Polaronic metal phases in $\mathrm{L}{\mathrm{a}}_{0.7}\mathrm{S}{\mathrm{r}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ uncovered by inelastic neutron and x-ray scattering

Polaronic metal phases in $L a_{0.7} S r_{0.3} Mn O_{3}$ uncovered by inelastic neutron and x-ray scattering

M. Maschek, D. Lamago, J.-P. Castellan, A. Bosak, D. Reznik, and F. Weber

Phys. Rev. B 93, 045112 – Published 11 January 2016

Abstract

Among colossal magnetoresistive manganites the prototypical ferromagnetic manganite $L a_{0.7} S r_{0.3} Mn O_{3}$ has a relatively small magnetoresistance, and has been long assumed to have only weak electron-lattice coupling. Here we report that $L a_{0.7} S r_{0.3} Mn O_{3}$ has strong electron-phonon coupling: Our neutron and x-ray scattering experiments show strong softening and broadening of transverse acoustic phonons on heating through the Curie temperature $T_{C} = 350 K$ . Simultaneously, we observe two phases where metallic resistivity and polarons coexist. The ferromagnetic polaronic metal phase between $200 K$ and $T_{C}$ is characterized by quasielastic scattering from dynamic CE-type polarons with the relatively short lifetime of $τ \approx 1 ps$ . This scattering is greatly enhanced above $T_{C}$ in the paramagnetic polaronic metal phase. Our results suggest that the strength of magnetoresistance in manganites scales with the inverse of the polaron lifetime, not the strength of electron-phonon coupling.

Received 7 May 2015
Revised 27 November 2015

DOI:https://doi.org/10.1103/PhysRevB.93.045112

Authors & Affiliations

M. Maschek¹, D. Lamago^1,2, J.-P. Castellan^1,2, A. Bosak³, D. Reznik⁴, and F. Weber¹

¹Institute for Solid State Physics, Karlsruhe Institute of Technology, D-76021 Karlsruhe, Germany
²Laboratoire Léon Brillouin (CEA-CNRS), CEA-Saclay, F-91911 Gif-sur-Yvette, France
³European Synchrotron Radiation Facility, F-38043 Grenoble Cedex, France
⁴Department of Physics, University of Colorado at Boulder, Boulder, Colorado 80309, USA

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 93, Iss. 4 — 15 January 2016

