Odd-parity Longitudinal Magnetoconductivity Reveals Time-Reversal Symmetry Breaking in Materials

The behaviour of electrons in materials under magnetic fields reveals fundamental insights into their internal structure, and recent research focuses on understanding how magnetism influences electrical conductivity. Sunit Das, Akash Adhikary, and Divya Sahani, alongside colleagues from the Indian Institute of Technology Kanpur and the Indian Institute of Science, demonstrate a surprising phenomenon in materials where time-reversal symmetry is broken, an ‘odd-parity magnetoconductivity’. This discovery challenges conventional understanding, as most materials exhibit even-parity conductivity, and the team’s work establishes a new, robust way to identify and characterise intrinsic magnetism. By combining theoretical modelling with detailed analysis of conductivity, the researchers reveal that this unusual conductivity originates from the interplay of electron behaviour and magnetic order, offering a powerful tool for materials science and potentially leading to novel spintronic devices.

Magnetotransport measurements serve as a sensitive probe of these properties, and this research demonstrates that magnetic materials can exhibit an unusual longitudinal magnetoconductivity that changes sign with the applied magnetic field. The team investigated this phenomenon through careful measurements and analysis, revealing a contribution arising from the unique electronic structure and symmetry properties of these materials. These findings establish a clear signature of broken time-reversal symmetry and provide a pathway for exploring novel magnetotransport phenomena.

Researchers derived expressions for both longitudinal and transverse conductivities using semiclassical transport theory, identifying their origin in Berry curvature and orbital magnetic moment. Crystalline symmetry analysis demonstrates that longitudinal odd-parity magnetoconductivity follows the same point-group symmetry as the cubic lattice, while transverse odd-parity magnetoconductivity requires a non-coplanar spin texture. The calculated magnetoconductivity tensors reveal a strong dependence on the direction of the applied magnetic field, with a maximum response observed when the field is aligned with a specific direction. Furthermore, the analysis indicates that the orbital magnetic moment contributes significantly to the overall magnetoconductivity, particularly in materials with strong spin-orbit coupling. These findings provide a comprehensive understanding of the microscopic mechanisms governing odd-parity magnetoconductivity and offer insights into the design of novel spintronic devices.

Topological Materials and Anomalous Hall Effects

This collection of references details research related to condensed matter physics, specifically focusing on topological materials, magnetotransport phenomena, and the anomalous and orbital Hall effects. The compilation covers a broad range of topics, including topological insulators, Weyl and Dirac semimetals, and the role of symmetry and crystal structure in determining electronic and transport properties.

The references explore the theoretical foundations of these phenomena, including linear response theory, Berry curvature, and orbital angular momentum. A significant portion of the work focuses on the anomalous Hall effect, covering both intrinsic and extrinsic mechanisms, and methods for controlling or suppressing it. The orbital Hall effect, closely related to the anomalous Hall effect, is also a prominent theme, with studies exploring its theoretical basis and potential experimental observation. Research into magnetotransport phenomena, such as magnetoresistance, is also well represented.

Many studies focus on specific materials, including graphene, borophene, Heusler alloys, and Kagome materials, investigating their topological properties and transport characteristics. Computational tools, such as those used for symmetry analysis, are frequently referenced, highlighting the importance of theoretical modelling in this field. The collection demonstrates a strong focus on understanding the role of Berry curvature in the anomalous Hall effect and distinguishing between intrinsic and extrinsic contributions. There is also considerable interest in manipulating these effects and developing new materials with tailored properties.

Odd-Parity Magnetoconductivity Reveals Broken Symmetry

This research establishes odd-parity magnetoconductivity as a distinct and robust signature of broken time-reversal symmetry in magnetic metals, offering a new way to investigate materials with complex magnetic properties. Unlike conventional magnetoconductivity, this newly discovered effect varies linearly with the applied field and arises from fundamental band-geometric properties of the material, specifically Berry curvature and orbital magnetic moments. Detailed analysis of crystalline symmetry reveals that longitudinal odd-parity magnetoconductivity behaves similarly to the anomalous Hall effect, while the transverse component follows different rules, providing an independent means of detecting broken time-reversal symmetry.

Calculations performed on valley-polarized gapped graphene demonstrate that this effect is strongest near the edges of energy bands and vanishes within the band gap, confirming its connection to the material’s electronic structure. Furthermore, numerical modelling shows a direct correlation between the magnitude of odd-parity magnetoconductivity and the strength of the underlying magnetic order, effectively allowing it to serve as a measure of time-reversal symmetry breaking. This work establishes odd-parity magnetoconductivity and its resistive counterpart as powerful tools for identifying topological magnetic phases and complementing anomalous Hall transport measurements.

The research identified additional contributions to conductivity that arise from both conventional and band-geometric effects, each scaling differently with scattering time. The team also investigated the behaviour of this effect in the quantum oscillation regime, finding both even and odd components in the oscillating magnetoconductivity, and successfully explaining previously observed experimental results.