Birefringent Spin-Lasers

Introducing spin-polarized carriers in semiconductor lasers reveals an alternative path to realize room-temperature spintronic applications, beyond the usual magnetoresistive effects[1]. Through carrier recombination, the angular momentum of the spin-polarized carriers is transferred to photons, thus leading to the circularly polarized emitted light. Surprisingly, a large birefringence[2], considered detrimental in both conventional and spin-lasers, has been demonstrated to lead to ultrafast operation with an order of magnitude faster modulation frequency [3] than in the best commercial lasers. By using transparent rate equations we explain how the birefringence can provide key differences in the modulation frequency of the intensity and polarization of light emitted from a laser. We reveal that for such ultrafast operation it is important to have a short spin relaxation time in the active region of the semiconductor lasers, typically made of quantum wells.
[1] I. Zutic et al., Semiconductor Spin-Lasers, Spintronics Handbook Spin Transport and Magnetism, 2nd ed., edited by E. Y. Tsymbal and I. Zutic (CRC Press, Boca Raton, FL, 2019)
[2] P. E. Faria Junior et al., PRB 92, 075311 (2015)
[3] M. Lindemann et al., Nature 568, 212 (2019)