Optical evidence of quantum rotor orbital excitations in orthorhombic manganites

TL;DR

This study provides optical evidence for quantum rotor orbital excitations in LaMnO3, revealing their potential influence on the material's complex electronic and magnetic properties, including superconductivity and magnetoresistance.

Contribution

The paper presents the first experimental observation of quantum rotor orbital excitations in orthorhombic manganites using optical spectroscopy.

Findings

Identification of narrow sidebands in optical spectra indicating quantum rotor excitations

Support from photoluminescence data corroborating the existence of these excitations

Implication of these excitations in understanding complex phenomena like superconductivity

Abstract

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.