Freek Massee
     Laboratoire de Physique des Solides, CNRS

Colossal magnetoresistant manganites


F. Massee & S. de Jong et al., Nature Physics 7, 978 (2011)
Bilayer manganites reveal polarons in the midst of a metallic breakdown

S. de Jong et al., PRB 80, 205108 (2009)
A high resolution, hard x-ray photoemission investigation of La2-2xSr1+2xMn2O7 (0.30 < x < 0.50): on microscopic phase separation and the surface electronic structure of a bilayered CMR manganite

S. de Jong et al., PRB 76, 235117 (2007)
Quasiparticles and anomalous temperature dependence of the low-lying states in the colossal magnetoresistant oxide La2-2xSr1+2xMn2O7 (x=0.36) from angle-resolved photoemission
colossal magnetoresistant manganitesUsing a combination of angle resolved photoemission and scanning tunneling microscopy, we show that the intrinsic spectral response of LSMO is pseudogapped.

Polarons in the midst of a metallic breakdown

Competition between local lattice distortions leading to anti-ferromagnetic, charge and orbital ordering on the one hand, and mixed valence character promoting metallic ferromagnetic double exchange on the other, determines the transport properties of the manganite materials family and is proposed to lie at the root of their colossal magnetoresistance (CMR) effect. Whereas metallicity thrives in the three dimensional member of the series (La,Sr)N+1MnNO3N+1 (LSMO), where N is the number of stacking layers, the bilayer analogue is metallic only in a narrow Sr-doping and temperature regime, giving rise to the largest CMR effect. The more strongly 2D, single layer compound shows neither metallic nor colossal magnetoresistant behaviour.

Using a combination of atomic scale scanning tunneling microscopy and spectroscopy, and small spot size (100 μm) angle resolved photoemission spectroscopy, we show that the intrinsic spectral response of these systems is pseudogapped, with negligible coherent spectral weight at EF anywhere in k-space at any temperature, across the CMR region of the phase diagram. Second, we show that the strong quasi-particle features seen in ARPES studies also above TC are due to the unavoidable presence of N>2 stacking-fault intergrowths. These new insights clear the way for a unified interpretation of the physical properties of colossal magnetoresistant bilayer LSMO in terms of strongly incoherent charge carriers, and suggest that local control of the dimensionality of such manganites - by means of tuning the stacking number, N - may offer a novel route to new functional nanostructures.

For more information, see Nature Physics 7, 978 (2011).