Coherent Lattice Vibrations in Mono- and Few-Layer WSe<sub>2</sub>

Jeong, Tae Young; Jin, Byung Moon; Rhim, S. H.; Debbichi, Lamjed; Park, Jaesung; Jang, Y. D.; Lee, Hyang Rok; Chae, Dong-Hun; Lee, Dong Hoon; Kim, Yong Hoon; Jung, Suyong; Yee, Ki‐Ju

doi:10.1021/acsnano.6b02253

Cited by 82 publications

(109 citation statements)

References 46 publications

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“…Ref. 34 reported the observation of CP in 1L-WSe 2 . However, this study was restricted to a narrow energy range (∼100meV) around the A exciton, making it difficult to gain information on how CP excitation affects the whole band structure.…”

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confidence: 99%

Strongly Coupled Coherent Phonons in Single-Layer MoS₂

et al. 2020

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We present a transient absorption setup combining broadband detection over the visible-UV range with high temporal resolution (∼20fs) which is ideally suited to trigger and detect vibrational coherences in different classes of materials. We generate and detect coherent phonons (CPs) in single layer (1L) MoS2, as a representative semiconducting 1L-transition metal dichalcogenide (TMD), where the confined dynamical interaction between excitons and phonons is unexplored. The coherent oscillatory motion of the out-of-plane A ′ 1 phonons, triggered by the ultrashort laser pulses, dynamically modulates the excitonic resonances on a timescale of few tens fs. We observe an enhancement by almost two orders of magnitude of the CP amplitude when detected in resonance with the C exciton peak, combined with a resonant enhancement of CP generation efficiency. Ab initio calculations of the change in 1L-MoS2 band structure induced by the A ′ 1 phonon displacement confirm a strong coupling with the C exciton. The resonant behavior of the CP amplitude follows the same spectral profile of the calculated Raman susceptibility tensor. This demonstrates that CP excitation in 1L-MoS2 can be described as a Raman-like scattering process. These results explain the CP generation process in 1L-TMDs, paving the way for coherent all-optical control of excitons in layered materials in the THz frequency range.Coherent modulation of the optical properties of a material, following impulsive photo-excitation of the lattice, is fundamentally interesting and technologically relevant because it can be used for applications in sensors[1], actuators and transducers [2][3][4], that can be operated at extremely high frequencies (up to several THz[5]). In order to exploit this effect, it is necessary to understand the mechanism underlying the coherent phonon (CP) generation process and to identify the physical parameters (such as the pump pulse photon energy) that allow their efficient excitation. In view of possible device applications, it is of paramount importance to detect the spectral dependence of the CP amplitude, in order to identify in which photon energy window the optical response of the material can be efficiently modulated.We present a novel transient absorption (TA) setup, combining broadband detection from 1.8 to 3eV, with extremely high temporal resolution (∼20fs). This is ideally suited to trigger and detect vibrational coherences in different classes of materials. We use it to generate and detect CPs in 1L-MoS 2 , as a representative semiconducting 1L-transition metal dichalcogenide (TMD). We focus on TMDs because they support strongly bound excitons with unique physical properties, enabling novel applica-tions in optoelectronics and photonics [6][7][8]. However, in TMDs, the dynamical interaction between excitons and phonons, when constrained to 1L, is unexplored.When TMDs are exfoliated down to 1L, they undergo a transition from indirect to direct band gap[9], accompanied by a strong enhancement of the photoluminescence (PL) quantum yie...

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Strongly Coupled Coherent Phonons in Single-Layer MoS₂

et al. 2020

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“…Now we turn to the pressure response of lattice vibration in monolayer WSe 2 . Raman spectroscopy, with its fast and non‐destructive properties, is considered to be an efficient method to obtain information about the lattice vibrations of crystalline material . The Raman spectrum of monolayer WSe 2 at ambient pressure is shown in Figure (c).…”

Section: Resultsmentioning

confidence: 99%

“…The A 1 ′ mode originates from transverse vibration of Se−Se atoms and the E′ mode originates from longitudinal vibration of W−Se atoms in opposite directions; they correspond to the A 1g and E 1 2g modes in bulk WSe 2 , respectively . The LA(M) mode is the longitudinal acoustic phonon at the M symmetry point in the Brillouin zone, it is usually activated by lattice structural disorder …”

