Observation of the chiral anomaly induced negative magneto-resistance in 3D Weyl semi-metal TaAs (1503.01304v1)

Abstract: Weyl semi-metal is the three dimensional analog of graphene. According to the quantum field theory, the appearance of Weyl points near the Fermi level will cause novel transport phenomena related to chiral anomaly. In the present paper, we report the first experimental evidence for the long-anticipated negative magneto-resistance generated by the chiral anomaly in a newly predicted time-reversal invariant Weyl semi-metal material TaAs. Clear Shubnikov de Haas oscillations (SdH) have been detected starting from very weak magnetic field. Analysis of the SdH peaks gives the Berry phase accumulated along the cyclotron orbits to be {\pi}, indicating the existence of Weyl points.

• The paper demonstrates the first direct experimental observation of chiral anomaly-induced negative magnetoresistance in TaAs under low temperatures and up to 9 T magnetic fields.
• The paper employs chemical vapor transport synthesis and magneto-transport measurements to reveal ultrahigh electron mobility reaching approximately 1.8×10^5 cm²V⁻¹s⁻¹ along with clear quantum oscillations.
• The paper validates theoretical predictions by aligning observed Fermi surfaces with first-principle calculations, thereby confirming the role of Weyl fermions in transport phenomena.

Overview of "Observation of the chiral anomaly induced negative magneto-resistance in 3D Weyl semi-metal TaAs"

This paper presents a comprehensive experimental investigation into the negative magneto-resistance (MR) induced by the chiral anomaly in a time-reversal invariant 3D Weyl semimetal (WSM), specifically tantalum arsenide (TaAs). The paper provides compelling experimental evidence supporting the chiral anomaly's impact on transport phenomena within this material class, a subject of considerable interest in condensed matter physics.

Experimental Observations and Findings

The paper reports the first direct experimental observation of the chiral anomaly's manifestation in the form of negative MR in a Dirac semimetal. This is demonstrated using TaAs single crystals synthesized via chemical vapor transport. The paper is significant for confirming theoretical predictions about the transport properties of WSMs. Measurements were performed at very low temperatures (down to 1.8 K) and under high magnetic fields (up to 9 T), revealing ultrahigh electron mobility coupled with distinct characteristics of MR.

Key results observed include:

• Negative Magneto-Resistance: TaAs exhibits significant negative MR when the magnetic field is aligned parallel to the electrical current, attributable to chiral anomaly effects. This result is one of the most definitive signatures of Weyl fermions.
• Shubnikov-de Haas Oscillations: The presence of clear Shubnikov-de Haas (SdH) oscillations from low magnetic fields signals the high quality of the crystal and supports the presence of Weyl fermions.
• Ultrahigh Mobility: TaAs displays ultrahigh electron mobility in the range of $\mu \approx 1.8 \times 10^5$ cm$^2$ V$^-1$ s$^-1$ at low temperatures, which substantiates its potential for future applications in electronic devices leveraging quantum physics phenomena.
• Material Structure and Stoichiometry: The use of first-principle calculations to predict numerous Weyl nodes due to the absence of an inversion center corroborates the material's nonsymmorphic space group structure. The observed Fermi surfaces from quantum oscillations align well with theoretical predictions.

Discussion on Theoretical and Practical Implications

The research underscores the profound significance of WSMs, such as TaAs, in bridging theoretical predictions with experimental verification. The confirmed observation of chiral anomaly-induced negative MR in TaAs provides a pathway for the exploration of new phases of matter characterized by topological properties. This effect, arising from the presence of closely aligned magnetic and electric fields, has potential ramifications for novel electronic devices, particularly in designing materials with custom transport properties.

From a theoretical perspective, these findings validate long-held predictions about WSMs, enhancing our understanding of topological matter. Practically, the results suggest promising applications in realizing high-efficiency electronic and spintronic devices. Materials like TaAs, due to their remarkable physicochemical properties, are suitable for use in designing non-dissipative spintronics, quantum computing components, and advanced sensing technologies.

Future Advancements and Research Directions

The paper opens several avenues for further research. Investigating other compounds within the TaAs family could reveal additional materials with similar or enhanced properties. Further exploration at various temperature ranges and magnetic field strengths might offer deeper insights into the robustness of the chiral anomaly-induced phenomena.

Additionally, investigating the material under different external stresses or combining it with other materials may lead to the development of composite systems with tailored electronic properties. The reproducibility of these phenomena in different material systems or structures remains an open question that could catalyze new developments in fundamental physics and engineering applications.