Strong nonlinear terahertz response induced by Dirac surface states in Bi2Se3 topological insulator

Giorgianni, F.; Chiadroni, E.; Rovere, Andrea; Guidi, M. Cestelli; Perucchi, A.; Bellaveglia, M.; Castellano, M.; Giovenale, D. Di; Pirro, Giampiero Di; Ferrario, M.; Pompili, R.; Vaccarezza, C.; Villa, F.; Cianchi, A.; Mostacci, A.; Petrarca, M.; Brahlek, Matthew; Koirala, Nikesh; Oh, Seongshik; Lupi, S.

doi:10.1038/ncomms11421

Cited by 146 publications

(111 citation statements)

References 57 publications

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“…Interestingly, we find this EQ response is intrinsically sensitive to the electron-hole symmetry of the band structure, becoming strictly zero at the charge neutral point. The understanding derived here is readily applicable to other related Dirac materials such as topological insulators [27], Dirac andWeyl semimetals [28]. Therefore, graphene provides a unique platform for investigating unusual nonlinear optical phenomena, which not only can expand the horizon of nonlinear optics in quantum materials, but also has a large potential in novel device applications [33,34].…”

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confidence: 76%

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Doping-Induced Second-Harmonic Generation in Centrosymmetric Graphene from Quadrupole Response

et al. 2019

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For centrosymmetric materials such as monolayer graphene, no optical second harmonic generation (SHG) is generally expected because it is forbidden under the electric-dipole approximation. Yet we observed a strong, doping induced SHG from graphene, with its highest strength comparable to the electric-dipole allowed SHG in non-centrosymmetric 2D materials. This novel SHG has the nature of an electric-quadrupole response, arising from the effective breaking of inversion symmetry by optical dressing with an in-plane photon wave vector. More remarkably, the SHG is widely tuned by carrier doping or chemical potential, being sharply enhanced at Fermi edge resonances, but vanishing at the charge neutral point that manifests the electron-hole symmetry of massless Dirac Fermions. The striking behavior in graphene, which should also arise in graphene-like Dirac materials, expands the scope of nonlinear optics, and holds the promise of novel optoelectronic and photonic applications. 3 Second harmonic generation (SHG) is the most fundamental second-order nonlinear optical process, described by ( ) ( ) ( ) ( ) ( ) [1]. In this process, the output signal is frequency doubled from the incident photon field of ( ).Here, ( ) ( ) is the rank-three nonlinear susceptibility tensor and depends on the incident frequency and photon wave vector q. Since q is typically small, a Taylorthe leading electric-dipole (ED) term, and ( ) ( ) is the often neglected electric-quadrupole/ magnetic-dipole term [1,2] or the EQ response for simplicity. For the electric-dipole allowed SHG to exist, the breaking of inversion symmetry is essential. Hence, SHG is a sensitive probe to symmetry-governed phenomena such as ferroelectricity [3], valley pseudospin [4], and phase transitions [5]. For 2D materials such as hexagonal boron nitride, transition metal dichalcogenide and monochalcogenide, their atomic lattices in monolayer form are non-centrosymmetric, giving rise to the electric-dipole allowed SHG. In fact, SHG has become an indispensable tool to characterize their crystal orientation, stacking symmetry and electronic features [6-10]. Yet for an isolated monolayer graphene, it is centrosymmetric and no electric-dipole SHG is allowed. The third-order optical nonlinearity such as third-harmonic generation [11-15] and four-wave mixing [14,16] was often regarded as the dominant nonlinear process in graphene. Only weak SHG was observed on supported monolayers, which was attributed to the inversion symmetry breaking by the underlying substrate [17] or an in-plane electric current [18,19]. Therefore, graphene provides a 4 unique platform to study unusual SHG responses such as valley polarization induced SHG [20,21] and the EQ response beyond the electric-dipole approximation [22,23], as theoretically proposed. In this work, we exclusively investigate the EQ response of SHG in graphene by introducing an in-plane photon wave vector at oblique incidence, which effectively break the overall inversion symmetry of the system [22-25]. By comparing with the SHG respo...

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confidence: 78%

Doping-Induced Second-Harmonic Generation in Centrosymmetric Graphene from Quadrupole Response

et al. 2019

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“…The electronic surface states of TIs consist of gapless bands characterized by a linear (Dirac) dispersion, which are protected from backscattering by time reversal symmetry [1,2]. In recent years, these novel materials have attracted significant interest, not only due to their unique electronic properties, but also because they hold promise for applications in quantum computing [2,3] and spintronic [4], as well as terahertz detection [5], thermoelectric [6] and tunable nonlinear optical devices [7].…”

