Terahertz circular birefringence in thin films of Sr$_2$IrO$_4$
ORAL
Abstract
Due to its similarity to La$_2$CuO$_4$, the parent compound for the high Tc superconductors, Sr$_2$IrO$_4$ has been in the spotlight of much recent research effort. Sr$_2$IrO$_4$ is one of the first examples of a spin-orbit-assisted Mott insulator. It undergoes a metal to insulator transition around 240 K, coincident with antiferromagnetic ordering that is accompanied by a weak ferromagnetic moment. Motivated by a recent nonlinear optical experiment that insinuates a magnetoelectric ground state of orbital currents in the unit cell, we investigate the circular birefringence and dichroism of THz radiation on thin films of Sr$_2$IrO$_4$. We have developed a novel technique to generate broadband circular polarized THz pulses, and use it to probe the nature of the ground state of Sr$_2$IrO$_4$. The THz measurements reveal a non-trivial behavior of the circular birefringence around the transition temperature and as a function of magnetic field. We will discuss these results in the context of the magnetic structure models in Sr$_2$IrO$_4$, and of the potential implication on its point group symmetry.
*The work at OSU was partially supported by the Center for Emergent Materials, an NSF MRSEC, under grant DMR-1420451 and Institute for Materials Research grant EMRG-G00019; and work at UK was supported by the NSF grant DMR-1454200
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