Skyrmionic magnons as mediators of topological superconductivity in a model system.

Topological superconductors are superconducting materials with unique properties, including the emergence of so-called Majorana states within the gap. These bound states can act as qubits, which makes topological superconductors particularly promising for creating quantum computing technologies.

Recently some physicists have been exploring the possibility of creating quantum systems that fuse superconductors with swirling configurations of atomic magnetic dipoles (spins), known as quantum sky crystals. Most of these efforts have proposed placing quantum wire crystals between superconductors to achieve topological superconductivity.

Kristian Molland and Asel Sudbo, researchers at the Norwegian University of Science and Technology, recently proposed an alternative model system for topological superconductivity, which does not involve superconducting materials. This theoretical model, which was presented in Physical review lettersinstead, uses a heavy metal, a ferromagnetic insulator, and a normal metal sandwich structure, in which the heavy metal induces a quantum wire crystal in the ferromagnet.

“We have been interested in new, low-dimensional types of quantum spin systems for a long time, and have been investigating the question of how quantum spin fluctuations in quantum sky crystals might affect ordinary metallic states and possibly lead to superconductivity of an unusual kind,” Sudbø told Phys.org. .

Previous work that has inspired us in particular and that we are building on, is The experimental work of Haynes et al on realizing quantum sky crystals, and two of our own paper on quantum sky crystals.”

in Paper published in 2011, Stefan Heinz of Keele University and colleagues at the University of Hamburg show that sky crystals can be realized in actual physical systems. Inspired by previous work by this research team, Sudbø and Mæland make a series of predictions, which serve as the basis for their newly proposed model system for topological superconductivity.

“We ourselves have not experimentally made these systems, but we are proposing materials that can be used to create such systems and study their properties,” said Sudbo. “We specifically investigated a novel method for creating topological superconductivity by means of ordinary metal debris with very specific rotation regimes in which the spins of the spins form a sky with a repeating pattern, a sky crystal. Previous proposals for creating topological superconductivity suggested linking swirmion crystals with superconductors. The approach makes no sense. to a superconductor in a sandwich.”

While not empirically realizing their proposed model system, Sudbø and Mæland attempted to determine its properties through a series of calculations. Specifically, they calculated a property of the induced superconducting state in the system, the so-called superconducting order coefficient, and found that it had a non-trivial structure.

“We were able to create a model system in which we can produce topological superconductivity in a heterostructure without a superconductor pre-existing in the sandwich,” said Sudbo. “Our system is a sandwich structure of a normal metal and a magnetic insulator, while previous proposals involved a sandwich structure of magnetic insulators and other superconductors.”

In the future, new studies can attempt to realize the model system proposed by these researchers in an experimental setting, and study its properties and potential for quantum computing applications. In the meantime, Sudbø and Mæland plan to explore other theoretically possible ways to achieve unconventional superconductivity.

“Overall, we will pursue unconventional superconductivity and pathways to topological superconductivity in heterostructures involving magnetic insulators with unusual and unconventional ground states as well as new types of spin excitations outside the ground state,” Sudbo said.

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