Modulation-doped-semiconductorlike behavior manifested in magnetotransport measurements of LixZrNCl layered superconductors

Transport properties in magnetic fields have been investigated for possibly exotic LixZrNCl superconductors with a wide range of doping concentration of 0.06 <= x <= 0.37. Application of magnetic field along c axis rapidly suppressed the superconducting transition temperature (T-c) while strongly broadening the width. Zero-temperature limit of upper critical field [H-c2 (0)] showed systematic and monotonic decrease upon increasing x. Detailed analysis with a phenomenological argument gave a simple relation of k(F)L alpha x and almost x-independent mu (k(F), L, and mu denote Fermi wave number, mean free path, and carrier mobility, respectively). These results combined with the temperature-independent Hall coefficient clearly indicate that the present system can be viewed as modulation-doped semiconductors in which conduction electrons suffer from minimal disorder scattering. This could be a key to the relatively high-T-c values realized in this class of layered superconductors.