In situ Raman spectroscopy of topological insulator Bi2Te3 films with varying thickness

Wang, Chunxiao; Zhu, Xie-Gang; Nilsson, Line; Wen, Jing; Wang, Guang; Shan, Xinyan; Zhang, Qing; Zhang, Shulin; Jia, Jin‐Feng; Xue, Qi‐Kun

doi:10.1007/s12274-013-0344-4

Cited by 81 publications

(84 citation statements)

References 19 publications

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“…The peak we attribute to a surface phonon is the weak feature which appears between the 2 and 1 2 modes at 159 cm -1 and 114 cm -1 for Bi2Se3 and Bi2Te3, respectively. This peak has been previously observed in thin films and few-monolayer samples of both compounds [16,18,31,32,33,34,35,36,37,38,39] and in single crystals of Bi2Se3 [39,40], but never 4 | P a g e before in bulk Bi2Te3. Note that these prior studies detected numerous other weak features in both compounds that were not observed in the present work.…”

supporting

confidence: 63%

“…The observation of extra Raman lines and, in particular, the lines we assign to surface phonons have been prevalently attributed in the literature to surface-induced symmetry breaking, which seemingly allows for scattering of nominally Raman forbidden, infrared-active modes [18,31,32,33,34,35,36,38,40]. For various reasons, we find such an interpretation to be incorrect.…”

Section: P a G Ementioning

confidence: 69%

“…Their origin remains controversial. Spectra of few-monolayer Bi2Te3 show lines at ~ 93 cm −1 and 114 cm −1 [18,31,32,33,34,35] and at ~ 160 cm −1 in Bi2Se3 [36,37], which were assigned to Raman-forbidden, infrared modes resulting from surface-induced symmetry breaking, while thin-film studies of Bi2Te3 reveal five additional peaks, one of which, at ~ 93 cm -1 , was assigned to a surface mode [38]. In bulk, single crystal of Bi2Se3, additional peaks at 68, 125, 129 and 160 cm -1 were observed and also assigned to Raman-forbidden polar modes [40].…”

mentioning

confidence: 99%

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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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supporting

confidence: 63%

Section: P a G Ementioning

confidence: 69%

mentioning

confidence: 99%

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Surface phonons in the topological insulators Bi2Se3 and Bi2Te3

Boulares

Shi

Kioupakis

et al. 2018

Solid State Communications

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“…In contrast to the blue-shift of the A 1g 1 and E g 2 modes, the Raman frequencies of the A 1g 2 peak exhibit a red-shift with the PDP value about À1.78 cm À1 /%. The red-shift of the out-of-plane 28 The FWHM of both A 1g 1 and E g 2 modes remains almost unchanged, implying that the phononÀphonon scattering stays the same (Figure 4d). Usually, the vibrational peaks broaden when contributions from tensile strain at outer surface and compressive strain at inner surface add up.…”

Section: Resultsmentioning

confidence: 95%

“…As expected, these modes soften with decreasing thickness, which is consistent with theoretical predictions. 25,26,28,32 In addition, a strong anisotropic behavior is observed for bent Bi 2 Se 3 nanoribbon, due to the two structurally different facets, the {0001} and the {0115} surface, of Bi 2 Se 3 nanoribbons grown along the AE1120ae direction. 33À36 Only when the nanoribbon is bent along the AE1120ae direction with the curved {0001} surface perpendicular to the substrate plane and with the exposed {0115} top surface do the frequencies of in-plane E g 2 and out-of-plane A 1g 1 modes exhibit a linear blue-shift with increasing strain, which is also strongly thickness dependent.…”

