Observation of an Amplitude Collapse and Revival of Chirped Coherent Phonons in Bismuth

Misochko, O. V.; Hase, Muneaki; Ishioka, Kunie; Kitajima, Masahiro

doi:10.1103/physrevlett.92.197401

Cited by 90 publications

(81 citation statements)

References 13 publications

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“…Further, collapse and revival of chirped coherent phonon oscillations were observed in the reflectivity data when the carrier density was increased further beyond a critical carrier density levels (3.5 × at 296K) [13]. This behavior was explained in terms of dynamics of a phonon wave packet in an anharmonic potential, where the packet periodically breaks up and revives to its original form, implying a nonclassical dynamics.…”

Section: Introductionmentioning

confidence: 91%

“…This linear sweep in the frequency with the pump-probe time delay, termed as phonon chirping, originates from the rapid change of photoexcited carrier density across the sample thickness due to carrier diffusion resulting in different amounts of phonon renormalization [10]. In case of a semimetal, bismuth [12,13] at carrier density of ∼ 3 × 10…”

Section: Introductionmentioning

confidence: 99%

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Temperature-dependent chirped coherent phonon dynamics in Bi ₂ Te ₃ using high-intensity femtosecond laser pulses

Kamaraju¹,

Kumar²,

Sood³

2010

EPL

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Degenerate pump-probe reflectivity experiments have been performed on a single crystal of bismuth telluride (Bi 2 Te 3 ) as a function of sample temperature (3K to 296K) and pump intensity using ∼ 50 femtosecond laser pulses with central photon energy of 1.57 eV. The time resolved reflectivity data show two coherently generated totally symmetric A 1g modes at 1.85 THz and 3.6THz at 296K which blue shift to 1.9 THz and 4.02 THz, respectively at 3K. At high photoexcited carrier density of ∼ 1.7 × 10 21 cm −3 , the phonon mode at 4.02 THz is two orders of magnitude higher positively chirped (i.e the phonon time period decreases with increasing delay time between the pump and the probe pulses) than the lower frequency mode at 1.9 THz. The chirp parameter, β is shown to be inversely varying with temperature. The time evolution of these modes is studied using continuous wavelet transform of the time-resolved reflectivity data.

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Section: Introductionmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Temperature-dependent chirped coherent phonon dynamics in Bi ₂ Te ₃ using high-intensity femtosecond laser pulses

Kamaraju¹,

Kumar²,

Sood³

2010

EPL

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“…A prototype sample has been crystalline bismuth [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], which shows strong oscillations in time-resolved reflectivity due to coherent oscillations of the A 1g optical phonon mode that are initiated upon excitation with a femtosecond laser pulse [9]. Measurements in bismuth motivated the development of the displacive excitation of coherent phonons (DECP) model of the lattice response to ultrafast optical absorption, in which sudden excitation of electrons from the valence to the conduction band leads to a nearly instantaneous alteration of the lattice potential energy surface.…”

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confidence: 99%

Carrier confinement and bond softening in photoexcited bismuth films

et al. 2015

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Femtosecond pump-probe spectroscopy of bismuth thin films has revealed strong dependencies of reflectivity and phonon frequency on film thickness in the range of 25−40 nm. The reflectivity variations are ascribed to distinct electronic structures originating from strongly varying electronic temperatures and proximity of the film thickness to the optical penetration depth of visible light. The phonon frequency is redshifted by an amount that increases with decreasing film thickness under the same excitation fluence, indicating carrier density-dependent bond softening that increases due to suppressed diffusion of carriers away from the photoexcited region in thin films. The results have significant implications for nonthermal melting of bismuth as well as lattice heating due to inelastic electron-phonon scattering. [4,5]. A prototype sample has been crystalline bismuth [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], which shows strong oscillations in time-resolved reflectivity due to coherent oscillations of the A 1g optical phonon mode that are initiated upon excitation with a femtosecond laser pulse [9]. Measurements in bismuth motivated the development of the displacive excitation of coherent phonons (DECP) model of the lattice response to ultrafast optical absorption, in which sudden excitation of electrons from the valence to the conduction band leads to a nearly instantaneous alteration of the lattice potential energy surface. Hase et al. discovered that the frequency of the A 1g mode in bismuth is redshifted with increasing excitation fluence and is chirped, gradually increasing in frequency with time following excitation [12]. Murray and coworkers showed that the phonon frequency reduction is due to carrier density-dependent softening of the lattice potential, and that photocarrier relaxation dynamics are responsible for the vibrational frequency chirp [13]. More recently, Fritz et al. conducted density functional theory (DFT) calculations of the lattice potential, and results were consistent with bond softening as a function of carrier density [16]. The calculations further showed that increasing carrier density reduces the Peierls distortion continuously and removes the distortion completely at about 2.7% excitation of the valence electrons, indicating that bismuth may undergo a photoinduced structural phase transition to a higher symmetry phase. The experimental and theoretical results reveal that the lattice structure and interatomic forces are influenced heavily by the carrier density, which varies in space and time due to the short (15 nm) optical penetration depth into the sample and the dynamics of carrier diffusion and recombination. In this paper, we investigate the effect of carrier diffusion and spatial distribution on ultrafast bond softening in highly photoexcited bismuth. To this end, we performed transient reflectivity experiments on bulk and thin-film bismuth samples. The results show distinct changes in both the transient reflectivity sign and magnitude and in the coheren...

