290S/290K Quantum Materials Seminar speakers Hongrui Zhang and Shubhayu Chatterjee (both UCB) on Wednesday, October 12 at 2:00 pm PST in Physics South 402

Time/Venue Wednesday, October 12 at 2:00 pm PST in Physics South 402
Host Bob Birgeneau
Speaker Hongrui Zhang (Ramesh Group)
A room-temperature layered polar magnet
The magnets with broken inversion symmetry exhibit many novel physical properties such as magnetoelectric coupling, topological spin texture etc. Such low-symmetry layered magnetic systems are, however, scarce. In this talk, I will discuss that we designed and synthesized a room-temperature, polar magnet in van der Waals Fe2.5Co2.5GeTe2 (FCGT). In this material, we experimentally observed a Néel-type skyrmion lattice and current-induced skyrmion lattice motion at room temperature, with a threshold current density, jth =1 ×106 A/cm-2. In addition, we also realized room-temperature, current-induced magnetization self-switching in thin single-phase FCGT. This discovery of polar magnet in van der Waals materials opens the pathway for the development of next-generation spintronic devices and provides an ideal platform for studies of topological and quantum effects in 2D.
Shubhayu Chatterjee (Yao & Zaletel Groups)
Tunable electrical control of magnetism in chiral graphene-TMD heterostructures 
Electrical control of magnetism has been a longstanding goal of the spintronics community. I will discuss our ongoing theoretical work on a set of two-dimensional heterostructures – chiral multilayer graphene sandwiched inside transition metal dichalcogenides (TMD), where such control can be potentially realized via a perpendicular electric field. First, we will demonstrate that the electric field leads to enhanced low-energy density of states and promotes flavor (spin/valley) polarization. Next, we will argue that the relative alignment of graphene and TMD can be used to tune the relative signs of the induced spin-orbit coupling (SOC) in the top and bottom graphene layers. Combining these ingredients will allow us to flip either spin (or valley) degree of freedom by simply switching the direction of the electric field.

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