Zhenisbek Tagay, Johns Hopkins University: Mathematical Aspects of Topological Insulators Conference

Zhenisbek Tagay, Johns Hopkins University, USA: Low-energy electrodynamics of quantum anomalous Hall state in magnetically doped topological insulator
The quantum Hall (QH) effect is a phenomenon described by the emergence of dissipationless chiral edge states that form when a large magnetic field is applied to a 2D conductor. Nearly fifteen years ago it was proposed that one can achieve a quantum anomalous (QAH) Hall state without external magnetic field by doping thin films of topological insulators (TIs) with ferromagnetically aligned Cr/V atoms. It was experimentally realized for the first time in thin films of Cr-doped (Bi,Sb)2Te3 about a decade ago.
In this talk I will discuss current state of experimental efforts in studying magnetically doped TIs. In particular, I will be talking about low-energy (terahertz) electrodynamics of QAH state in Cr-doped (Bi,Sb)2Te3, which were recently shown to exhibit quantized Hall conductance up to T = 2K in dc transport measurements. Unusual frequency dependence observed in our data suggests strong magnetic gap disorder present in the system. Our work highlights the different effect that this type of disorder can have on the dc vs. ac QAH effect.