Anisotropic Fermi Surfaces Generate Hall-like Response Without Magnetic Fields or Berry Curvature

The emergence of Hall-like signals without magnetic fields or complex topological properties represents a significant challenge in condensed matter physics, and recent work by Abhiram Soori from the University of Hyderabad, and colleagues, addresses this problem by demonstrating a novel mechanism for generating these signals. The team reveals that anisotropic and rotated Fermi surfaces, the boundaries in momentum space defining electron behaviour, can produce a measurable transverse response in electron transport, even without external magnetic fields or Berry curvature. This discovery establishes a symmetry-based route to engineer Hall-like signals in materials lacking conventional magnetic or topological characteristics, potentially opening new avenues for designing electronic devices and exploring fundamental physics. The research demonstrates that the degree of anisotropy directly influences the magnitude of this effect, and crucially, the signal vanishes when mirror symmetry is restored, providing a clear pathway for control and manipulation.

Anisotropic Bands Generate Hall-like Effect

Researchers have discovered a new way to generate a Hall-like effect in materials, producing a measurable voltage perpendicular to the direction of current flow, even without applying a magnetic field or relying on complex topological properties. The team demonstrates that anisotropy, a direction-dependent characteristic of a material’s electronic band structure, combined with rotation of the Fermi surface, creates this effect. This arises from broken symmetry within the band structure and is confirmed using both a simplified continuum model and a more detailed lattice model, allowing precise control over material properties.

The magnitude of this Hall-like response increases with the degree of anisotropy and disappears when the material regains symmetry through specific rotation angles, providing clear experimental indicators for verification. Unlike the quantum Hall effect, this predicted response is not fixed at specific values but changes continuously with adjustments to the material’s parameters. The results reveal a contribution to transverse conductivity dependent on symmetry, distinct from conventional mechanisms.

The researchers suggest that altermagnetic materials, possessing intrinsically anisotropic band structures, offer a natural platform for observing this effect, although ferromagnetic electrodes may be necessary to control spin species. More broadly, this work reveals a principle applicable to a range of low-symmetry materials, including strained metals and anisotropic two-dimensional materials, offering a route to engineer Hall-like signals without relying on traditional mechanisms.

The authors acknowledge that the observed effect is sensitive to the degree of anisotropy and the precise alignment of the Fermi surface, requiring careful material design and characterization for experimental realization. Future research may focus on exploring the potential of this mechanism in diverse material systems and investigating its interplay with other electronic phenomena.