Physicists at the Massachusetts Institute of Technology (MIT) have developed a new material that can exhibit two exotic forms of superconductivity when manipulated in the right way. The material demonstrates a unique quality; upon the application of a magnetic field, it becomes a finite momentum superconductor – a kind of superconductivity first hypothesized in the 1960s.
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Up until now, stabilizing this exotic form of superconductivity has proven to be an extremely difficult task.
Led by Joseph Checkelsky, lead principal investigator of the work and the Mitsui Career Development Associate Professor of Physics, the team developed the material just over a year ago, and their latest work (published in the journal Nature) explains the new physics.
In recent years there has been a rising stream of special superconductors that are two-dimensional (2D), or only a few atomic layers thick. However, due to the delicate nature of 2D materials, they can be somewhat difficult to study.
Natural Superlattice
The material the MIT team first fabricated just over 12 months ago is a layered crystal known as a natural superlattice, meaning that the same sample of material can be modified to generate various patterns of superconductivity.
The MIT team believes that the material has the potential application in quantum computing, but they also state it could reveal the theoretical assumptions about the nature of superconductivity itself.
Our analysis suggests that the hierarchy of energy scales for SOC, superconductivity and small interlayer coupling may be conducive for topological superconductivity.
Joseph Checkelsky, Lead Principal Investigator and the Mitsui Career Development Associate Professor of Physics
The composition of the material is divided into two layers: one is an ultrathin superconducting film, and the other is a protective ultrathin spacer layer. These layers can then be stacked, which in turn produces a large, layered crystal that acts as a 2D superconductor.
Checkelsky and his team were then able to apply a number of tools and calculations for the characterization of the material in order to make their findings.
Superconductors
What makes a material a superconductor is its capacity to carry two electrons together in what is known as a Copper pair. However, not all superconductors demonstrate the same properties. Exotic forms of superconductor activity appear in some materials when the Cooper pair can move across a relatively great distance unobstructed.
In effect, when this phenomenon is witnessed, and the Cooper pair is able to travel a significant distance unimpeded, the ‘cleaner’ the material is thought to be.
The material developed by the MIT team is exceptionally clean, which is one of the features that allows it to exhibit an exotic superconducting state.
The system exhibits prominent diamagnetism from the Meissner effect, which gives way at higher fields to a mixed state indicative of type II superconductivity. The response is largely reversible, indicative of this system’s cleanliness.
Joseph Checkelsky, Lead Principal Investigator and the Mitsui Career Development Associate Professor of Physics
Furthermore, as the material is believed to be a finite momentum superconductor, it can be manipulated to form various patterns of Cooper pairs which move between Landau levels.
Two Exotic Potentials For One
Landau levels are quantum mechanical orbits with discrete equidistant energy values, which could help the MIT team create different patterns of superconductivity and control over Landau levels in the same material.
The material also showed evidence for topological superconductivity, which moves the charge around the edge or boundary of a material. This opens up further application potential as combing two types of superconductivity could usher in a new wave of computing technology.
This suggests opportunities to study bosonic LLs, topological superconductivity, and their interplay via transport, scattering, scanning probe and exfoliation techniques.
Joseph Checkelsky, Lead Principal Investigator and the Mitsui Career Development Associate Professor of Physics
The team will conduct further investigation on the material they have developed to see if it does indeed conform to topological superconductivity, confirming the existence of two forms of exotic superconductivity in one material.
It’s been a lot of fun realizing this new material. As we’ve dug into understanding what it can do, there have been a number of surprises. It’s really exciting when new things come out that we don’t expect.
Joseph Checkelsky, Lead Principal Investigator and the Mitsui Career Development Associate Professor of Physics
References and Further Reading
Devarakonda, A., et al., (2021) Signatures of bosonic Landau levels in a finite-momentum superconductor. Nature, [online] 599(7883), pp.51-56. Available at: https://doi.org/10.1038/s41586-021-03915-3
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