Tuning the valley and chiral quantum state of Dirac electrons in van der Waals heterostructures

TL;DR

This paper demonstrates direct observation and control of electron chirality and pseudospin in graphene heterostructures using magnetic fields, revealing new ways to manipulate Dirac electrons' quantum states.

Contribution

It introduces a novel technique to visualize and tune the chiral quantum states of Dirac electrons in van der Waals heterostructures.

Findings

Direct visualization of electron chirality in graphene.

Magnetic field used to resolve chiral state contributions.

Ability to prepare electrons in specific valley chiral states.

Abstract

Chirality is a fundamental property of electrons with the relativistic spectrum found in graphene and topological insulators. It plays a crucial role in relativistic phenomena, such as Klein tunneling, but it is difficult to visualize directly. Here we report the direct observation and manipulation of chirality and pseudospin polarization in the tunneling of electrons between two almost perfectly aligned graphene crystals. We use a strong in-plane magnetic field as a tool to resolve the contributions of the chiral electronic states that have a phase difference between the two components of their vector wavefunction. Our experiments not only shed light on chirality, but also demonstrate a technique for preparing graphene's Dirac electrons in a particular quantum chiral state in a selected valley.