Can light spark superconductivity? A new study reignites debate

Brief blasts of ray mightiness make immoderate materials into fleeting superconductors. A caller study strengthens nan lawsuit for this arguable claim, first made much than a decade ago. But while immoderate physicists are convinced, others stay skeptical.

Superconductors transmit energy without resistance, typically only astatine debased temperatures. But since 2011, immoderate scientists person claimed that definite materials, erstwhile deed pinch intense, ultrashort laser pulses, can briefly go superconductors at temperatures acold supra their normal limit, including room temperature. 

The erstwhile investigation showed a impermanent alteration successful nan reflectivity of cuprates, compounds containing copper and oxygen, erstwhile blasted pinch light. That alteration indicated a driblet successful guidance lasting specified trillionths of a second, aliases picoseconds. Critics based on that nan alteration could beryllium caused by effects different than superconductivity. 

The caller study claps back. One cuprate expels magnetic fields when deed pinch light, physicist Andrea Cavalleri and colleagues study July 10 in Nature. That expulsion, they say, is simply a hallmark of superconductivity known arsenic the Meissner effect (SN: 7/6/15).

The study is “basically an unmistakable signature of superconductivity,” says physicist Dmitri Basov of Columbia University, who was not progressive pinch nan research.

Not everyone is truthful convinced by nan caller work. “They’re seeing this alteration that lasts for [about] a picosecond, and it’s not instantly evident that it’s nan aforesaid point arsenic nan Meissner effect,” says physicist Steve Dodge of Simon Fraser University successful Burnaby, Canada.

Superconductors pull aggravated liking from physicists, successful portion because of their technological potential. A superconductor that operates astatine precocious temperatures could let for much businesslike powerfulness transmission, for example, perchance redeeming immense amounts of energy. And mysteries still shroud nan phenomenon. Cuprates are superconducting astatine higher temperatures than most, and it’s still not afloat understood why.

Scientists knew that ray could disrupt superconductivity, but nan thought that ray could besides commencement it was unexpected and controversial. And successful erstwhile studies, “things were a spot subjective, they benignant of ‘smelled’ for illustration a superconductor but … you couldn’t really beryllium sure,” says Cavalleri, of nan Max Planck Institute for nan Structure and Dynamics of Matter successful Hamburg.

So Cavalleri and colleagues group their sights connected nan Meissner effect. They studied a type of cuprate called yttrium barium copper oxide, aliases YBCO. That’s a people of compounds that had antecedently shown signs of light-induced superconductivity. 

But precisely measuring magnetic section changes complete picoseconds is nary easy feat. “No existing method allows you to do this measurement,” Cavalleri says.

The squad devised a strategy that utilized a crystal of gallium phosphide placed adjacent to nan YBCO to measurement magnetic fields. In experiments performed wrong a preexisting magnetic field, nan researchers deed nan YBCO pinch nan laser, and sent a 2nd laser done nan crystal. The travel done nan crystal changed nan laser’s polarization — nan predisposition of its electromagnetic waves — successful a measurement dictated by nan magnetic section wrong nan crystal. That effect allowed nan squad to find really nan magnetic section changed adjacent nan YBCO arsenic it was bombarded pinch ray astatine somesthesia usually supra nan YBCO’s superconducting limit. 

If nan YBCO became a superconductor, it would expel magnetic fields from wrong owed to nan Meissner effect. That would consequence successful a stronger magnetic section astatine nan YBCO’s edge, which is precisely what nan squad found. The measurements had to beryllium made highly quickly to seizure nan short-lived Meissner effect, Basov says. “This is simply a superb conception and superb execution.” 

Physicist Nan-Lin Wang of Peking University is convinced that magnetic fields are expelled erstwhile nan laser beat hits nan YBCO. But whether that implies superconductivity arsenic it is usually defined is unclear. It might be nan consequence of preexisting, small-scale superconducting currents being amplified, alternatively than of typical large-scale superconductivity. “The underlying physics could beryllium very complicated,” he says.

But Dodge contends that thing different than superconductivity could beryllium responsible. At precocious intensities of light, he notes, analyzable and unexpected phenomena tin occur. “I would for illustration to spot … immoderate observant scrutiny to guarantee that they’re not mistaking immoderate different effect for a Meissner effect.” What, exactly, is down nan alteration successful nan magnetic section is not clear, Dodge says. While he’s still skeptical of nan superconductivity claim, he says “it’s a worthwhile research because it raises immoderate questions that I surely don’t cognize nan reply to.”