Magneto-elasto-resistivity in FeSe

FeSe stands out among iron-based superconductors due to its extended nematic phase without the onset of long-range magnetic order. While strain-dependent electrical resistivity has been extensively explored to probe nematicity, its influence on magneto-transport properties remains less understood. In this work, we present measurements of the magneto-elasto-resistivity in FeSe as a function of temperature and applied magnetic field. Using a minimal multiband Boltzmann model for transport we derive analytical expressions that capture the magnetic behavior of the whole set of experimental data both in the paramagnetic and in the nematic phase. These findings indicate that a multiband framework can robustly describe the magneto-elasto-transport properties in FeSe and arguably in other iron-based superconductors.

💡 Research Summary

In this work the authors investigate the magneto‑elasto‑resistivity (MER) of FeSe, a prototypical iron‑based superconductor that exhibits a pronounced nematic transition at TS ≈ 90 K without developing long‑range magnetic order. By combining uniaxial strain (applied along the crystallographic 110 direction) with four‑probe transport measurements under magnetic fields up to 15 T, they obtain a comprehensive dataset covering the temperature range from 280 K down to the superconducting state (TC ≈ 9 K). Two high‑quality single crystals (labeled S1 and S2) are studied, allowing the authors to verify reproducibility and to explore both out‑of‑plane (B‖c) and in‑plane (B⊥c) field orientations.

The experimental findings can be summarized as follows. Above the structural transition the elastoresistivity (ER) shows a Curie‑Weiss‑like increase with decreasing temperature, characterized by a characteristic temperature T* ≈ 71 K. In this regime the MER is completely independent of the applied magnetic field, regardless of its magnitude (0–15 T) or orientation. Below TS the ER changes sign and becomes negative, while the MER measured with B‖c grows rapidly with decreasing temperature and displays a clear linear dependence on B² for fields larger than ≈ 4 T. The magnitude of this field‑dependent contribution increases as the temperature is lowered, producing a pronounced upturn of MER at the lowest temperatures. By contrast, when the magnetic field is applied within the FeSe planes, the MER curves for ±15 T overlap perfectly with the zero‑field data at all temperatures, indicating that the in‑plane field has essentially no effect on the strain‑induced resistivity anisotropy.

To rationalize these observations the authors develop a minimal two‑band Boltzmann transport model. Each band n (n = 1, 2) is characterized by an isotropic zero‑strain resistivity ρ₀ⁿ and a strain‑coupling coefficient γₙ, such that the band‑resolved longitudinal resistivities become ρₓⁿ = ρ₀ⁿ + ½ γₙ ε and ρ_yⁿ = ρ₀ⁿ − ½ γₙ ε, where ε is the dimensionless strain. In the presence of an out‑of‑plane magnetic field Bz the total resistivity tensor takes the familiar form

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