High-magnetic-field electronic phase transition in graphite observed by magnetoresistance anomaly

The magnetoresistance of pure graphite has been measured at low temperatures down to 0.48 K, under a steady magnetic field up to 28.5 T with the use of a hybrid magnet. A striking anomaly in the magnetoresistance was found at fields above 22 T. The fact that the critical field of the anomaly has a strong temperature dependence suggests the onset of an electronic phase transition, and makes an explanation of this phenomenon in terms of known one-electron properties of graphite unlikely.