Very strong magnetic-field dependence of the oxygen isotope shift of the charge-ordering transition inLa0.5Ca0.5MnO3

Abstract

Oxygen isotope effect on the charge-ordering transition was studied in La0.5Ca0.5MnO3 . Upon replacing 16 O with 18 O, the charge-ordering temperature increases by 9 K under zero magnetic field. With an increase of the magnetic field, the oxygen isotope shift increases rapidly and reaches a magnitude of about 40 K under a magnetic field of 5.4 T. The present results cannot be explained by the existing theories of the charge-ordering transition in manganites. @S0163-1829~99!00601-3# It is well known that the observation of the oxygenisotope effect in conventional superconductors is important for the development of the microscopic theory of superconductivity. Recently, Zhao and co-workers 1‐3 have initiated the studies of oxygen isotope effects in the colossal magnetoresistive manganese perovskites. The observed strong oxygen isotope effects in the manganites give clear evidence for the existence of small lattice polarons in these systems. The isotope effects along with many other experimental results 4‐7 strongly support those theoretical models 8,9 where a strong coupling of conduction electrons to local Jahn-Teller distortions is considered to be important for the basic physics in manganites.