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confidence: 99%

Surface-Facet-Dependent Phonon Deformation Potential in Individual Strained Topological Insulator Bi₂Se₃ Nanoribbons

et al. 2015

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Strain is an important method to tune the properties of topological insulators. For example, compressive strain can induce superconductivity in Bi2Se3 bulk material. Topological insulator nanostructures are the superior candidates to utilize the unique surface states due to the large surface to volume ratio. Therefore, it is highly desirable to monitor the local strain effects in individual topological insulator nanostructures. Here, we report the systematical micro-Raman spectra of single strained Bi2Se3 nanoribbons with different thicknesses and different surface facets, where four optical modes are resolved in both Stokes and anti-Stokes Raman spectral lines. A striking anisotropy of the strain dependence is observed in the phonon frequency of strained Bi2Se3 nanoribbons grown along the ⟨112̅0⟩ direction. The frequencies of the in-plane Eg(2) and out-of-plane A1g(1) modes exhibit a nearly linear blue-shift against bending strain when the nanoribbon is bent along the ⟨112̅0⟩ direction with the curved {0001} surface. In this case, the phonon deformation potential of the Eg(2) phonon for 100 nm-thick Bi2Se3 nanoribbon is up to 0.94 cm(–1)/%, which is twice of that in Bi2Se3 bulk material (0.52 cm(–1)/%). Our results may be valuable for the strain modulation of individual topological insulator nanostructures.

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Manipulating Spin‐Lattice Coupling in Layered Magnetic Topological Insulator Heterostructure via Interface Engineering

Maity,

Dey,

Ghosh

et al. 2024

Adv Funct Materials

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Induced magnetic order in a topological insulator (TI) can be realized either by depositing magnetic adatoms on the surface of a TI or engineering the interface with epitaxial thin film or stacked assembly of 2D van der Waals (vdW) materials. Herein, the observation of spin‐phonon coupling in the otherwise non‐magnetic TI Bi2Te3 is reported, due to the proximity of FePS3 (an antiferromagnet (AFM), TN ≈ 120 K), in a vdW heterostructure framework. Temperature‐dependent Raman spectroscopic studies reveal deviation from the usual phonon anharmonicity originated from spin‐lattice coupling at the Bi2Te3/FePS3 interface at/below 60 K in the peak position (self‐energy) and linewidth (lifetime) of the characteristic phonon modes of Bi2Te3 (106 and 138 cm−1) in the stacked heterostructure. The Ginzburg‐Landau (GL) formalism, where the respective phonon frequencies of Bi2Te3 couple to phonons of similar frequencies of FePS3 in the AFM phase, is adopted to understand the origin of the hybrid magneto‐elastic modes. At the same time, the reduction of characteristic TN of FePS3 from 120 K in isolated flakes to 65 K in the heterostructure, possibly due to the interfacial strain, which leads to smaller Fe‐S‐Fe bond angles as corroborated by computational studies using density functional theory (DFT). Besides, inserting hexagonal boron nitride within Bi2Te3/FePS3 stacking regains the anharmonicity in Bi2Te3. Controlling interfacial spin‐phonon coupling in stacked heterostructure can have potential application in surface code spin logic devices.

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In situ Raman spectroscopy of topological insulator Bi2Te3 films with varying thickness

Cited by 81 publications

References 19 publications

Surface phonons in the topological insulators Bi2Se3 and Bi2Te3

Surface phonons in the topological insulators Bi2Se3 and Bi2Te3

Surface-Facet-Dependent Phonon Deformation Potential in Individual Strained Topological Insulator Bi₂Se₃ Nanoribbons

Manipulating Spin‐Lattice Coupling in Layered Magnetic Topological Insulator Heterostructure via Interface Engineering

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In situ Raman spectroscopy of topological insulator Bi2Te3 films with varying thickness

Cited by 81 publications

References 19 publications

Surface phonons in the topological insulators Bi2Se3 and Bi2Te3

Surface phonons in the topological insulators Bi2Se3 and Bi2Te3

Surface-Facet-Dependent Phonon Deformation Potential in Individual Strained Topological Insulator Bi2Se3 Nanoribbons

Manipulating Spin‐Lattice Coupling in Layered Magnetic Topological Insulator Heterostructure via Interface Engineering

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Surface-Facet-Dependent Phonon Deformation Potential in Individual Strained Topological Insulator Bi₂Se₃ Nanoribbons