Observation of tunnel magnetoresistance in a superconducting junction with Zeeman-split energy bands

The change of the quasiparticle density of states in a superconductor due to the Zeeman splitting can lead to highly responsive spintronic devices. This is demonstrated here in the magnetotunneling studies of a supercondcutor/insulator/ferromagnet tunnel junction. A tunnel magnetoresistance (TMR) as large as 36% is obtained, resulting from the conductance variation due to spin-split quasiparticle tunneling, and only occurs in the superconducting state. Our results show that in addition to the naturally existent spin imbalance in ferromagnets (upon which conventional TMR is obtained), we can manipulate tunnel conductance by tailoring spin dependent density of states with interfacial exchange fields, and even with a tunnel junction with both superconducting electrodes.