Quantum Interferences in Ultraclean Carbon Nanotubes

Electronic analogs of optical interferences are powerful tools to investigate quantum phenomena in condensed matter. In carbon nanotubes (CNTs), it is well established that an electronic Fabry-Perot interferometer can be realized. Other types of quantum interferences should also arise in CNTs, but have proven challenging to realize. In particular, CNTs have been identified as a system to realize the electronic analog of a Sagnac interferometer---the most sensitive optical interferometer. To realize this Sagnac effect, interference between nonidentical transmission channels in a single CNT must be observed. Here, we use suspended, ultraclean CNTs of known chiral index to study both Fabry-Perot and Sagnac electron interferences. We verify theoretical predictions for the behavior of Sagnac oscillations and the persistence of the Sagnac oscillations at high temperatures. As suggested by existing theoretical studies, our results show that these quantum interferences may be used for electronic structure characterization of carbon nanotubes and the study of many-body effects in these model one-dimensional systems.