Seminar By Gang Cao, University of Colorado at Boulder

Title: Control of chiral orbital currents in a colossal magnetoresistance material

Host: Peng Xiong

Abstract: Colossal magnetoresistance is an extraordinary enhancement of the electric conductivity in the presence of a magnetic field, an important property of matter that has been studied for decades.

It is conventionally associated with a magnetic-field-induced spin polarization, which drastically reduces spin scattering, thus electric resistance. Our earlier studies uncover an intriguing exception to this rule in that the electric resistivity in a magnetic insulator is reduced by up to 7 orders of magnitude only when a spin polarization is absent [1]. Here I report a newly identified quantum state in a honeycomb material where chiral orbital currents flowing along edges of crystal unit cells dictate electric conductivity, providing a key element driving the novel colossal magnetoresistance [2] and a current-sensitive Hall effect [3]. The control of the exotic quantum state, along with implications of this discovery, will be presented and discussed after a brief review of conventional colossal magnetoresistance and loop currents in other materials.

References:

1. Colossal magnetoresistance via avoiding fully polarized magnetization in ferrimagnetic insulator Mn₃Si₂Te₆, Yifei Ni, Hengdi Zhao, Yu Zhang, Bing Hu, Itamar Kimchi and Gang Cao, Letter of Phys. Rev. B 103, L161105 (2021); DOI:10.1103/PhysRevB.103.L161105
2. Control of chiral orbital currents in a colossal magnetoresistance material, Yu Zhang, Yifei Ni, Hengdi Zhao, Sami Hakani, Feng Ye, Lance DeLong, Itamar Kimchi, and Gang Cao, Nature 611, 467-472 (2022); DOI: 10.1038/s41586-022-05262-3
3. Current-sensitive Hall effect in a chiral-orbital-current state, Yu Zhang, Yifei Ni, Pedro Schlottmann, Rahul Nandkishore, Lance E. DeLong, and Gang Cao, https://arxiv.org/abs/2309.06610