Coherent Resonant Tunneling through Double Metallic Quantum-Well States

Study of resonant tunneling through multi-metallic quantum well (QW) structure is not only important for the fundamental understanding of quantum transport, but also for the great potential to generate advanced functionalities of spintronic devices. However, it remains challenging to engineer such structure due to the short electron phase coherence length in metallic QW system. Here, we demonstrate the successful fabrication of double-QW structure in a single fully epitaxial MTJ heterostructure, where two Fe QW layers are sandwiched between three MgAlOx tunnel barriers. We show clear evidence of the coherent resonant tunneling through the discrete QW states in the two QWs. Compared to the single QW structure, the resonant tunneling in double-QW MTJ produces strong conductivity oscillations with much narrower peak width (about half) owing to the enhanced energy filtering effect. This study presents a comprehensive understanding of the resonant tunneling mechanism in MTJ with multiple QWs, which is essential for future development of new spintronic devices operating in the quantum tunneling regime.