Layer and orbital interference effects in photoemission from transition metal dichalcogenides

Rostami, Habib; Volckaert, Klara; Lanatà, Nicola; Mahatha, S. K.; Sanders, Charlotte E.; Bianchi, Marco; Lizzit, Daniel; Bignardi, Luca; Lizzit, Silvano; Miwa, Jill A.; Balatsky, Alexander V.; Hofmann, Philip; Ulstrup, Søren

doi:10.1103/physrevb.100.235423

Cited by 15 publications

(15 citation statements)

References 61 publications

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“…For the resonance condition | ω 0 − E g | /τ 0 around K (i.e. small q), we can write the population as [27]…”

Section: (B)mentioning

confidence: 99%

“…We seek an explanation of the measured dichroism by calculating the polarization-dependent photoemission intensity from the transiently populated CB around K. A full account of the theory is given in Ref. 27. As a simplified expression we use…”

mentioning

confidence: 99%

“…, where êp is the polarization unit vector of the probe pulse (see Fig. 1(a)) and k f is the wavevector of the free electron [27,28]. The wave functions and dispersion are determined by diagonalizing a k • p Hamiltonian given by ĤBL (q, τ z , s z ) = ñ ĤSL (−q, −τ z , s z ) Ĥ⊥ (q, τ z ) Ĥ † ⊥ (q, τ z ) ĤSL (q, τ z , s z ) ô ,…”

mentioning

confidence: 99%

“…We then solve the semiconductor Bloch equations [34] as described in detail in Ref. 27, and obtain the excited CB population shown in Fig. 2…”

mentioning

confidence: 99%

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Momentum-resolved linear dichroism in bilayerMoS2

et al. 2019

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Inversion-symmetric crystals are optically isotropic and thus naively not expected to show dichroism effects in optical absorption and photoemission processes. Here, we find a strong linear dichroism effect (up to 42.4%) in the conduction band of inversion-symmetric bilayer MoS2, when measuring energy-and momentum-resolved snapshots of excited electrons by time-and angle-resolved photoemission spectroscopy. We model the polarization-dependent photoemission intensity in the transiently-populated conduction band using the semiconductor Bloch equations and show that the observed dichroism emerges from intralayer single-particle effects within the isotropic part of the dispersion. This leads to optical excitations with an anisotropic momentum-dependence in an otherwise inversion symmetric material.Optical selection rules in absoprtion experiments are powerful tools that can be used to determine the symmetry of electronic states in solids [1]. Given the similarity of the processes underlying optical absorption and photoemission, selection rules have also been exploited in angle-resolved photoemission spectroscopy (ARPES) for decades [2]. More recently, optical dichroism has been used in ARPES to study orbital degrees of freedom [3][4][5], as well as the Berry curvature of the initial Bloch states [6, 7]. A particularly interesting opportunity for polarization-dependent excitations arises in single-layer (SL) transition metal dichalcogenides (TMDCs) such as MoS 2 , where the helicity of circularly polarized light strongly couples to the valley and spin degrees of freedom [8, 9], permitting the generation of a finite valley polarization [10, 11].Adding time-resolution (TR) to ARPES in a pumpprobe experiment leads to a process involving two optical excitations. This opens the possibility of exploiting not only the selection rules governing the photoemission process, but also those giving rise to the initial optical excitation into a transiently populated conduction band (CB) state [12][13][14][15][16][17][18]. Indeed, the creation of a finite valleypolarization in SL WS 2 has recently been followed in momentum space by TR-ARPES using circularly polarized pump pulses [19,20]. Here, we extend such an experiment to the case of bilayer (BL) MoS 2 in the 2H structure, which is inversion-symmetric and hence an optically isotropic material. Surprisingly, we observe a substantial linear dichroism effect. Our results can be reconciled with the momentum-dependent excited state population determined by solving the semiconductor Bloch equations within the framework of a low energy k · p model that ac-counts for intra-and interlayer interactions between the d orbitals forming the valence band maximum (VBM) and conduction band minimum (CBM) aroundK (K ). These findings underline the necessity of accounting for selection rules governing the optical excitation in addition to the photoemission matrix elements when interpreting the intensity in dichroic TR-ARPES.Our BL MoS 2 sample is grown on Ag(111) and has predominantly one domain orie...

