New quantum criticality discovered in superconductivity

November 2, 2018 by Laura Millsaps, Ames Laboratory
Credit: CC0 Public Domain

Using solid state nuclear magnetic resonance (ssNMR) techniques, scientists at the U.S. Department of Energy's Ames Laboratory discovered a new quantum criticality in a superconducting material, leading to a greater understanding of the link between magnetism and unconventional superconductivity.

Most iron-arsenide superconductors display both magnetic and structural (or nematic) transitions, making it difficult to understand the role they play in superconducting states. But a compound of calcium, potassium, iron, and arsenic, and doped with small amounts of nickel, CaK(Fe1−xNix)4As4, first made at Ames Laboratory, has been discovered to exhibit a new magnetic state called a hedgehog spin-vortex crystal antiferromagnetic state without nematic transitions.

"Spin or nematic fluctuations can be considered to play an important role for ," said Yuji Furukawa, a senior scientist at Ames Laboratory and a professor of Physics and Astronomy at Iowa State University. "With this particular material, we were able to examine only the magnetic fluctuations, and NMR is one of the most sensitive techniques for examining them." He continued, "using 75As NMR, we discovered that CaK(Fe1−xNix)4As4 is located at a hedgehog spin-vortex crystal antiferromagnetic critical point which is avoided due to . The discovery of the magnetic without nematicity in CaK(Fe1−xNix)4As4 suggests that the spin fluctuations are the primary driver of superconductivity."

Furukawa's discovery was a collaboration between Ames Laboratory's world-leading SSNMR team and the lab's condensed matter physicists, including Paul Canfield, a senior scientist at Ames Laboratory and a Distinguished Professor and the Robert Allen Wright Professor of Physics and Astronomy at Iowa State University.

"This is a new type of magnetic order," said Canfield. "You have this interesting interaction between superconductivity and magnetism from high temperatures in the normal state. This gives us some sense that this may be coming from this near quantum critical antiferromagnetic transition."

The research is further discussed in the paper, "Hedgehog Spin-vortex Crystal Antiferromagnetic Quantum Criticality in CaK(Fe1−xNix)4As4 revealed by NMR," published in Physical Review Letters.

Explore further: Missing link to novel superconductivity revealed

More information: Q.-P. Ding et al. Hedgehog Spin-Vortex Crystal Antiferromagnetic Quantum Criticality in CaK(Fe1−xNix)4As4 Revealed by NMR, Physical Review Letters (2018). DOI: 10.1103/PhysRevLett.121.137204

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3 comments

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Ralph
5 / 5 (3) Nov 02, 2018
This changes everything. It is so unexpected. I never dreamed there might be a hedgehog spin-vortex crystal antiferromagnetic state without nematic transitions.
Hyperfuzzy
1 / 5 (1) Nov 02, 2018
I have no idea what you found; a new twist on avoiding the "bumps" that rattle everything; or do you cause redirection!? Every center responds.
Macksb
not rated yet Nov 03, 2018
Yes: "The discovery...suggests that the spin fluctuations are the primary driver of superconductivity." This confirms a unified thesis for all types of superconductivity that I have proposed in many prior posts on Physorg.

One such Macksb post relates to this specific four way antiferromagnetic order. See "Scientists uncover the microscopic origin of a magnetic phase in iron-based superconductors," Physorg, April 28, 2015.

By the way, the phrase "hedgehog spin vortex" is unduly complex. Spin is a periodic oscillation—one type of many. A hedgehog spin vortex is a system of four periodic oscillators perfectly opposed to each other in two by two diagonal pairs (thus 90 degrees apart to their nearest neighbors).

Cooper pairs of BCS are conceptually similar. They involve two periodic oscillations—spin (again) and orbit. In Cooper pairs, the two spins are exactly opposed; and the orbits are exactly opposed. Occam's Razor.

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