Direct high-speed modulation of circular polarization (Pc) of coherent light will open the way for new communication technology and offers the possibility to overcome the main bottleneck of the optical telecommunications. Here, by using spin-orbit torque (SOT) with spin Hall effect to control the spin injector magnetization, we report for the first time to achieve electrical control of the circular polarization of light emitted from a quantum dot based light emitting diode (LED) at room temperature [1]. The circular polarization can be modulated between ±25% at 250K and ±16% at 290K after pulsed current switching injector magnetization. A repetition of more than 60 times do not reveal any degradation at the injector/semiconductor interface. Our achievement will directly contribute the implementation of the new optical telecommunication technology with Pc modulation.
[1] P. A. Dainone, et al. “Controlling the helicity of light by electrical magnetization switching”, Nature, to be published.
The recently discovered unidirectional spin-Hall magnetoresistance in nonmagnet-ferromagnet (NM-FM) bilayer structures is believed the only way to electrically sense the in-plane 180-degree magnetization rotation in such NM-FM systems without adding additional terminals or structures. On the other front, spintronic memory and logic devices involving topological insulators (TIs) are being studied intensively due to TI’s exciting potential of efficiently generate spins. In our work, we observed the unidirectional spin-Hall and Rashba−Edelstein magnetoresistance (USRMR) in topological insulator-ferromagnet (TI-FM) layer heterostructures for the first time.
TI films (Bi2Se3 or (Bi1−xSbx)2Te3) were first grown by molecular beam epitaxy and then transferred to a magnetron sputtering chamber where the CoFeB and capping MgO were deposited. Then the stacks were patterned into Hall bars and tested with harmonic measurements in a Quantum Design PPMS. The measured longitudinal second harmonic resistance contains the USRMR signal plus contributions from other thermoelectric effects. Then series of transverse second harmonic measurements with various external magnetic field strengths were carried out to carefully determine the contributions of these effects. Finally, the data was analyzed, and results show non-zero USRMR. By varying the temperature, TI thickness and TI material and comparing the USRMR performances, we have also concluded that the topological surface states of TI played important roles in generating USRMR signal. The transport properties and conditions seem to govern heavily on the USRMR performance. And the largest USRMR was observed in 6 quintuple layer thick Bi2Se3 sample at 150K and being more than twice as large as the best reported USMR in Ta/Co samples.
Many key technologies of our society, including artificial intelligence (AI) and big data, have been enabled by the invention of transistor and its ever-decreasing size and ever-increasing integration at a large scale. There is a clear scaling limit to the conventional transistor technology, however. Many recently proposed advanced transistors are also having an uphill fight in lab because of necessary performance tradeoffs and limited scaling potential. In this talk, we argue for a new pathway that could enable exponential scaling for multiple generations. This pathway involves layering multiple technologies that are beyond the available functions of conventional and newly proposed transistors. We believe that this potential pathway is becoming clear through recent worldwide effort. In this talk, I will brief you my group’s recent progress on two selected topics along this line, one on the STT-RAM and one on spin logic. Meanwhile I will also introduce a team effort of C-SPIN Center of STARnet program, where systems designers, devices builders, materials scientists and physicist all work under one roof to tackle the scaling issue and overcome key technology barriers. Several successful examples such as the logic in memory, cognitive computing, probabilistic computing and reconfigurable information processing will be discussed.
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