Zeeman-splitting-induced topological nodal structure and anomalous Hall conductivity in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>ZrTe</mml:mi><mml:mn>5</mml:mn></mml:msub></mml:math>
Yichul Choi, John W. Villanova, Kyungwha Park
Abstract
We investigate the topological nodal structure of three-dimensional (3D) ${\mathrm{ZrTe}}_{5}$ driven by Zeeman splitting as a function of the direction of external magnetic (B) field by using a Wannier-function-based tight-binding (WFTB) model obtained from first-principles calculations. It is known that small external stimuli can drive 3D ${\mathrm{ZrTe}}_{5}$ into different topological phases including Dirac semimetal. In order to emphasize the effect of Zeeman splitting, we consider 3D ${\mathrm{ZrTe}}_{5}$ in a strong topological insulator phase with a small band gap. With Zeeman splitting greater than the band gap, the WFTB model suggests that a type-I nodal ring protected by (glide) mirror symmetry is formed when the B field aligns with the crystal $a$ or $b$ axes, and that a pair of type-I Weyl nodes are formed otherwise, when conduction and valence bands touch. We show that a pair of separate Weyl nodes can disappear through formation of a nodal ring, rather than requiring two Weyl nodes with opposite chirality to come together. Interestingly, a type-II nodal ring appears from crossings of the top two valence bands when the B field is applied along the $c$ axis. This nodal ring gaps out to form type-II Weyl nodes when the B field rotates in the $bc$ plane. Comparing the WFTB and linearized $k\ifmmode\cdot\else\textperiodcentered\fi{}p$ model, we find inadequacy of the latter at some $\mathbf{B}$ field directions. Further, using the WFTB model, we numerically compute the intrinsic anomalous Hall conductivity ${\ensuremath{\sigma}}_{ac}$ induced by Berry curvature as a function of chemical potential and B field direction. We find that ${\ensuremath{\sigma}}_{ac}$ increases abruptly when the B field is tilted from the $a$ axis within the $ab$ plane. Our WFTB model also shows significant anomalous Hall conductivity induced by avoided level crossings even in the absence of Weyl nodes.