Raman Study of the Anomalous TO Phonon Structure in GaP with Controlled Isotopic Composition

Widulle, F.; Ruf, T.; Göbel, A.; Schönherr, E.; Cardona, M.

doi:10.1103/physrevlett.82.5281

Cited by 52 publications

(45 citation statements)

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“…In this manner, the DOS can be taken to be independent of the isotopic masses and can be shifted rigidly along the frequency scale so as to obtain the best fit to the experimental widths, thus compensating errors in the ab initio calculations of the dispersion relations. The overall agreement of the measured widths with the calculated ones is excellent, the coupling constant jV 3 j 2 being close to that found for the TO phonons of GaP [13].…”

Section: Ab Initio Calculationssupporting

confidence: 70%

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Dependence of phonon widths on pressure and isotopic mass: ZnO

Serrano

Widulle

Romero

et al. 2003

Physica Status Solidi (b)

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Considerable attention has been devoted recently to the dependence of the widths of the Raman phonons of semiconductors on pressure and on isotopic mass. The dependence on pressure is usually small and monotonic unless the phonon happens to be close to a singularity of the two-phonon density of states (DOS) which determines its width. In the latter case, strong nonmonotonic dependences of the phonon width on pressure and on isotopic mass can appear. We have investigated the E high 2 phonons of ZnO crystals with different isotopes and observed a wide range of FWHM depending on isotopic masses. Ab initio calculations of the two-phonon DOS provide an explanation for this variation of the FWHM: the E high 2 frequency falls on a sharp ridge of the 2-DOS corresponding to combinations of TA and LA phonons. Changes in isotopic mass result in a motion of the E high 2 frequency up and down that ridge which produces the changes in FWHM. These phenomena suggest a decrease of the FWHM with pressure which seems to be present in existing data obtained at 300 K. Similar phenomena are discussed for the E low 2 phonons. Applications of the isotope and pressure techniques to the elucidation of two-phonon spectra will be presented.Introduction Since the pioneering work of Weinstein for GaP [1] it is known that the widths and lineshapes of phonons can, in some cases, be strongly modified by application of pressure. The diamond anvil cell is an excellent tool for such investigations [2] which yield detailed information about the anharmonic decay mechanisms responsible for linewidths and lineshapes. The reason for the drastic lineshape changes observed by Raman spectroscopy in CuCl [3], CuBr [4], GaP [5] and, to a lesser extent Si [6] and CuI [7] is that, in these cases, the anharmonic self-energy is determined by decay into two phonons close to Van Hove singularities at the edge of the Brillouin zone. The fact that the corresponding two-phonon density of states (DOS) has strong singularities near Raman LO (CuBr) or TO (CuCl, GaP) phonons, together with strong anharmonic coupling constants, gives rise to complex lineshapes which are determined not only by the imaginary part but also by the real part of the selfenergy. Similar effects have been observed for the Raman LO phonons in CuBr. In these examples the application of hydrostatic pressure leads to a ''hardening" of the optical modes, which then shift to higher frequencies, and a ''softening" of the transverse acoustic (TA) ones.

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Section: Ab Initio Calculationssupporting

confidence: 70%

“…The vertical lines represent the d-function peaks of the harmonic TO phonons (see Ref. [13] for details).…”

mentioning

confidence: 99%

Dependence of phonon widths on pressure and isotopic mass: ZnO

Serrano

Widulle

Romero

et al. 2003

Physica Status Solidi (b)

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“…18 The anharmonicity constants C 3,4 can either be calculated by using modern ab initio methods 19,20 or evaluated from experimental data available for some anharmonic crystals. [21][22][23][24][25] The above approximation of ⌽ ͑3,4͒ also leads to the k-independent matrix elements m 3 and m 4 = m 4 in Eqs. ͑1͒ and ͑3͒.…”

Section: ͑4͒mentioning

confidence: 95%

“…[21][22][23][24] The used experimental data refers to the decay of a long-wavelength TO phonon into shortwavelength longitudinal-acoustic and transverse-acoustic ͑TA͒ phonons. To adapt the inferred values of V 3 to m 3 in Eqs.…”

Section: ͑4͒mentioning

confidence: 99%

Terahertz response of acoustically driven optical phonons

2010

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The manipulation of transverse-optical ͑TO͒-phonon polaritons and the associated terahertz ͑THz͒ light field by means of an ultrasound acoustic wave is proposed and illustrated by calculating the TO-phonon-mediated THz response of acoustically pumped CuCl and TlCl crystals. We show the high-contrast acoustically induced change in the THz reflectivity and multiple THz Bragg replicas, which are associated with the far-infraredactive TO-phonon resonance driven by the ultrasonic wave. The effect, which stems from phonon anharmonicity and deals with the resonantly enhanced acousto-optical susceptibilities, refers to an operating acoustic intensity I ac ϳ 1 -100 kW/ cm 2 and frequency ac ϳ 0.1-1 GHz. Due to the anomalously small interaction length between the acoustic and optical fields, possible applications of the effect are in THz spectroscopy and THz acousto-optic devices.

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“…However, this quasiparticle approach must be modified whenever accidental degeneracies occur between quasiharmonic phonons and singularities in the two-phonon density of states (DOS). Prior work has found that the line-shapes of the TO(Γ) Raman peaks in GaP, [2,3] CuCl, [4,5] and ZnS [6,7] are profoundly altered by resonant mixing between the TO(Γ) mode and Brillouin Zone boundary (ZB) TA + LA combinations. In fact, this mixing is sufficiently large in CuCl and ZnS at room temperature (RT) and 1 atm.…”

Section: Introductionmentioning

confidence: 99%

Pressure‐Raman study of resonant TO(Γ)–two‐phonon decay processes in ZnS: Comparison of three isotope compositions

Tallman¹,

Serrano²,

Cantarero³

et al. 2004

Physica Status Solidi (b)

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Pressure-Raman studies (to 15 GPa, at 300 K and 16 K) are reported on 64 Zn 34 S, 68Zn 32 S, and natural ZnS to compare the effects of resonant 3-phonon mixing on the TO(Γ) phonons for the different isotope compositions. Under pressure the TO(Γ) Raman profiles exhibit several distinct features, and a sharp Lorentzian TO(Γ) peak eventually emerges at a threshold pressure P Th that differs for each isotope composition. These effects are due to resonant mixing of the TO(Γ) phonon with TA + LA combination modes. Calculations based on a bond-charge model and perturbation theory reproduce the observed pressure variations in the shape and the width of the TO(Γ) peaks. It is shown that these changes relate to singularities in the TA + LA density of states. Mass scaling of the TO(Γ) and TA + LA modes explains the isotope effect on P Th , and leads to the estimate γ LA(W) ∼1.2.

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Raman Study of the Anomalous TO Phonon Structure in GaP with Controlled Isotopic Composition

Cited by 52 publications

References 10 publications

Dependence of phonon widths on pressure and isotopic mass: ZnO

Dependence of phonon widths on pressure and isotopic mass: ZnO

Terahertz response of acoustically driven optical phonons

Pressure‐Raman study of resonant TO(Γ)–two‐phonon decay processes in ZnS: Comparison of three isotope compositions

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