Valley-polarized and bipolar quantum Hall phases in the strain-controlled PbSnSe multivalley system

Abstract

Abstract Multivalley systems offer an additional degree of freedom as electrons and holes can emerge at different momenta of the Brillouin zone. In such systems, a valley pseudospin is required to describe the quantum states. The valley pseudospin offers rich physics going from encoding of information by its polarization (valleytronics), to exploring novel phases of matter when its degeneracy is changed. Here, we introduce the multivalley Pb1-xSnxSe system as a new platform for valleytronic physics and devices. By strain engineering, we reveal fully valley-polarized quantum Hall (QH) phases, showing an effective strain control of the valley pseudospin for quantum transport. The valley splitting is shown to be highly sensitive to strain and can even exceed the fundamental band gap in this material. This leads to the emergence of a novel QH phase - the “bipolar QH phase”, heralded by the coexistence of counter propagating chiral edge states at different valleys in one and the same quantum well layer. This reveals that spatially overlaid counter-propagating chiral edge states emerging at different valleys do not interfere with each other.