Scientists have revealed a method for controlling superconductivity.

The study has been published in the journal Physical Review Materials. The exploration of the interaction between ferromagnetic and superconducting materials spans several decades. Superconductivity and ferromagnetism have traditionally been viewed as competing states. Research has long demonstrated that in three-dimensional systems (comprising at least dozens of atomic layers), the presence of ferromagnets can suppress superconductivity.

A new impetus for the development of proximity effect physics has emerged with the discovery of two-dimensional materials (often referred to as van der Waals materials). These materials, which possess unique physical properties, enable the creation of heterostructures with distinctive characteristics that are proposed for use in high-tech applications such as quantum computers and advanced sensors.

Since the discovery of graphene by PhysTech graduates Andrei Geim and Konstantin Novoselov, physicists have actively investigated the electrical and magnetic properties of two-dimensional materials. Recent research has further solidified interest in van der Waals heterostructures, showing how the properties of conducting electrons can influence the physical characteristics of these systems.

The new work by scientists from MIPT and their colleagues aims to achieve an ambitious goal: to understand how magnetic and superconducting effects can be controlled in such structures, as well as what discoveries these processes may lead to in the field of spintronics.

The researchers focused on the proximity effect in bilayer 2D van der Waals heterostructures, using the superconductor NbSe2 and the ferromagnet VSe2 as examples. The interaction between magnetic and superconducting properties in van der Waals heterostructures is of particular interest because the interface between the materials essentially encompasses the entire heterostructure.

Proximity effects are phenomena arising from the mutual influence of electrons from different materials on each other. Even in three-dimensional heterostructures, the interaction between various layers can vary significantly depending on their thickness and the nature of the materials. In the case of two-dimensional heterostructures, the variety of possible effects becomes even greater.

Moreover, two-dimensional materials have an intriguing feature—their electronic properties can be significantly regulated by applying gate voltage. In the context of heterostructures (layered structures made of different materials), this method allows for the control of interactions between layers. Through modeling multilayer systems using electronic spectra of individual layers, researchers found that the influence of ferromagnets on superconductivity can be significantly enhanced by applying gate voltage.

During their work, the scientists simulated the system using a strong coupling Hamiltonian, which enabled the analysis of the dependence of the superconducting order parameter on the exchange field of the ferromagnetic layer. Detailed calculations of electronic spectra were performed using density functional theory methods.

“We presented results showing that it is possible not only to turn superconductivity on and off but also to manipulate spin splitting in electronic spectra. Furthermore, the simultaneous presence of spin splitting and strong spin-orbit coupling opens up prospects for creating electrically tunable two-dimensional Zeeman (spin-split) superconductors,” explained Grigory Bobkov, a researcher at the MIPT laboratory of photoelectron spectroscopy of quantum functional materials. “By varying the applied voltage, we gain the ability to change the amplitude and sign of spin splitting in superconducting spectra, which opens up new exciting opportunities in the fields of spintronics and spin caloritronics.”

“Considering the specific example of the heterostructure made of NbSe2 and VSe2, we explored the physics of proximity effects in 2D van der Waals heterostructures. We found that the electronic spectra, and consequently the superconducting characteristics, depend on the strength of the interaction between the layers. We were able to clearly demonstrate how changes in the chemical potentials of the layers lead to changes in the behavior of electronic spectra, as well as alterations in the amplitude and sign of spin splitting,” said Alexander Bobkov, a senior researcher at the MIPT Center for Advanced Methods of Mesophysics and Nanotechnology. “The results of our work highlight the potential for creating highly efficient thermoelectric devices and open up prospects in low-dissipative spintronics.”

The results obtained demonstrated that the behavior of the system can exhibit diverse characteristics depending on the chemical potentials and the degree of hybridization between the layers. They not only provide a deeper understanding of the physics of interactions in multilayer heterostructures but also open new possibilities for designing high-efficiency devices based on 2D materials for applications in spintronics.

The work was supported by a project from the Russian Science Foundation.