Ultrafast carrier and phonon dynamics in Bi2Se3 crystals

Qi, J.; Chen, X.; Yu, Wenlong; Cadden-Zimansky, Paul; Smirnov, Dmitry; Tolk, N. H.; Miotkowski, I.; Cao, Helin; Chen, Y. P.; Wu, Y. Z.; Qiao, Shuang; Jiang, Zhigang

doi:10.1063/1.3513826

Applied Physics Letters

2010

DOI: 10.1063/1.3513826

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Ultrafast carrier and phonon dynamics in Bi2Se3 crystals

J. Qi

X. Chen

Wenlong Yu

et al.

Abstract: Ultrafast time-resolved differential reflectivity of Bi 2 Se 3 crystals is studied using optical pump-probe spectroscopy. Three distinct relaxation processes are found to contribute to the initial transient reflectivity changes. The deduced relaxation timescale and the sign of the reflectivity change suggest that electron-phonon interactions and defect-induced charge trapping are the underlying mechanisms for the three processes. After the crystal is exposed to air, the relative strength of these processes is … Show more

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Cited by 131 publications

(138 citation statements)

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“…2(b)]. The resulting frequency corresponds to longitudinal optical (LO) phonons excited in bulk Bi 2 Se 3 , 11,16,17 implying that the cooling of photoexcited hot carriers in thick films occurs through the electron-LO-phonon scattering (Fröhlich interaction). Once the thickness of films decreases, the oscillatory part of the TR signals disappears and  D1 approaches the minimal value of ~ 1.5 ps (6-nm film) [Inset in Fig.…”

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confidence: 99%

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Ultrafast carrier dynamics in thin-films of the topological insulator Bi2Se3

Glinka¹,

Babakiray²,

Johnson³

et al. 2013

Applied Physics Letters

108

213

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Transient reflectivity measurements of thin films, ranging from 6 to 40 nm in thickness, of the topological insulator Bi 2 Se 3 revealed a strong dependence of the carrier relaxation time on the film thickness. For thicker films the relaxation dynamics are similar to those of bulk Bi 2 Se 3 , where the contribution of the bulk insulating phase dominates over that of the surface metallic phase. The carrier relaxation time shortens with decreasing film thickness, reaching values comparable to those of noble metals. This effect may result from the hybridization of Dirac cone states at the opposite surfaces for the thinnest films.Topological insulators (TIs) are novel electronic materials that have an insulator-type band gap in the bulk (for Bi 2 Se 3 E g ~ 0.3 eV) but have protected gapless conducting phase on their surface due to the combination of spin-orbit interactions and time-reversal symmetry. 1,2 The most effective experimental methods currently used to monitor metallic two-dimensional (2D) Dirac surface states (SS) of TIs are angle-resolved photoemission spectroscopy (ARPES) and time-resolved ARPES (TrARPES). 1-7 These techniques are equally sensitive to SS and the bulk atoms residing in the close proximity to the surface as a consequence of the extremely small penetration depth (a few nm) of incident energetic photons used for photoemission, combined with the limited escape depth of the electrons (also a few nm). Finite-size effects have also been studied for thin Bi 2 Se 3 films of only a few nm thick and a crossover of the three-dimensional (3D) TI Bi 2 Se 3 to the 2D limit (gapped SS) has been observed when the thickness is below six quintuple layers (~ 6 nm). 8 Reaching a similar sensitivity to SS using traditional optical pump-probe techniques (like transient reflectivity (TR)/transmission), which use less energetic photons in the visible/infrared range, seems problematic since the absorption length of the laser light normally used for these measurements (a few tens of nm) significantly exceeds the range where the effect of SS can actually be monitored. As a result, for bulk single crystals of Bi 2 Se 3 the transient optical response is dominated by the bulk contribution. To overcome the problem one can use SS/surface sensitive methods. An example of this approach has recently been demonstrated by illuminating Bi 2 Se 3 with circularly polarized near-infrared light. 9 The resulting photocurrent which reverses its direction with a reversal of the helicity of the light unambiguously proves the SS origin of the optical response. Another surface sensitive technique exploits the centrosymmetric nature of TI's, which governs exclusively the surface-related response which results in an optical second harmonic generation (SHG) process. 10,11 In this Letter we report on a new way to distinguish between the contributions from the TI (Bi 2 Se 3 ) bulk 3D states and the 2D gapless SS, which is based on differences in the carrier relaxation rates for the insulating and metallic phases. We demonstrate that the car...

