Ultraquantum magnetoresistance in single-crystalline $\beta $-Ag$_2$Se

TL;DR

This study reports the first growth of single-crystalline $eta$-Ag$_2$Se and investigates its magnetoresistance, revealing negative longitudinal MR beyond the quantum limit, indicating novel fermionic charge-pumping effects in this material.

Contribution

It presents the first synthesis and detailed magnetoresistance measurements of single-crystalline $eta$-Ag$_2$Se, uncovering new quantum phenomena in this well-known material.

Findings

Negative longitudinal MR observed beyond the quantum limit

Quantum limit as low as 3 Tesla in $eta$-Ag$_2$Se

Charge-pumping effect between opposite chiral fermions

Abstract

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 $\beta $-Ag$_2$Se (Naumannite), a compound has been known for the unusual, linear-field-dependent MR in its polycrystalline form for over a decade. With the quantum limit (QL) as low as 3 Tesla, a moderate field produced by a superconductor magnet available in many laboratories can easily drive the electrons in Ag$_2$Se to an unprecedented state. We observed significant negative longitudinal MR beyond the QL, which was understood as a `charge-pumping' effect between the novel fermions with opposite chiralities. Characterization of the single-crystalline Ag$_2$Se and the fabrication of electric devices working above the QL, will represent a new direction for the study of these exotic electrons.