Quantum Geometry Induced Nonlinear Transport in Altermagnets,Physical Review Letters

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Quantum Geometry Induced Nonlinear Transport in Altermagnets
Physical Review Letters ( IF 8.1 ) Pub Date : 2024-09-05 , DOI: 10.1103/physrevlett.133.106701
Yuan Fang _{1,

2} , Jennifer Cano _{1,

3} , Sayed Ali Akbar Ghorashi ₁

Affiliation

Quantum geometry plays a pivotal role in the second-order response of

P T

-symmetric antiferromagnets. Here we study the nonlinear response of 2D altermagnets protected by

C_{n} T

symmetry and show that their leading nonlinear response is third order. Furthermore, we show that the contributions from the quantum metric and Berry curvature enter separately: the longitudinal response for all planar altermagnets only has a contribution from the quantum metric quadrupole (QMQ), while transverse responses in general have contributions from both the Berry curvature quadrupole (BCQ) and QMQ. We show that for the well-known example of

d

-wave altermagnets the Hall response is dominated by the BCQ. Both longitudinal and transverse responses are strongly dependent on the crystalline anisotropy. While altermagnets are strictly defined in the limit of vanishing spin orbit coupling (SOC), real altermagnets exhibit weak SOC, which is essential to observe this response. Specifically, SOC gaps the spin-group protected nodal line, generating a response peak that is sharpest when SOC is weak. Two Dirac nodes also contribute a divergence to the nonlinear response, whose scaling changes as a function of SOC. Finally, we apply our results to thin films of the 3D altermagnet

{RuO}_{2}

. Our work uncovers distinct features of altermagnets in nonlinear transport, providing experimental signatures as well as a guide to disentangling the different components of their quantum geometry.

中文翻译：

量子几何诱导的交变磁体中的非线性输运

量子几何在第二次研究中发挥着举足轻重的作用

d

-订单响应

P T

-对称反铁磁体。在这里，我们研究受保护的二维交流磁体的非线性响应

C_{n} T

对称性并表明它们的主要非线性响应是三阶的。此外，我们表明量子度量和贝里曲率的贡献是分开输入的：所有平面交替磁体的纵向响应仅具有来自量子度量四极（QMQ）的贡献，而横向响应通常具有来自贝里曲率四极的贡献(BCQ) 和 QMQ。我们证明，对于众所周知的 d 波交流磁体示例，霍尔响应由 BCQ 主导。纵向和横向响应都强烈依赖于晶体各向异性。虽然交变磁体在消失自旋轨道耦合 (SOC) 的限制下被严格定义，但真实的交变磁体表现出较弱的 SOC，这对于观察这种响应至关重要。具体来说，SOC 与自旋群保护的节点线有间隙，产生当 SOC 较弱时最尖锐的响应峰值。两个 Dirac 节点也会对非线性响应产生发散，其尺度随着 SOC 的函数而变化。最后，我们将结果应用于 3D 交流磁体的薄膜