Signatures of the Adler-Bell-Jackiw chiral anomaly in a Weyl Fermion semimetal (1601.04208v2)

Abstract: Weyl semimetals provide the realization of Weyl fermions in solid-state physics. Among all the physical phenomena that are enabled by Weyl semimetals, the chiral anomaly is the most unusual one. Here, we report signatures of the chiral anomaly in the magneto-transport measurements on the first Weyl semimetal TaAs. We show negative magnetoresistance under parallel electric and magnetic fields, that is, unlike most metals whose resistivity increases under an external magnetic field, we observe that our high mobility TaAs samples become more conductive as a magnetic field is applied along the direction of the current for certain ranges of the field strength. We present systematically detailed data and careful analyses, which allow us to exclude other possible origins of the observed negative magnetoresistance. Our transport data, corroborated by photoemission measurements, first-principles calculations and theoretical analyses, collectively demonstrate signatures of the Weyl fermion chiral anomaly in the magneto-transport of TaAs.

• The paper demonstrates negative longitudinal magnetoresistance in TaAs, confirming the Adler-Bell-Jackiw chiral anomaly.
• It employs ARPES, first-principles calculations, and detailed magneto-transport measurements to validate the Weyl fermion behavior.
• The findings link Weyl fermion topology to quantum transport properties, offering new perspectives for electronic and quantum device research.

Overview of Adler-Bell-Jackiw Chiral Anomaly in a Weyl Fermion Semimetal

The paper in question investigates the manifestation of the Adler-Bell-Jackiw (ABJ) chiral anomaly within the distinctive context of Weyl semimetals, specifically focusing on TaAs. Weyl semimetals have garnered attention for providing a solid-state framework to explore Weyl fermions, which in high-energy physics are massless fermions carrying specific chirality. The chiral anomaly is particularly intriguing as it signifies the breach of a classical conservation law due to quantum mechanical phenomena, breaking symmetry in a way that influences both fundamental and applicable facets of physics.

Main Contributions & Methodology

At the core of this research is the identification of negative longitudinal magnetoresistance (LMR) in Weyl semimetal TaAs under parallel alignment of electric and magnetic fields. This anomaly is counterintuitive in the scope of classical transport theories, where resistivity typically increases with applied magnetic fields. However, the work shows how the unique attributes of Weyl fermions manifest in condensed matter systems, hinting at high-energy physics phenomena such as the chiral anomaly.

This was substantiated through rigorous analysis using angle-resolved photoemission spectroscopy (ARPES) to observe real-time electronic dispersions, supported by first-principles calculations to establish an accurate picture of the low-energy excitations. The authors complement this with an extensive range of temperature and angular dependencies measured through magneto-transport experiments to confirm the observed negative LMR is indeed resulting from the Weyl fermions. They effectively rule out alternative explanations, ensuring a robust claim on the presence of the chiral anomaly.

Key Findings & Implications

The authors present comprehensive data, including transport characteristics and ARPES measurements, revealing that TaAs features a nontrivial topology with separated Weyl nodes in momentum space. This separation allows the electronic transport to reflect the characteristic Berry curvature effects, typical of the chiral anomaly. Importantly, such signatures provide a novel means of probing fundamental quantum symmetries in a condensed matter framework, potentially expanding the interface between high-energy and condensed matter physics.

Numerical Results and Theoretical Assertions

Quantitatively, the work highlights the dependency of chiral coefficient $C_W$ on the Fermi energy, following a $1/E_F^2$ relationship, which strongly points to the contributions of the Weyl nodes rather than any trivial band structure. This assertion is pivotal as it connects the observed physical phenomena directly to the properties of Weyl fermions, nullifying doubts about alternative origins.

The negative LMR is interpreted as a signature of the chiral magnetic effect, and the paper speculates on the feasibility of this effect being harnessed for potential quantum computing applications where control of such transport anomalies could be leveraged.

Future Perspectives

This paper sets a compelling precedent for condensed matter studies aligning with particle physics principles. Future research could focus on exploring the control and tuning of these anomalies via external agents like doping, strain, or electromagnetic fields, potentially entering new territories in the design of electronic devices or quantum simulators mimicking cosmological conditions or early universe physics. Furthermore, extending this analysis to other Weyl semimetals could broaden our understanding of the universality and variability of such quantum anomalies across different materials.

In summary, this paper meticulously delineates the observation of quantum anomalies within a solid-state platform, emphasizing its significance across fundamental physics and fostering dialogue between historically disparate domains of scientific inquiry.