condensed matter

In the latest experiment of its kind, researchers have captured the most compelling evidence to date that unusual particles lurk inside a special kind of superconductor. The result, which confirms theoretical predictions first made nearly a decade ago at the Joint Quantum Institute (JQI) and the University of Maryland (UMD), will be published in the April 5 issue of Nature. The stowaways, dubbed Majorana quasiparticles, are different from ordinary matter like electrons or quarks—the stuff that makes up the elements of the periodic table. Unlike those particles, which as far as physicists know can’t be broken down into more basic pieces, Majorana quasiparticles arise from coordinated patterns of many atoms and electrons and only appear under special conditions. They are endowed with unique features that may allow them to form the backbone of one type of quantum computer, and researchers have been chasing after them for years. The latest result is the most tantalizing yet for Majorana hunters, confirming many theoretical predictions and laying the groundwork for more refined experiments in the future. In the new work, researchers measured the electrical current passing through an ultra-thin semiconductor connected to a strip of superconducting aluminum—a recipe that transforms the whole combination into a special kind of superconductor.Experiments of this type expose the nanowire to a strong magnet, which unlocks an extra way for electrons in the wire to organize themselves at low temperatures. With this additional arrangement the wire is predicted to host a Majorana quasiparticle, and experimenters can look for its presence by carefully measuring the wire’s electrical response. The new experiment was conducted by researchers from QuTech at the Technical University of Delft in the Netherlands and Microsoft Research, with samples of the hybrid material prepared at the University of California, Santa Barbara and Eindhoven University of Technology in the Netherlands. Experimenters compared their results to theoretical calculations by JQI Fellow Sankar Das Sarma and JQI graduate student Chun-Xiao Liu.

The 2015 discovery of a Weyl semimetal—and the Weyl fermions it harbored—provoked a flurry of activity from researchers around the globe. A quick glance at a recent physics journal or the online arXiv preprint server testifies to the topic’s popularity. The arXiv alone has had more than 200 papers on Weyl semimetals posted in 2016.Researchers at JQI and the Condensed Matter Theory Center (CMTC) at the University of Maryland have been interested in Weyl physics since before last summer’s discovery, publishing 18 papers on the topic over the past two years. In all, more than a dozen scientists at Maryland have been working to understand the fundamental properties of these curious new materials.

For decades, particle accelerators have grabbed headlines while smashing matter together at faster and faster speeds. But in recent years, alongside the progress in high-energy experiments, another realm of physics has been taking its own exciting strides forward.That realm, which researchers call condensed matter physics, studies chunks of matter moving decidedly slower than the protons in the LHC. In fact, the materials under study—typically solids or liquids—are usually sitting still. That doesn't make them boring, though. Their calm appearance can often hide exotic physics that arises from their microscopic activity."In condensed matter physics, the energy scales are much lower," says Pallab Goswami, a postdoctoral researcher at JQI and the Condensed Matter Theory Center (CMTC) at the University of Maryland. "We want to go to lower energies and find new phenomena, which is exactly the opposite of what is done in particle physics."

A trio of researchers who laid the foundation for understanding numerous exotic phases of matter have split the 2016 Nobel Prize in Physics.The Royal Swedish Academy of Sciences awarded the prize "for theoretical discoveries of topological phase transitions and topological phases of matter" to three laureates: David Thouless of the University of Washington, Duncan Haldane of Princeton University and Michael Kosterlitz of Brown University."It is a very, very well-deserved prize," says JQI Fellow and CMTC Director Sankar Das Sarma. "This work led to an extremely exciting area and that excitement is still growing."The research behind the prize "illustrates, in a very nice way, the interplay between physics and mathematics," Thors Hans Hansson, a physicist at Stockholm Univsersity, said in an interview following the announcement ceremony. He explained the mathematics behind the prize during the ceremony using a cinnamon bun, a bagel and a pretzel.