Mapping out the Fermi surface of CMR manganites*

The rare-earth manganites have been the subject of intensive research for many years. Despite this attention, many questions still remain, especially regarding the low-temperature ferromagnetic phase that exhibits colossal magnetoresistance (CMR). By applying pulsed magnetic fields of up to 100 T, we have been able to observe two series of magnetic quantum oscillations in the resistivity of high-quality La_1-xSr_xMnO₃ crystals in the CMR phase. The oscillations exhibit frequencies less than 1 kT and their temperature dependence yields effective masses around 2m_{e .} These observations suggest that the large “woolsack” Fermi surface sections predicted by bandstructure calculations fragment into smaller pockets at low temperatures, in a manner analogous to the behavior of the Fermi surface of the hole-doped cuprates.