The application of lasers is ubiquitous in current society, including optical communication, DVDs, art, medicine, and military. In addition to the unique properties of conventional lasers, spin lasers possess several features superior to their counterparts. For instance, they promise reduced threshold currents, enhanced emission intensities, polarization control with enhanced bandwidths, which enables to open up new applications, such as secure communication, chirality studies, high speed modulators and many other advanced optical devices. The most important fact to generate spin-polarized lasers is to create spin imbalance of electrons in semiconductor active layer. Currently, two ways to achieve spin laser action are based on electrical pumping by a magnetic electrode and optical pumping by a circularly polarized light source. However, spin injection by a magnetic electrode suffers from a poor efficiency due to the spin perturbation when spin-polarized electrons pass through the interface between magnetic electrode and semiconductor. On the other band, optical pumping by a circularly polarized light source is not suitable for practical application. Therefore, the progress on the study of spin polarized lasers is rather slow. In the work, a new paradigm is developed to design spin-lasers, which does not need electrical pumping by a ferromagnetic spin aligner or optical pumping by a circularly polarized light source. The spin-lasers are made with a composite consisting of nanostructured semiconductors and half-metal nanoparticles. Owing to the suitable band alignment between semiconductor and half-metal, spin down electrons and light hales can easily transfer into half-metal, while spin-up electrons and heavy holes remain in semiconductor. Consequently, the population imbalance of spin-polarized electrons can be achieved by the self-assembled process due to the inherent nature of the band structure. Based on this new self-polarized spin imbalance mechanism, the existing difficulties can be circumvented and highly efficient light emitting devices and spin-nanolasers derived from nitride semiconductors have been demonstrated. This new mechanism can be applied to many other material systems to generate spin lasers covering a wide range of spectrum, which should be very useful and timely. New paradigm of self-polarized spin imbalance arising from the band alignment between semiconductor and half-metal, where EF is the Femi level. Spin-down electrons and light holes (LH+) can easily transfer into half-metal, while spin-up electrons and heavy holes (HH+) remain in semiconductor. The recombination of spin-up electrons and heavy holes will generate spin-polarized light. Reference Ju-Ying Chen, Tong-Ming Wong, Che-Wei Chang, Chen-Yuan Dong, and Yang-Fang Chen* “Selfpolarized spin-nanolasers”, Nature Nanotechnology, 9, 845 (2014). Professor Yang-Fang Chen Department of Physics yfchen@phys.ntu.edu.tw