superconductivity

One of the biggest achievements of quantum physics was recasting our vision of the atom. Out was the early 1900s model of a solar system in miniature. Instead, quantum physics showed that electrons meander around the nucleus in clouds that look like tiny balloons. These balloons are known as atomic orbitals, and they come in all sorts of different shapes—perfectly round, two-lobed, clover-leaf-shaped. That’s all well and good for individual atoms, but when atoms come together to form something solid—like a chunk of metal, say—the outermost electrons in the atoms link arms and lose sight of the nucleus they came from, forming many oversized balloons that span the whole chunk of metal. Now, researchers have produced the first experimental evidence that one metal—and likely others in its class—have electrons that manage to preserve a more interesting, multi-lobed structure as they move around in a solid.

Atomically thin sheets of carbon, called graphene, have caught many scientists' attention in recent years. Researchers have discovered that stacking layers of graphene two or three at a time and twisting the layers opens fertile new territory for them to explore. Research into these stacked sheets of graphene is like the Wild West, complete with the lure of striking gold and the uncertainty of uncharted territory. Researchers at JQI and the Condensed Matter Theory Center (CMTC) at the University of Maryland are busy creating the theoretical physics foundation that will be a map of this new landscape. And there is a lot to map; the phenomena in graphene range from the familiar like magnetism to more exotic things like strange metallicity, different versions of the quantum Hall effect, and the Pomeranchuk effect—each of which involve electrons coordinating to produce unique behaviors. One of the most promising veins for scientific treasure is the appearance of superconductivity (lossless electrical flow) in stacked graphene.

Truly two-dimensional objects are rare.  Even a thin piece of paper is trillions of atoms thick.  When physicists do succeed in producing 2D systems, quantum interactions can lead to new phenomena and Nobel prizes.  Two examples:  graphene---single-atom-thick sheets of carbon atoms---has unique mechanical, electrical, and optical properties; and two-dimensional electron gases (2DEG)---planar collections of electrons supported at the interface between certain semiconductors such as gallium arsenide---allow the observation of such emergent behaviors as the quantum Hall eff