Stabilization of isolated Fe atoms on a 1-nm-thick MgO/Fe(001) insulating surface via critical tunneling for a robust quantum spin platform

Atomically flat insulating films are essential for decoupling adsorbates from metallic substrates and preserving the intrinsic electronic and spin properties of single-atom quantum bits (qubits). Here, we show that the widely used MgO/Fe(001) spintronic system provides a robust platform for single-atom qubits. Using scanning tunneling microscopy (STM) at 4.6 K under ultrahigh vacuum, we investigate ∼1-nm-thick MgO films exhibiting high crystalline quality, a well-defined band gap, and a low defe