Condensed Matter Seminars

Information technology backed by sophisticated semiconductor devices have deeply changed our society in the past two decades, with AI-driven tools such as ChatGPT posited to bring even deeper impact. However, in the physics governing devices behind most of these applications, we have only utilized the charge carried by electrons, while ignoring the other inherent quantum property, the spin.  My research focuses on the understanding of the spin degree of freedom of electrons at nanoscales. First I will give an introduction on a few key phenomena in the field of spintronics, such as the coherent tunneling of spins by controlling the symmetry of the wavefunctions, and the exchange scattering effect in materials with compensated magnetization where the spins can be manipulated in the picosecond time scale. Then I will present in detail one of our research directions in which we attempt to control the order parameter of magnetic systems by using electric fields, instead of magnetic fields or spin-polarized currents. Through the voltage controlled magnetic anisotropy effect where the energy of the system can be modified by the redistribution of wavefunctions induced by external electric potentials, a 100-fold reduction in switching current density has been realized. We have demonstrated that both the magnetic anisotropy and saturation magnetization of a metallic ferromagnet can be controlled by voltage, leading to a new method to modify the interlayer exchange coupling of the system, directly verified by in-situ X-ray magnetic circular dichroism experiment. In addition to the ferromagnetic order, the antiferromagnetic order can also be effectively manipulated by electric fields. Finally, I will describe our recent effort to reduce the switching energy of magnetic tunnel junctions. By controlling the spin-orbit interaction of the system using a remote doping technique, we have achieved a record-low switching energy of ~3 fJ using sub-ns voltage pulses.