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]. The unique nature and 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.
Biosketch
Gang Cao is a professor of physics and Director of Center for Experiments on Quantum Materials
at University of Colorado at Boulder. Prior to the current appointment, he was Jack and Linda
Gill Eminent Professor at University of Kentucky (2002-2016), and staff scientist at National High
Magnetic Field Laboratory (1993-2002), respectively. He received his Ph.D. in Physics under
direction of Prof. Jack E. Crow at Temple University in Philadelphia in 1993. His research interests
focus on discovery, synthesis, and study of correlated, spin-orbit-coupled materials and high-field,
high-pressure and low-temperature properties of these materials. He has published more than 260
articles and two books. His most recent book entitled “Physics of Spin-Orbit-Coupled Oxides”
(Oxford University Press, 2021) reviews most recent work in the burgeoning field of 4d- and 5dtransition
metal oxides he helped initiate in the mid 1990s. Gang Cao was elected Fellow of the
American Physical Society (DCMP) in 2009. For more information, visit
https://www.colorado.edu/lab/cao/
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
