A new study pins down a major factor behind the appearance of superconductivity—the ability to conduct electricity with 100 percent efficiency—in a promising copper-oxide material.

Scientists used carefully timed pairs of laser pulses at SLAC National Accelerator Laboratory's Linac Coherent Light Source (LCLS) to trigger superconductivity in the material and immediately take x-ray snapshots of its atomic and electronic structure as superconductivity emerged.

They discovered that so-called "charge stripes" of increased electrical charge melted away as superconductivity appeared. Further, the results help rule out the theory that shifts in the material's atomic lattice hinder the onset of superconductivity.

Armed with this new understanding, scientists may be able to develop new techniques to eliminate charge stripes and help pave the way for room-temperature superconductivity, often considered the holy grail of condensed matter physics. The demonstrated ability to rapidly switch between the insulating and superconducting states could also prove useful in advanced electronics and computation.

The compound used in this study was a layered material consisting of lanthanum, barium, copper, and oxygen grown at Brookhaven Lab by physicist Genda Gu. Each copper oxide layer contained the crucial charge stripes.

To excite the material and push it into the superconducting phase, the scientists used mid-infrared laser pulses to "melt" those frozen ripples. These pulses had previously been shown to induce superconductivity in a related compound at a frigid 10 Kelvin (minus 442 degrees Fahrenheit).

To capture these stripes in action, the collaboration turned to SLAC's LCLS x-ray laser, which works like a camera with a shutter speed faster than 100 femtoseconds, or quadrillionths of a second, and provides atomic-scale image resolution. LCLS uses a section of SLAC's 2-mile-long linear accelerator to generate the electrons that give off x-ray light.

The researchers used the so-called "pump-probe" approach: an optical laser pulse strikes and excites the lattice (pump) and an ultrabright x-ray laser pulse is carefully synchronized to follow within femtoseconds and measure the lattice and stripe configurations (probe). Each round of tests results in some 20,000 x-ray snapshots of the changing lattice and charge stripes, a bit like a strobe light rapidly illuminating the process.

To measure the changes with high spatial resolution, the team used a technique called resonant soft x-ray diffraction. The LCLS x-rays strike and scatter off the crystal into the detector, carrying time-stamped signatures of the material's charge and lattice structure that the physicists then used to reconstruct the rise and fall of superconducting conditions.

The x-ray scattering measurements revealed that the lattice distortion persists for more than 10 picoseconds (trillionths of a second)—long after the charge stripes melted and superconductivity appeared, which happened in less than 400 femtoseconds. Slight as it may sound, those extra trillionths of a second make a huge difference.

"The findings suggest that the relatively weak and long-lasting lattice shifts do not play an essential role in the presence of superconductivity," a researcher said. "We can now narrow our focus on the stripes to further pin down the underlying mechanism and potentially engineer superior materials."

This story is reprinted from material from Brookhaven National Laboratory, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.