Superconductors conduct electricity without dissipating energy. Superconductivity depends on electrons not repelling each other as the particles do in ordinary materials. Instead, the particles form weakly bonded duos known as Cooper pairs that can flow with zero resistance. Superconductivity vanishes whenever anything disrupts Cooper pairs, such as jostling from atoms, and as a result superconductivity often disappears at high temperatures and under high magnetic fields.
Ye and his colleagues discovered that molybdenum sulfide, a common dry lubricant, remains superconducting even under external magnetic fields as strong as 37.5 Tesla. In comparison, the magnets in medical MRI machines reach up to 3 Tesla strength. The researchers experimented with molybdenum sulfide transistors cooled to 12K or colder and found that when molybdenum sulfide becomes superconducting, its electronic structure generates a magnetic field roughly 100 Tesla in strength. This internal field can protect the superconductor’s electron pairs from weaker external magnetic fields.
[pullquote]The researchers found that when molybdenum sulfide becomes superconducting, its electronic structure generates a magnetic field roughly 100 Tesla in strength. This internal field can protect the superconductor’s electron pairs from weaker external magnetic fields.[/pullquote]
The research relied on ionic gating, a new device technology that enables electric field strength 100 times stronger than those found in traditional field effect transistors, and suggests a new superconducting state with pairing protected by an internal magnetic filed of 100 Tesla can be induced by strong gating.
Ye hopes the findings may one day lead to improved superconducting electronics. Superconductivity is key to ultrasensitive magnetic sensors known as superconducting quantum interference devices, or SQUIDs, that are used in applications such as analyzing brain activity, medical imaging and oil prospecting. Ye says these new findings could one day lead to SQUIDs that can operate even in powerful magnetic fields.
Another use for magnet-resistant superconductors could be quantum computing, according to Ye. The electron pairs in superconductors can form quasiparticles known as Majorana fermions, which can in theory encode data in a way that is not easily disrupted by thermal fluctuations, unlike current quantum computing systems. Magnet-resistant superconductors could make such quantum computers even more robust.
Molybdenum sulfide belongs to a family of materials known as transition metal dichalcogenides (TMD), many of which are also superconductors. Ye and his colleagues now plan analyze other TMDs to see if superconductivity in these similar materials is equally robust against external magnetic fields.