We propose an altermagnet/altermagnet topological superconductor/altermagnet (AM/AMTSC/AM) heterojunction exhibiting a filtering effect, where the vast majority of incident electrons are locally reflected, and only a small portion passes through the center region of the AMTSC. Within an appropriate parameter range, the AMTSC hosts chiral Majorana edge states (CMES), causing the transmission coefficient and the crossed Andreev reflection coefficient of the heterojunction to remain equal and exhibit quantized plateaus. By tuning system parameters, the number of CMES can be changed, thereby controlling the plateau values to be 1/2, 1/4, or 0. When the system has anisotropy, the plateaus corresponding to the AMTSC with $s$-wave pairing and $s+s_{\pm }$-wave pairing exhibit different variation trends. In the absence of anisotropy, quantized plateaus can also appear for the $s+d$-wave pairing. Moreover, the chemical potential and the spin polarization orientation angle of the AM can also adjust the plateau values and enrich these variations. All these phenomena originate from the CMES in the AMTSC and the tunneling between them, which exhibit strong robustness against disorder and can work stably over a wide range of system parameters.

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• Andreev reflection
• Antiferroelectricity
• Edge states
• Proximity effect
• Altermagnets
• Bogoliubov-de Gennes equations