Observation of the Magnetic Field Induced Fermi Surface Expansion in Aperiodic Quantum Oscillations

Abstract Magnetic field‐induced quantum oscillations in resistivity have been extensively used to explore Fermi surfaces in quantum materials. This is enabled by the robustness of the Fermi surface to a magnetic field and the validity of the semiclassical Onsager's quantization relation for Landau levels (LLs). Challenging this conventional understanding, evidence of magnetic field‐induced expansion of the Fermi surface is presented. This is captured by our observations of magnetic field induced aperiodic quantum oscillations in resistivity at the conducting interfaces of LaVO 3 ‐KTaO 3 (LVO‐KTO) and EuO‐KTaO 3 (EO‐KTO). It is showed that these aperiodic oscillations occur in systems with a small Fermi surface, where the magnetic susceptibility‐induced corrections to the Fermi surface become substantial. Physically, these arise from the magnetic susceptibility‐induced modifications in the Free energy, resulting in the generalization of the semiclassical quantization rule for LLs. The magnetic field‐induced Fermi surface expansion is corroborated via the measurements of nonlinear Landau fan diagrams, deviations in the Lifshitz–Kosevich (LK) fit of longitudinal magnetoresistivity, and the magnetic field dependence of the effective cyclotron mass extracted from transport measurements. These findings provide a new perspective and fresh insights into the intriguing physics of magnetic field‐based probes of the Fermi surface.