Weak Charge-Lattice Coupling Requires Reinterpretation of Stripes of Charge Order inLa1−xCax

Abstract

Modulations in manganites attributed to stripes of charge/orbital/spin order are thought to result from strong electron-lattice interactions that lock the superlattice and parent lattice periodicities. Surprisingly in La1-xCaxMnO3 (x>0.5,90 K), convergent beam (3.6 nm spot) electron diffraction patterns rule out charge stacking faults and indicate a superlattice with uniform periodicity. Moreover, large area electron diffraction peaks are sharper than simulations with stacking faults. Since the electron-lattice coupling does not lock the two periodicities (to yield stripes) it may be too weak to strongly localize charge.

Lattice-form-dependent orbital shape and charge disproportionation in charge- and orbital-ordered manganites

“…This result is in contrast with the belief at the early stage of the research of the CO-OO phenomena, but in accord with the recent results 16,17,18,19,20,21,22,23,24,25 . This indicates that various interactions, such as electron-lattice, Coulomb repulsion, and magnetic interactions, should be taken into account to correctly understand the nature of chargeordered state.…”

“…Many diffraction and theoretical studies have reported the checkerboard type charge order of Mn 3+ and Mn 4+ ions with charge disproportionation and stripe-type orbital order, explaining a complex antiferromagnetic spin order at low temperatures in half-doped manganites 7,8,9,10,11,12,13,14,15,16 . On the other hand, another model with less distinct charge disproportionation has also been proposed 17,18,19,20,21,22,23,24,25 . For example, taking into account the on-site Coulomb interaction, Brink et al have suggested 17 that maximum value of charge disproportionation is as little as 20%.…”

Large lattice distortions associated with the magnetic transition in La0.7Sr0.3MnO3Weber1, Argyriou2, Prokhnenko3 et al. 2013Phys. Rev. B9270View full textAdd to dashboardCite

“…Increased trapping potential reduces T C and increases the strength of CM R. This mechanism is supposed to exp lain the decrease in ferro magnetic transition temperatures and increased magnetoresistance going from La 0.7 Sr 0.3 MnO 3 (T C =355 K) to La 0.75 Ca 0.25 MnO 3 (T C =240 K) and La 1.2 Sr 1.8 Mn 2 O 7 (T C =120 K). On the other hand, the picture of strong electron-lattice interaction has been questioned for thin films of La 1-x Ca x MnO 3 , x ≥ 0.5 [10]. We used neutron scattering to measure temperaturedependence of 2 in La 0.7 Sr 0.3 MnO 3 in order to investigate the relationship between U 2 and the electrical resistivity known fro m the literature.…”

Investigation of the electronic structure of the charge-ordered phase in epitaxial and polycrystallineLa1−xCaxMnO3Schmidt1 2008Phys. Rev. B370901View full textAdd to dashboardCite

“…20 However, in a more recent electron diffraction study this conventional interpretation was claimed to be insufficient. 17 In LCMO x = 0.52 the charge modulation was found to be uniform and to have a non-integer periodicity even by reducing the electron spot size to 3.6 nm, which is below the expected stacking fault distance implanted into the hypothesized q = 0.5·a* Mn 3+ /Mn 4+ plane stacking by doping to x = 0.52 (Fig.1d). The authors in this study (Ref.17) assumed that these unconventional charge modulations arise solely from the cationic valence electron structure, and in consequence, they claimed that the localised Mn 3+ /Mn 4+ plane stacking or stripe models may be insufficient to explain these findings.…”

“…16,17 This new view of CO mechanisms developed from findings of commensurate and incommensurate charge periodicities in CO LCMO at x ≥ 0.5, [16][17][18] and a weak commensurate phase for x < 0.5. 19 The periodicities of such charge modulations (along the a crystallographic orientation) were shown to differ from the original lattice periodicity and the modulation wave vector q was found to be correlated to the doping level x below the CO transition temperature T CO by q ≈ (1-x)·a*, where a* is the reciprocal space vector of the parent orthorhombic Pnma unit cell.…”