arXiv subjects

J. D. Grassi

Publications and source records attributed to J. D. Grassi.

3 recordsLinked to original sources

arXiv2026

Dimensionality-Driven Electronic and Orbital Transitions Mediating Interfacial Magnetism in LaNiO3/CaMnO3 Observed In Situ

Emergent magnetic states at oxide interfaces arise from the interplay of charge transfer, orbital reconstruction, and dimensional confinement, offering a route to engineered correlated-electron behavior in nanoscale spintronic materials. Here, we combine in situ synthesis, polarization-dependent angle-resolved photoelectron spectroscopy, X-ray magnetic circular dichroism, and first-principles electronic-structure calculations to investigate LaNiO3/CaMnO3 superlattices. We show that reducing the LaNiO3 thickness drives a metal-insulator transition accompanied by loss of electronic coherence and an orbital-polarization crossover in the ultrathin limit. These changes weaken charge transfer across the interface and suppress the interfacial Mn magnetic moment in CaMnO3, revealing that the emergent ferromagnetic state is directly governed by electronic confinement in LaNiO3. The insulating state and orbital reconstruction are reproduced by density functional theory combined with dynamical mean-field theory. Together, these results establish a direct and tunable coupling among electronic, orbital, and magnetic degrees of freedom in oxide heterostructures.

cond-mat.str-el↗

arXiv2023

Direct experimental evidence of tunable charge transfer at the $LaNiO_{3}/CaMnO_{3}$ ferromagnetic interface

Interfacial charge transfer in oxide heterostructures gives rise to a rich variety of electronic and magnetic phenomena. Designing heterostructures where one of the thin-film components exhibits a metal-insulator transition opens a promising avenue for controlling such phenomena both statically and dynamically. In this letter, we utilize a combination of depth-resolved soft X-ray standing-wave and hard X-ray photoelectron spectroscopies in conjunction with polarization-dependent X-ray absorption spectroscopy to investigate the effects of the metal-insulator transition in $LaNiO_{3}$ on the electronic and magnetic states at the $LaNiO_{3}/CaMnO_{3}$ interface. We report on a direct observation of the reduced effective valence state of the interfacial Mn cations in the metallic superlattice with an above-critical $LaNiO_{3}$ thickness (6 u.c.) due to the leakage of itinerant Ni 3d $e_{g}$ electrons into the interfacial $CaMnO_{3}$ layer. Conversely, in an insulating superlattice with a below-critical $LaNiO_{3}$ thickness of 2 u.c., a homogeneous effective valence state of Mn is observed throughout the $CaMnO_{3}$ layers due to the blockage of charge transfer across the interface. The ability to switch and tune interfacial charge transfer enables precise control of the emergent ferromagnetic state at the $LaNiO_{3}/CaMnO_{3}$ interface and, thus, has far-reaching consequences on the future strategies for the design of next-generation spintronic devices.

cond-mat.mtrl-sci↗

arXiv2021

Tuning band alignment at a semiconductor-crystalline oxide heterojunction via electrostatic modulation of the interfacial dipole

We demonstrate that the interfacial dipole associated with bonding across the SrTiO3/Si heterojunction can be tuned through space charge, thereby enabling the band alignment to be altered via doping. Oxygen impurities in Si act as donors that create space charge by transferring electrons across the interface into SrTiO3. The space charge induces an electric field that modifies the interfacial dipole, thereby tuning the band alignment from type-II to type-III. The transferred charge, resulting in built-in electric fields, and change in band alignment are manifested in electrical transport and hard x-ray photoelectron spectroscopy measurements. Ab initio models reveal the interplay between polarization and band offsets. We find that band offsets can be tuned by modulating the density of space charge across the interface. Functionalizing the interface dipole to enable electrostatic altering of band alignment opens new pathways to realize novel behavior in semiconducting heterojunctions.

cond-mat.mtrl-sci↗