Reuse & Permissions

Access Options

Article Available via CHORUS

Download Accepted Manuscript

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
(a)–(c) Color-coded contour plots of raw neutron scattering data obtained for $L a_{0.7} S r_{0.3} Mn O_{3}$ on the thermal triple-axis spectrometer (TAS) 1T, LLB, for $100 \leq T \leq 375 K$ . Constant- $Q$ scans at $Q = (2 - h, 2 + h, 0), 0.1 \leq h \leq 0.5,$ and $Δ h = 0.05 r . l . u .$ were performed with energy steps of $Δ E = 0.25 meV$ . For readability, the intensity scale was adjusted at different temperatures according to the Bose factor of a phonon at an energy of $E = 9 meV$ . (d),(e) Color-coded contour plots of raw neutron scattering taken at (d) $T = 155 K$ and (e) $T = 375 K$ along an off-symmetry direction $Q = (1.5 + h, 2 + h, 0), 0 \leq h \leq 0.5, Δ h = 0.05 r . l . u .$ , and $Δ E = 0.25 meV$ . (f) Sketch of the scattering geometry in the $(H K 0)$ plane in reciprocal space. Open squares denote various Brillouin zone centers (see labels). Dots mark the position in $Q$ where energy scans were performed, shown in (a)–(c) (full/red symbols) and (d)–(e) (open/blue symbols). The arrow connects the origin with the zone center at $τ = (2, 2, 0)$ .
Reuse & Permissions
Figure 2
Representative inelastic neutron scattering spectra of $L a_{0.7} S r_{0.3} Mn O_{3}$ . Energy scans at $Q = (2 - h, 2 + h, 0)$ with (a)–(c) $h = 0.15$ , (d)–(f) $h = 0.25,$ and (g)-(i) $h = 0.5$ at $T = 100 K$ (left), $T = 300 K$ (middle), and $T = 375 K$ (right). Solid (red) lines are fits consisting of a damped harmonic oscillator for the TA mode (solid and blue), a Lorentzian for quasielastic scattering described in the text (solid and black), and the estimated background (dashed, see text). The small Gaussian component (thin black line) in (a)–(f) denotes a spurious signal.
Reuse & Permissions
Figure 3
Representative inelastic x-ray scattering spectra of $L a_{0.7} S r_{0.3} Mn O_{3}$ . Energy scans at $Q = (2 - h, 2 + h, 0)$ with (a)–(d) $h = 0.25$ and (e)–(h) $h = 0.5$ at $200 \leq T \leq 400 K$ . Solid (red) lines are fits consisting of a damped harmonic oscillator for the TA mode (solid and blue), a Lorentzian for quasielastic scattering (solid and black), an estimated experimental background (dashed), and a Gaussian for a small spurious signal (thin). The amplitude of the elastic scattering was fixed to the value observed at low temperatures. Phonon intensities were set as well by the low-temperature observations and allowed to vary only according to the Bose factor and the factor $1 / ℏ ω_{phon}$ in the scattering cross section (for more details, see text).
Reuse & Permissions
Figure 4
Wave-vector and temperature dependences of phonon renormalization and quasielastic scattering in $L a_{0.7} S r_{0.3} Mn O_{3}$ . Temperature dependences of (a) the ferromagnetic intensity of the (100) Bragg position and (b) the quasielastic scattering intensity, (c) the observed phonon softening $Δ E = E_{phon, 5 K} - E_{phon} (T),$ (d) the phonon linewidth $Γ_{phon}$ at $h = 0.25$ (dots) and $0.5$ (open squares). Inelastic neutron scattering results for the quasielastic intensity in (b) (circles) are scaled to match the high-temperature x-ray results (dots). (e) Dispersion of the TA phonon along the [110] direction at 100 and $375 K$ obtained from inelastic neutron scattering. Lines represent a shell model calculation for a cubic unit cell of $L a_{0.7} S r_{0.3} Mn O_{3}$ reproduced from Ref. [27]. (f)–(h) Wave-vector dependences at temperatures $100 \leq T \leq 375 K$ of (f) $Δ E (q)$ , (g) $Γ_{phon} (q)$ (HWHM), and (h) the quasielastic intensities associated with CE-type polarons. As the character of the TA phonon is transferred to the nominal first TO phonon near the zone boundary, we plot results of the latter for $0.4 \leq h \leq 0.5$ . Data in (h) and at $T = 350 K$ in (f) and (g) were obtained by IXS. All other results are based on INS. Solid lines are Gaussian fits to the data. Data are offset for clarity and the corresponding zeros are shown as color-coded dashed lines on the right side of the panel. Vertical dashed lines denote the position of the ordering wave vector of the CE-type COO $q_{CE} = (1 / 4, 1 / 4, 0)$ .
Reuse & Permissions

Physical Review B

covering condensed matter and materials physics

Polaronic metal phases in $L a_{0.7} S r_{0.3} Mn O_{3}$ uncovered by inelastic neutron and x-ray scattering

M. Maschek, D. Lamago, J.-P. Castellan, A. Bosak, D. Reznik, and F. Weber

Phys. Rev. B 93, 045112 – Published 11 January 2016

Abstract

Authors & Affiliations

Article Text (Subscription Required)

References (Subscription Required)

Issue

Access Options

Physical Review B

covering condensed matter and materials physics

Polaronic metal phases in La0.7Sr0.3MnO3 uncovered by inelastic neutron and x-ray scattering

M. Maschek, D. Lamago, J.-P. Castellan, A. Bosak, D. Reznik, and F. Weber

Phys. Rev. B 93, 045112 – Published 11 January 2016

Abstract

Authors & Affiliations

Article Text (Subscription Required)

References (Subscription Required)

Issue

Access Options

Authorization Required

Other Options

Download & Share

Images

Figure 1

Figure 2

Figure 3

Figure 4

Log In

Search

Article Lookup

Paste a citation or DOI

Enter a citation

Polaronic metal phases in $L a_{0.7} S r_{0.3} Mn O_{3}$ uncovered by inelastic neutron and x-ray scattering