Aug
18
Progress Reported For Superconductivity Research
August 18, 2022 | Leave a Comment
*Stay with this post a minute for clarity, its worth it.
Superconductivity is a fascinating state of matter in which an electrical current can flow without any resistance. Usually, it can exist in two forms. One is destroyed easily with a magnetic field and has ‘even parity’, i.e. it has a point symmetric wave function with respect to an inversion point, and one which is stable in magnetic fields applied in certain directions and has ‘odd parity’, i.e. it has an antisymmetric wave function.
*The “destroyed easily” point helps understanding part of the problem in finding the superconductor that changes history.
Consequently, the latter should present a characteristic angle dependence of the critical field where superconductivity disappears. But odd-parity superconductivity is rare in nature; only a few materials support this state, and in none of them has the expected angle dependence been observed. In a new publication in Physical Review X, the group by Elena Hassinger and collaborators show that the angle dependence in the superconductor CeRh2As2 is exactly that expected of an odd-parity state.
Angle dependence of the superconducting critical fields in CeRh2As2 determined by ac-susceptibility, magnetic torque and specific heat. The observed behavior is in excellent agreement with the expected one of even and odd-parity superconductivity. Image Credit: Max Planck Institute for Chemical Physics of Solids. Click this link to go to the Physical Review X page for this, other images and the study paper.
CeRh2As2 was recently found to exhibit two superconducting states: A low-field state changes into a high-field state at 4 T when a magnetic field is applied along one axis. For varying field directions, the team measured the specific heat, magnetic susceptibility, and magnetic torque of this material to obtain the angle dependence of the critical fields. They found that the high-field state quickly disappears when the magnetic field is turned away from the initial axis. These results are in excellent agreement with the team’s model identifying the two states with even- and odd-parity states.
CeRh2As2 presents an extraordinary opportunity to investigate odd-parity superconductivity further. It also allows for testing mechanisms for a transition between two superconducting states, and especially their relation to spin-orbit coupling, multiband physics, and additional ordered states occurring in this material.
***
For general science observers of the superconductor field the progress has been slow and lets say, exasperating. Most folks have been led to think through reports that there will be a material discovered to provide a history making solution.
However the fact is the field is still very much in the zone of “what is going on” when the superconduction effect appears and why does it, i.e. need cold conditions, some materials and alloys work and others don’t and other questions that make up quite a list.
That said, the field is in the basic discovery mode. Trial and error progress has been quite a bit of help, but this news gets to the fundamentals, asking questions and getting deep information revealing “what is going on”. If the field stays in the guessing game mode this kind of research is going to improve the odds. If the basics are researched even further the field may well get to the point where the depth of understanding allows designing and engineering materials. One day we may read about AI and programs that predict materials.
This team’s work is important and its progress indeed. Its because the next question, “Why does this happen?” may soon have an answer within reach. That’s the question and others like it whose answers start real progress.
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