Magnetic field induced topological semimetals near a quantum critical point of pyrochlore iridates

TL;DR

This paper explores how magnetic fields influence topological semimetal phases near a quantum critical point in pyrochlore iridates, revealing new phases driven by competing energy scales and spin-orbit coupling.

Contribution

It introduces a framework for understanding magnetic field-induced topological phases near QCP in pyrochlore iridates, emphasizing the role of quadratic band crossing and magnetic multipole moments.

Findings

Various topological semimetal phases can be generated near QCP.

Magnetic energy scales can be controlled via magnetic multipole moments.

Degenerate states at QBC show anisotropic Zeeman effects.

Abstract

Motivated by the recent experimental observation of anomalous magneto-transport properties near the Mott quantum critical point (QCP) of pyrochlore iridates, we study the generic topological band structure near QCP in the presence of magnetic field. We have found that the competition between different energy scales can generate various topological semi-metal phases near QCP. Here the central role is played by the presence of a quadratic band crossing (QBC) with four-fold degeneracy in the paramagnetic band structure. Due to the large band degeneracy and strong spin-orbit coupling, the degenerate states at QBC can show an anisotropic Zeeman effect as well as the conventional isotropic Zeeman effect. Through the competition between three different magnetic energy scales including the exchange energy between Ir electrons and two Zeeman energies, various topological semimetals can be generated near QCP. Moreover, we have shown that these three magnetic energy scales can be controlled by modulating the magnetic multipole moment (MMM) of the cluster of spins in a unit cell, which can couple to the intrinsic MMM of the degenerate states at QBC. We propose the general topological band structure under magnetic field achievable near QCP, which would facilitate the experimental discovery of novel topological semimetal states in pyrochlore iridates.