Quantized Spin Pumping in Topological Ferromagnetic-Superconducting Nanowires.

Area of Science:

• Condensed Matter Physics
• Quantum Computing

Background:

• Semiconducting nanowires with spin-orbit coupling, superconductivity, and ferromagnetism are candidates for hosting Majorana zero modes.
• Majorana zero modes are exotic quasiparticles with potential applications in topological quantum computing.

Purpose of the Study:

• To investigate spin pumping phenomena in hybrid nanowires.
• To establish a method for distinguishing topological Majorana zero modes from trivial Andreev bound states.

Main Methods:

• Theoretical study of spin pumping due to magnetization precession in single-subband nanowires.
• Analysis of conductance and entropy changes in relation to spin pumping.

Main Results:

• Spin pumping is robustly quantized in the topologically nontrivial phase, while charge pumping is not.
• A one-to-one correspondence exists between quantized conductance, entropy change, and spin pumping for topological Majorana zero modes.
• These observables are uncorrelated for accidental zero-energy Andreev bound states in the trivial phase.

Conclusions:

• Observation of correlated, quantized peaks in conductance, entropy change, and spin pumping provides strong evidence for Majorana zero modes.
• Distinguishing topological Majorana zero modes from quasi-Majorana modes is elaborated.
• Interference effects on spin pumping in short nanowires at low energies are discussed.