Rapid scan ESR: A versatile tool for the spin relaxation studies at (sub)THz frequencies

Abstract

The development of pulse electron spin resonance (ESR) spectroscopy at microwave frequencies above 100 GHz is rather challenging and expensive due to the low output power of modern high-frequency solid state electronics. However, there is a number of scientific problems that require spin relaxation measurements at THz frequencies. The rapid scan ESR is an alternative technique that does not require high microwave power and still provides information on the spin relaxation times. The method takes advantage of fast sweeps of the excitation microwave frequency over the ESR line. When the frequency sweep reaches a sufficiently high rate, distinct oscillations (also called wiggles) appear in the ESR spectrum. These oscillations bear information about T2 electron spin relaxation time, which can be extracted via fitting the rapid scan spectrum using the modified Bloch equations. In this Perspective Letter, we introduce the recent advances in this technique and discuss the future steps necessary to make the THz rapid scan ESR a convenient and easy to use tool.