Posted in | Quantum Physics

Using Terahertz Spectroscopy to Unravel New State of Matter in Iron Pnictide Superconductor

An astonishingly long-lived, new state of matter has been discovered in an iron pnictide superconductor by a group of experimentalists from the U.S. Department of Energy’s Ames Laboratory and theoreticians from the University of Alabama at Birmingham.

Ames Laboratory researchers used laser pulses of less than a trillionth of a second in much the same way as flash photography, in order to take a series of snapshots. Called terahertz spectroscopy, this technique can be thought of as “laser strobe photography” where many quick images reveal the subtle movement of electron pairings inside the materials using long-wavelength, far-infrared light. (Image credit: US Department of Energy, Ames Laboratory)

The new state of matter unravels a laser-induced formation of collective behaviors competing with superconductivity.

Superconductivity is a strange state of matter, in which the pairing of electrons makes them move faster. One of the big problems we are trying to solve is how different states in a material compete for those electrons, and how to balance competition and cooperation to increase temperature at which a superconducting state emerges.

Jigang Wang, Physicist, Ames Laboratory; Professor, Iowa State University.

In order to gain in-depth knowledge, laser pulses of less than one-trillionth of 1 second were used by Wang and his colleagues in a fashion quite similar to flash photography, to take a series of snapshots. This technique is termed terahertz spectroscopy and can be considered as “laser strobe photography,” where the subtle movement of electron pairs inside the materials is revealed by several quick images using long-wavelength, far-infrared light.

The ability to see these real time dynamics and fluctuations is a way to understanding them better, so that we can create better superconducting electronics and energy-efficient devices.

Jigang Wang, Physicist, Ames Laboratory; Professor, Iowa State University.

The study has been further described in a paper titled “Non-equilibrium Pair Breaking in Ba(Fe1−xCox)2As2 Superconductors: Evidence for Formation of Photo-Induced Excitonic State,” authored by X. Yang, L. Luo, M. Mootz, A. Patz, S. L. Bud’ko, P. C. Canfield, I. E. Perakis, and J. Wang; and published in Physical Review Letters.

Paul Canfield, an Ames Laboratory scientist and an ISU professor who is an expert in the design and characterization of iron pnictides, developed the single crystal sample used in this study. Martin Mootz and Ilias E. Perakis, at the University of Alabama at Birmingham, developed the theory to explain the observation.

The U.S. Army Research Office supported the spectroscopy work. The U.S. Department of Department of Energy’s (DOE) Office of Science supported the sample growth and characterization. Theory work at the University of Alabama at Birmingham was also supported by the DOE.

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