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“…For the resonance condition | ω 0 − E g | /τ 0 around K (i.e. small q), we can write the population as [27]…”

Section: (B)mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

“…We then solve the semiconductor Bloch equations [34] as described in detail in Ref. 27, and obtain the excited CB population shown in Fig. 2…”

mentioning

confidence: 99%

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Momentum-resolved linear dichroism in bilayerMoS2

et al. 2019

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“…symmetry breaking in cuprate superconductors [21,22], to highlight the symmetry-reduced surface states out of bulk states [23], and to unravel the orbital character of heavy fermions [24]. While being fruitful, the diverse utility and interpretations of CD ARPES are also under scrutiny [25][26][27][28][29][30][31][32][33][34][35][36][37][38]. It has been debated which of the symmetry breaking, time reversal or mirror reflection, is sensed in the dichroic sig-nals of the cupartes [27]; some studies showed that the sign of CD flips when the incident photon energy (hν) is varied [28,[32][33][34][35]; the CD pattern can also evolve as the incidence angle is increased [35].…”

Section: Introductionmentioning

confidence: 99%

Classification of the symmetry of photoelectron dichroism broken by light

Ishida,

Chung,

Kwon

et al. 2020

Preprint

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We investigate how the direction of polarized light can affect the dichroism pattern seen in angleresolved photoemission spectroscopy. To this end, we prepared a sample composed of highly-oriented Bi(111) micro-crystals that macroscopically has infinite rotational and mirror symmetry of the point group C∞v and examined whether the dichroism pattern retains the C∞v symmetry under the stationary configuration of the light and sample. The direction of the light was imprinted in the pattern. Thereby, we apply group theory and classify the pattern with the configuration of light taken into account. We complete the classification by discussing the cases when the out-of-plane component of the polarization can be neglected, when the incidence angle is either 0 • or 90 • , when the polarization is either elliptic or linear, and also when the sample is a crystal.

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Recent Advances in Moiré Superlattice Systems by Angle‐Resolved Photoemission Spectroscopy

Li,

Wan,

2023

Advanced Materials

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The last decade has witnessed a flourish in two‐dimensional (2D) materials including graphene and transition metal dichalcogenides (TMDs) as atomic‐scale Legos. Artificial moiré superlattices via stacking 2D materials with a twist angle and/or a lattice mismatch have recently become a fertile playground exhibiting a plethora of emergent properties beyond their building blocks. These rich quantum phenomena stem from their nontrivial electronic structures that have been effectively tuned by the moiré periodicity. Modern angle‐resolved photoemission spectroscopy (ARPES) can directly visualize electronic structures with decent momentum, energy, and spatial resolution, thus could provide enlightening insights into fundamental physics in moiré superlattice systems and guides for designing novel devices. In this review, firstly a brief introduction is given on advanced ARPES techniques and basic ideas of band structures in a moiré superlattice system. Then ARPES research results of various moiré superlattice systems are highlighted, including graphene on substrates with small lattice mismatches, twisted graphene/TMD moiré systems, and high‐order moiré superlattice systems. Finally, we discuss on important questions that remain open, challenges in current experimental investigations and present an outlook on this field of research.This article is protected by copyright. All rights reserved

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Layer and orbital interference effects in photoemission from transition metal dichalcogenides

Cited by 15 publications

References 61 publications

Momentum-resolved linear dichroism in bilayerMoS2

Momentum-resolved linear dichroism in bilayerMoS2

Classification of the symmetry of photoelectron dichroism broken by light

Recent Advances in Moiré Superlattice Systems by Angle‐Resolved Photoemission Spectroscopy

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