Thermodynamic and electron diffraction signatures of charge and spin ordering in La1-xCaxMnO3

The large-magnetoresistance compounds ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ have been studied using specific heat, sound velocity $(v)$, and electron diffraction. For $0.63\ensuremath{\le}x\ensuremath{\le}0.67$ charge ordering is observed at 260 K and accompanied by a dramatic $(g10%)$ increase in $v$. This simultaneous occurrence of electron and lattice ordering features implies extremely strong electron-phonon coupling, known to exist for the octahederally coordinated ${d}^{4}$ ion and originating in the Jahn-Teller effect. A dynamic manifestation of this Jahn-Teller coupling has been suggested by Millis et al. as the origin for colossal magnetoresistance.