When it comes to high-temperature superconductors, “high” is a relative term. In the field of superconductivity, “high temperature” means anything that can still be superconductive over 30 degrees Kelvin (K), or a balmy -405 degrees Fahrenheit (F).

The first high-temperature superconductor was discovered in 1986, in ceramic compounds of copper and oxygen known as cuprates. These materials could reach superconductivity around 35 degrees Kelvin or -396.67 degrees Fahrenheit.  In the following decades, that temperature limit increased and, to date, researchers have achieved superconductivity in cuprates at temperatures up to 135 degrees Kelvin.

It’s important progress, to be sure, but room-temperature superconductivity, which requires operation at 300 degrees Kelvin, is still a long way off, if not impossible.

One of the biggest obstacles is that researchers still don’t understand the complete underlying mechanisms of cuprate superconductivity and why there is such variability in superconducting transition temperature among cuprate compounds.

Now, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) may have the answer. The researchers, led by Xin Li, assistant professor of materials science at SEAS, found that the strength of a particular chemical bond in cuprate compounds impacts the temperature at which the material achieves superconductivity.

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