Magnetic Proximity Coupling to Van der Waals Transition Metal Dichalcogenides

Speaker: Shiao-Po Tsai
Affiliation: Ph.D. Candidate


Transition metal dichalcogenide, also known as TMD material, is a potential semiconductor candidate in industry for its Van der Waals structure, decent mobility, and direct band-gap in monolayer form. Recently, because of the K and K’ valley degeneracy in its honeycomb and vertical translation asymmetry structure, combining with the strong spin-orbit coupling originated from its heavy transition metal, the valleytronics and spintronics manipulation in TMD catch researchers’ attention for the further possibilities in increasing degree of freedom of semiconductor devices. Together with its original properties such as direct band-gap for opto-electronics, flexibility and light weight, piezoelectricity and chemical charge transfer mechanism, TMD also possesses the feasibility to integrate emerging logic and RF devices concepts, such as quantum tunneling, strained structure, finFET structure, negative capacitance effect, flexible and foldable electronics, opto and chemical sensors, and below 3nm down-scaling. With the versatility of the applications, TMD is certainly a great playground for semiconductor devices and internet of things (IoT).

This defense focuses on the introduction of magnetism into TMD through proximity effect, investigating coupling of valley pseudospin in TMD with adjunct layer. Till now most of the magnetic TMD researches rely on magnetic element doping, which is detrimental for the fabrication control and 2-D nature preservation. On the premise that 2-D structure is preserved, the properties such as the valleytronics in TMD is secured and the discussion of valley pseudospin and real spin is thus valid. The magnetic proximity effect, on the other hand, provides the source of magnetic coupling without change or damage original TMD properties, which is more suitable in investigating the inner physics. In the defense, room temperature spin polarization in MoS2/YIG heterostructure will be shown, and comprehensive studies of the exchange coupling will be demonstrated. Besides ferromagnetic coupling to TMD, the antiferromagnetic proximity coupling effect will also be displayed, which provides a stepstone for future THz and field free switching researches in 2-D materials.


Shiao-Po Tsai is currently a Ph.D candidate in Device Research Lab, UCLA, working with Prof. Kang L. Wang. He received his B.S. degree in electrical engineering in 2010 from National Taiwan University (NTU), Taiwan, and his M.S. degree in electronic engineering in 2012 from NTU as well, working with Prof. Chung-Chih Wu. In his master thesis work he pioneered the solution processed ZTO thin film transistors for transparent, flexible, and display electronics. Shiao-Po’s current research interests include 2-D Van der Waals materials, low-dimensional physics, magnetism, spintronics, valleytronics, and opto-electronics. Outside of school, he enjoys hiking and fitness.

For more information, contact Prof. Kang L. Wang ()

Date(s) - Nov 01, 2019
2:00 pm - 4:00 pm

E-IV Maxwell Room #57-124
420 Westwood Plaza - 5th Flr. , Los Angeles CA 90095