Observation of Berry curvature and chirality in Mn3Ge Weyl semimetal using polarized SANS

Antiferromagnetic (AFM) Weyl semimetals, such as Mn3Ge, are topological materials exhibiting anomalous transport properties, including the anomalous Hall effect (AHE), anomalous magneto-optic Kerr effect (MOKE), and anomalous Nernst effect, all driven by nonvanishing Berry curvature. Mn3Ge stands out for its noncollinear AFM structure in the a-b plane, which breaks time-reversal symmetry, resulting in a large Berry curvature. This Berry curvature, arising from broken time-reversal symmetry, acts like an intrinsic magnetic field, leading to real-space effects similar to ferromagnetic (FM) materials. Since neutrons also sense the Berry phase, we propose that small-angle neutron scattering (SANS) of AFM Weyl semimetals, such as Mn3Ge, will show field-dependent patterns akin to those observed in FM systems. This experiment could provide new insights into the interaction between neutrons and Berry phase. Moreover, when a small magnetic field (at least 20 mT) is applied in the x-y crystallographic plane, an imbalance of magnetic domains with specific (net) chirality is created, leading to nonzero Berry curvature and observable effects like AHE and MOKE. We anticipate that the net chirality of magnetic domains can be detected using polarized SANS (SANSPOL), revealing asymmetry in the SANS cross-section when the magnetic field is applied within the x-y plane. This experiment will enhance the understanding of Berry curvature and chiral magnetism in AFM systems.

反铁磁（AFM）外尔半金属（如Mn3Ge）是一类具有反常输运特性的拓扑材料，包括反常霍尔效应（AHE）、反常磁光克尔效应（MOKE）和反常能斯特效应，这些特性均由非零贝里曲率驱动。Mn3Ge因其在a-b平面内的非共线反铁磁结构而备受关注，该结构破坏了时间反演对称性，从而产生大的贝里曲率。这种源于时间反演对称性破缺的贝里曲率，其作用类似于本征磁场，从而产生与铁磁（FM）材料相似的实空间效应。由于中子也能感知贝里相位，我们推测反铁磁外尔半金属（如Mn3Ge）的小角中子散射（SANS）将呈现出与铁磁体系中观测到的类似的场依赖图案。该实验有望为中子与贝里相位之间的相互作用提供新的见解。此外，当在x-y晶面施加一个小磁场（至少20毫特斯拉）时，会产生具有特定（净）手性的磁畴失衡，从而导致非零贝里曲率及可观测效应（如AHE和MOKE）。我们预期，磁畴的净手性可通过极化小角中子散射（SANSPOL）检测到，从而揭示当磁场施加于x-y平面时小角中子散射截面的不对称性。该实验将加深对反铁磁体系中贝里曲率和手性磁性的理解。