Electronic Confinement and Ordering Instabilities in Colossal Magnetoresistive Bilayer Manganites

J. Trinckauf, T. Hänke, V. Zabolotnyy, T. Ritschel, M. O. Apostu, R. Suryanarayanan, A. Revcolevschi, K. Koepernik, T. K. Kim, M. v. Zimmermann, S. V. Borisenko, M. Knupfer, B. Büchner, and J. Geck

Phys. Rev. Lett. 108, 016403 – Published 4 January 2012

Abstract

We present angle-resolved photoemission studies of $({La}_{1 - z} \Pr_{z})_{2 - 2 x} {Sr}_{1 + 2 x} {Mn}_{2} O_{7}$ with $x = 0.4$ and $z = 0.1$ , 0.2, and 0.4 along with density functional theory calculations and x-ray scattering data. Our results show that the bilayer splitting in the ferromagnetic metallic phase of these materials is small, if not completely absent. The charge carriers are therefore confined to a single ${MnO}_{2}$ layer, which in turn results in a strongly nested Fermi surface. In addition to this, the spectral function also displays clear signatures of an electronic ordering instability well below the Fermi level. The increase of the corresponding interaction strength with $z$ and its magnitude of $\sim 400 meV$ make the coupling to a bare phonon highly unlikely. Instead we conclude that fluctuating order, involving electronic and lattice degrees of freedom, causes the observed renormalization of the spectral features.

Received 17 April 2011

DOI:https://doi.org/10.1103/PhysRevLett.108.016403

Authors & Affiliations

J. Trinckauf¹, T. Hänke¹, V. Zabolotnyy¹, T. Ritschel¹, M. O. Apostu², R. Suryanarayanan³, A. Revcolevschi³, K. Koepernik¹, T. K. Kim¹, M. v. Zimmermann⁴, S. V. Borisenko¹, M. Knupfer¹, B. Büchner¹, and J. Geck¹

¹Leibniz Institute for Solid State and Materials Research IFW Dresden, Helmholtzstraße 20, 01069 Dresden, Germany
²Alexandru Ioan Cuza University of Iasi, 11th Carol I Boulevard, 700506 Iasi, Romania
³LPCES - ICMMO - Bât 410 Université Paris-Sud XI, 15, rue Georges Clémenceau, 91405 Orsay Cedex, France
⁴HASYLAB at DESY, Notkestraße 85, 22603 Hamburg, Germany

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Vol. 108, Iss. 1 — 6 January 2012

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Images

Figure 1
Fermi surface (FS) of $({La}_{0.9} \Pr_{0.1})_{1.2} {Sr}_{1.8} {Mn}_{2} O_{7}$ measured at 23 K with out-of-plane polarization. The green solid lines in (a) and (b) show the calculated FS with the full LSDA interlayer hopping $t_{perp} = 0.7 eV$ and $t_{perp} = 0 eV$ , respectively. (c) FS map measured with the sample rotated by 45° and out-of-plane polarization. (d) The autocorrelation function of the FS map in (c). $q_{1}$ and $q_{2}$ indicate nesting vectors. The spectra have been integrated $\pm 40 meV$ around the Fermi level. (e) EDC integrated several meV around $k_{F}$ for in-plane and out-of-plane polarization normalized to its maximum. The relative spectral weight of the features near $E_{F}$ is much bigger with out-of-plane polarization, revealing a small Fermi edge showing that the samples are indeed metallic. These states make up the FS maps in (a)–(c). (f) MDC of a spectra parallel to $k_{x}$ at $k_{y}$ around $k = (k_{x}, - 0.7)$ . No BLS can be seen even though the TB model for the FMM phase predicts a band splitting of around $0.1 \times 2 π / a$ .Reuse & Permissions
Figure 2
(a) Measured spectrum of $({La}_{0.9} \Pr_{0.1})_{1.2} {Sr}_{1.8} {Mn}_{2} O_{7}$ along $M − X − M$ after subtraction of a nondispersive background feature compared to the TB bands for a BLS of 0.7 eV (black solid line) and no BLS (black dashed line). (b) Constant momentum plot of the spectrum shown in (a). The dots are a guide to the eye emphasizing the backbending of the momentum dispersion. (c) Dispersion of the EDC maxima of spectrum (a) (black squares) compared to a fitted model function (red open circles). Marker size represents photoemission or spectral intensity. The false-color plot shows the same spectra as in (a) and (b), but each EDC is normalized to its maximum to enhance states with weak intensity. The backbending is clearly observable. (d) Comparison of the gap size for $z = 0.1$ and $z = 0.4$ . Dispersion is taken from the EDC maxima of spectra measured along $Γ − M$ . All spectra were measured with in-plane polarization at 23 K.Reuse & Permissions
Figure 3
X-ray diffuse scattering data of $({La}_{1 - z} \Pr_{z})_{1.2} {Sr}_{1.8} {Mn}_{2} O_{7}$ with $z = 0.2$ and $z = 0.4$ for different temperatures around $T_{C}$ . The weak symmetry forbidden $(4, 0, 1)$ Bragg peak is due to a small amount of stacking faults. Therefore, the (401) intensities of the two samples cannot directly be compared. Above the Curie temperature of around 90 K ( $z = 0.2$ ) and 45 K ( $z = 0.4$ ) broad superstructure reflections at $(4 \pm 0.25, 0, 1)$ are observed. The data sets at 88 K ( $z = 0.2$ ) and 45 K ( $z = 0.4$ ) were taken just above $T_{C}$ . The ordered regions melt upon entering the FMM phase.Reuse & Permissions

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