Robust Flat Magnetoresistivity in D0$_3$-Fe$_3$Ga Driven by Chiral Anomaly

Abstract: Topologically non-trivial nodes emerging from flat-band crossings not only enhance unconventional topological responses but also play a fundamental role in exploring correlation-driven topological physics. Here, we report the exceptionally robust chiral-anomaly-dominated transport in D0_3-Fe_3Ga. First, we observe a combination of positive and negative magnetoresistance, ideal planar longitudinal magnetoresistance (PLMR), and the planar Hall effect (PHE). Second, ultra-low-temperature resistivity exhibits pronounced non-Fermi-liquid (NFL) behavior, accompanied by the emergence of giant intrinsic anomalous Hall conductivity (AHC), in excellent agreement with our DFT calculations, which confirm the existence of tilted Weyl points arising from crossings of nearly three-dimensional (3D) flat bands. Most remarkably, we detect an exceptionally robust flat magnetoresistance (flat-MR) that persists without decay up to 33 T. This set of phenomena provides strong evidence that the Fermi level intersects the flattened Weyl crossings, offering confirmation of a topological flat-band semimetal. D0_3-Fe_3Ga presents a promising magnetic platform for quantum device innovations.

• The paper demonstrates that DO3-Fe3Ga exhibits flat-band-derived Weyl points near the Fermi level, leading to robust chiral anomaly-induced magnetotransport.
• The authors employ precise crystal growth, comprehensive DFT calculations, and detailed transport measurements to uncover non-Fermi-liquid behavior and an anomalously high Hall conductivity.
• The work highlights that the interplay of strong electronic correlations and topological features in DO3-Fe3Ga opens promising avenues for quantum device applications.

Robust Chiral-Anomaly-Induced Magnetotransport in DO$_3$-Fe$_3$Ga

Introduction

This work addresses a longstanding bottleneck in experimental topological condensed matter physics: the realization and characterization of a three-dimensional (3D) nodal flat-band topological semimetal in a ferromagnetic system. The authors focus on DO$_3$-Fe$_3$Ga, exploring proximity-induced flat-band Weyl crossings protected by crystal symmetry and their transport signatures, specifically the manifestation of robust chiral-anomaly-dominated responses. Prior research on such flat-band nodal systems has been impeded by strict material quality requirements and the difficulty of tuning the Fermi level with sufficient precision. This study presents a detailed synthesis, measurement, and theoretical analysis of high-quality DO$_3$-Fe$_3$Ga single crystals, enabling the unambiguous identification of topological responses intrinsic to the flattened Weyl cone states.

Crystal Growth and Electronic Structure

Single crystals of Fe$_3$Ga were grown via chemical vapor transport, yielding highly ordered bulk samples with a measured lattice constant of 6.13 Å. Transmission electron microscopy and energy-dispersive X-ray spectroscopy confirmed phase purity and stoichiometry. The residual resistivity ratio (RRR) exceeds previous reports, indicating substantial suppression of defects and disorder.

Density functional theory (DFT) calculations, based on the precise experimental lattice parameters, revealed that the DO$_3$ phase supports nearly flat-band crossings forming a nodal web in the absence of spin-orbit coupling (SOC). Upon incorporating SOC, these nodal structures resolve into Weyl points with pronounced tilt, located extremely close to the Fermi energy. This sensitivity of the Weyl-point positions to the crystal lattice constant underscores the material's proximity to a topological quantum phase boundary, allowing external tuning via pressure or strain.

Non-Fermi-Liquid Transport and Giant Anomalous Hall Response

Temperature-dependent resistivity down to 60 mK exhibits a clear non-Fermi-liquid (NFL) power law $\rho(T) = \rho_0 + AT^n$ with $n=1.53$, deviating strongly from the $_3$0 expectation of conventional metals. This anomalous scaling, in conjunction with the large fitted $_3$1 coefficient, situates DO$_3$2-Fe$_3$3Ga above canonical transition metals in the Kadowaki-Woods plot, indicating strong electronic correlations induced by the high density-of-states at the Weyl nodes.

Hall measurements reveal an anomalous Hall conductivity (AHC) that reaches 1400 S/cm at 2 K, exceeding both previous experimental values and the theoretical maximum for this family of materials. DFT-derived Berry curvature calculations, incorporating the experimentally determined band structure, corroborate that this enhancement cannot be ascribed to extrinsic mechanisms but arises from the Berry curvature singularities at the flat-band-derived Weyl points. The temperature independence of the intrinsic AHC across a wide range validates the topological origin of the response and demonstrates the strong intrinsic nature of the anomalous transport.

Magnetoresistivity: Evidence for Chiral Anomaly

Magnetotransport data under high magnetic fields up to 33 T display several hallmark signatures of a Weyl semimetal with a Fermi level pinned near flat-band Weyl points:

• Longitudinal magnetoresistance (MR) exhibits quadratic-to-linear field dependence at low temperatures, consistent with the chiral anomaly pump mechanism.
• Sustained negative MR for $_3$4 and large positive MR for $_3$5 extending up to the highest fields without saturation.
• Exceptionally robust "flat MR" is observed at intermediate ($_3$645$_3$7 and 135$_3$8) field orientation angles, an effect rarely present in other topological semimetals, and entirely non-decaying up to 33 T.

Rigorous artifact exclusion protocols, including the "squeezing test," confirm that the negative MR is intrinsic and not attributable to current-jetting or inhomogeneity, solidifying the assignment to the chiral anomaly.

Planar Hall and Longitudinal Magnetoresistance: Distinguishing Topological and Conventional Mechanisms

Both planar Hall effect (PHE) and planar longitudinal magnetoresistance (PLMR) are measured with detailed angular and temperature dependence. The experimental data are inconsistent with the conventional AMR (anisotropic MR) phenomenology alone and require the superposition of both positive and negative MR components, which is precisely predicted for chiral anomaly-induced topological states. The authors develop an extended fitting framework that simultaneously accounts for PHE and PLMR amplitudes and their phase shift, offering a stringent diagnostic for the presence of topological nodal crossings. Notably, the phase relation between PHE and PLMR shifts at $_3$9 K, reflecting a crossover from chiral anomaly-dominated to AMR-dominated transport.

Theoretical Implications and Future Directions

The results establish DO$_3$0-Fe$_3$1Ga as a rare magnetic topological semimetal exhibiting both strong intrinsic Berry curvature phenomena and clear chiral anomaly signatures, with the peculiar property of flat-band-enhanced electronic correlations. The sensitivity of the Weyl-point positions and the associated AHC to the lattice parameter offers a promising platform for investigating strain- or pressure-induced topological transitions—a scenario analogous to the type-II Weyl phase in MoTe$_3$2.

From a practical perspective, the combination of high Curie temperature ($_3$3800 K), robust topological transport, and large AHC renders this material system a compelling candidate for quantum device applications, including 3D anomalous Hall effect devices and possible intrinsic topological superconductivity if further tuned.

Conclusion

This study demonstrates the synthesis and comprehensive characterization of high-quality DO$_3$4-Fe$_3$5Ga single crystals, providing direct evidence for flat-band Weyl nodes at the Fermi level. The interplay of strong correlations, robust chiral anomaly signatures, and an unprecedented flat MR persisting to 33 T differentiates this system from prior magnetic topological semimetals. These findings establish clear criteria for detecting flat-band-induced topological physics in 3D materials and suggest numerous avenues—ranging from fundamental studies of NFL behavior in topological matter to practical implementation in spintronic and quantum information devices.