Tuning Electronic states and Phases of Transition Metal Oxides

Transition Metal Oxides (TMOs) exhibit unique and multifunctional physical phenomena directly related to the spin and orbital degrees of freedom of the transition metal d-states and their interplay with the lattice. Moreover, altering the electronic structure of ultra-thin layers of TMOs is a crucial first step toward designing complex heterostructures where new phases and phenomena emerge.



The first example, heterostructures made of SrIrO₃ (SIO) and SrRuO₃ (SRO) ultrathin layers, shows formation of the metallic phase despite both constituents being insulators. Combing transport, magnetic, and angle-resolved photoemission experiments (ARPES) with the first principal calculation, we disclose that the insulator-to-metal transition is driven by the interface occurrence of an astonishing Dzyaloshinskii-Moriya interaction (DMI) at the SIO-SRO interface, which induces interface ferromagnetism [1].

The second case depicts that the magnetic and electronic properties of ultrathin NdNiO₃ (NNO) film in proximity to ferromagnetic (FM) La_2/3Sr_1/3MnO₃ (LSMO) layer drastically contradict its bulk form. Employing X-ray magnetic circular dichroism (XMCD), ARPES, and the first principal calculation reveal the direct magnetic coupling between the nickelate film and the manganite layer, which causes an unusual ferromagnetic (FM) phase in NNO. Consequently, the insulating AFM ground state in the NNO layer is quenched in proximity to the FM layer.



Both results demonstrate that heterogeneous engineering of magnetic interactions can be a powerful tool to generate and control emergent electronic properties that do not exist in ultrathin pure film.



Overall, our studies established approaches to manipulating the properties and phases (electronic and magnetic) in TMOs, signifying their perspectives as quantum materials for novel applications.