Scientists discover mysterious anomaly in superconducting material

Scientists are currently working to understand the unique properties of materials that exhibit superconductivity, which is the ability to carry electric current with no resistance. Harnessing this phenomenon could revolutionize power transmission, computing, and energy efficiency. In order to unravel the complexities of these materials, researchers are studying their different phases.

Kazuhiro Fujita, a physicist at the U.S. Department of Energy’s Brookhaven National Laboratory, emphasizes the importance of comprehending the various phases of superconducting materials. In a recent study published in Physical Review X, Fujita and his team focused on investigating an intriguing observation in a copper-oxide superconductor’s coexisting phase alongside the superconducting phase.

The researchers noticed a peculiar disappearance of vibrational energy in the crystal lattice of the material. X-ray studies revealed that the atoms within the material exhibit specific vibration modes, but as the material is cooled, one of these modes ceases to exist.

Fujita explains that their study aimed to understand the relationship between the lattice structure and the electronic structure of the material to shed light on this phenomenon. To conduct their research, the Brookhaven team employed a spectroscopic imaging scanning tunneling microscope (SI-STM). This tool allowed them to scan the material’s surface with remarkable precision on the scale of trillionths-of-a-meter, enabling them to map the atoms and measure the distances between them. Simultaneously, they could also measure the electric charge at each atomic-scale location.

The team’s sensitive measurements enabled them to determine the average positions of the vibrating atoms and observe how these positions became fixed when the vibrations ceased. They also established a direct connection between the vanishing vibrations and the emergence of a “charge density wave,” which refers to a modular distribution of charge density within the material.

Kazuhiro Fujita (left) with Brookhaven Lab co-authors Genda Gu and John Tranquada, all members of Brookhaven Lab’s Condensed Matter Physics and Materials Science Department, in front of the spectroscopic imaging scanning tunneling microscope (SI-STM) used in this study. Credit: Brookhaven National Laboratory

By gaining insights into the relationship between the lattice structure, electronic structure, and vibrational behavior of superconducting materials, scientists hope to unravel the mechanisms behind superconductivity fully. This knowledge can pave the way for the development of efficient power transmission systems, high-speed computers, and other energy-saving innovations.

According to Fujita, the electrons involved in the charge density wave (CDW) are localized, meaning they occupy fixed positions. These electrons are distinct from the more mobile electrons responsible for carrying current in the superconducting phase. The localized electrons arrange themselves in a repeating pattern of varying densities, resembling side-by-side ladders.

The appearance of this density pattern causes a distortion in the normal vibrations of the atoms within the material, causing their positions to shift along the direction of the “rungs” of the ladder-like pattern. As the temperature decreases and the charge density wave emerges, the vibrational energy decreases correspondingly.

Fujita explains that by simultaneously measuring the distribution of electric charge and the atomic structure, researchers can observe how the emergence of the charge density wave locks the atoms in their distorted positions. This observation suggests that the charge density wave interacts with the lattice as the atoms vibrate, suppressing the vibrations and distorting the lattice structure.

The spectroscopic imaging scanning tunneling microscope (SI-STM) used in this study at Brookhaven National Laboratory. Credit: Brookhaven National Laboratory

Fujita acknowledges that while the recent study has provided another clue about the coupling of two characteristics in one phase of a superconducting material, there is still much more to unravel regarding these materials’ properties.

He emphasizes that there are numerous variables at play, with electrons and the lattice being just two of them. To gain a comprehensive understanding of these materials, scientists must take into account all of these variables and investigate their interactions with each other.

Fujita emphasizes the complexity of the task, as researchers need to explore and comprehend the intricate interplay between different factors to fully grasp the behavior of superconducting materials. Unraveling these mysteries is crucial to unlock the full potential of these materials and pave the way for advancements in various fields.

Source: Brookhaven National Laboratory

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