfNCl (which have superconducting T c up to 25 K) that is a symmetric interlayer combination of d xy , d x 2 − y 2 character. Doping leads to simple K -centered three-fold symmetrical cylindrical Fermi surfaces that concentrate low-energy scattering into distinct regions of momentum. The lack of any observed magnetic tendencies, together with our calculation of small electron-phonon strength, suggests a pairing mechanism that is distinct from known superconductors.