The electrical characteristic measurement pattern diagram of δ-doped SrTiO3 structure

Integral (even) Quantum Hall Effect Found in δ-doped SrTiO3 Constructs

On May 27, 2016, the Japan Institute of Physical Chemistry (Richard), the University of Tokyo, and Tohoku University announced that they have produced a high quality single crystal thin film of a transition metal oxide, strontium titanate (SrTiO3). The “quantum Hall effect” was successfully observed in the two-dimensional electronic structure with electrons enclosed in a plane. The realization of the Quantum Hall effect in transition metal oxides with a strong electron-related structure is a research result that contributes to the development of new physical properties in which two-dimensional electrons are combined with superconducting and ferromagnetic materials. Use energy logic circuits, memory, and other fields.

In the past, the quantum Hall effect could only be observed by the electrons of the s-orbital and p-orbital electrons, which are weak in the electronic correlation (electron interactions), as the carrier electrons. Only high-purity silicon and gallium arsenide (GaAs) can be observed. Semiconductors, graphene and other few substances. On the other hand, transition metal oxides have been known as electron-related d-orbital electrons as carrier electrons and can exhibit various properties such as superconductivity and ferromagnetism. Although the two-dimensional electrons of SrTiO3 are d electrons, the mobility is relatively high. Therefore, many researchers have tried before and hope to realize the quantum Hall effect, but they have not been able to meet the two conditions that produce this effect—the electron density is low and High mobility.

Researchers from Riken and others have developed a "gas source molecular beam epitaxy (MBE) device" that can produce highly crystalline transition metal oxide thin films using high-purity raw materials. Molecular beam epitaxy (MBE) uses a method of heating and evaporating a high-purity raw material to produce a thin film. However, the vapor pressure of the transition metal is low, and the raw material supply speed is not stable. Therefore, misalignment of components occurs and film defects occur. Instead of heating the transition metal monomer to evaporate, the gas source MBE uses a source of volatile organic metal gas with a relatively high vapor pressure. In combination with the substrate heating technology based on semiconductor lasers, high-quality crystals are finally produced.

The research team used this gas source MBE device to design and fabricate about 200 nm thick δ-doped SrTiO3 structures (a three-layer structure consisting of 100 nm thick SrTiO3, 10 nm thick La doped SrTiO3, and 100 nm thick SrTiO3). The electron donor (La) releasing electrons in the wells of the vector-only subwell structure has been added. The researchers controlled the electron concentration through the transistor configuration, measured the electrical characteristics under extremely low temperature and applied magnetic fields, and then successfully discovered the integer quantum Hall effect. The Hall resistance is one-fourth (-0.25, +0.25) and one-sixth (−0.167, +0.167) of the quantum resistance (h/e2) in these magnetic fields (−12T, +12T, -7T, + In 7T), the sheet resistance shows a very small value.

Using the first-principles calculation software to calculate the electronic state of the two-dimensional structure, two-dimensional electrons occupy two different 3d electron bands of titanium in SrTiO3. Furthermore, the temperature dependence of the vibration amplitude of the thin-film resistive magnetic field and the first-principles calculation software were also used to estimate that the effective masses of the two energy bands of the two-dimensional electron are about 0.6 times and 1.2 times the mass of the free electron, respectively. This mass is more than one digit higher than other two-dimensional electrons that exhibit the quantum Hall effect, demonstrating strong electronic correlation effects.

According to reports, in the future, the research team will use the gas source MBE to make other transition metal oxide films, so that the research field of high-quality heterojunctions that exceed semiconductors will be extended to d-electronics, thus discovering new quantum effects and oxide electronic fields. Development contributes. The results of this study were published on the online version of Nature Communications, an international scientific journal, on May 27th. (Special Contributor: Kudosuke)

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