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confidence: 99%

“…For thicker films (40 nm) the decay-time constant of  D1 = 3.11 ps agrees well with those previously reported for Bi 2 Se 3 single crystals. 11,16,17 Furthermore, the thick films have an oscillatory behavior in the TR signals, which can be extracted and fit by a damped cosine function with a frequency of 2.19 THz [ Fig. 2(b)].…”

mentioning

confidence: 99%

Ultrafast carrier dynamics in thin-films of the topological insulator Bi2Se3

Glinka¹,

Babakiray²,

Johnson³

et al. 2013

Applied Physics Letters

108

213

View full text Add to dashboard Cite

show abstract

“…Previously, ultrafast pump-probe spectroscopy has been employed to study the phonon and carrier dynamics in Bi 2 Se 3 (BS) 9,10 , Bi 2 Te 3 (BT) 11,12,13 , Sb 2 Te 3 14 etc. The differential reflectivity measured by pump-probe spectroscopy revealed fast and slow oscillations which have been attributed to surface optical and bulk acoustic phonons respectively 15 . However these claims have not been conclusively substantiated.…”

mentioning

confidence: 99%

“…These fast and slow oscillations are attributed to surface optical and bulk acoustic phonon modes respectively 15 . To confirm, Raman scattering spectra of these samples were taken using blue laser (488 nm) with a power of 6 mW and a magnification of 50×.…”

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confidence: 99%

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Surface optical and bulk acoustic phonons in the topological insulator, Bi2Se2Te

Mukhopadhyay

Chaudhuri

Sarkar

et al. 2015

Applied Physics Letters

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We explore the phonon dynamics in thin films of the topological insulator material Bi 2 Se 2 Te using ultrafast pump-probe spectroscopy. The time resolved differential reflectivity in these films exhibit fast and slow oscillations. We have given a careful analysis of variation of phonon frequency as a function of film thickness, which we attribute to the existence of standing acoustic modes. However, no variation in the frequency of the optical phonon modes was found with film thickness. This indicates that the optical phonons intrinsically belong to the surface of topological insulators. The controllability of acoustic phonons by way of varying the film thickness will have tremendous implications in the application of these materials in low power spintronic device operating at room temperature. Keywords: topological insulators, optical phonons, acoustic phononsThe newly discovered 3D topological insulators (TIs) represent a class of exotic quantum state of matter with an insulating bulk and conducting surface states 1,2 . These conducting surface states exhibit a relativistic energy-momentum dispersion owing to the nontrivial Z 2 topology of the bulk electronic wave-function 3 . As a consequence, these surface states form a Dirac cone between bulk valence band and bulk conduction band which has been confirmed by angle resolved photo-emission spectroscopy (ARPES) studies 4,5 . Additionally, the surface states are "topologically" protected from back-scattering. Helical spin texture due to high spin-orbit interaction, a π Berry phase and the presence of odd number of Dirac cones are responsibe for this topological protection. Furthermore, the constraint of time reversal symmetry ensures that the surface electrons are not scattered from non-magnetic impurities and defect states. Apart from these, TI materials also exhibit interesting magneto-optical properties which arise due to the presence of axionic term 6 . These exciting properties have made TIs a subject of intense research both theoretically as well as experimentally over the past few years. TIs also promise important practical application in quantum computation and low power spintronic device applications 7 .

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Helicity‐Dependent Photovoltaic Effect in Bi₂Se₃ Under Normal Incident Light

Besbas

Banerjee

Son

et al. 2016

Advanced Optical Materials

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Topological insulators (TIs) form a new class of materials with insulating bulk and surface conduction ensured by topologically protected surface states (TPSS). We investigate the impact of the helicity of a normally incident laser beam on the photovoltaic effect in the TI Bi2Se3. The observation of a helicity dependent photovoltaic effect for normally incident light indicates the presence of out-of-plane spin components for some TPSSs due to the hexagonal warping. In addition, fluctuations in the electrostatic potential at the surface locally break the rotational symmetry of the film allowing the helicity dependent photovoltaic effect. Our result suggests that engineering local electrostatic potentials in Bi2Se3 would allow the control of optically generated spin currents, which may be useful for applications in spin-optoelectronics.

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Ultrafast carrier and phonon dynamics in Bi2Se3 crystals

Cited by 131 publications

References 19 publications

Ultrafast carrier dynamics in thin-films of the topological insulator Bi2Se3

Ultrafast carrier dynamics in thin-films of the topological insulator Bi2Se3

Surface optical and bulk acoustic phonons in the topological insulator, Bi2Se2Te

Helicity‐Dependent Photovoltaic Effect in Bi₂Se₃ Under Normal Incident Light

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Ultrafast carrier and phonon dynamics in Bi2Se3 crystals

Cited by 131 publications

References 19 publications

Ultrafast carrier dynamics in thin-films of the topological insulator Bi2Se3

Ultrafast carrier dynamics in thin-films of the topological insulator Bi2Se3

Surface optical and bulk acoustic phonons in the topological insulator, Bi2Se2Te

Helicity‐Dependent Photovoltaic Effect in Bi2Se3 Under Normal Incident Light

Contact Info

Product

Resources

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Helicity‐Dependent Photovoltaic Effect in Bi₂Se₃ Under Normal Incident Light