In the history of condensed matter physics, reinvestigation of a well-studied material with enhanced quality sometimes led to important scientific discoveries. A well-known example is the discovery of fractional quantum Hall effect in high quality GaAs/AlGaAs heterojunctions. Here we report the first single crystal growth and magnetoresistance (MR) measurements of the silver chalcogenide β-Ag2Se (Naumannite), a compound has been known for the unusual, linear-field-dependent MR in its polycrystalline form for over a decade. With the quantum limit (QL) as low as 3 Tesla, a moderate field produced by a superconductor magnet available in many laboratories can easily drive the electrons in Ag2Se to an unprecedented state. We observed significant negative longitudinal MR beyond the QL, which was understood as a `charge-pumping' effect between the novel fermions with opposite chiralities. Characterization of the single-crystalline Ag2Se and the fabrication of electric devices working above the QL, will represent a new direction for the study of these exotic electrons.
@article{arxiv.1502.02324,
title = {Ultraquantum magnetoresistance in single-crystalline $\beta $-Ag$_2$Se},
author = {Chenglong Zhang and Haiwen Li and Tay-Rong Chang and Su-Yang Xu and Wei Hua and Hua Jiang and Zhujun Yuan and Junliang Sun and Horng-Tay Jeng and M. Zahid Hasan and X. C. Xie and Shuang Jia},
journal= {arXiv preprint arXiv:1502.02324},
year = {2017}
}