Spin-polarization and diode effect in thermoelectric current through altermagnet-based superconductor heterostructures

Abstract: The recent advent of a new class of magnetic material named as altermagnet (AM), characterized by a combination of momentum-dependent spin-splitting with zero net magnetization, has opened up promising prospects for spintronic applications. We theoretically explore how the altermagnetic spin-splitting affects the thermoelectric quasiparticle current in AM-based superconducting heterostructures. Our setup comprises of a bilayer system where a $d$-wave AM is proximity coupled to an ordinary $s$-wave superconductor (SC). We calculate the thermoelectric current carried by the quasiparticles applying a finite thermal bias accross the junction. The behavior of the thermoelectric current with the system's base temperature and chemical potential is very similar to that in traditional SC heterostructures. Remarkably, the dissipative thermoelectric current found in the AM junction is spin-split and thus generates finite spin-polarization in the AM-based junction, which can approach $100\%$ spin-polarization in the strong altermagnetic phase. We further investigate the thermoelectric current in AM-based Josephson junction (JJ) and illustrate how to achieve the diode effect in this AM-based JJ. The efficiency of our proposed thermoelectric diode reaches upto $\sim 80\%$ and changes its sign depending on the strength of the AM, enhancing the potential for spin-calotronics applications.