An experiment years in the making has directly visualized superconductivity on the atomic scale in cuprate crystals, revealing the cause of its superconductivity feature.
BCS Theory and Cooper Pairs
According to the BCS theory, vibrations passing between rows of atoms glue electrons together. A ripple is created when a negatively charged electron travels between positively charged atomic nuclei, pulling them toward it. Another electron is attracted by that ripple. The two electrons overcome their strong electrical attraction to create a Cooper pair. However, the Cooper pair was not supposed to happen.
Cooper pairs behave like light particles, breaking a different quantum mechanical law from the one that states that electrons cannot overlap. A large number of Cooper pairs combine to form a single quantum mechanical state known as a superfluid that loses awareness of the atoms it travels through.
Superconductivity and the Superexchange Quantum Phenomenon
Superconductivity becomes inevitable when electrons pair together due to additional quantum entanglement.
The superconducting behavior of mercury and the majority of other metallic elements is explained by the BCS theory, which also explains why this behavior ends above a few kelvins. The weakest of glues is created by atomic ripples. Increasing the heat causes the atoms to vibrate and remove the lattice vibrations.
The late Philip Anderson, an American Nobel laureate and condensed matter physics superstar, asserted a theory called the superexchange quantum phenomenon. It results from the ability of electrons to hop, which lies at the core of the adhesive. When electrons can move quickly between different places, their position at any one time is unclear while their momentum is well-defined. Particles will typically gravitate toward a condition with a sharper momentum because it has a lower momentum and, hence, a lower energy.
Superconductivity and Hopping Energy
In 2020, scientists discovered a cuprate known as bismuth strontium calcium copper oxide (BSCCO) had an unusual property that enabled their ideal experiment.
In BSCCO, the surrounding sheets of atoms press the layers of copper and oxygen atoms into a wavy pattern. This alters the separations between specific atoms, which impacts how much energy is needed to hop. The variance provided experimentalists with hopping energies in a single sample instead of neat lattices.
They mapped the hopping energies across the cuprate by attaching electrons to some atoms and removing them from others using a conventional scanning microscope with a metal tip. The density of Cooper pairs surrounding each atom was then measured by switching in a cuprate tip. One image has horizontal pink and black stripes, while the other has blue and black stripes.
Since hopping energy and superconductivity strength are related, Davis' discovery strongly suggests that superexchange functions as the glue that enables high-temperature superconductivity.
Ali Yazdani, a Princeton University physicist who has developed comparable techniques to study cuprates and other unusual manifestations of superconductivity concurrently with Davis' group, said that it's a nice piece of work because it brings a new technique to further show that the idea has legs.
ALSO READ: Physicists Finally Achieved Room-Temperature Superconductivity
Research Advancement
The study advances the field's long-standing goal of enhancing cuprate superconductivity's underlying mechanism in order to create revolutionary new materials that can conduct electricity at even greater temperatures.
According to Eurekalert, the team thinks that this discovery could prove a historic step towards developing room-temperature superconductors and several applications in maglev trains, nuclear fusion reactors, high-energy particle accelerators and quantum computers.
Lead author J. C. Séamus Davis said, "I've worked on this problem for 25 years, and I hope I have solved it." Davis's research was published in Proceedings of the National Academy of Sciences.
According to Phys.org, Davis claimed that, for 40 years, this issue has been one of physics research's "Holy Grail" issues. Many individuals think that the development of inexpensive, widely accessible room-temperature superconductors will be just as momentous for human civilisation as the invention of electricity.
The new measurement matches a prediction based on the superexchange theory. André-Marie Tremblay, a physicist at the University of Sherbrooke in Canada, said that he was amazed by the quantitative agreement.
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