Direct Observation of Anisotropic Coulomb Interaction in a Topological Nodal Line Semimetal.

The fundamental characteristics of collective interactions in topological band structures can be revealed by the exploration of charge screening in topological materials. In particular, distinct anisotropic screening behaviors are predicted to occur in Dirac nodal line semimetals (DNLSMs) due to their peculiar anisotropic low-energy dispersion. Despite the recent extensive theoretical research, experimental observations of exotic charge screening in DNLSMs remain elusive, which is partly attributed to the coexisting trivial bands near the Fermi energy. This study reports the first direct observation of highly anisotropic charge-screening behavior in the DNLSM SrAs. Through atomically resolved conductance measurements, a highly anisotropic charge-screening pattern around charged impurities on a surface is demonstrated. Moreover, the combination of model studies and first-principles calculations reveals the unique nature of the screening anisotropy in DNLSMs. The results of this study are expected to pave the way for understanding the profound collective behavior of interacting low-energy fermions in topological materials.