Anomalous enhancement of the electron dephasing rate from magnetoresistance data in Bi2Sr2CuO6

The low-temperature magnetoresistance (MR) in Bi2Sr2CuO6 is highly anisotropic. By fitting the orbital MR with the weak-localization expression, we derive a carrier dephasing rate 1 that varies as T-13. This implies that the energy levels are greatly broadened at low temperatures. Both the energy scale derived from 1 vs T and the behavior of the longitudinal MR suggest a strong coupling between the holes and the Cu spins. We discuss implications of the large dephasing rate, and contrast the MR with that of conventional disordered metals.