Superradiance of Spin Defects in Silicon Carbide for Maser Applications

TL;DR

This paper demonstrates the potential of silicon carbide spin defects to serve as maser gain media, achieving superradiant microwave emission through optical pumping and magnetic tuning, advancing maser technology beyond traditional conditions.

Contribution

It introduces silicon vacancy defects in silicon carbide as a new maser medium and develops methods to optimize population inversion and superradiant emission.

Findings

Achieved population inversion in SiC spin defects.

Developed high-Q microwave resonator for superradiance.

Demonstrated superradiant stimulated microwave emission.

Abstract

Masers as telecommunication amplifiers have been known for decades, yet their application is strongly limited due to extreme operating conditions requiring vacuum techniques and cryogenic temperatures. Recently, a new generation of masers has been invented based on optically pumped spin states in pentacene and diamond. In this study, we pave the way for masers based on spin S = 3/2 silicon vacancy (V$_{Si}$) defects in silicon carbide (SiC) to overcome the microwave generation threshold and discuss the advantages of this highly developed spin hosting material. To achieve population inversion, we optically pump the V$_{Si}$ into their $m_S$ = $\pm$1/2 spin sub-states and additionally tune the Zeeman energy splitting by applying an external magnetic field. In this way, the prerequisites for stimulated emission by means of resonant microwaves in the 10 GHz range are fulfilled. On the way to realising a maser, we were able to systematically solve a series of subtasks that improved the underlying relevant physical parameters of the SiC samples. Among others, we investigated the pump efficiency as a function of the optical excitation wavelength and the angle between the magnetic field and the defect symmetry axis in order to boost the population inversion factor, a key figure of merit for the targeted microwave oscillator. Furthermore, we developed a high-Q sapphire microwave resonator (Q ~ 10$^4$ - 10$^5$) with which we find superradiant stimulated microwave emission. In summary, SiC with optimized spin defect density and thus spin relaxation rates is well on its way of becoming a suitable maser gain material with wide-ranging applications.