Synopsis: Twisting Microscopic Currents

A helical arrangement of microscopic currents could explain the unusual optical properties of cuprate superconductors.
Synopsis figure
S. S. Pershoguba et al., Phys. Rev. Lett. (2013)

How charges pair up and flow with zero resistance in copper-oxide-based (“cuprate”) high-temperature superconductors is still unknown. Many physicists believe the answer lies in explaining the pseudogap phase of these materials—the state above the superconducting transition temperature in which the energy spectrum of electrons starts to form a partial gap. As reported in Physical Review Letters, insight into how electrons interact in the pseudogap phase may come from a new theory explaining an usual optical effect in the cuprates.

Experiments have shown that polarized light reflected from the surface of a cuprate in the pseudogap phase has a slightly rotated angle of polarization. The effect—called Kerr rotation—occurs in magnetic materials (microscopes use it to distinguish magnetic domains.) But in a magnet, which has a distinct north and south pole, the Kerr rotation angle changes sign when the sample is flipped on its back. In cuprates, this sign change is absent, an effect that has been difficult to explain.

Sergey Pershoguba and his colleagues at the University of Maryland, College Park, show that the peculiar Kerr effect is explicable if the light is interacting with local magnetic fields that twist by 90 degrees from one copper-oxide layer to the next. These fields could come from microscopic loops of current near each copper atom—an idea that has been proposed to explain the physics of the pseudogap phase. Unlike most theories for the pseudogap phase, which assume electron interactions are confined to the copper-oxide plane, Pershoguba et al.’s model implies interactions between electrons in different planes matter, too. – Jessica Thomas


More Features »


More Announcements »

Subject Areas


Previous Synopsis

Next Synopsis

Atomic and Molecular Physics

New Atomic Trios Follow the Rules

Read More »

Related Articles

Synopsis: Graphene Helps Catch Light Quanta

Synopsis: Graphene Helps Catch Light Quanta

The use of graphene in a single-photon detector makes it dramatically more sensitive to low-frequency light. Read More »

Viewpoint: A Roadmap for a Scalable Topological Quantum Computer
Condensed Matter Physics

Viewpoint: A Roadmap for a Scalable Topological Quantum Computer

A team of experimentalists and theorists proposes a scalable protocol for quantum computation based on topological superconductors. Read More »

Synopsis: Superconductivity Model Misses Its Target

Synopsis: Superconductivity Model Misses Its Target

Researchers have added dopant atoms to a quantum spin liquid in an effort to make it superconduct, but the material upended theory by remaining an insulator. Read More »

More Articles