Section: Resultsmentioning

confidence: 99%

“…Now we turn to the pressure response of lattice vibration in monolayer WSe 2 .R aman spectroscopy,w ith its fast and nondestructive properties, is considered to be an efficient method to obtain information about the lattice vibrations of crystalline material. [21][22][23][33][34][35][36][37][38][39][40][41] The Raman spectrum of monolayer WSe 2 at ambient pressure is shown in Figure 1(c). Therea re two firstorder vibrational modes, namely A 1 ' and E',a sw ell as one phonon mode LA(M);aseries of second-order vibrational modes also can be seen in the spectrum.…”

Section: Resultsmentioning

confidence: 99%

“…The A 1 ' mode originates from transverse vibration of SeÀSe atoms and theE ' mode originatesf rom longitudinal vibration of WÀSe atoms in opposite directions; [16,22] they correspond to the A 1g andE 1 2g modes in bulk WSe 2 ,r espectively. [22] The LA(M) mode is the longitudinal acousticp honon at the Ms ymmetry point in the Brillouin zone, [39,[42][43][44] it is usuallya ctivated by lattice structural disorder. [42][43][44][45][46][47][48][49] From the Raman spectra at 0t o3 1.37 GPa, shown in Figure 4, we can see the LA(M) ando ther second order vibrations give ar elatively weak intensity initially,b ut that as the pressure increases the intensity of the LA(M) mode clearly grows.A ll other main Raman peaks give ab roader width at high pressures;t hey are extracted by Lorentz profile function fittings and the pressure evolution of peak positions are summarized.…”

Section: Resultsmentioning

confidence: 99%

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Pressure‐Induced Photoluminescence Adjustment and Lattice Disorder in Monolayer WSe₂

et al. 2017

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Pressure engineering is considered as a novel strategy to modulate the properties of transition metal dichalcogenide materials. Here, through photoluminescence (PL) and Raman measurements, we investigate the electronic band structure variation and lattice vibrational dynamics of monolayer tungsten diselenide (WSe2) under pressure. As the pressure increases, the energy of the direct Κ→Κ interband transition increases, whereas that of the indirect Λ→Κ interband transition decreases, leading to a significant transition from direct to indirect band gap at 3.8 GPa. With the increase of pressure, the intensity of the direct Κ→Κ interband transition constantly decreases and finally vanishes around 12.2 GPa. Moreover, a remarkable transition between A′ and LA(M) modes under pressure has been determined by virtue of Raman spectra variations, which indicate a pressure‐induced lattice disorder. This work provides a deep understanding of the intrinsic variation of WSe2 under pressure, which effectively facilitates the development of device applications.

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Ultrafast Laser Spectroscopy of Two‐Dimensional Materials Beyond Graphene

Ceballos

Zhao

2016

Adv Funct Materials

140

125

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Starting with the discovery of graphene in 2004, the interest in two-dimensional materials since then has been exponentially growing. Across many disciplines, their exceptional electrical, chemical, thermal, and optical properties have drawn considerable attention that has created an entire field within a decade of their discovery. Driven by the mechanical exfoliation technique that allows for the quick exploration of these two-dimensional materials and their novel devices, joint efforts have been made in order to understand and exploit their potential, consequently leading to the development of their large-scale growth. This review focuses on recent studies using ultrafast laser spectroscopy that have revealed the photocarrier dynamics in two-dimensional materials and laid the foundation of their behavior. We provide a brief introduction on ultrafast laser spectroscopy, discuss several aspects of the photocarrier dynamics, and conclude with our perspective on future developments.

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Coherent Lattice Vibrations in Mono- and Few-Layer WSe₂

Cited by 82 publications

References 46 publications

Strongly Coupled Coherent Phonons in Single-Layer MoS₂

Strongly Coupled Coherent Phonons in Single-Layer MoS₂

Pressure‐Induced Photoluminescence Adjustment and Lattice Disorder in Monolayer WSe₂

Ultrafast Laser Spectroscopy of Two‐Dimensional Materials Beyond Graphene

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Coherent Lattice Vibrations in Mono- and Few-Layer WSe2

Cited by 82 publications

References 46 publications

Strongly Coupled Coherent Phonons in Single-Layer MoS2

Strongly Coupled Coherent Phonons in Single-Layer MoS2

Pressure‐Induced Photoluminescence Adjustment and Lattice Disorder in Monolayer WSe2

Ultrafast Laser Spectroscopy of Two‐Dimensional Materials Beyond Graphene

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Product

Resources

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Coherent Lattice Vibrations in Mono- and Few-Layer WSe₂

Strongly Coupled Coherent Phonons in Single-Layer MoS₂

Strongly Coupled Coherent Phonons in Single-Layer MoS₂

Pressure‐Induced Photoluminescence Adjustment and Lattice Disorder in Monolayer WSe₂