Spatially Inhomogeneous Metal-Insulator Transition in Doped Manganites
M. Fäth,
1
S. Freisem,
1
A. A. Menovsky,
12
Y. Tomioka,
3
J. Aarts,
1*
J. A. Mydosh
1
Scanning tunneling spectroscopy was used to investigate single
crystals and thin films of
La1-xCaxMnO3 (with x of about 0.3), which exhibit colossal
magnetoresistance. The different spectroscopic signatures of the
insulating (paramagnetic) and metallic (ferromagnetic) phases enable
their spatial extent to be imaged down to a lateral scale of the order
of 10 nanometers. Above the bulk transition temperature
Tc, the images show mostly insulating
behavior. Below Tc, a phase separation is
observed where inhomogeneous structures of metallic and more insulating areas coexist and are strongly field dependent in their size and structure. Insulating areas are found to persist far below
Tc. These results suggest that the
transition and the associated magnetoresistance behavior should be
viewed as a percolation of metallic ferromagnetic domains.
1 Kamerlingh Onnes Laboratory, Leiden
University, Post Office Box 9504, 2300 RA Leiden, Netherlands.
2 Van der Waals-Zeeman Laboratory,
University of Amsterdam, Valckenierstraat 67, 1018 XE Amsterdam,
Netherlands.
3 Joint Research Center for Atom
Technology, 1-1-4 Higashi, Tsukuba, Ibaraki 305-0046, Japan.
*
To whom correspondence should be addressed. E-mail:
aarts{at}phys.leidenuniv.nl