Section: Introductionmentioning

confidence: 99%

Surface phonons in the topological insulators Bi2Se3 and Bi2Te3

Boulares

Shi

Kioupakis

et al. 2018

Solid State Communications

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Bi2Se3 and Bi2Te3 show features in the range ~ 50-160 cm -1 , which have been assigned alternatively to Raman-forbidden, bulk infrared modes arising from symmetry breaking at the surface or to surface phonons, which couple to the topologically protected electronic states. Here, we present temperature-and wavelength-dependent Raman studies showing additional modes we ascribe to surface phonons in both Bi2Se3 and Bi2Te3. Our assignment is supported by density functional theory calculations revealing surface phonons at frequencies close to those of the extra peaks in the Raman data. The theoretical results also indicate that these modes are not a consequence of spin-orbit coupling and, thus, that their occurrence is unrelated to the topological properties of these materials.1 | P a g e I. INTRODUCTIONTopological insulators (TIs) are a new class of materials that are insulating in the bulk but exhibit metallic surfaces, which arise from strong spin-orbit coupling and particular properties of their band structure. The electronic surface states of TIs consist of gapless bands characterized by a linear (Dirac) dispersion, which are protected from backscattering by time reversal symmetry [1,2]. In recent years, these novel materials have attracted significant interest, not only due to their unique electronic properties, but also because they hold promise for applications in quantum computing [2,3] Bi2Se3 and Bi2Te3 are layered compounds, which have been extensively studied in the past due to their exceptional thermoelectric properties [8]. They were also among the first compounds identified as three-dimensional TIs [9,10,11,12]. Because of its crucial relevance to their surface conductivity properties, the study of electron-phonon coupling [13] and, moreover, the search for vibrations localized at the surface have been the subject of many studies in recent years [14,15,16,17]. In particular, inelastic helium scattering [14,15], surface enhanced Raman scattering [16] and time-resolved photoemission measurements [17] in Bi2Se3 and Bi2Te3 show features that were attributed to surface modes as well as strong electron-phonon coupling at the surface.Also, weak features observed in Raman spectra were attributed to surface effects unrelated to the topological surface states [18].Here, we present experimental results on the temperature-and excitation-wavelength (λL−) dependence of Raman scattering, as well as first-principles phonon calculations for bulk and fewquintuple-layer Bi2Se3 and Bi2Te3. Other than the expected, and previously reported Raman-active bulk modes [19,20], we find weak peaks at low temperatures in both compounds, which we ascribe 2 | P a g e to surface vibrational modes. Density functional theory calculations, which do not consider spinorbit coupling, support such an assignment in that they reveal a pair of surface-modes, the lowerfrequency of which is very close in frequency with the peaks found in the Raman experiments.Arguments are also given suggesting that spin-orbit effects are not important in determi...

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“…have ignited intensive interest due to their novel electronic and photonic properties, which are distinct from those of their bulk counterparts, such as defectfree topological transport [1][2][3] , linear dichorism 4,5 , superconductivity 6,7 , and plasmonics 8,9 . It has been proved experimentally that few-layer 2D materials can strongly interact with light 10,11 , which indicates they are promising materials with great potential in optoelectronic devices for communication, sensing, and imaging, particularly in the visible and near-infrared range.…”

Section: Introductionmentioning

confidence: 99%

Towards sensitive terahertz detection via thermoelectric manipulation using graphene transistors

Liu

Tang

et al. 2018

NPG Asia Mater

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Graphene has been highly sought after as a potential candidate for hot-electron terahertz (THz) detection benefiting from its strong photon absorption, fast carrier relaxation, and weak electron-phonon coupling. Nevertheless, to date, graphene-based thermoelectric THz photodetection is hindered by low responsivity owing to relatively low photoelectric efficiency. In this work, we provide a straightforward strategy for enhanced THz detection based on antenna-coupled CVD graphene transistors with the introduction of symmetric paired fingers. This design enables switchable photodetection modes by controlling the interaction between the THz field and free hot carriers in the graphene-channel through different contacting configurations. Hence a novel "bias-field effect" can be activated, which leads to a drastic enhancement in THz detection ability with maximum responsivity of up to 280 V/W at 0.12 THz relative to the antenna area and a Johnson-noise limited minimum noise-equivalent power (NEP) of 100 pW/Hz 0.5 at room temperature. The mechanism responsible for the enhancement in the photoelectric gain is attributed to thermophotovoltaic instead of plasma self-mixing effects. Our results offer a promising alternative route toward scalable, wafer-level production of high-performance graphene detectors.

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Strong nonlinear terahertz response induced by Dirac surface states in Bi2Se3 topological insulator

Cited by 146 publications

References 57 publications

Doping-Induced Second-Harmonic Generation in Centrosymmetric Graphene from Quadrupole Response

Doping-Induced Second-Harmonic Generation in Centrosymmetric Graphene from Quadrupole Response

Surface phonons in the topological insulators Bi2Se3 and Bi2Te3

Towards sensitive terahertz detection via thermoelectric manipulation using graphene transistors

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