Loading...
Please wait, while we are loading the content...
Similar Documents
Ultrafast Transient Absorption Spectroscopy of Valley Carrier Dynamics in Atomically Thin Transition Metal Dichalcogenides.
| Content Provider | Semantic Scholar |
|---|---|
| Author | Mai, Cong Hung |
| Copyright Year | 2017 |
| Abstract | MAI, CONG. Ultrafast Transient Absorption Spectroscopy of Valley Carrier Dynamics in Atomically Thin Transition Metal Dichalcogenides. (Under the direction of Dr. Kenan Gundogdu). Atomically thin material is a new class of materiel first experimentally discovered around 2005. These two-dimensional material exhibits exotic properties compared to their bulk counterpart thus they are ideal candidates for a wide range of device applications in electronics and optoelectronics. Among these, one novel application that attracts tremendous attention is to manipulate the valley degree of freedom of carriers. Such control of valleys can be used in information processing and storage, in analogue to well-studied electronics and spintronics. Specifically, K and K’ valleys in atomically thin hexagonal materials such as graphene and monolayer transition metal dichalcogenides (TMDCs) open up possibilities for such manipulations. Due to absence of bandgap as well as preserved inversion symmetry, valleys in graphene are hard to control. In contrast, valley population in monolayer TMDCs such as monolayer MoS2 and WS2 can be easily injected by circular polarization light thanks to a large bandgap and broken inversion symmetry. While valley injection in monolayer TMDCs has been demonstrated, valley relaxations in these materials, which are central to valleytronic application, are unknown. In this thesis, we present first direct measurement of valley relaxations in monolayer TMDCs enabled by our homebuilt robust ultrafast transient absorption system. Our results show that single particle valley relaxation mechanisms are not primary relaxation channels. Rather, the many-body interaction, especially exchange interactions, leads to fast valley relaxations in these materials. Thanks to unique sensitivity of transient absorptions to non-emissive features, we also find that dark excitons and/or biexcitons play a role in valley relaxations. These findings have influenced both theoretical and experimental efforts in valleytronics development. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://repository.lib.ncsu.edu/bitstream/handle/1840.20/34972/etd.pdf?isAllowed=y&sequence=1 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
