Electrons Line Dance in a Superconductor

High resolution imaging and spectroscopy definitively confirms a state of matter called a “pair density wave.”

Image courtesy of Brookhaven National Laboratory
Schematic of the binding energy of electrons in a copper-oxide superconductor as measured by advanced microscopy. The size of the blue and yellow blobs surrounding each atom indicates the size of the energy gap. The red rods indicate the atoms’ spin.

The Science

Scientists have confirmed a long-standing theoretical prediction for high-temperature superconductors. Superconductors are materials that can move electricity with no loss of current. In a superconductive state, like-charged electrons overcome their repulsion to pair up and flow freely. Different states of matter make superconductivity possible. One of those theorized states of matter is called a pair density wave. The scientists confirmed pair density waves using advanced microscopic imaging techniques.

The Impact

The research demonstrates the co-existence of a pair density wave in cuprate. This material is a well-known, high-temperature superconductor. High-temperature superconductors can carry electric current with no energy loss when cooled to a critical temperature.  Because of their efficiency, these superconductors could revolutionize energy transmission and electronics.

Summary

Scientists have been trying for decades to decipher the electronic details of high-temperature superconductors due to their potential applications in energy and other technologies. Researchers have recently focused on a pair-density-wave state as a leading candidate to be the fundamental order parameter that characterizes superconductivity. To explore the theoretical predictions, researchers used spectroscopic imaging scanning tunneling microscopy (SI-STM) to visualize the single-electron tunneling. They used a special superconducting tip to enhance the signal-to-noise ratio of the SI-STM measurements. This allowed the researchers to observe superconducting energy gap modulations. Using this approach, researchers discovered strong energy modulations with an eight-unit-cell periodicity in cuprate (Bi2Sr2CaCu2O8+δ, also known as B-2212). Simultaneous imaging of the energy spectrum of individual atoms demonstrated that the PDW coexists with superconductivity.

The energy gap modulations mirror other research by the group that indicated the existence of modulating patterns of electronic and magnetic characteristics—sometimes referred to as ‘stripes’—that also occur with the same periodicity in certain high-temperature cuprate superconductors. The current findings suggest that the pair density wave plays a significant role in the properties of superconductors. Understanding this state may help to decipher how superconducting properties emerge under different conditions, including temperature, magnetic field, and charge-carrier density.

Contact

Kazuhiro Fujita
Brookhaven National Laboratory
kfujita@bnl.gov  

Funding

This research is primarily supported by the Department of Energy Office of Science, Basic Energy Sciences program.

Publications

Du, Z. et al. “Imaging the energy gap modulations of the cuprate pair-density-wave state.” Nature 580, 65 (2020) [DOI: 10.1038/s41586-020-2143-x].  

Related Links

Scientists See Energy Gap Modulations in a Cuprate Superconductor, Brookhaven National Laboratory News

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