Exciton-Dominated Ultrafast Optical Response in Atomically Thin PtSe2

Seongkwang Bae, Sanghee Nah, Doeon Lee, Muhammad Sajjad, Nirpendra Singh, Ku Min Kang, Sanghoon Kim, Geun Ju Kim, Jaekyun Kim, Hionsuck Baik, Kyusang Lee, Sangwan Sim

Research output: Contribution to journalArticlepeer-review

18 Scopus citations

Abstract

Strongly bound excitons are a characteristic hallmark of 2D semiconductors, enabling unique light–matter interactions and novel optical applications. Platinum diselenide (PtSe2) is an emerging 2D material with outstanding optical and electrical properties and excellent air stability. Bulk PtSe2 is a semimetal, but its atomically thin form shows a semiconducting phase with the appearance of a band-gap, making one expect strongly bound 2D excitons. However, the excitons in PtSe2 have been barely studied, either experimentally or theoretically. Here, the authors directly observe and theoretically confirm excitons and their ultrafast dynamics in mono-, bi-, and tri-layer PtSe2 single crystals. Steady-state optical microscopy reveals exciton absorption resonances and their thickness dependence, confirmed by first-principles calculations. Ultrafast transient absorption microscopy finds that the exciton dominates the transient broadband response, resulting from strong exciton bleaching and renormalized band-gap-induced exciton shifting. The overall transient spectrum redshifts with increasing thickness as the shrinking band-gap redshifts the exciton resonance. This study provides novel insights into exciton photophysics in platinum dichalcogenides.

Original languageBritish English
Article number2103400
JournalSmall
Volume17
Issue number45
DOIs
StatePublished - 11 Nov 2021

Keywords

  • excitons
  • layered two-dimensional materials
  • platinum diselenide
  • transient absorption microscopy
  • ultrafast exciton dynamics

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