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Chapter1. ​Introduction.- Chapter2. Time-resolved absorption spectroscopy.- Chapter3. Intervalley biexcitons in monolayer MoS2.- Chapter4. Valley-selective optical Stark effect in monolayer WS2.- Chapter5. Intervalley biexcitonic optical Stark effect in monolayer WS2.- Chapter6. Large, valley-exclusive Bloch--Siegert shift in monolayer WS2.- Chapter7. Lennard--Jones-like potential of 2D excitons in monolayer WS2.- Chapter8. WUV based Time-resolved ARPES.

Edbert Jarvis Sie was awarded a PhD in physics by Massachusetts Institute of Technology in 2017. He is now a postdoctoral research fellow at Stanford University.

This thesis presents optical methods to split the energy levels of electronic valleys in transition-metal dichalcogenides (TMDs) by means of coherent light-matter interactions. The electronic valleys present in monolayer TMDs such as MoS2, WS2, and WSe2 are among the many novel properties exhibited by semiconductors thinned down to a few atomic layers, and have have been proposed as a new way to carry information in next generation devices (so-called valleytronics). These valleys are, however, normally locked in the same energy level, which limits their potential use for applications. The author describes experiment performed with a pump-probe technique using a transient absorption spectroscopy on MoS2 and WS2. It is demonstrated that hybridizing the electronic valleys with light allows one to optically tune their energy levels in a controllable valley-selective manner. In particular, by using off-resonance circularly polarized light at small detuning, one can tune the energy level ofone valley through the optical Stark effect. Also presented within are observations, at larger detuning, of a separate contribution from the so-called Bloch--Siegert effect, a delicate phenomenon that has eluded direct observation in solids. The two effects obey opposite selection rules, enabling one to separate the two effects at two different valleys.<p></p>

Nominated as an outstanding Ph.D. thesis by Massachusetts Institute of Technology, USA Presents results that are vital for the emerging field of valleytronics Offers insights into the novel optical and electronic properties or monolayer transition-metal dichalcogenides Describes innovative spectroscopic techniques for semiconductor physics Includes supplementary material: sn.pub/extras

Nominated as an outstanding Ph.D. thesis by Massachusetts Institute of Technology, USA<div><br></div><div>Presents results that are vital for the emerging field of valleytronics</div><div><br></div><div>Offers insights into the novel optical and electronic properties or monolayer transition-metal dichalcogenides</div><div><br></div><div>Describes innovative spectroscopic techniques for semiconductor physics</div><div><br></div><div><br></div>