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https://www.ias.ac.in/article/fulltext/jcsc/115/05-06/0767-0774

Manganites; colossal magnetoresistance; strongly correlated electron systems; metal-insulator transitions and other electronic transitions; Jahn-Teller polarons and electron-phonon interaction

Manganites of the LA_1−xCa_xMnO₃ family show a variety of new and poorly understood electronic, magnetic and structural effects. Here we outline a new approach recently proposed by us, where we argue that due to strong Jahn-Teller (JT) coupling with phonons the twofold degeneratee_g states at the Mn sites dynamically reorganize themselves into localised, JT polaronsl with exponentially small inter-site hopping, and band-like, nonpolaronic statesb, leading to anew 2-band model for manganites which includes strong Coulomb and Hund’s couplings. We also discuss some results from a dynamical mean-field theory treatment of the model which explains quantitatively a wide variety of experimental results, including insulator-metal transitions and CMR, in terms of the influence of physical conditions on the relative energies and occupation of thel andb states. We argue that this microscopic coexistence of the two types of electronic states, and their relative occupation and spatial correlation is the key to manganite physics.

T V Ramakrishnan^{1 2} H R Krishnamurthy^{1 2} S R Hassan^{1 2} G Venketeswara Pai^{1 3}

1. Centre for Condensed Matter Theory, Department of Physics, Indian Institute of Science, Bangalore - 560 012, India
2. Condensed Matter Theory Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur PO, Bangalore - 560 064, India
3. The Abdus Salam International Centre for Theoretical Physics, 11 Strada Costiera, Trieste - 34014, Italy

Published

12 October 2003