Probing two-level systems with electron spin inversion recovery of defects at the Si/SiO2 interface

The main feature of amorphous materials is the presence of excess vibrational modes at low energies, givingrise to the so-called "boson peak" in neutron and optical spectroscopies. These same modes manifest themselvesas two-level systems (TLSs) causing noise and decoherence in qubits and other sensitive devices. Here, wepresent an experiment that uses the spin relaxation of dangling bonds at the Si/(amorphous)SiO2interface as aprobe of TLSs. We introduce a model that is able to explain the observed nonexponential electron spin inversionrecovery and provides a measure of the degree of spatial localization and concentration of the TLSs close to theinterface, their maximum energy, and its temperature dependence.