Signature of the chiral anomaly in a Dirac semimetal: a current plume steered by a magnetic field

TL;DR

This paper reports experimental evidence of the chiral anomaly in the Dirac semimetal Na$_3$Bi, demonstrated by a field-steered current plume and anisotropic negative magnetoresistance, confirming theoretical predictions about Weyl node behavior under magnetic fields.

Contribution

The study provides the first direct experimental observation of a chiral anomaly signature in Na$_3$Bi, including a novel current plume steered by magnetic fields and highly anisotropic magnetoresistance.

Findings

Observation of a negative, highly anisotropic magnetoresistance.

Detection of a narrow, field-steered current plume.

Signatures consistent with the chiral anomaly in Dirac semimetals.

Abstract

In this talk, we describe recent experimental progress in detecting the chiral anomaly in the Dirac semimetal Na$_3$Bi in the presence of a magnetic field. The chiral anomaly, which plays a fundamental role in chiral gauge theories, was predicted to be observable in crystals by Nielsen and Ninomiya in 1983 [1]. Theoretical progress in identifying and investigating Dirac and Weyl semimetals has revived strong interest in this issue [2-6]. In the Dirac semimetal, the breaking of time-reversal symmetry by a magnetic field $\bf B$ splits each Dirac node into two chiral Weyl nodes. If an electric field $\bf E$ is applied parallel to $\bf B$, charge is predicted to flow between the Weyl nodes. We report the observation in the Dirac semimetal Na$_3$Bi of a novel, negative and highly anisotropic magnetoresistance (MR). We show that the enhanced conductivity has the form of a narrowly defined plume that can be steered by the applied field. The novel MR is acutely sensitive to deviations of $\bf B$ from $\bf E$, a feature incompatible with conventional transport. The locking of the current plume to the field appears to be a defining signature of the chiral anomaly.