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Stanford Physicist’s Decades-Long Quest for the Perfect Keys to Unlock the Mysteries of Superconductivity

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For many years Z-X Shen has ridden a wave of curiosity about the unusual habits of electrons that may levitate magnets.

Zhi-Xun Shen vividly remembers his center faculty physics trainer demonstrating the energy of X-rays by eradicating a bit of radioactive materials from a jar saved in a cupboard, dropping it right into a bucket and having college students put their arms between the bucket and a phosphor display screen to reveal the bones hidden beneath the pores and skin and flesh.

“That left an impression,” Shen recalled with a smile. Generally he wonders if that second set the stage for every part that adopted.

Shen didn’t, he admits, have a powerful curiosity in physics. There wasn’t a lot incentive to research in mid-Nineteen Seventies China. The nation was in the grip of the Cultural Revolution of 1966, which had shut down all the universities and left most of the nation, together with the city south of Shanghai the place his dad and mom labored in medication, in poverty. However as Shen and his mom watched his brother board a bus to the countryside for “reeducation” at a compelled labor camp one chilly morning, she turned to him and mentioned, “You might be our hope for a university schooling.”

Nonetheless, given the household’s circumstances, faculty appeared like an unattainable dream. Then an unlikely sequence of occasions modified every part.

In 1977, the Cultural Revolution ended and universities re-opened.

Zhi-Xun Shen. Credit score: Courtesy of SLAC

When the identical inspiring center faculty trainer organized a physics competitors, then-16-year-old Shen entered and got here in first at each stage – faculty, district, metropolis, and province. It was fascinating and constructed his self-confidence, cementing his feeling that physics was the subject for him, however the place may it probably lead?

Shen gained a university spot earlier than graduating highschool however held again a yr on the recommendation of his father, then entered the physics program at Fudan College in Shanghai.

And in his third yr as a physics main, he took an entrance examination for a program simply launched by Chinese language-American Nobel laureate Tsung-Dao Lee that introduced a restricted quantity of Chinese language college students to the U.S. for superior research in physics.

That’s how, in March 1987, Shen discovered himself in a jam-packed, all-night convention session that got here to be often known as the Woodstock of Physics, the place almost 2,000 scientists shared the newest developments associated to the discovery of a brand new class of quantum supplies often known as high-temperature superconductors. These unique supplies conduct electrical energy with zero loss at a lot greater temperatures than anybody had thought doable, and expel magnetic fields so forcefully that they’ll levitate a magnet. Their discovery had revolutionary implications for society, promising higher magnetic imaging machines for medication, completely environment friendly electrical transmission for energy strains, maglev trains and issues we haven’t dreamed up but.

“I used to be in a position to get there early and get a seat in the room the place the talks had been happening,” Shen recalled. “To me, it was the most enjoyable factor – a very new frontier of science abruptly opened up.”

In one other extraordinary stroke of luck, he occurred to be in an ideal place to soar into this new frontier, not simply to probe the quantum states of matter that underlie superconductivity however to develop ever-sharper instruments for doing so.

As a PhD pupil at Stanford College, he’d been utilizing extraordinarily brilliant X-ray beams to examine associated supplies at what’s now SLAC Nationwide Accelerator Laboratory, simply up the hill from the foremost campus. As quickly as the assembly ended, he set about making use of the method he’d been utilizing, known as angle-resolved photoemission spectroscopy, or ARPES, to the new superconductors.

Greater than three many years later, with many vital discoveries to his credit score however the full puzzle of how these supplies work nonetheless unsolved, Shen is the Paul Pigott Professor of Bodily Sciences at Stanford’s College of Humanities and Sciences and a professor of photon science at SLAC. He and his colleagues are placing the ending touches on what could also be the world’s most superior system for probing unconventional superconductors and different unique varieties of matter to see what makes them tick.

Key components of the system are only a few steps away from the X-ray beamline at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL) the place Shen carried out these first experiments. One of them is a lately upgraded setup the place scientists can precision-build samples of superconducting materials one atomic layer at a time, shuttle them by a tube and a vacuum chamber into the SSRL beamline with out exposing them to air and make measurements with many occasions greater decision than was ever doable earlier than. The supplies they construct are additionally transported to the world’s first X-ray free-electron laser, SLAC’s Linac Coherent Gentle Supply, for precision measurements not doable by different means.

These experimental setups had been designed with a singular goal in thoughts: to unravel the weirdly collaborative habits of electrons, which Shen and others consider is the key to unlocking the secrets and techniques of superconductivity and different phenomena in a broad vary of quantum supplies.

Shen’s quest for solutions to this riddle is pushed by his curiosity about “how this outstanding phenomenon that shouldn’t have occurred, occurred,” he mentioned. “You can argue that it’s a macroscopic quantum phenomenon – nature desperately attempting to reveal itself. It solely occurs as a result of these electrons work collectively in a sure method.”

The primary superconductors, found in 1911, had been metals that grew to become completely conducting when chilled beneath 30 kelvins, or minus 406 levels Fahrenheit. It took about 50 years for theorists to clarify how this labored: Electrons interacted with vibrations in the materials’s atomic lattice in a method that overcame the pure repulsion between their damaging costs and allowed them to pair up and journey effortlessly, with zero resistance. What’s extra, these electron pairs overlapped and shaped a condensate, an altogether totally different state of matter, whose collective habits may solely be defined by the nonintuitive guidelines of quantum mechanics.

Scientists thought, for varied causes, that this might not happen at greater temperatures. So the discovery in 1986 of supplies that superconduct at temperatures up to minus 225 levels Fahrenheit was a shock. Weirder nonetheless, the beginning supplies for this manner of superconductivity had been insulators, whose very nature could be anticipated to thwart electron journey.

In an ideal steel, Shen defined, every of the particular person electrons is ideal in the sense that it may well circulation freely, creating {an electrical} present. However these good metals with good particular person electrons aren’t superconducting.

In distinction, the electrons in supplies that give rise to superconductivity are imperfect, in the sense that they’re not free to circulation in any respect. However as soon as they resolve to cooperate and condense right into a superconducting state, not solely do they lose that resistance, however they’ll additionally expel magnetic fields and levitate magnets.

“So in that sense, superconductivity is way superior,” Shen mentioned. “The habits of the system transcends that of the people, and that fascinates me. You and I are made of hydrogen, carbon and oxygen, however the indisputable fact that we are able to have this dialog isn’t a property of these particular person parts.”

Though many theories have been floated, scientists nonetheless don’t know what prompts electrons to pair up at such excessive temperatures in these supplies. The pursuit has been a protracted street – it’s been 33 years since that loopy Woodstock night time ­– however Shen doesn’t thoughts. He tells his college students {that a} grand scientific problem is sort of a puzzle you remedy one piece a time. Higher instruments are steadily bringing the full image into focus, he says, and we’ve got already come a great distance.

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