Altermagnetic Flatband-Driven Fermi Surface Geometry for Giant Tunneling Magnetoresistance

TL;DR

This paper demonstrates that flatband-driven Fermi surface geometries in altermagnets significantly enhance tunneling magnetoresistance, leading to record-high TMR ratios in altermagnetic tunnel junctions, with potential for advanced spintronic devices.

Contribution

It reveals how specific Fermi surface geometries in synthesized altermagnets can minimize spin overlap and dramatically boost TMR, introducing new material candidates for high-performance spintronics.

Findings

Achieved TMR over 10^3% in KV2Se2O-based AMTJ.

Enhanced TMR to ~10^6% with insulating barrier.

Identified flat Fermi sheets as key to high TMR performance.

Abstract

Altermagnetism, characterized by zero net magnetization and symmetry-protected spin-split band structures, has recently emerged as a promising platform for spintronics. In altermagnetic tunnel junctions (AMTJs), the suppression of tunneling in the antiparallel configuration relies on the mismatch between spin-polarized conduction channels in momentum space. However, ideal nonoverlapping spin-polarized Fermi surfaces are rarely found in bulk altermagnets. Motivated by the critical influence of Fermi surface geometry on tunneling magnetoresistance (TMR), we investigate three experimentally synthesized altermagnets -- bulk $\mathrm{V_2Te_2O}$, $\mathrm{RbV_2Te_2O}$, and $\mathrm{KV_2Se_2O}$ -- to elucidate how flatband-driven Fermi surfaces minimize spin-channel overlap and boost AMTJ performance. Notably, $\mathrm{RbV_2Te_2O}$ and $\mathrm{KV_2Se_2O}$ host flat altermagnetic Fermi sheets, which confine spin degeneracy to minimal arc-like or nodal-like regions. Such Fermi surface geometry drastically reduces spin overlap, resulting in an unprecedented intrinsic TMR well over $10^3\%$ in the $\mathrm{KV_2Se_2O}$-based AMTJ. Incorporating an insulating barrier further enhances the TMR to $\sim10^6\%$, surpassing most conventional MTJs. These results not only establish $\mathrm{KV_2Se_2O}$ as a compelling candidate AMTJ material, but also highlight the critical role of flatband Fermi surface geometry in achieving high-performance altermagnetic-spintronic device technology.