MagLab scientists publish trailblazing superconductivity study

May 7, 2014 by Kathleen Laufenberg, Florida State University
FSU doctoral student Xiaoyan Shi.

( —A pioneering study on superconductivity by MagLab physicist Dragana Popović and collaborators has been published in Nature Physics. It unveils results that shatter long-held beliefs about the effects of magnets on superconductors.

The paper—"Two-stage -tuned superconductor-insulator transition in underdoped La2-xSrxCuO4"—published online May 4, describes a surprising discovery about the destruction of high-temperature superconductivity by strong magnetic fields.

Superconductors are materials that conduct electricity without resistance at very low temperatures—but they are also known to lose that property if the temperature becomes too high or the magnetic field too strong. Knowing precisely how this happens holds the promise of spectacular advances for future technologies.

"We strove to solve a fundamental puzzle underpinning the physics of high-temperature superconductors", said Popović, a Florida State University Distinguished University Scholar and a MagLab senior scientist.

"People still do not really understand what exactly happens in these high-temperature superconducting materials, but to probe their behavior, it is common to apply magnetic fields," she said. "We wanted to take a deep look at the effects of the magnetic fields on superconductors, to learn precisely how the magnetic field destroys the superconductivity in the vicinity of the absolute zero of temperature."

The MagLab experimental group, which also included Xiaoyan Shi, a doctoral student, and Ping Lin, a postdoctoral research associate, conducted a three-year study of unprecedented detail and scope on how the compound of lanthanum, strontium, copper, and oxygen (La2-xSrxCuO4) transitioned from a superconducting state to an insulating one.

"Everyone assumed this transition from superconductor to insulator would be immediate," Popović said. "You start with a superconductor, you apply a high magnetic field to kill it, and right away you obtain an insulator."

But the team discovered something totally unexpected. They observed that magnetic fields reveal not just one phase transition, but two, separating three distinct phases of vortex matter, or quantum current whirls that control the superconducting state.

"What we found, first of all, was striking evidence that quantum physics controls these phase transitions," she said. "And secondly, in contrast to what has been traditionally assumed, we discovered undeniable evidence of an intermediate phase, separating the superconductor from the insulator."

And that is a fundamental new breakthrough in the field of superconductivity. Vladimir Dobrosavljević, a professor in FSU's department of Physics and director of the MagLab Condensed Matter-Theory, who collaborated on the paper, notes: "The results of this experimental study will drive the theorists back to the drawing board: We'll have to re-think the basic many-body of quantum vortices."

Explore further: Scientists observe quantum superconductor-metal transition and superconducting glass

More information: "Two-stage magnetic-field-tuned superconductor–insulator transition in underdoped La2-xSrxCuO4." Xiaoyan Shi, et al. Nature Physics (2014) DOI: 10.1038/nphys2961. Received 21 August 2013 Accepted 02 April 2014 Published online 04 May 2014

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5 / 5 (3) May 07, 2014
Forgive my ignorance but could this intermediate phase be similar to a topological insulator?
5 / 5 (5) May 07, 2014
Yes, why not. After all, the topological insulators are sorta "bad superconductors" (they're highly conductive, but on their surface only). The another question is, what one should imagine under the word "similar".
5 / 5 (3) May 07, 2014
Thank you, appreciate your response.
2.5 / 5 (2) May 07, 2014
This seems to indicate they built essentially a magnetic transistor using a supercomputer. Turn up the magnetic field, the resistance of the "conductor" becomes high, reduce the magnetic field, the resistance of the conductor becomes zero. A great switching device.
5 / 5 (1) May 07, 2014
This seems to indicate they built essentially a magnetic transistor using a supercomputer. Turn up the magnetic field, the resistance of the "conductor" becomes high, reduce the magnetic field, the resistance of the conductor becomes zero. A great switching device.

This is true, but not the new part. The switching off of the super-conductor by magnetic field has been established. There may be some potential use there, though the cold temps and energy to create the magnetic field necessary seem to me to make it an inefficient method of switching.

The new aspect is the intermediate phase transition. I'm also unclear if this is topological insulator, "standard" poor conductor, or what. Interesting, though.
5 / 5 (1) May 08, 2014
We'll have to re-think the basic many-body physics of quantum vortices.
That line made me laugh. "basic". har har
May 08, 2014
This comment has been removed by a moderator.
not rated yet May 12, 2014
With all due respect, I cannot see anything that is new: But of course Nature ONLY publishes mediocre claptrap.

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