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“…For example, squeezed optical fields can be produced by parametric amplification or four-wave mixing. Recently, there has been interest in extending the study of nonclassical fields to lattice vibrations in condensed matter but except for a few studies of squeezing, [7][8][9][10][11][12] and amplitude collapse and revival, 13 there has been relatively little work on phonon fields. Squeezing of phonons generated by secondorder Raman scattering was predicted 7 and later reported 9,11 in low temperature, femtosecond pump-probe transmission measurements on KTaO 3 .…”

mentioning

confidence: 99%

Absence of phase-dependent noise in time-domain reflectivity studies of impulsively excited phonons

Hussain

Andrews

2010

Phys. Rev. B

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There have been several reports of phase-dependent noise in time-domain reflectivity studies of optical phonons excited by femtosecond laser pulses in semiconductors, semimetals, and superconductors. It was suggested that such behavior is associated with the creation of squeezed phonon states although there is no theoretical model that directly supports such a proposal. We have experimentally re-examined the studies of phonons in bismuth and gallium arsenide, and find no evidence of any phase-dependent noise signature associated with the phonons. We place an upper limit on any such noise at least 40-50 dB lower than previously reported. DOI: 10.1103/PhysRevB.81.224304 PACS number͑s͒: 78.47.jg, 63.20.Ϫe, 42.50.Lc Coherent phonons in semiconductors, superconductors, metals, and insulators have been widely studied in the time domain since the first report of their excitation by femtosecond laser pulses in about 1990.1,2 The most general excitation mechanism is impulsive stimulated Raman scattering ͑ISRS͒.3 A special case of ISRS in opaque materials is sometimes referred to as the displacive mechanism 1 and is associated with electronic excitation from bonding to antibonding orbitals. Longitudinal optical phonons in semiconductors can also be driven by the transient polarization associated with the screening of surface space-charge fields following interband excitation. 2The amplitude of a phonon mode may be decomposed into two quadrature components with the time dependences cos t and sin t. In a coherent state, the closest quantum counterpart to a classical field, the fluctuations in the two quadratures have the same variance and are randomly distributed in phase. The product of the variances in each quadrature is the minimum allowed by the Heisenberg uncertainty principle. Minimum uncertainty states in which the fluctuations in one quadrature have a variance that falls below the zero-point quantum noise level are called squeezed states. 4 Squeezed electromagnetic fields were experimentally studied for the first time in the mid-1980s ͑Ref. 5͒ and nonclassical light is now an established area of research.6 A phasedependent nonlinear process is necessary to generate a squeezed state. For example, squeezed optical fields can be produced by parametric amplification or four-wave mixing. Recently, there has been interest in extending the study of nonclassical fields to lattice vibrations in condensed matter but except for a few studies of squeezing, 7-12 and amplitude collapse and revival, 13 there has been relatively little work on phonon fields. Squeezing of phonons generated by secondorder Raman scattering was predicted 7 and later reported 9,11 in low temperature, femtosecond pump-probe transmission measurements on KTaO 3 . In this case the mechanism is a three-phonon parametric process analogous to that used to produce coherent two-photon states. This type of experiment has been extended to the creation of coexcited coherent and squeezed vibrations 10 and to squeezed spin waves 14 in MnF 2 but in no case has the...

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Observation of an Amplitude Collapse and Revival of Chirped Coherent Phonons in Bismuth

Cited by 90 publications

References 13 publications

Temperature-dependent chirped coherent phonon dynamics in Bi ₂ Te ₃ using high-intensity femtosecond laser pulses

Temperature-dependent chirped coherent phonon dynamics in Bi ₂ Te ₃ using high-intensity femtosecond laser pulses

Carrier confinement and bond softening in photoexcited bismuth films

Absence of phase-dependent noise in time-domain reflectivity studies of impulsively excited phonons

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Observation of an Amplitude Collapse and Revival of Chirped Coherent Phonons in Bismuth

Cited by 90 publications

References 13 publications

Temperature-dependent chirped coherent phonon dynamics in Bi 2 Te 3 using high-intensity femtosecond laser pulses

Temperature-dependent chirped coherent phonon dynamics in Bi 2 Te 3 using high-intensity femtosecond laser pulses

Carrier confinement and bond softening in photoexcited bismuth films

Absence of phase-dependent noise in time-domain reflectivity studies of impulsively excited phonons

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Temperature-dependent chirped coherent phonon dynamics in Bi ₂ Te ₃ using high-intensity femtosecond laser pulses

Temperature-dependent chirped coherent phonon dynamics in Bi ₂ Te ₃ using high-intensity femtosecond laser pulses