Flat optical conductivity in ZrSiS due to two-dimensional Dirac bands

• Published in: arXiv.org
• Main Authors: Schilling, M B, Schoop, L M, Lotsch, B V, Dressel, M, Pronin, A V
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 30.07.2017
• Subjects: Band theory; Collapse; Conductivity; Graphene; Momentum; Optical measurement; Physics - Materials Science; Physics - Mesoscale and Nanoscale Physics; Physics - Strongly Correlated Electrons; Spin-orbit interactions; Upper bounds
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1707.09620

ZrSiS exhibits a frequency-independent interband conductivity \(\sigma(\omega) = \rm{const}(\omega) \equiv \sigma_{\rm{flat}}\) in a broad range from 250 to 2500 cm\(^{-1}\) (30 - 300 meV). This makes ZrSiS similar to (quasi)two-dimensional Dirac electron systems, such as graphite and graphene. We assign the flat optical conductivity to the transitions between quasi-two-dimensional Dirac bands near the Fermi level. In contrast to graphene, \(\sigma_{\rm{flat}}\) is not supposed to be universal but related to the length of the nodal line in the reciprocal space, \(k_{0}\). When \(\sigma_{\rm{flat}}\) and \(k_{0}\) are connected by a simple model, we find good agreement between experiment and theory. Due to the spin-orbit coupling, the discussed Dirac bands in ZrSiS possess a small gap \(\Delta\), for which we determine an upper bound max(\(\Delta\)) = 30 meV from our optical measurements. At low temperatures the momentum-relaxation rate collapses, and the characteristic length scale of momentum relaxation is of the order of microns below 50 K.