A research team led by Prof. LIN Hao from the High Magnetic Field Laboratory at the Hefei Institutes of Physical Science of the Chinese Academy of Sciences, in collaboration with multiple international research teams, has successfully achieved an atomically controlled insulator-to-metal transition in iridate/manganate heterostructures.
Their findings were recently published in Nature Communications.
Conductive interfaces in insulator-insulator heterostructures are central to modern electronics. Compared with band insulator, a correlation insulator typically has a richer phase diagram that even covering both insulating and metallic states by itself. However, a conductive interface in heterostructures composed of two correlated insulators are rarely reported.
In this research, the team investigated heterostructures composed of a 5d iridate, CaIrO3 (CIO), and a 3d manganite, La0.67Sr0.33MnO3 (LSMO). While CaIrO3 is a Dirac semimetal and La0.67Sr0.33MnO3 is a robust half-metal in the bulk phase, both materials can be stabilized into insulating states under a strong electronic correlation. The combination forms a platform to explore emerging metallicity at their interface.
The researchers synthesized the heterostructures using a precise deposition method, creating layers with varying thicknesses of CIO and LSMO. Under a strong electronic correlation, both materials became insulators, yet the resulting heterostructure exhibited electrical properties that varied depending on the thickness of the CIO layer.
A key finding was the heterostructure's high saturation field, exceeding 30 Tesla at 20 K, much higher than the individual components alone. This suggested the presence of electronic phase separation, where metallic clusters formed a conductive path when subjected to a high magnetic field.
The team's investigation also revealed that the insulator-to-metal transition was driven by a nontrivial percolation effect, a result of the charge transfer at the interface. By carefully controlling the electronic correlation, they successfully induced the insulator-to-metal transition in certain heterostructures, although the CIO thickness is only of a single unit-cell.
This research not only provides new insights into the behavior of correlated insulator heterostructures but also highlights their potential in the design of next-generation electronic devices.
(a) In-plane magnetic field-dependent magnetoresistance (MR) of LSMO-LSAT film and 3CIO/20LSMO heterostructure at various temperatures. (b) Evolution of the insulating strength p(150K)/p(300K) with CIO thickness and in-plane lattice parameter a. Dashed line represents where the insulator-to-metal transition occurs. (Image by HAO Lin)
The schematical diagram of the percolation-type insulator-to-metal transition. The conductive path is highlighted by red curves. (Image by HAO Lin)
