Polaron melting and ordering as key mechanisms for colossal resistance effects in manganites

doi:10.1073/pnas.0702748104

Polaron melting and ordering as key mechanisms for colossal resistance effects in manganites

*Institute of Materials Physics, University of Goettingen, Friedrich-Hund-Platz 1, 37077 Goettingen, Germany; and
^‡Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, NY 11973

Edited by C. N. R. Rao, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India, and approved June 8, 2007 (received for review March 23, 2007)

Abstract

Polarons, the combined motion of electrons in a cloth of their lattice distortions, are a key transport feature in doped manganites. To develop a profound understanding of the colossal resistance effects induced by external fields, the study of polaron correlations and the resulting collective polaron behavior, i.e., polaron ordering and transition from polaronic transport to metallic transport is essential. We show that static long-range ordering of Jahn–Teller polarons forms a polaron solid which represents a new type of charge and orbital ordered state. The related noncentrosymmetric lattice distortions establish a connection between colossal resistance effects and multiferroic properties, i.e., the coexistence of ferroelectric and antiferromagnetic ordering. Colossal resistance effects due to an electrically induced polaron solid–liquid transition are directly observed in a transmission electron microscope with local electric stimulus applied in situ using a piezo-controlled tip. Our results shed light onto the colossal resistance effects in magnetic field and have a strong impact on the development of correlated electron-device applications such as resistive random access memory (RRAM).

Footnotes

^†To whom correspondence may be addressed. E-mail: jooss{at}ump.gwdg.de or zhu{at}bnl.gov
↵ ^§Present address: Department of Physics, University of Illinois, Chicago, IL 60607.
Author contributions: C.J. designed research; C.J., L.W., T.B., R.F.K., M.B., M.A.S., S.S., and J.H. performed research; C.J., L.W., R.F.K., M.B., J.H., and Y.Z. analyzed data; C.J. wrote the paper; and Y.Z. coordinated research.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0702748104/DC1.
Abbreviations:

JT,

Jahn–Teller;

CB,

checkerboard;

CMR,

colossal magnetoresistance;

PCMO,

Pr1−xCaxMnO3;

TEM,

transmission electron spectroscopy;

HRTEM,

high-resolution TEM;

CER,

colossal electroresistance effect.