Fig. 1: Orbital symmetry change and normal-state transport in epitaxial V/MgO/Fe-based junctions.
a The main conductance bands, labeled with their respective orbital symmetries, are superimposed to each region. Arrows denote electron spin. At the Fermi level, EF, in vanadium, only electrons with Δ2 symmetry are present, while they are absent in iron. Therefore, a symmetry change is necessary for the electron transport across the V/MgO/Fe junction. This is enabled by the Rashba spin-orbit coupling (SOC) at the V/MgO interface. MgO acts both as (i) symmetry filter at EF, relatively transparent for Δ1 electrons in iron at the normal incidence (vanishing wave vector along the interface, k|| = 0), while having a strong barrier for Δ2 electrons and (ii) enabling the symmetry and spin changes allowing electron tunneling into the iron. An equivalent resistor model indicates that the SOC barrier dominates over the usual barrier from the MgO region. b Typical normal-state conductance of different tunnel junctions of a lateral size 20 × 20 μm2, as a function of their number of V/MgO barriers. Each dot: sample-averaged conductance. Each extra V/MgO barrier diminishes the conductance by an order of magnitude. c In-plane tunnel magnetoresistance (TMR) of a spin-valve junction (inset), showing parallel and antiparallel magnetization configurations, changing with an applied magnetic field, H, and the typical coercive field of the hard Fe/Co magnetic layer. d Across the less-resistive Fe/MgO/Fe junction, the transport is dominated by Δ1 electrons without SOC barrier. e, f The absence (presence) of SOC removes (enables) orbital symmetry mixing, explaining the measured relative magnitudes of conductance in (b).
