Iron-based superconductors exhibit s-wave symmetry

Iron-based superconductors exhibit s-wave symmetry: In conventional superconductors, the Cooper pairs have s-wave pairing symmetry, which takes the shape of a sphere. In contrast, Cooper pairs in the cuprate family of high-temperature superconductors exhibit d-wave pairing symmetry, which looks a bit like a four-leaf clover. The leaves, or lobes, are areas where the superconducting gap is finite. At the points where two leaves join, known as nodes, the superconducting gap goes to zero.
However, iron-based superconductors do not fall nicely into either of these two categories...

They discovered a signature that could not have originated from a d-wave pairing – a striking difference from the cuprate family.
This finding, the first measurement of its kind, provides solid experimental evidence that iron-based superconductors fall into the regime of s-wave pairing symmetry seen in conventional superconductors, and suggests that both nodal and nodeless gaps could arise from the same mechanism. This could lead to a unified theoretical framework for both phenomena, making the research an important step toward unveiling the mechanism of iron-based superconductivity.

Lasers could produce much sought-after band gaps in graphene

Lasers could produce much sought-after band gaps in graphene: In a new study, Foa Torres and his coauthors have addressed this problem. By analyzing the way that a laser field interacts with electrons in graphene, the researchers have predicted that shining a mid-infrared laser on graphene can produce band gaps in its electronic structure. Further, the researchers predict that the band gaps could be tuned by controlling the laser polarization. As Foa Torres explained, the key to how polarized light "opens up" band gaps in graphene involves electrons interacting with the laser field.
“Imagine an electron moving, say from left to right, into a region illuminated by the laser field,” he said. “Then what happens is that the electron interacts with the radiation by absorbing or emitting photons. This interaction leads to the electron being reflected or backscattered, as it would have hit a wall: the band gap. In contrast with usual band gaps, this one is dynamically produced by the laser.”

New ways to tune electrical conductivity revealed by electron interaction

New ways to tune electrical conductivity revealed by electron interaction: In compounds made from the heavier transition metals, the outermost electrons circle the atoms in the so-called ‘5d electron shell’, which is relatively distant from the core. For electrons that occupy this shell there is an unusually strong interaction between their magnetic property, called spin, and the orbital motion around the atomic nucleus. The energy of this spin–orbit interaction is as large as the electron’s energy of motion or the energy arising from the electrostatic interaction between the electrons. This has dramatic consequences on their electronic properties, according to Yunoki, who led the research team. “Literally anything can happen in 5d electron systems because of the subtle balance of those three fundamental energy scales.”

Enhanced efficiency when determining band gap in solids

Enhanced efficiency when determining band gap in solids: "To get a more accurate prediction of band gaps, Chan and Ceder created a method that involves altering the use of density functional theory so that an itemized list of individualized states is not the only consideration. “We also recognize that there are a number of interactions between electrons. So we look at the total energy, which includes these interactions,” Chan explains.
Not only do Chan and Ceder make use of the total energy, but they also demonstrate that the band gap can be viewed as a property of the ground state. “This changes the way we view the band gap, seeing that it is a part of the ground state,” Chan says."