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.
References:
[1] Yifei Ni, Hengdi Zhao, Yu Zhang, Bing Hu, Itamar Kimchi and Gang Cao, Phys. Rev. B 103, L161105 (2021).
[2] Hengdi Zhao, Sami Hakani, Feng Ye, Lance DeLong, Itamar Kimchi, and Gang Cao, Nature 611, 467 (2022).
BIOGRAPHY
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 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 5d- transition metal oxides he helped initiate in the mid-1990s. Gang Cao was elected Fellow of the American Physical Society (DCMP) in 2009.
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