• quantum chemistry • simulations • Superconductivity

A new study has revealed that the mystery behind the superconductivity process can be unraveled using quantum chemistry. We all know that superconductivity is that phenomena in which there is zero electrical resistance and electricity flow indefinitely without any power dissipation. Superconductivity occurs when the material is cooled below a characteristic critical temperature. The first high-temperature superconductor materials, known as cuprates, were discovered in the 1980s. But, no one knows properly how this high-temperature super-conductivity works. Scientists only know that the phenomenon is related to electrons sticking together or glued together in pairs but have no idea about the nature of the electron glue that binds them together.

So, Caltech’s Garnet Chan, Bren Professor of Chemistry, along with his colleagues, decided to try and figure out how the high-temperature superconductor materials work. For the research, they decided to use quantum chemistry method. Hence the research team developed numerical simulations, with the help of quantum mechanics equations and mapped out the fluid motions of the electrons in different materials.

The simulated model showed that the high-temperature superconducting materials order themselves into a striped pattern of charges, known as ‘rivers of charges,’ just before they attain the superconducting behavior. The precise numerical simulations made by Chance and colleagues confirmed that no other patterns of charges display a striped state. When they tried to squeeze the strips, they found that the electrons spontaneously got paired up which indicates that the rivers of charges display similar characteristics as that of the electron glue. I like problems that people have banged their heads on for decades, and I think many scientists would agree that high-temperature superconductivity is probably one of the most perplexing phenomena observed in materials,” said Chan.

He further informed that although the possibility for striped behavior had been raised previously, it was only one among a multitude of candidate competing patterns. Furthermore, people had no idea whether or not such stripes were good for superconductivity or in fact killed the superconducting state. Chan said that their results not only show that stripes are real but that they have an intimate connection to how superconductivity arises. For the new study, the researchers used four completely different types of numerical methods to simulate high-temperature superconducting materials and found out that charges spontaneously organize themselves into the striped pattern. These new numerical simulations are more precise than the existing Hubbard model-a mathematical model developed in the 1960s that explains about the electronic behavior of many materials.

Lead author of the study, Bo-Xiao Zheng former Ph.D. student at Caltech and Princeton, said that they have provided a definitive numerical solution to one of the most important models in condensed matter physics, which has strong connections with high-temperature superconductivity. The research paper titled ‘Stripe order in the underdoped region of the two-dimensional Hubbard model’ was published in the journal Science.

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