Biotechnology

Running superconductivity at room temperature with a flash of light

To study superconducting materials in their “normal”, non-superconducting state, scientists typically rule out superconductivity by exposing the material to a magnetic field on the left. SLAC scientists have found that disabling superconductivity with a flash of light, on the right, leads to a normal state with very similar fundamental physics, which is also unstable and can contain short bursts of superconductivity at room temperature. These results open a new way to create superconductivity at room temperature stable enough for practical devices. Credit: Greg Stewart / National SLAC Accelerator Laboratory

Scientists find that the launch of superconductivity by a flash of light involves the same fundamental physics that operates in the more stable states needed for devices, opening up a new pathway to creating superconductivity at room temperature.

Just as people can learn more about themselves by going beyond their comfort zone, researchers can learn more about the system by pushing it, making it a little unstable – scientists call it “out of balance” – and observing that occurs when it returns to a more stable state.

In the case of a superconducting material known as yttrium-barium-copper oxide, or YBCO, experiments have shown that under certain conditions knocking it out of balance with a laser pulse allows it to superconduct – conduct electricity without loss – when much closer to room temperature than the researchers expected. This could be a big deal, given that scientists have been dealing with superconductors at room temperature for more than three decades.

But are observations of this volatile state relevant to how high-temperature superconductors will operate in the real world, where applications such as power lines, Muggle trains, particle accelerators, and medical equipment require them to be stable?

A study published in Advances in science February 9, 2022 suggests that the answer is yes.

“People thought that while this type of research was useful, it wasn’t very promising for future applications,” said Jun-Sik Lee, a researcher at the National Accelerator Laboratory of the SLAC Department of Energy and head of an international research group. which was engaged in leaving the study.

“But now we have shown that the fundamental physics of these unstable states is very similar to the physics of the stable ones. Thus, it opens up enormous possibilities, including the possibility that other materials can also be transferred to a transient superconducting state by light. This is an interesting state, which we do not see otherwise. “

How does it look normal?

YBCO is a compound of copper oxide, or cuprate, a member of the family of materials, which was discovered in 1986 to conduct zero-resistance electricity at much higher temperatures than scientists thought.

Like conventional superconductors that were discovered more than 70 years ago, YBCO transitions from normal to superconducting when cooled below a certain transition temperature. At this point, the electrons pair up to form a condensate – a kind of electronic soup – which effortlessly conducts electricity. Scientists have a solid theory of how this happens in older superconductors, but there is still no consensus on how it works in non-traditional ones such as YBCO.

One way to attack a problem is to examine the normal condition YBCO, which in itself is very strange. The normal state contains a number of complex, intertwined phases of matter, each of which can help or hinder the transition to superconductivity, which fight for dominance and sometimes overlap. Moreover, in some of these phases the electrons seem to recognize each other and act collectively as if they are pulling each other.

This is a real tangle, and researchers hope that his best understanding will shed light on how and why these materials become superconducting at temperatures well above the theoretical limit predicted for conventional superconductors.

It is difficult to study these exciting normal states at the high temperatures where they occur, so scientists typically cool their YBCO samples to the point where they become superconducting and then turn off the superconductivity to restore normal state.

Switching is usually done by exposing the material to a magnetic field. This is the best approach because it leaves the material in a stable configuration – one that you will need to create a practical device.

Superconductivity can also be turned off by a pulse of light, Lee said. This creates a normal state that is a bit balanced – out of balance – where interesting things can happen, from a scientific point of view. But the fact that it is unstable has led scientists to fear that everything they learn there can also be applied to durable materials similar to those needed for practical use.

Waves that remain in place

In this study, Lee and his colleagues compared two switching approaches – magnetic fields and light pulses – focusing on how they affect a peculiar phase of matter known as charge density waves, or VZPs, that appear in superconducting materials. CDWs are waveforms with higher and lower electron densities, but unlike ocean waves they do not move.

Two-dimensional CDWs were discovered in 2012, and in 2015 Lee and his staff discovered a new type of 3D CDW. Both types are closely intertwined with high-temperature superconductivity, and they can serve as markers of the transition point where superconductivity is turned on or off.

To compare what CDW in YBCO looks like when its superconductivity is turned off by light and magnetism, the research team conducted experiments on three X-ray light sources.

They first measured the properties of the intact material, including charge density waves, at the Stanford Synchrotron Radiation Source (SSRL) SLAC.

The material samples were then exposed to high magnetic fields at the SACLA synchrotron facility in Japan and laser light at the X-ray free electron laser (PAL-XFEL) of the Pohang Laboratory in Korea so that changes in their CDW could be measured.

“These experiments have shown that exposure to magnetism or light creates similar 3D patterns of CDWs,” said SLAC staffer and co-author of the study, Sanhong Song. states caused by either approach have the same fundamental physics, and they suggest that laser light may be a good way to create and study transients that can be stabilized for practical applications — including, potentially, superconductivity at room temperature.

Reference: “Characterization of photoinduced normal state through charge density wave in superconducting YBa2Cu3Oh6.67»Hoon Chang, Sanghong Son, Takumi Kihara, Ijin Liu, San Joon Lee, San Yong Park, Minsk Kim, Hyun Do Kim, Giacomo Kaslavich, Suguru Nakata, Yuya Kubota, Itira Inaue, Kenji Tamasaku, Makina Yabashi, Hemin Lee, Hemin Lee Son, Hiroyuki Nodiri, Bernhard Keimer, Chi-Chang Kao and Jun-Sik Lee, February 9, 2022, Advances in science.
DOI: 10.1126 / sciadv.abk0832

Researchers from the Pohang Accelerator Laboratory and the Pohang University of Science and Technology in Korea; University of Tohoku, RIKEN Spring-8 The Center and the Japanese Synchrotron Radiation Research Institute in Japan; and the Max Planck Institute for Solid State Research in Germany also contributed to this work, which was funded by the US Department of Science. SSRL is a US Department of Science user facility.



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