  While the effects of lattice mismatch-induced strain, mechanical strain, as
well as the intrinsic strain of thin films are sometimes detrimental, resulting
in mechanical deformation and failure, strain can also be usefully harnessed
for applications such as data storage, transistors, solar cells, and strain
gauges, among other things. Here, we demonstrate that quantum transport across
magnetic tunnel junctions (MTJs) can be significantly affected by the
introduction of controllable mechanical strain, achieving an enhancement factor
of ~2 in the experimental tunneling magnetoresistance (TMR) ratio. We further
correlate this strain-enhanced TMR with coherent spin tunneling through the MgO
barrier. Moreover, the strain-enhanced TMR is analyzed using non-equilibrium
Green's function (NEGF) quantum transport calculations. Our results help
elucidate the TMR mechanism at the atomic level and can provide a new way to
enhance, as well as tune, the quantum properties in nanoscale materials and
devices.
