By Josh Perry, Editor
Researchers from the U.S. Department of Energy (DOE) Lawrence Berkeley National Laboratory (Berkeley, Calif.) discovered that electron spin is a key property to explain the high-temperature superconductivity of cuprates.
Co-lead author Chiu-Yun Lin peers into a viewing port of the SARPES detector.
(Peter DaSilva/Berkeley Lab)
According to a report from the lab, electron spin was largely ignored by scientists when studying superconductors because the focus was on the interactions between electrons (electron correlation). Studying Bi-2212 (bismuth strontium calcium copper oxide) with a unique detector, Berkeley Lab researchers discovered a distinct pattern to the electron spins.
“Spin-orbit coupling was often neglected in the studies of cuprate superconductors, because many assumed that this kind of electron interaction would be weak when compared to electron correlation,” the report said.
Following the initial finding, scientists worried that the spin pattern could have been caused by the laser light or an external interaction. Researchers used the lab’s SARPES (spin- and angle-resolved photoemission spectroscopy) detector to map the electron spin pattern and used the lab’s Advanced Light Source (ALS), which uses soft X-ray light for studying material properties, to excite the electrons.
“After tens of experiments at the ALS, where the team of researchers connected the SARPES detector to Beamline 10.0.1 so they could access this powerful light to explore the spin of the electrons moving with much higher momentum through the superconductor than those they could access in the lab, they found that Bi-2212’s distinct spin pattern – called ‘nonzero spin’ – was a true result,” the article explained.
The research was recently published in Science. The abstract stated:
“Cuprate superconductors have long been thought of as having strong electronic correlations but negligible spin-orbit coupling. Using spin- and angle-resolved photoemission spectroscopy, we discovered that one of the most studied cuprate superconductors, Bi2212, has a nontrivial spin texture with a spin-momentum locking that circles the Brillouin zone center and a spin-layer locking that allows states of opposite spin to be localized in different parts of the unit cell.
“Our findings pose challenges for the vast majority of models of cuprates, such as the Hubbard model and its variants, where spin-orbit interaction has been mostly neglected, and open the intriguing question of how the high-temperature superconducting state emerges in the presence of this nontrivial spin texture.”