Researchers discover tunable 2D electron gas at the heterointerface of 5d iridate

Recently, Professor Yang Xiaoping’s research group at the Institute of High Magnetic Fields, Hefei Institute of Physical Sciences, Chinese Academy of Sciences, discovered a tunable and controllable monolayer two-dimensional electron gas (2DEG) localized at the heterointerface.

The research results were published in the journal ACS Applied Electronic Materials.

The Mott insulator-metal transition is an important topic in condensed matter physics because of its potential for device applications and superconductivity upon doping. In 5d iridates, spin-orbit coupling (SOC) is much stronger than in 3d transition metal oxides, comparable to crystal field splitting and electron-electron interactions. This splits the Ir 5d-t2g band into Jeff = 3/2 and Jeff = 1/2 subbands.

Currently, artificial heterointerface techniques are widely used to manipulate the electronic structure and properties of materials.

In this study, the researchers used density functional theory to investigate the electronic properties of the (SrIrO3)m/(LaTiO3)1 superlattice. They observed that integer charge transfer occurs between LaTiO3 and SrIrO3 due to the combined effects of interfacial polarity differences and oxygen octahedral distortion.

The number of electrons transferred on each Ir atom can be controlled by doping the A sites of LaTiO3 or by varying the number m of SrIrO3 layers, thereby tuning the oxidation state of Ir. This gave rise to a variety of electronic states, including nonmagnetic band insulators, ferromagnetic metals, ferrimagnetic Mott insulators, and ferrimagnetic metals.

Mixed valence states appear when there are at least two layers of SrIrO3. This leads to an insulator-metal transition when the SrIrO3 layer number m is 3 or more.

Most interestingly, the charge transfer and the formation of two-dimensional electron gas (2DEG) occur only in the single atomic layer of IrO2 where the materials are in contact, regardless of the thickness of the SrIrO3 layer. This is different from the 3d LaAlO3/SrTiO3 system, where the 2DEG extends deep into the material beyond just the interface.

These findings provide new insights into the development of new nanoscale oxide electronic devices and the exploration of two-dimensional unconventional iridate superconductivity.