Orbital Order Melting at Reduced Dimensions

Abstract

The orbital degree of freedom, strongly coupled with the lattice and spin, is an important factor when designing correlated functions. Whether the long-range orbital order is stable at reduced dimensions and, if not, what the critical thickness is remains a tantalizing question. Here, we report the melting of orbital ordering, observed by controlling the dimensionality of the canonical eg 1 orbital system LaMnO3. Epitaxial films are synthesized with vertically aligned orbital ordering planes on an orthorhombic substrate, so that reducing film thickness changes the two-dimensional planes into quasi-one-dimensional nanostrips. The orbital order appears to be suppressed below the critical thickness of about six unit cells by changing the characteristic phonon modes and making the Mn d orbital more isotropic. Density functional calculations reveal that the electronic energy instability induced by bandwidth narrowing via the dimensional crossover and the interfacial effect causes the absence of orbital order in the ultrathin thickness.

Polycrystalline La0.66Gd0.04Ca0.3MnO3 for magnetic-response applications: concurrent anisotropic magnetoresistance and magneto-transport under a low magnetic field

“…Based on the normal modes Q 2 of the JT distortion, the distance between two O 1 2− and Mn 3+ ions on the z axis remains constant or decreases, while a pair of O 2 2− at the x–y -face was far away from the Mn 3+ and the opposite motion in another pair. 40 In terms of the LaMnO 3.006 structure, the bond distances calculated via the Rietveld refinement can be considered a reliable and valid criterion for estimating the JT distortion. 41 In this respect, the W Mn–O–Mn parameter was adopted to further measure the JT distortion.…”