Hyper‐Raman spectra and frequency dependence of soft mode damping in SrTiO<sub>3</sub>

Денисов, В. Н.; Podobedov, V. B.; Scott, J. F.

doi:10.1002/jrs.1250140413

Cited by 29 publications

(10 citation statements)

References 22 publications

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“…5B) even though the THz driving field spectral content is flat over the soft mode frequency range. A similar shift in spectral weight has been observed in hyper-Raman measurements of bulk STO at higher temperatures and was there attributed to coupling between the TO 1 and TO 2 modes 30 . The combination of excitation with single-cycle THz radiation and ultrafast x-ray diffraction expands the capabilities of THz spectroscopy.…”

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confidence: 78%

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Ultrafast X-ray diffraction probe of terahertz field-driven soft mode dynamics in SrTiO3

Kozina

Driel

Chollet

et al. 2017

Structural Dynamics

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We use ultrafast X-ray pulses to characterize the lattice response of SrTiO3 when driven by strong terahertz fields. We observe transient changes in the diffraction intensity with a delayed onset with respect to the driving field. Fourier analysis reveals two frequency components corresponding to the two lowest energy zone-center optical modes in SrTiO3. The lower frequency mode exhibits clear softening as the temperature is decreased while the higher frequency mode shows slight temperature dependence.

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supporting

confidence: 78%

“…A similar shift in spectral weight has been observed in hyper-Raman measurements of bulk STO at higher temperatures and was there attributed to coupling between the TO 1 and TO 2 modes. 31 …”

mentioning

confidence: 99%

Ultrafast X-ray diffraction probe of terahertz field-driven soft mode dynamics in SrTiO3

Kozina

Driel

Chollet

et al. 2017

Structural Dynamics

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“…# , equation (3b), we neglect any nonlinear terms. Equation It is striking that we observe a response at the 7.6 THz mode because in bulk STO this phonon is silent (neither IR nor Raman active) 36 . Ellipsometry measurements on our thin-film sample at room temperature show no IR activity in this frequency window (see supplement).…”

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confidence: 78%

Terahertz-driven phonon upconversion in SrTiO3

et al. 2019

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Direct manipulation of the atomic lattice using intense long-wavelength laser pulses has become a viable approach to create new states of matter in complex materials. Conventionally, a high frequency vibrational mode is driven resonantly by a mid-infrared laser pulse and the lattice structure is modified through indirect coupling of this infrared-active phonon to other, lower frequency lattice modulations. Here, we drive the lowest frequency optical phonon in the prototypical transition metal oxide SrTiO3 well into the anharmonic regime with an intense terahertz field. We show that it is possible to transfer energy to higher frequency phonon modes through nonlinear coupling. Our observations are carried out by directly mapping the lattice response to the coherent drive field with femtosecond x-ray pulses, enabling direct visualization of the atomic displacements.In many complex condensed matter systems, small changes to the crystal lattice structure can drastically alter electronic properties including conductivity, polarization, orbital, charge, and spin-order 1-6 . Exploration of a phase diagram conventionally requires changing external parameters such as chemical composition, temperature, static pressure, strain or magnetic fields 6-9 . Additionally, optical excitation using ultrashort laser pulses has been used to dynamically change the electronic and crystal structure 2-5,10,11 . This method allows access to nonequilibrium states of matter that show unconventional and unique properties. Recent developments in mid-infrared laser sources have enabled a new route to control material properties: resonant excitation of phonon modes to dynamically alter the lattice structure and phonon-phonon coupling are exploited to coherently control inaccessible (i.e. non-infraredactive) phonon modes 12 . This approach is often dubbed "nonlinear phononics" and requires precisely tuned mid-infrared radiation and impulsive excitation 13 .Here we show a completely novel approach to alter the lattice structure by driving the lowest frequency optical phonon of the incipient ferroelectric SrTiO3 (STO) into the strongly nonlinear regime by using intense broadband terahertz (THz) radiation. Specifically, we demonstrate that it is possible to transfer energy from a low-frequency phonon mode to higherfrequency modes. We anticipate that our approach will open up a deeper understanding of quantum materials through direct manipulation of the lattice structure and the utilization of dynamic coupling of vibrational modes. STO has a low-frequency zone-center transverse optical (TO) phonon that is infrared (IR)active and highly temperature dependent [14][15][16] . This so called soft-mode phonon mediates the ferroelectric phase transition in primarily displacive ferroelectrics such as BaTiO3 or PbTiO3 17-19 .In bulk STO, while the soft mode shifts to lower frequencies with decreasing temperature, the system never reaches a ferroelectric state due to quantum fluctuations 20 . The temperature dependence and large anharmonicity make this mode ide...

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“…Compared to the soft modes in standard ferroelectrics such as SrTiO 3 and BaTiO 3 , the magnitude that the A 1 g mode hardens as the temperature is raised is small and in order to see the hardening, ∆ω lattice has to be subtracted. However, the temperature dependent behaviors are similar where the phonon frequencies harden and linewidths broaden as the temperature increases 29,30 . The small magnitude we observed may be due to the energy of the A 1 g mode being comparatively high and the quartic anharmonic term balanced to a large extent by the cubic anharmonic term.…”

Section: Temperature Dependence Of Phonon Energymentioning

confidence: 94%

Understanding the evolution of anomalous anharmonicity in Bi2Te3−xSex

et al. 2017

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Anharmonic effect in thermoelectrics has been a central topic for decades in both condensed matter physics and material science. However, despite the long believed strong and complex anharmonicity in the Bi2Te3−xSex series, experimental verification of anharmonicity and its evolution with doping remains elusive. We fill this important gap with high resolution, temperature dependent Raman spectroscopy in high quality single crystals of Bi2Te3, Bi2Te2Se and Bi2Se3 over the temperature range from 4 K to 293 K. The Klemens's model was employed to explain the renormalization of their phonon linewidths. The phonon energy of Bi2Se3 and Bi2Te3 are analyzed in detail from three aspects, lattice expansion, cubic and quartic anharmonicity. For the first time, we explain the evolution of the anharmonicity in various phonon modes and across the series. In particular we find the interplay between cubic and quartic anharmonicity is governed by their distinct dependence on the phonon density of states, providing insights into anomalous anharmonicity designing of new thermoelectrics.

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Hyper‐Raman spectra and frequency dependence of soft mode damping in SrTiO₃

Cited by 29 publications

References 22 publications

Ultrafast X-ray diffraction probe of terahertz field-driven soft mode dynamics in SrTiO3

Ultrafast X-ray diffraction probe of terahertz field-driven soft mode dynamics in SrTiO3

Terahertz-driven phonon upconversion in SrTiO3

Understanding the evolution of anomalous anharmonicity in Bi2Te3−xSex

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Hyper‐Raman spectra and frequency dependence of soft mode damping in SrTiO3

Cited by 29 publications

References 22 publications

Ultrafast X-ray diffraction probe of terahertz field-driven soft mode dynamics in SrTiO3

Ultrafast X-ray diffraction probe of terahertz field-driven soft mode dynamics in SrTiO3

Terahertz-driven phonon upconversion in SrTiO3

Understanding the evolution of anomalous anharmonicity in Bi2Te3−xSex

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Product

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Hyper‐Raman spectra and frequency dependence of soft mode damping in SrTiO₃