by josh perry, editor
[email protected]

a team of researchers from the brookhaven national laboratory (upton, n.y.) have used high-intensity pulses of infrared light to detect a hidden state of electronic order in a layered material composed of lanthanum, barium, copper, and oxygen (lbco) at higher temperatures than previously indicated.

physicist genda gu holds a single-crystal rod of lbco—a compound made of lanthanum, barium, copper, and oxygen—in brookhaven's state-of-the-art crystal growth lab. (brookhaven national laboratory)

according to a report from brookhaven, the discovery expands knowledge of cuprates, compounds with copper and oxygen layers sandwiched between other elements, which become superconducting at higher temperatures than traditional superconductors.

“understanding why cuprates behave the way they do could help scientists design better high-temperature superconductors, eliminating the cost of expensive cooling systems and improving the efficiency of power generation, transmission, and distribution. imagine computers that never heat up and power grids that never lose energy,” the report explained.

researchers are trying to determine what the features of superconducting are with the goal of eventually creating superconducting materials at room temperature.

“previous experiments showed that, above the temperature at which lbco becomes superconducting, resistance occurs when the electrical transport is perpendicular to the planes but is zero when the transport is parallel,” the article continued. “theorists proposed that this phenomenon might be the consequence of an unusual spatial modulation of the superconductivity, with the amplitude of the superconducting state oscillating from positive to negative on moving from one charge stripe to the next.”

it added, “the stripe pattern rotates by 90 degrees from layer to layer, and they thought that this relative orientation was blocking the superconducting electron pairs from moving coherently between the layers.”

researchers grew a crystal of lbco in a infrared image furnace that uses two bright lamps to heat the material to 2,500°f and a team at the max planck institute for structure and dynamics of matter examined the cylindrical rod with high-energy laser pulses aimed perpendicular to the planes and measured the intensity of reflected light.

the research was recently published in science. the abstract stated:

“unconventional superconductivity in the cuprates coexists with other types of electronic order. however, some of these orders are invisible to most experimental probes because of their symmetry. for example, the possible existence of superfluid stripes is not easily validated with linear optics, because the stripe alignment causes interlayer superconducting tunneling to vanish on average.

“here we show that this frustration is removed in the nonlinear optical response. a giant terahertz third harmonic, characteristic of nonlinear josephson tunneling, is observed in la_1.885ba_0.115cuo₄ above the transition temperature t_c = 13 kelvin and up to the charge-ordering temperature t_co = 55 kelvin.

“we model these results by hypothesizing the presence of a pair density wave condensate, in which nonlinear mixing of optically silent tunneling modes drives large dipole-carrying supercurrents.”