Transparency of graphene and other direct-gap two-dimensional materials

Merthe, Daniel J.; Kresin, Vladimir Z.

doi:10.1103/physrevb.94.205439

Cited by 27 publications

(23 citation statements)

References 19 publications

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“…For our sample used in the main text, the length L ≃ 5µm; The absorption ratio for a monolayer crystal is roughly α ≈ 0.01 [46][47][48]; The relaxation time tao can be estimated from our transport measured electron mobilityĨ CPGE in Fig. 3d of the main text; The measured CPGE currents (Ĩ CPGE ) are ploted in Fig.…”

Section: Experimental Estimation Of the Berry Curvature Dipolementioning

confidence: 99%

Electrically switchable Berry curvature dipole in the monolayer topological insulator WTe2

et al. 2018

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Recent experimental evidence for the quantum spin Hall (QSH) state in monolayer WTe 2 has linked the fields of twodimensional materials and topological physics [1][2][3][4][5][6][7] . This twodimensional topological crystal also displays unconventional spin-torque 8 and gate-tunable superconductivity 7 . Whereas the realization of the QSH has demonstrated the nontrivial topology of the electron wavefunctions of monolayer WTe 2 , the geometrical properties of the wavefunction, such as the Berry curvature 9 , remain unstudied. Here we utilize mid-infrared optoelectronic microscopy to investigate the Berry curvature in monolayer WTe 2 . By optically exciting electrons across the inverted QSH gap, we observe an in-plane circular photogalvanic current even under normal incidence. The application of an out-of-plane displacement field allows further control of the direction and magnitude of the photocurrent. The observed photocurrent reveals a Berry curvature dipole that arises from the nontrivial wavefunctions near the inverted gap edge. The Berry curvature dipole and strong electric field effect are enabled by the inverted band structure and tilted crystal lattice of monolayer WTe 2 . Such an electrically switchable Berry curvature dipole may facilitate the observation of a wide range of quantum geometrical phenomena such as the quantum nonlinear Hall 10,11 , orbital-Edelstein 12 and chiral polaritonic effects 13,14 . One of the early landmarks of condensed matter physics was the classification of metals, insulators and semiconductors by studying the energy-momentum dispersion-or band structure-of the electrons in crystalline solids. Despite this remarkable success, the quantum nature of the electron states means that they can only be fully described by their quantum wavefunctions, whereas the band structure concerns only the energy and momentum eigenvalues of the wavefunctions. Therefore, a central question in modern condensed matter physics is whether there exist new phenomena that arise from other properties of quantum wavefunctions beyond the band structure 9 . For instance, the study of the global-or topological-properties of electronic wavefunctions continues to give rise to novel topological phases, including the QSH states, three-dimensional topological insulators and Weyl semimetals. These topological materials feature robust surface states and often exhibit protected transport and optical responses. Another direction is to study the local-or geometrical-properties of wavefunctions. One important property is the local curvature of the wavefunction, defined as the Berry curvature. Originally employed to explain the anomalous Hall conductivities of ferromagnets 9 , the importance of the Berry curvature is increasingly recognized in a wide range of areas in condensed matter physics, including nonlocal transport and chiral optical responses in noncentrosymmetric metals and semiconductors [10][11][12][15][16][17][18][19][20] , unconventional pairing in superconductors 21 , and topological plasmonic and excitonic ...

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Section: Experimental Estimation Of the Berry Curvature Dipolementioning

confidence: 99%

Electrically switchable Berry curvature dipole in the monolayer topological insulator WTe2

et al. 2018

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“…A variety of experiments confirm [9,10,11,12,13] that the measured transmittance is indeed compatible with the effective single-particle model of relativistic Dirac fermions in graphene. A number of different theoretical works have exploited this fact to calculate the light absorption rate in graphene from a "relativistic" quantum electrodynamics perspective [14,15,16,17,18,19,20,21,22]. An interesting question that remains open is up to what extent this effective model is valid in the representation of this optical property, since it arises from a tight-binding microscopic atomistic model that involves only the nearest neighbor hopping.…”

Section: Introductionmentioning

confidence: 99%

Optical conductivity and transparency in an effective model for graphene

et al. 2018

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Motivated by experiments confirming that the optical transparency of graphene is defined through the fine structure constant and that it could be fully explained within the relativistic Dirac fermions in 2D picture, in this article we investigate how this property is affected by next-to-nearest neighbor coupling in the low-energy continuum description of graphene. A detailed calculation within the linear response regime allows us to conclude that, somewhat surprisingly, the zero-frequency limit of the optical conductivity that determines the transparency remains robust up to this correction.

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“…where α is the fine structure constant [8,44]. This transparency condition is a unique feature from twodimensional materials, and our composite material shows similar characteristics.…”

Section: Transmittance Reflectance and Absorptance Of The Effectmentioning

confidence: 66%

Tunable Optical Responses of a Graphene-Gold Nanoparticle Composite for Visible Light

Cheon¹,

Lee

Baik

et al. 2017

New Physics: Sae Mulli

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Applying Maxwell-Garnett' s effective medium model, we theoretically study the optical properties of graphene with gold nanoparticles as a function of the particle volume fraction, size of the particles, chemical potential, and temperature. To account for the visible spectrum at energies less than 3 eV, we consider up to the second order of the optical conductivity calculated using the tightbinding model. Randomly distributed gold nanoparticles have a strong influence on the optical responses of graphene, such as its absorption, reflection, and transmission, thus allowing enhanced optoelectronic properties. We find that the composite can be made to serve as a potential tunable photonic material for a reflective optical modulator by controlling the local plasmonic resonance of the nanoparticle, volume fraction, and chemical potential.

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Transparency of graphene and other direct-gap two-dimensional materials

Cited by 27 publications

References 19 publications

Electrically switchable Berry curvature dipole in the monolayer topological insulator WTe2

Electrically switchable Berry curvature dipole in the monolayer topological insulator WTe2

Optical conductivity and transparency in an effective model for graphene

Tunable Optical Responses of a Graphene-Gold Nanoparticle Composite for Visible Light

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