'We Can Modify Electron Spins as Required by Applying an External Magnetic Field'

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Researchers from HSE, MIPT, and the Russian Academy of Sciences Institute of Solid State Physics, jointly with colleagues from the UK, Switzerland, and China, have conducted a study on the characteristics of thin films composed of platinum and niobium. Both the experiments and the theoretical calculations have confirmed that when in contact with a superconductor, platinum exhibits a spin, creating a potential for its effective use for data transmission. Platinum atoms have no magnetic moment, paving the way for the development of even smaller chips utilising this novel structure compared to conventional spintronics. The paper has been published in Nature Communications.

One of the foremost objectives in contemporary science is the development of a new elemental base for data processing devices. Current semiconductor technologies are nearing their limits, and concerns are growing that the trend described by Moore's Law stating that the number of transistors on a microchip doubles every two years is slowing down and may soon come to a complete halt due to purely physical constraints, as it is impossible to produce a transistor smaller than a single atom. Therefore, new devices will need to rely on alternative physical principles.

Scanning tunneling spectroscopy data on Au(5)/Pt(x)/Nb(50)/Si(subs) (nm).

Nature Communications

Superconducting spintronics presents a promising solution to this challenge. In contrast to electronics, the information carrier here is not an electron's charge but rather its spin, which refers to the orientation of its rotational axis. According to the Pauli Exclusion Principle, two electrons in an atom must have opposite spins: one directed upward, and one directed downward. This makes it possible to associate one with zero and the other with one, enabling the recording of information in binary form. For such devices to function, it is essential to control the orientations of electron spins while minimising heat losses. In superconductors, electrons move without encountering resistance, but they do so in a distinctive manner by forming Cooper pairs. Within a Cooper pair, one electron's spin is oriented upward while the other's is oriented downward, resulting in a net spin of zero, and such a configuration cannot transmit information encoded in the spin.  To obtain pairs in which both spins are oriented upwards, conventional approaches involve the use of structures where a thin layer of ferromagnetic material interfaces with the superconductor. However, this approach has its drawbacks, with the primary concern being that the intrinsic magnetic fields within ferromagnetic materials lead to interactions among the computational elements.

Irina Bobkova

Irina Bobkova, Professor at the HSE Faculty of Physics and Head of the Laboratory of Spin Phenomena in Superconducting Nanostructures and Devices at MIPT, explains: 'We opted for an alternative approach to the problem and used platinum instead of ferromagnets. Since platinum has no magnetic moment of its own, we can modify electron spins as required by applying an external magnetic field. The experiments have confirmed our hypothesis.'

The platinum-niobium 'sandwiches' developed by the researchers will make it possible to construct smaller, more compact computing devices. The experiment demonstrated that when a thin layer of platinum interacts with a superconductor, Cooper pairs penetrate into the platinum layer due to the proximity effect. Through the application of a magnetic field, the physicists successfully reoriented the electron spins of these pairs, thus validating the feasibility of information transmission.

The study team includes researchers from MIPT, HSE, the RAS Institute of Solid State Physics (Russia), the University of St Andrews and the Rutherford-Appleton Laboratory (UK), the Paul Scherrer Institute (Switzerland), and Shanghai Jiao Tong University (China).