We present a rectifying manganite-titanate heterojunction exhibiting a magnetic field tunable depletion layer. This creates a large positive magnetocapacitance, a direct measure of the fieldinduced reduction of the effective depletion width across the junction. Furthermore, the reduction of the junction barrier shifts the forward bias characteristics, giving exponentially-enhanced differential magnetoresistance, occurring despite the absence of a spin filter. These results provide a unique probe of a Mott insulator/band insulator interface, and further suggest new electronic devices incorporating the magnetic field sensitivity of these strongly correlated electron materials. PACS numbers: 75.70.Cn, 75.47.Lx, 73.40.Ei 1 There is a continual search for new methods and materials to utilize magnetic response in electronic devices, ranging from dilute magnetic semiconductors, 1 metal superlattices, 2 magnetic oxides, 3 as well as hybrid structures among them. Perovskite manganites exhibit strong electronspin coupling, manifesting dramatic magnetoresistance near the simultaneous magnetic and metal-insulator transition, 3 as well as a fully spin-polarized ground state. 4 The later feature has been explored in spin-polarized transport at grain boundaries 5 and thin film tunnel junctions. 6 Electron-doped SrTiO 3 has long been used as a semiconducting element in rectifying junctions. 7,8 Oxygen vacancies, as well as substitutional doping such as Nb on the Ti-site in SrTiO 3 , generate conduction electrons. 9 Recently, diode characteristics have been demonstrated in manganite-titanate junctions, 10-13 where the manganite hole concentration was initially minimized to resemble semiconductor p-i-n or p-n junctions, corresponding to bulk insulating concentrations. Ferromagnetic metallic manganites are formed by doping holes in the antiferromagnetic Mott insulator LaMnO 3 , with the metal-insulator transition occurring for ~ 17 % hole doping in La 1-x Sr x MnO 3 . 3 We have found that rectification can be observed even for much higher hole concentrations, and focus here on junctions using La 0.7 Sr 0.3 MnO 3-δ to vary across the ferromagnetic state. For La 0.7 Sr 0.3 MnO 3-δ /Nb:SrTiO 3 junctions, we find a significant increase in the junction capacitance in an applied magnetic field. Corresponding to this decrease in the depletion width, the reduction of the current barrier gives rise to exponential differential magnetoresistance. The modification of the electronic structure at the heterointerface by magnetic field is enabled by the unusual features arising from strong charge-spin coupling, giving a direct probe of the correlated electron equivalent of semiconductor band bending.

We have studied the phase diagram of LaVOx films grown on (001) SrTiO3 substrates by pulsed laser deposition. With increasing oxygen partial pressure, the growth phase diagram varies between epitaxial perovskite LaV3+O3 single crystal films and polycrystalline monoclinic LaV5+O4. An interesting feature is the lack of an accessible phase corresponding to V4+, resulting in an extended region of phase coexistence of LaVO3 and LaVO4. Atomically flat LaVO3 could be grown in both layer-by-layer and step-flow growth modes, making this a promising candidate for incorporating strongly correlated electrons in atomic-scale perovskite heterostructures.

We have prepared an atomically flat and insulating (110) SrTiO3 surface by annealing at high temperature under varying oxygen partial pressure. At low pressure, the polar surface is stabilized by oxygen vacancies, resulting in an atomically flat surface characterized by (110) unit-cell steps. The vacancies can be filled while maintaining this surface structure, providing an atomically ideal (110) substrate. We demonstrate two-dimensional homoepitaxial and heteroepitaxial growth, establishing the potential of this growth orientation for controlling interface states arising from polarity discontinuities in perovskite heterostructures.

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