Electrical Tuning of Valley Magnetic Moment via Symmetry Control

TL;DR

This paper demonstrates the electrical control of valley magnetic moments in bilayer MoS2 by breaking inversion symmetry with a perpendicular electric field, enabling tunable Berry curvature and magnetic properties for quantum electronic applications.

Contribution

It introduces a novel method to electrically tune valley magnetic moments in bilayer MoS2 through symmetry control, verified by optical circular dichroism measurements.

Findings

Orbital magnetic moment can be continuously tuned from -15% to 15%.

Tuning is achieved by applying gate voltage in bilayer MoS2 transistors.

Monolayer MoS2 shows gate-independent dichroism, confirming the role of symmetry.

Abstract

Crystal symmetry governs the nature of electronic Bloch states. For example, in the presence of time reversal symmetry, the orbital magnetic moment and Berry curvature of the Bloch states must vanish unless inversion symmetry is broken. In certain 2D electron systems such as bilayer graphene, the intrinsic inversion symmetry can be broken simply by applying a perpendicular electric field. In principle, this offers the remarkable possibility of switching on/off and continuously tuning the magnetic moment and Berry curvature near the Dirac valleys by reversible electrical control. Here we demonstrate this principle for the first time using bilayer MoS2, which has the same symmetry as bilayer graphene but has a bandgap in the visible that allows direct optical probing of these Berry-phase related properties. We show that the optical circular dichroism, which reflects the orbital magnetic moment in the valleys, can be continuously tuned from -15% to 15% as a function of gate voltage in bilayer MoS2 field-effect transistors. In contrast, the dichroism is gate-independent in monolayer MoS2, which is structurally non-centrosymmetric. Our work demonstrates the ability to continuously vary orbital magnetic moments between positive and negative values via symmetry control. This represents a new approach to manipulating Berry-phase effects for applications in quantum electronics associated with 2D electronic materials.