Department News

Condensed Matter Physics

Research Highlight: Good vibrations

Research Highlight: Good vibrations

On the top is a model of a carbon nanotube (CNT) to which alkane chains have been attached. Below are “bad” and “good” normal modes for conduction of heat through the system, as calculated by Abdellah Ait-Moussa, a student working with Prof. Mullen. A “bad” mode only couples to atoms in the CNT; a good one couples to the side chains as well as the CNT, so that the vibration and the energy it carries goes through the whole system. The goal of the research is to optimize the side chains to maximize the flow of heat. Improving heat conduction into CNT’s may lead to plastics that conduct heat as well as metals.

Research Highlight: Topology driven by interactions

Research Highlight: Topology driven by interactions

Nodal-line semimetals are a class of materials where the Fermi surface has the form of closed loops with low energy Dirac fermions as quasiparticles. Interactions can spontaneously break symmetries and open an energy gap around those lines. When the gap has nodes around the nodal line, as in the 3D quantum anomalous Hall effect, which is topological, the nodes form Weyl points connected by Fermi arcs, as shown above. Those fermi arcs describe topologically protected surface states, with a non-universal Hall conductivity. Prof. Bruno Uchoa’s group is interested in the interplay of strong many-body interactions and novel macroscopic manifestations of quantum phenomena. 

Research Highlight: Bumm Group

Research Highlight: Bumm Group

The scanning tunneling microscope (STM) provides an atomic view of surfaces with picometer precision. In recent work, graduate student Mitch Yothers working in the Bumm group has demonstrated analytical tools the group is developing to extract statistical information from STM images. The example above starts with a 25 nm × 25 nm atomically resolved image of graphite which contained 11,372 unit cells (not shown). After removing systematic distortion from the image and identifying the location of each atom in the image, the unit cell images can be averaged to produce the averaged unit cell images (gray scale). The standard deviation of the location of the atoms is shown as 1 σ and 2 σ atomic confidence intervals (ellipses).