A novel combination of materials, each possessing distinct electrical characteristics, possesses all the elements necessary for a special kind of superconductivity that might serve as the foundation for more reliable quantum computing.
A team led by Penn State researchers has demonstrated superconductivity at the interface between the fusion of two magnetic materials, a ferromagnet (Cr-doped (Bi, Sb)2Te) and an antiferromagnet (FeTe). The system has all the components required for a unique type of superconductivity called chiral topological superconductivity, which could provide the basis for more robust quantum computing. Left: Schematic lattice structure and cross-sectional STEM image. Right: R-T curve (top) and superconductivity gap (bottom). Image Credit: Provided by the Chang Lab/Penn State. All Rights Reserved
The new material combination, developed by a group headed by Penn State researchers, may also offer a platform for investigating physical properties resembling those of chiral Majoranas, which are hypothetical particles that are mysterious and thought to be another promising building block for quantum computing.
The study was published on February 8th, 2024, in the journal Science. The study details the researchers' integration of the two magnetic materials, which they deemed as a crucial step toward their current goal of realizing emergent interfacial superconductivity.
Superconductors, or materials devoid of electrical resistance, find widespread application in high-power magnets used in particle accelerators and magnetic resonance imaging (MRI), as well as in other technologies where optimizing the flow of electricity is essential.
When materials known as magnetic topological insulators-thin films made of just a few atoms thick that have been made magnetic and prevent electrons from moving past their edges- are mixed with superconductors - together, the unique electrical characteristics of each part result in “chiral topological superconductors.”
Building topological quantum computers may be made easier by the topology, or specific geometries and symmetries of matter, which produce special electrical phenomena in the superconductor.
Because the quantum bits in quantum computers store data simultaneously in a range of possible states, unlike traditional computers, which store data as a one or a zero, quantum computers have the potential to perform complex calculations in a fraction of the time it takes traditional computers. By utilizing the way in which electrical properties are arranged, topological quantum computers go beyond quantum computing and become more resilient to decoherence—the information loss that occurs when a quantum system is not completely isolated.
Creating chiral topological superconductors is an important step toward topological quantum computation that could be scaled up for broad use. Chiral topological superconductivity requires three ingredients: superconductivity, ferromagnetism, and a property called topological order. In this study, we produced a system with all three of these properties.
Cui-Zu Chang, Henry W. Knerr Early Career Professor and Co-Corresponding Author, Physics, The Pennsylvania State University
The iron chalcogenide (FeTe), a promising transition metal for superconductivity, and a topological insulator that has been made magnetic were stacked together by the researchers using a process known as molecular beam epitaxy. FeTe is an antiferromagnet - whose electrons rotate in two different directions. But the topological insulator is a ferromagnet, or a type of magnet whose electrons spin in the same direction.
The structure and electrical characteristics of the resultant combined material were characterized by the researchers using a range of imaging techniques and other methods. They also verified the presence of all three essential components of chiral topological superconductivity at the interface between the materials.
The field’s previous efforts have concentrated on the combination of nonmagnetic topological insulators and superconductors. The researchers claim that ferromagnet addition has proven especially difficult.
Normally, superconductivity and ferromagnetism compete with each other, so it is rare to find robust superconductivity in a ferromagnetic material system. But the superconductivity in this system is actually very robust against the ferromagnetism. You would need a very strong magnetic field to remove the superconductivity.
Chao-Xing Liu, Professor and Co-Corresponding Author, Physics, The Pennsylvania State University
Chang adds, “It’s actually quite interesting because we have two magnetic materials that are non-superconducting, but we put them together and the interface between these two compounds produces very robust superconductivity. Iron chalcogenide is antiferromagnetic, and we anticipate its antiferromagnetic property is weakened around the interface to give rise to the emergent superconductivity, but we need more experiments and theoretical work to verify if this is true and to clarify the superconducting mechanism.”
Chang noted the University’s contributions to facilitating the finding.
Penn State recently provided the resources for acquiring a state-of-the-art imaging system, a low temperature scanning tunneling microscope, which was crucial in justifying our experimental claims. I’m delighted that we were able to rapidly make an important scientific discovery with this investment.
Cui-Zu Chang, Henry W. Knerr Early Career Professor and Co-Corresponding Author, Physics, The Pennsylvania State University
The system, according to the researchers, will be helpful in the hunt for material systems that display behaviors akin to those of Majorana particles, hypothetical subatomic particles first postulated in 1937. Majorana particles have the unusual ability to function as their own antiparticle, which may one day enable them to be employed as quantum bits in computers.
Chang says, “Providing experimental evidence for the existence of chiral Majorana will be a critical step in the creation of a topological quantum computer. Our field has had a rocky past in trying to find these elusive particles, but we think this is a promising platform for exploring Majorana physics.”
The Penn State research team at the time of the study included Moses Chan, an emeritus professor of physics at Evan Pugh University, postdoctoral researcher Hemian Yi, graduate students Yi-Fan Zhao, Ruobing Mei, Zi-Jie Yan, Ling-Jie Zhou, Ruoxi Zhang, Zihao Wang, Stephen Paolini, and Run Xiao, assistant research professors Ke Wang and Anthony Richardella, and Verne M. Willaman Professor of Physics and Professor of Materials Science and Engineering Nitin Samarth.
The other members of the research team are Purnima Balakrishnan and Alexander Grutter at the National Institute of Standards and Technology; John Singleton and Laurel Winter at the National High Magnetic Field Laboratory; Xianxin Wu at the Chinese Academy of Sciences; Jiaqi Cai and Xiaodong Xu at the University of Washington; Ying-Ting Chan and Weida Wu at Rutgers University; and Thomas Prokscha, Zaher Salman, and Andreas Suter at the Paul Scherrer Institute of Switzerland.
The US Department of Energy is funding this research. The US National Science Foundation (NSF), the Materials Research Science and Engineering Center for Nanoscale Science at Penn State, the Air Force Office of Scientific Research, the Army Research Office, the state of Florida, and the Gordon and Betty Moore Foundation's EPiQS Initiative all contributed additional support. Penn State's 2DCC, an NSF-funded user facility, was utilized to synthesize and characterize the thin film materials used in this study.
Journal Reference:
Yi, H., et.al (2024) Interface-induced superconductivity in magnetic topological insulators. Science. doi.org/10.1126/science.adk1270.
Source: https://www.psu.edu/