Metastable ferroelectricity in optically strained SrTiO
            <sub>3</sub>

Nova, Tobia F.; Disa, Ankit; Fechner, Michael; Cavalleri, Andrea

doi:10.1126/science.aaw4911

Cited by 320 publications

(234 citation statements)

References 50 publications

Supporting

Mentioning

225

Contrasting

Order By: Relevance

“…The transient changes in optical density (denoted as ΔOD) comparing pump‐on and pump‐off conditions in the near‐infrared wavelength range ( Figure a) consist of a derivative‐like line‐shape, centered around the exciton peak at 750 nm, which oscillates above and below zero in sub‐picosecond timescales. Such periodic oscillations, which signify coherent optical phonons (COPs), have been observed in (semi)metals, [ 24 ] insulators, [ 25,26 ] and semiconductors, including MAPbI 3 itself [ 27,28 ] (but in the condition of above‐bandgap optical pumping). A key feature of using non‐resonant optical pumping here is that our data are completely free from parasitic electronic excitations; the latter usually give rise to large background in transient signals around the exciton peak due to a nonequilibrium redistribution of charge carriers near the band edge.…”

Section: Resultsmentioning

confidence: 99%

“…Our observations are consistent with the formation of a rotationally disordered octahedral network in the tetragonal phase of MAPbI 3 as determined from MeV ultrafast electron diffraction experimentation, [ 11 ] as well as the spontaneous symmetry breaking in the respective cubic phase. [ 47 ] Our work sheds light on further manipulating COPs in the structurally diverse HOIPs [ 48 ] for the generation of effective magnetic fields [ 17 ] as well as the access to nonequilibrium ferroelectric phases [ 6,25,26 ] and quantum phases, [ 49,50 ] which have been previously pursued with materials such as oxide perovskites. The similarity (and difference) of the rotations of octahedra between 3D and 2D hybrid perovskites, and between inorganic and hybrid perovskites, are among the remaining questions, since it has been demonstrated that hydrogen bonding plays an important role in mediating the octahedral tilts.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Direct Observation of Bandgap Oscillations Induced by Optical Phonons in Hybrid Lead Iodide Perovskites

Guo

Xia

Gong

et al. 2020

Adv Funct Materials

View full text Add to dashboard Cite

Hybrid organic-inorganic perovskites such as methylammonium lead iodide have emerged as promising semiconductors for energy-relevant applications. The interactions between charge carriers and lattice vibrations, giving rise to polarons, have been invoked to explain some of their extraordinary optoelectronic properties. Here, time-resolved optical spectroscopy is performed, with off-resonant pumping and electronic probing, to examine several representative lead iodide perovskites. The temporal oscillations of electronic bandgaps induced by coherent lattice vibrations are reported, which is attributed to antiphase octahedral rotations that dominate in the examined 3D and 2D hybrid perovskites. The off-resonant pumping scheme permits a simplified observation of changes in the bandgap owing to the A g vibrational mode, which is qualitatively different from vibrational modes of other symmetries and without increased complexity of photogenerated electronic charges. The work demonstrates a strong correlation between the lead-iodide octahedral framework and electronic transitions, and provides further insights into the manipulation of coherent optical phonons and related properties in hybrid perovskites on ultrafast timescales.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Direct Observation of Bandgap Oscillations Induced by Optical Phonons in Hybrid Lead Iodide Perovskites

Guo

Xia

Gong

et al. 2020

Adv Funct Materials

View full text Add to dashboard Cite

show abstract

“…[18,19] A particularly interesting case of switching occurs when the new phase is a "hidden state," i.e., a metastable and, thus, transient state of matter. Examples of such states include transient ferroelectric order in a paraelectric, [183,184] transient superconductivity-like states in superconductors in the normal-conductor phase, [185] and the heating of the spin system of a ferrimagnet without changing its total magnetization (see also Figure 26). [22] …”

Section: Condensed Mattermentioning

confidence: 99%

Laser‐Driven Strong‐Field Terahertz Sources

Fülöp

Tzortzakis

Kampfrath

2019

Advanced Optical Materials

285

147

View full text Add to dashboard Cite

reason for this interest relies on the fact that THz radiation can couple resonantly to numerous fundamental motions of ions, electrons, and electron spins in all phases of matter. For example, in solids, the THz range overlaps with the frequency of lattice vibrations (phonons), the collision rates of conduction electrons, the binding energy of bound electron-hole pairs (excitons), and the precession frequency of spin waves (magnons). Consequently, THz radiation, both continuous-wave and pulsed, has been used for characterization of and gaining insight into elementary processes in complex materials. The majority of these studies used relatively weak THz fields and, thus, probed the linear response of the material, without inducing notable material modifications.Only recently, however, completely new avenues in THz science were opened up by triggering nonlinear THz responses of materials. [3][4][5][6][7][8][9][10][11][12][13] Instead of using weak fields to primarily observe selected THz modes such as phonons or magnons, strong fields allow one to actively drive them to unprecedentedly large amplitudes, potentially thereby resulting in novel states of matter. [6,8,11] For example, simulations suggest that exciting matter with intense THz transients may lead to massive modifications of electrically [14] or magnetically [15] ordered domains and enable the acceleration of free ions to ≈1 MeV, [16] and postacceleration to 50-100 MeV energies. [17] Remarkable experimental results such as switching of magnetic order, [18,19] parametric amplification of optical phonons, [20] novel insights into spin-lattice coupling, [21,22] and acceleration of free electrons in a THz linear accelerator [23] were achieved only recently. This progress has been made possible by the development of laser-driven table-top THz sources routinely providing pulses with unprecedented energies and peak electric and magnetic field strengths throughout the entire THz spectral range. Different laser-based THz pulse generation techniques can be used to access different parts of the spectral range extending from 0.1 to 10 THz. Some of the recently developed technologies enable the generation of radiation with even larger bandwidth or tuning range up to 100 THz and beyond, which lead to an extension of what is called the THz spectral range. An overview of the approximate spectral coverage and the achieved highest pulse energies and peak electric-field strengths of various laserdriven technologies is given in Figure 1. ScopeIn this work, the basic principles of femtosecond-laser-driven intense pulsed THz sources and their recent development are reviewed. These sources are capable of delivering peak electric field strengths on the MV cm −1 scale. Corresponding typical THz pulse energies are on the µJ-to-mJ level, depending on A review on the recent development of intense laser-driven terahertz (THz) sources is provided here. The technologies discussed include various types of sources based on optical rectification (OR), spintronic emitters, and laserfilame...

