Novel quantum materials can exhibit surprising or even revolutionary physical properties that lead to critical advances in science and technology. Colossal magnetoresistance (CMR) is an extraordinary enhancement of the electric conductivity with applied magnetic field, which is an important property of matter that has been studied for decades. CMR is commonly associated with a magnetic-field-induced spin polarization that drastically reduces spin scattering and electric resistance. We have uncovered intriguing exceptions to this rule; that is the electric resistivity of some magnetic insulators is significantly reduced only when a spin polarization is absent [1,2]. We have identified a novel quantum state in which chiral orbital currents (COC) flow along electronic bonds that form the edges of crystal unit cells that dictate electric conductivity. COC form a key element that drives novel CMR and Hall effect in ferrimagnetic Mn3Si2Te6 [3, 4]. The unique nature of the COC quantum state will be compared to conventional CMR, as well as the possible occurrence of COC in other materials.
References:
- Physics of Spin-Orbit-Coupled Oxides, Gang Cao and Lance E. De Long, Oxford University Press; Oxford, 2021.
- 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).
- 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).
- Current-sensitive Hall effect in a chiral-orbital-current state, Yu Zhang, Yifei Ni, Pedro Schlottmann, Rahul Nandkishore, Lance E. DeLong, and Gang Cao, Nature Communications 15, 3579 (2024).