Tuning the entanglement between orbital reconstruction and charge transfer at a film surface

Abstract

The interplay between orbital, charge, spin, and lattice degrees of freedom is at the core of correlated oxides. This is extensively studied at the interface of heterostructures constituted of two-layer or multilayer oxide films. Here, we demonstrate the interactions between orbital reconstruction and charge transfer in the surface regime of ultrathin (La,Sr)MnO3, which is a model system of correlated oxides. The interactions are manipulated in a quantitative manner by surface symmetry-breaking and epitaxial strain, both tensile and compressive. The established charge transfer, accompanied by the formation of oxygen vacancies, provides a conceptually novel vision for the long-term problem of manganites—the severe surface/interface magnetization and conductivity deterioration. The oxygen vacancies are then purposefully tuned by cooling oxygen pressure, markedly improving the performances of differently strained films. Our findings offer a broad opportunity to tailor and benefit from the entanglements between orbit, charge, spin, and lattice at the surface of oxide films.

Electrical Manipulation of Orbital Occupancy and Magnetic Anisotropy in Manganites

“…Application of the field-effect transistor principle to achieve doping variation has modulated the magnetic or electric performances and phase transition in manganites, [16,17] which is expected to provide an approach to tuning orbital occupancy reversibly. The main technological challenge for measuring the change of the orbital order under the influence of an electric field is that the detection of orbital occupancy using x-ray linear dichroism (XLD), calls for an exposed sample with a robust remanent electric field effect, [18] which cannot be achieved by conventionally electrostatic modification of carrier density. [10,11] Fortunately, the relaxation of the gating effect generated by ionic liquid in manganites is negligible even after gate voltage is turned off, guaranteeing ex situ measurements of the orbital.…”

“…[10,11] Fortunately, the relaxation of the gating effect generated by ionic liquid in manganites is negligible even after gate voltage is turned off, guaranteeing ex situ measurements of the orbital. [19] , where x could be controlled by the Sr concentration, [4] oxygen pressure during film growth, [18] and gate voltage. [20] We investigate samples of (La,Sr)MnO 3 (Figure 2b).…”

“…The measurement temperature for XLD is 300 K as the interference from ferromagnetism is negligible at a comparatively high temperature, enhancing the accuracy of the XLD signals. [18] The spectra normalization was made by dividing the spectra by a factor such that the L 3 pre-edge and L 2 post-edge have identical intensities for the two polarizations. After that, the pre-edge spectral region was set to zero and the peak at the L 3 edge was set to one.…”

Reversible control of magnetism in La0.67Sr0.33MnO3 through chemically-induced oxygen migration

“…The XA spectra of the uncapped LSMO film are consistent with the mixed Mn 3þ and Mn 4þ valence expected in LSMO films, with a weak shoulder peak which may indicate a small amount of strain induced oxygen vacancy formation near the LSMO surface. [28][29][30][31][32] Such peaks are commonly observed in LSMO films, and this peak is greatly enhanced in the Gd capped sample, which shows a sharp deviation in the XA lineshape. Based on the position and increased intensity of this L 3 shoulder peak, we conclude that additional oxygen vacancies are formed and a significant fraction of the interfacial Mn is in the 2þ valence state.…”

“…Based on the position and increased intensity of this L 3 shoulder peak, we conclude that additional oxygen vacancies are formed and a significant fraction of the interfacial Mn is in the 2þ valence state. [31][32][33][34][35] The main L 3 peak (E % 641 eV) is also shifted to slightly lower energy, indicating movement from mixed Mn 3þ and Mn 4þ to pure Mn 3þ . [33][34][35] The decreased relative intensity of the L 2 edge for Gd-capped samples is consistent with this interpretation.…”