show abstract

“…The polar phase required for exhibiting these properties can, however, be induced artificially by modification of the lattice. Large biaxial strain, light pulses, and elemental substitutions can convert SrTiO 3 into a ferroelectric material, whereas strain gradients can induce a polarization via the flexoelectric effect or oxygen vacancies migration . Electron diffraction measurements furthermore show that the top TiO 2 surface layer of SrTiO 3 undergoes surface relaxation and oxygen ions move outward from the surface relative to the titanium ions, leading to a polarization of this layer .…”

mentioning

confidence: 99%

Surface Pyroelectricity in Cubic SrTiO₃

et al. 2019

View full text Add to dashboard Cite

material gives rise to a range of interesting properties such as superconductivity, [1] high electron mobility, [2,3] ferromagnetism [4,5] and 2D electron gases. [6] In the multitude of the properties exhibited by SrTiO 3 , pyroelectricity, ferroelectricity, and piezoelectricity are markedly absent as these properties are symmetry prohibited in centrosymmetric crystal lattices. The polar phase required for exhibiting these properties can, however, be induced artificially by modification of the lattice. Large biaxial strain, [7] light pulses, [8,9] and elemental substitutions [10] can convert SrTiO 3 into a ferroelectric material, whereas strain gradients can induce a polarization via the flexoelectric effect [11,12] or oxygen vacancies migration. [13] Electron diffraction measurements furthermore show that the top TiO 2 surface layer of SrTiO 3 undergoes surface relaxation and oxygen ions move outward from the surface relative to the titanium ions, leading to a polarization of this layer. [14][15][16] This is supported by shell model and density functional theory calculations. However, the calculations also predict that the SrO layers underneath display a polarization opposite to that of the TiO 2 surface layer, [17][18][19] leaving the question of the predicted net polarization and a possible pyroelectricity at the surface wide open.Symmetry-imposed restrictions on the number of available pyroelectric and piezoelectric materials remain a major limitation as 22 out of 32 crystallographic material classes exhibit neither pyroelectricity nor piezoelectricity. Yet, by breaking the lattice symmetry it is possible to circumvent this limitation. Here, using a unique technique for measuring transient currents upon rapid heating, direct experimental evidence is provided that despite the fact that bulk SrTiO 3 is not pyroelectric, the (100) surface of TiO 2 -terminated SrTiO 3 is intrinsically pyroelectric at room temperature. The pyroelectric layer is found to be ≈1 nm thick and, surprisingly, its polarization is comparable with that of strongly polar materials such as BaTiO 3 . The pyroelectric effect can be tuned ON/OFF by the formation or removal of a nanometric SiO 2 layer. Using density functional theory, the pyroelectricity is found to be a result of polar surface relaxation, which can be suppressed by varying the lattice symmetry breaking using a SiO 2 capping layer. The observation of pyroelectricity emerging at the SrTiO 3 surface also implies that it is intrinsically piezoelectric. These findings may pave the way for observing and tailoring piezo-and pyroelectricity in any material through appropriate breaking of symmetry at surfaces and artificial nanostructures such as heterointerfaces and superlattices. PyroelectricitySrTiO 3 has been the object of immense attention for over half a century owing to its multifunctional nature and popularity as a template for epitaxial growth of artificial nanostructures such as heterostructures, superlattices, and vertically aligned nanostructures. It is a classic example whe...

show abstract

Metastable ferroelectricity in optically strained SrTiO ₃

Cited by 320 publications

References 50 publications

Direct Observation of Bandgap Oscillations Induced by Optical Phonons in Hybrid Lead Iodide Perovskites

Direct Observation of Bandgap Oscillations Induced by Optical Phonons in Hybrid Lead Iodide Perovskites

Laser‐Driven Strong‐Field Terahertz Sources

Surface Pyroelectricity in Cubic SrTiO₃

Contact Info

Product

Resources

About

Metastable ferroelectricity in optically strained SrTiO 3

Cited by 320 publications

References 50 publications

Direct Observation of Bandgap Oscillations Induced by Optical Phonons in Hybrid Lead Iodide Perovskites

Direct Observation of Bandgap Oscillations Induced by Optical Phonons in Hybrid Lead Iodide Perovskites

Laser‐Driven Strong‐Field Terahertz Sources

Surface Pyroelectricity in Cubic SrTiO3

Contact Info

Product

Resources

About

Metastable ferroelectricity in optically strained SrTiO ₃

Surface Pyroelectricity in Cubic SrTiO₃