19 Feb 2016
World innovation news
Materials & Manufacturing
Unveiling New Properties of Electrical Superconductivity in Cuprates
Physicists of the University of Waterloo, in Ontario, Canada, discovered new properties regarding electrical superconductivity. In particular, they studied a structure called Cuprate, a type of copper oxide ceramic that contains copper anions in bidimensional atomic layers coupled with oxygen with each layer separated by atoms of other materials. Certain cuprates varieties are considered as high-temperature superconductors.
High-temperature superconductivity occurs at temperatures higher than the required for ordinary metallic superconductors. In comparison, some metals reach superconductivity below 30 K (-243.2 °C) but cuprates can reach this state at 138 K (-135 °C).
These new findings present a direct empirical evidence of what is known as electronic nematicity in cooled materials. It happens when the electron clouds of superconducting materials align and orient them into specific patterns, stripes or checkboards, that favors ultrafast transport of electricity and therefore, superconductivity.
According to Professor Hawthron, “these patterns and symmetries have important consequences for superconductivity – they can compete, coexist or possibly even enhance superconductivity”. More importantly, this feature seems to be common among cuprate high-temperature superconductors. This finding could lead to explain why superconductivity occurs at higher temperatures in certain materials.
Working with a novel technique called soft x-ray scattering at the Canadian Light Source synchrotron in Saskatoon, this group probed electron scattering happening at specific layers in the cuprate crystal. The copper dioxide (Cu02) layers are the hosts of the electronic nematicity phenomenon while the interlayer regions only register crystalline distortions.
The pneumaticity property commonly refers to the effect that occurs in liquid crystals under the presence of an electric field that makes them align in specific directions depending on the orientation of this field. Liquid crystals are present in electronic displays and in nature, many proteins and cell membranes. In the case of cuprates, it is the electronic orbitals that align, like a series of rods, when cooled below a critical point.
One technique widely used to make cuprates superconductors is by doping the crystal. Doping means introducing foreign atoms with the purpose of increase or reduce the available electrons that will transport electricity. Underdoping cuprates with strontium, lanthanum or europium create distortions in the lattice that can either enhance or reduce the strength of the nematicity. The authors of this study found that underdoped cuprates present higher probability of electronic nematicity than those doped at optimal rates to obtain higher superconducting barrier temperatures.
Although, it is not yet well understood why nematicity occurs, these results can shed light in finding the holy grail in superconductivity: a material that transport electricity with almost no loses at room temperature. This particular work can help in the future to understand how nematicity can change by controlling the crystalline structure of a material.
This study can be found in this link.
Luis Felipe Gerlein Reyes
Luis Felipe Gerlein R. is a Ph.D. candidate at ÉTS. His research interests include nanofabrication and characterization of optoelectronic devices based on lead chalcogenides, carbon-based nanostructures and perovskite materials.
Program : Electrical Engineering