Phase-Rotated Altermagnets as Chern Valves for Topological Transport

Abstract

Motivated by the emerging control of Berry-curvature textures in altermagnets, we explore a two-terminal configuration where a topological-insulator film is interfaced with two altermagnetic electrodes whose crystalline phases can be rotated independently. The proximity coupling imprints each momentum-dependent of the altermagnet spin texture onto the Dirac surface states, giving rise to an angular mass whose sign follows the lattice orientation. Adjusting the phase of one electrode redefines this mass pattern, thereby tuning the number and spatial distribution of chiral edge channels. This results in discrete conductance steps and a reversible inversion of the thermoelectric coefficient-achieved without external magnetic fields or net magnetization. A compact Dirac model captures both the quantized switching and its resilience to moderate disorder. Overall, this symmetry-driven mechanism provides a practical and low-dissipation route to programmable topological transport via lattice rotation.

Figures (1)

• Figure 1: Chern-valve concept and angular-mass topology. (a) Schematic of the AM|TI|AM junction with altermagnets at crystalline phases $\varphi_L$ and $\varphi_R$ inducing angle-dependent masses $m_{L/R}(\theta)$ on the Dirac states. A sign inversion across an interface ($m_Lm_R<0$) creates a chiral edge mode (red arrow). (b) Upper panel: angular masses $m_L(\theta)$ and $m_R(\theta)$ for $\Delta\varphi=\pi/3$, showing two principal lobes reflecting $C_2$ and $C_4$ harmonics. Lower panel: binary signal marking Chern-active sectors where $m_L(\theta)m_R(\theta)<0$. (c) Integer Chern-channel count $N_{\mathrm{ch}}$ (gray, step-like) and active fraction $\mathcal{L}(\Delta\varphi)$ (red, continuous) versus phase difference $\Delta\varphi$, showing quantized plateaus. Numerical simulations employ representative parameters for RuO$_2$|Bi$_2$Se$_3$ interfaces: $m_2\approx 2$ meV, $m_4\approx 0.5$ meV, Fermi velocity $v_F=5\times 10^5$ m/s, and temperature $T=15$ K. (d) Normalized anomalous Hall and thermoelectric Hall conductivities exhibiting $C_2/C_4$ harmonic phase shifts locked to $\phi$. (e) Phase diagram of the Chern-valve response $N_{\mathrm{ch}}(\mu,\Delta\varphi)$ across the $(\mu,\Delta\varphi)$ plane. White regions correspond to $N_{\mathrm{ch}}=0$ (aligned altermagnetic masses without sign inversion), while red regions denote finite $N_{\mathrm{ch}}$ where chiral edge channels are active. The purple contour marks the condition $\alpha_{xy}^{\mathrm{tot}}=0$, separating regions of opposite transverse thermoelectric polarity. This map demonstrates that the quantized channel topology and the thermo-Hall polarity remain robust over a wide range of electrochemical conditions.