Giant ultrafast photo-induced shear strain in ferroelectric BiFeO3

Abstract

Generation of strain using light is a key issue for future development of ultrasonic devices. Up to now, photo-induced GHz-THz acoustic phonons have been mainly explored in metals and semiconductors, and in artificial nanostructures to enhance their phononic emission. However, despite their inherent strong polarization (providing natural asymmetry) and superior piezoelectric properties, ferroelectric oxides have been only poorly regarded. Here, by using ultrafast optical pump-probe measurements, we show that photogeneration/photodetection of coherent phonons in BiFeO3 ferroelectric leads, at room temperature, to the largest intensity ratio ever reported of GHz transverse acoustic wave versus the longitudinal one. It is found that the major mechanism involved corresponds to screening of the internal electric fields by light-induced charges, which in turn induces stress by inverse piezoelectric effect. This giant opto-acoustic response opens new perspectives for the use of ferroelectric oxides in ultrahigh frequency acoustic devices and the development of new GHz-THz acoustic sources.

Nanophononics: state of the art and perspectives

“…These materials exhibit large electron-phonon coupling parameters, large electro-mechanical response and also augmented piezoelectric coefficients. Hence they open new pathways for exciting and controlling lattice and electron dynamics simultaneously [131,[143][144][145]. Coherent phonon dynamics in topological insulators is also a subject of active research [146][147][148][149] where the electron-phonon coupling appears to set a limit on the natural spin polarized surface electrons transport [150,151].…”

“…The detection is achieved through a Brillouin process (Brillouin zone point q = 2k) that reveals high frequencies up to the THz regime [130]. (c) Generation of LA and TA mode in BiFeO3 ferroelectric materials driven by photoinduced inverse piezoelectric effect based on the photoinduced screening of the internal ferroelectric polarization [131]. The experiments were conducted on various grains in polycristalline sample.…”

Laser operated piezoelectricity in Ag0.5Pb1.75GeS4 and Ag0.5Pb1.75GeS3Se crystals

“…In this work due to coexistence of two cations (Pb and Ag) one can expect an occurrence of nonlinear (nonmonotonous) laser energy dependence with respect to piezoelectricity. Among the mechanisms defining the observed effect it should be point out the photoinduced polarizablity, excitation of the anharmonic phonons, photoinduced space charge density acentricity [8][9][10].…”

Phonon Spectroscopy with Chirped Shear and Compressive Acoustic Pulses

“…Depending on the methods of phonon generation and detection, it is possible to operate with broadband [4,5] or close to monochromatic phononic wave packets [2,6,7]. It is also possible to control phonon polarization, longitudinal or transverse, associated with compressive or shear elastic perturbations, respectively [8][9][10][11][12][13]. Information about the phonon spectrum is obtained in most of the experiments by performing a fast Fourier transform (FFT) of the optical reflectivity signal measured in the temporal domain with femtosecond resolution.…”

“…TA phonons bringing shear perturbation to nano-objects modulate the atom displacements described by the shear modulus and thus provide, together with LA phonons, a complete characterization of the vibrational properties of a nano-object. The interaction of electrons [18,19], magnons [20][21][22], and photons [11,23] with phonons in many types of defects and nanostructures depends on the phonon mode, with large differences for LA and TA modes due to wavelength and the different physical coupling mechanisms, e.g., deformation potential and piezoelectric electron-phonon coupling. Thus, spectroscopy using TA phonons is essential to fully characterize the interactions.…”