topological insulator

Everything radiates. Whether it's a car door, a pair of shoes or the cover of a book, anything hotter than absolute zero (i.e., pretty much everything) is constantly shedding radiation in the form of photons, the quantum particles of light.A twin process—absorption—is usually also present. As photons carry away energy, passers-by from the environment can be absorbed to replenish it. When absorption and emission occur at the same rate, scientists say that an object is in equilibrium with its environment. This often means that object and environment share the same temperature.Far away from equilibrium, new behaviors can emerge. In a paper published August 1, 2019 as an Editors’ Suggestion in the journal Physical Review Letters, scientists at JQI and Michigan State University suggest that certain materials may experience a spontaneous twisting force if they are hotter than their surroundings.

Researchers at the University of Maryland have captured the most direct evidence to date of a quantum quirk that allows particles to tunnel through a barrier like it’s not even there. The result, featured on the cover of the June 20, 2019 issue of the journal Nature, may enable engineers to design more uniform components for future quantum computers, quantum sensors and other devices. The new experiment is an observation of Klein tunneling, a special case of a more ordinary quantum phenomenon. In the quantum world, tunneling allows particles like electrons to pass through a barrier even if they don’t have enough energy to actually climb over it. A taller barrier usually makes this harder and lets fewer particles through.Klein tunneling occurs when the barrier becomes completely transparent, opening up a portal that particles can traverse regardless of the barrier’s height. Scientists and engineers from UMD’s Center for Nanophysics and Advanced Materials (CNAM), the Joint Quantum Institute (JQI) and the Condensed Matter Theory Center (CMTC), with appointments in UMD’s Department of Materials Science and Engineering and Department of Physics, have made the most compelling measurements yet of the effect.

Scientists studying an exotic material have found a potential application for its unusual properties, a discovery that could improve devices found in most digital electronics.Under the right conditions the material, a compound called samarium hexaboride, is a topological insulator—something that conducts electricity on its surface but not through its interior. The first topological insulators were only recently created and demonstrated in labs.Now, a team of physicists at JQI and the University of California, Irvine, may have found a use for tiny crystals of samarium hexaboride. When pumped with a small but constant electric current and cooled to near absolute zero, the crystals can produce a current that oscillates. The frequency of that oscillation can be tuned by changing the amount of pump current or the crystal size.

An old material gets a new name, and with it, topological insulators have another chance to shine. Samarium hexaboride (SmB₆) has been around since the late 1960s--but understanding its low temperature behavior has remained a mystery until recently. Experimentalists* have recently confirmed that this material is the first true 3D topological insulator—as originally predicted by JQI/CMTC^☨ theorists in 2010.

JQI experimentalists under the direction of Ian Spielman are in the business of using lasers to create novel environments for neutral atoms. For instance, this research group previously enticed electrically neutral atoms to act like charged particles moving in magnetic and electric fields. The behavior of particles in strong electromagnetic fields, along with arbitrary control of the said fields, is central to both condensed matter physics, and quantum information science.

Condensed matter physicists including researchers in Sankar Das Sarma’s group* at the University of Maryland, have been in hot pursuit of Majorana fermions. Originally predicted in 1937 by Ettore Majorana, these exotic particles serve as their own anti-particles. Quantum information scientists believe that the condensed matter realization of Majorana fermions represent robust ‘topological’ qubits and would open new possibilities in quantum computation.