2 research outputs found
Strong Exciton-Phonon Coupling as a Fingerprint of Magnetic Ordering in van der Waals Layered CrSBr
The layered, air-stable van der Waals antiferromagnetic compound CrSBr
exhibits pronounced coupling between its optical, electronic, and magnetic
properties. As an example, exciton dynamics can be significantly influenced by
lattice vibrations through exciton-phonon coupling. Using low-temperature
photoluminescence spectroscopy, we demonstrate the effective coupling between
excitons and phonons in nanometer-thick CrSBr. By careful analysis, we identify
that the satellite peaks predominantly arise from the interaction between the
exciton and an optical phonon with a frequency of 118 cm-1 (~14.6 meV) due to
the out-of-plane vibration of Br atoms. Power-dependent and
temperature-dependent photoluminescence measurements support exciton-phonon
coupling and indicate a coupling between magnetic and optical properties,
suggesting the possibility of carrier localization in the material. The
presence of strong coupling between the exciton and the lattice may have
important implications for the design of light-matter interactions in magnetic
semiconductors and provides new insights into the exciton dynamics in CrSBr.
This highlights the potential for exploiting exciton-phonon coupling to control
the optical properties of layered antiferromagnetic materials.Comment: 21 pages, together with supp
Untangling the Intertwined: Metallic to Semiconducting Phase Transition of Colloidal MoS2 Nanoplatelets and Nanosheets
2D semiconducting transition metal dichalcogenides (TMDCs) are highly promising materials for future spin- and valleytronic applications and exhibit an ultrafast response to external (optical) stimuli which is essential for optoelectronics. Colloidal nanochemistry on the other hand is an emerging alternative for the synthesis of 2D TMDC nanosheet (NS) ensembles, allowing for the control of the reaction via tunable precursor and ligand chemistry. Up to now, wet-chemical colloidal syntheses yielded intertwined/agglomerated NSs with a large lateral size. Here, we show a synthesis method for 2D mono- and bilayer MoS2 nanoplatelets with a particularly small lateral size (NPLs, 7.4 nm ± 2.2 nm) and MoS2 NSs (22 nm ± 9 nm) as a reference by adjusting the molybdenum precursor concentration in the reaction. We find that in colloidal 2D MoS2 syntheses initially a mixture of the stable semiconducting and the metastable metallic crystal phase is formed. 2D MoS2 NPLs and NSs then both undergo a full transformation to the semiconducting crystal phase by the end of the reaction, which we quantify by X-ray photoelectron spectroscopy. Phase pure semiconducting MoS2 NPLs with a lateral size approaching the MoS2 exciton Bohr radius exhibit strong additional lateral confinement, leading to a drastically shortened decay of the B exciton which is characterized by ultrafast transient absorption spectroscopy. Our findings represent an important step for utilizing colloidal TMDCs, for example small MoS2 NPLs represent an excellent starting point for the growth of heterostructures for future colloidal photonics