Quantum scientists have discovered a phenomenon in purple bronze, a one-dimensional metal, that switches between insulating and superconducting states. This switch is triggered by minimal stimuli, such as heat or light, and is due to “emergent symmetry.” This breakthrough, which began with the study of magnetoresistance in metals, could lead to the development of complete switches in quantum devices, a potential milestone in quantum technology.
Quantum scientists have discovered a phenomenon in purple bronze that could be key to developing the “perfect switch” for quantum devices, switching between insulators and superconductors.
The research was led by the University of Bristol. sciencediscovered that these two opposing electronic states exist in purple bronze, a unique one-dimensional metal composed of individual conducting chains of atoms.
For example, small changes in a material caused by small stimuli such as heat or light can cause an instantaneous transition from an insulating state with zero conductivity to a superconductor with unlimited conductivity or vice versa. This polarity diversity, known as “emergent symmetry,” has the potential to provide an ideal on/off switch for future quantum technology developments.
![Representation of emergent symmetry](https://scitechdaily.com/images/Representation-of-Emergent-Symmetry-777x578.jpg 777w,https://scitechdaily.com/images/Representation-of-Emergent-Symmetry-400x297.jpg 400w,https://scitechdaily.com/images/Representation-of-Emergent-Symmetry-768x571.jpg 768w,https://scitechdaily.com/images/Representation-of-Emergent-Symmetry.jpg 1243w)
This image shows a representation of emergent symmetry, showing perfectly symmetrical water droplets emerging from a layer of snow. In contrast, ice crystals in snow have a complex shape and are therefore less symmetrical than water droplets. The purple color indicates the purple bronze material in which this phenomenon was discovered.Credit: University of Bristol
13 years journey
Lead author Nigel Hussey, Professor of Physics University of BristolHe said: “This is a truly exciting discovery that could provide the perfect switch for tomorrow’s quantum devices.
“This amazing journey began in my lab 13 years ago, when two PhD students, Xiaofeng Xu and Nick Wakeham, measured the magnetoresistance (change in resistance caused by a magnetic field) of purple bronze. It was time.”
In the absence of a magnetic field, the resistance of the purple bronze was highly dependent on the direction in which the current flowed. Its temperature dependence was also quite complex. At room temperature, the resistor is a metal, but as the temperature drops, the resistance reverses and it appears to become an insulator. Then, at the lowest temperature, the resistance drops sharply again as it transitions to a superconductor. Despite this complexity, magnetoresistance surprisingly turns out to be quite simple. It was essentially the same regardless of the current or field alignment direction and followed a perfectly linear temperature dependence from room temperature to the superconducting transition temperature.
“Unable to find a consistent explanation for this puzzling behavior, the data remained dormant, unpublished, for the next seven years. Such interruptions are unusual in quantum research, but the reason is not a lack of statistics. ,” Professor Hussey explained.
“Such simplicity of magnetic reactions always belies a complex origin, and in the end the possibility of its resolution will only come through a chance encounter.”
A chance encounter leads to a breakthrough
In 2017, Professor Hussey was working at Radboud University when he saw an advertisement for a seminar on purple bronze by physicist Dr. Piotr Chuzinski. His interest was piqued because at the time, few researchers devoted entire seminars to this little-known material.
Professor Hussey said: “At the seminar, Chudzinski proposed that the increase in resistivity could be caused by interference between conduction electrons and elusive composite particles known as ‘dark excitons.’ After the seminar we chatted and together we proposed an experiment to test his theory. Subsequent measurements basically confirmed that. ”
Encouraged by this success, Professor Hussey revived Schuh and Wakeham’s magnetoresistive data and showed it to Dr. Chudzinski. His two central features of the data, linearity with respect to temperature and independence with respect to current and magnetic field orientation, suggest that the material itself may exhibit both insulating and superconducting behavior depending on how it is grown. That piqued Chudzinski’s interest, as did the fact that there was.
Rather than completely converting into an insulator, Dr. Chuzinski believes that interactions between charge carriers and previously introduced excitons cause the former to move toward the boundary between insulator and superconducting states as the temperature decreases. I thought that it might have a gravitational pull. At the boundary itself, the probability that the system is an insulator or a superconductor is essentially the same.
Professor Hussey said: “Such physical symmetry is an unusual condition, and as the temperature decreases, such symmetry develops in metals, thus the term ’emergent symmetry’ is a world first. Definitely.”
Physicists are familiar with the phenomenon of symmetry breaking, where cooling reduces the symmetry of an electronic system. The complex arrangement of water molecules within ice crystals is an example of such symmetry breaking. But the opposite is a very rare, if not unique, occurrence. Returning to the water/ice analogy, as we cool the ice further, the complexity of the ice crystals “melts” again, making it symmetrical and smooth like a water drop.
Emergent symmetry: a rare phenomenon
Dr Chudzinski, currently a research fellow at Queen’s University Belfast, said: In a nutshell, this is the essence of emergent symmetry. The person in question is our material, purple bronze, and our magician is nature itself. ”
To further test whether this theory has any basis, Maarten Berben, another PhD student working at Radboud University, investigated an additional 100 crystals containing insulators and superconductors. .
Professor Hussey added: “After Maarten’s hard work, the story is now complete and it is clear why different crystals exhibit such widely different ground states. In the future, this ‘sharpness’ could be exploited in quantum circuits. It may be possible to create a switch and cause a small stimulus to cause orders of magnitude large changes in the switch’s resistance. ”
Reference: “Emergent symmetries in low-dimensional superconductors at the Motnes edge” P. Chudzinski, M. Berben, Xiaofeng Xu, N. Wakeham, B. Bernáth, C. Duffy, RDH Hinlopen, Yu-Te Hsu, S. Wiedmann, P. Tinnemans, Rongying Jin, M. Greenblatt, NE Hussey, November 16, 2023. science.
DOI: 10.1126/science.abp8948