  In magnetic compounds with Jahn-Teller (JT) ions (such as Mn3+ or Cu2+), the
ordering of the electron or hole orbitals is associated with cooperative
lattice distortions. There the role of JT effect, although widely recognised,
is still elusive in the ground state properties. We suggest that, in these
materials, there exist elementary excitations whose energy spectrum is
described in terms of the total angular momentum eigenstates and is quantised
as in quantum rotors found in JT centers. We observed features originating from
these excitations in the optical spectra of a model compound LaMnO3 using
ellipsometry technique. They appear clearly as narrow sidebands accompanying
the electron transition between the JT split orbitals on neighbouring Mn3+
ions, strongly influenced by anisotropic spin correlations. We present these
results together with new experimental data on photoluminescence and its
kinetics found in LaMnO3, which lend additional support to the ellipsometry
implying the existence of the quantum rotor orbital excitations. We note that
the discovered elementary excitations of quantum rotors may play an important
role in many unusual properties observed in these materials upon doping, such
as high-temperature superconductivity and colossal magnetoresistance.
