Anomalous Hall Effect in ZrTe5

Abstract: ZrTe$_5$ has been of recent interest as a potential Dirac/Weyl semimetal material. Here, we report the results of experiments performed via in-situ 3D double-axis rotation to extract the full $4\pi$ solid angular dependence of the transport properties. A clear anomalous Hall effect (AHE) was detected for every sample, with no magnetic ordering observed in the system to the experimental sensitivity of torque magnetometry. Interestingly, the AHE takes large values when the magnetic field is rotated in-plane, with the values vanishing above $\sim 60$ K where the negative longitudinal magnetoresistance (LMR) also disappears. This suggests a close relation in their origins, which we attribute to Berry curvature generated by the Weyl nodes.

• The paper reveals that a substantial anomalous Hall effect in ZrTe5 is captured using in-situ 3D double-axis rotation to map its full 4π angular dependence.
• The paper shows that Hall signals saturate rapidly in the ab-plane while exhibiting anisotropic sensitivity in the ac-plane.
• The paper finds that the anomalous Hall effect vanishes above 60K, paralleling the disappearance of negative longitudinal magnetoresistance and indicating Berry curvature effects from Weyl nodes.

Anomalous Hall Effect in ZrTe$_5$: Implications and Observations

The paper undertakes a thorough examination of the anomalous Hall effect (AHE) in the material ZrTe$_5$, offering critical insights into its transport properties and potential underlying mechanisms. The exploration is primarily motivated by the interest in ZrTe$_5$ as a potential Dirac/Weyl semimetal, given its interesting topological properties and previously observed negative longitudinal magnetoresistance (LMR) associated with chiral anomaly effects.

Key Findings and Methodology

The research employs state-of-the-art techniques, specifically in-situ 3D double-axis rotation, to investigate the full $4\pi$ solid angular dependence of the anomalous Hall signals in ZrTe$_5$. A significant AHE is detected across all the examined samples, displaying large values when the magnetic field is rotated in-plane. The AHE value interestingly vanishes above approximately 60 K, a temperature that coincides with the disappearance of negative LMR. This correlation strongly suggests a related origin of these phenomena, which is attributed to Berry curvature effects induced by Weyl nodes.

Investigations were conducted in various planes, including the out-of-plane ($ab$-plane) and in-plane ($ac$-plane), with the rotation in the $bc$-plane providing mixed behavior. In the $ab$-plane, the AHE signals exhibit rapid saturation, whereas, in the $ac$-plane, the signals are not as sensitive to the magnetic field's angular orientation, indicating a potential anisotropic response within the plane. The temperature dependence of the AHE supports the hypothesis that the phenomena are linked to the Weyl nodes, establishing the critical temperature of around 60 K as pivotal for observing the AHE.

Theoretical and Practical Implications

The work implies that the observed AHE in ZrTe$_5$ arises from Berry curvature due to Weyl nodes rather than magnetic ordering, as confirmed by the absence of magnetic ordering from torque magnetometry measurements. This conclusion points to the existence of Weyl nodes in ZrTe$_5$, although theoretical predictions for such nodes have been lacking or inconsistent. The findings raise intriguing hypotheses regarding the conditions under which Weyl nodes might be realized in ZrTe$_5$, such as through the breaking of time-reversal symmetry (TRS) due to high Zeeman energy or variation in structural parameters leading to phase transitions.

Practically, the presence of AHE in a non-magnetic material like ZrTe$_5$ widens the understanding of Hall effects, encouraging further considerations of topological implications in transport phenomena without reliance on ferromagnetic ordering. Additionally, the observation of the anomalous Nernst effect (ANE) emphasizes the multifaceted nature of the Hall and related effects, reinforcing the connection to topological properties.

Future Research Directions

The study suggests several avenues for future research, primarily targeting the clarification and verification of the theoretical implications of these findings concerning Weyl nodes. Further investigations could aim at resolving the discrepancies in ARPES studies and integrating theoretical models to develop a robust understanding of the topological properties of ZrTe$_5$. These could involve detailed studies on the influence of doping, pressure, and external magnetic fields alongside computational models to predict and verify the formation and characteristics of Weyl semimetal phases in the compound.

In conclusion, the research provides a detailed and multifaceted perspective on the anomalous Hall effect in ZrTe$_5$, paving the way for both experimental and theoretical advancements in the understanding of topological phenomena in non-magnetic materials.