  Double barrier heterostructures are model systems for the study of electron
tunneling and discrete energy levels in a quantum well (QW). Until now resonant
tunneling phenomena in metallicQW have been observed for limited thicknesses
(1-2 nm) under which electron phase coherence is conserved. In the present
study we show evidence of QW resonance states in Fe QW up to12 nmthick and at
room temperature in fully epitaxial doubleMgAlOxbarrier magnetic tunnel
junctions. The electron phase coherence displayed in this QWis of unprecedented
quality because ofa homogenous interface phase shift due to the small lattice
mismatch at the Fe/MgAlOx interface. The physical understanding of the critical
role of interface strain on QW phase coherence will greatly promote the
development of the spin-dependent quantum resonant tunneling applications.
