The oxide heterostructure [(YFeO 3 ) 5 (LaFeO 3 ) 5 ] 40 , which is magnetically ordered and piezoelectric at room temperature, has been constructed from two weak ferromagnetic AFeO 3 perovskites with different A cations using RHEED-monitored pulsed laser deposition. The polarisation arises through the removal of inversion centres present within the individual AFeO 3 components. This symmetry reductionis a result of combining ordering on the A site, imposed by the periodicity of the grown structure, with appropriate orientations of the octahedral tilting characteristic of the perovskite units themselves, according to simple symmetry-controlled rules. The polarisation is robust against A site interdiffusion between the two layers which produces a sinusoidally modulated occupancy that retains the coupling of translational and point symmetries required to produce a polar structure. Magnetization and magneto-optical Kerr rotation measurements show that the heterostructure's magnetic structure is similar to that of the individual components. Evidence of the polarity was obtained from second harmonic generation and piezoelectric force microscopy measurements. Modeling of the piezoresponse allows extraction of d 33 (approximately 10 pC/N) of the heterostructure, which is in agreement with DFT calculations. IntroductionThe breaking of inversion symmetry to generate a polarization is a prerequisite for the technologically important properties of ferro-and piezoelectricity used in capacitors and actuators, while the breaking of time-reversal symmetry is required for the magnetically ordered states such as antiferro-and ferromagnetism used in information storage. It is however chemically challenging to combine both properties in a single material, because there is a competition in the electronic structure requirements between many of the mechanisms responsible for forming each Oxide heterostructures display emergent phenomena controlled by charge, orbital and spin reconstruction at the internal interfaces within the thin films. 6 Inversion and timereversal symmetries have been broken together in tricolor heterostructures employing multiple component compositions and symmetries 7 , or by using substrate-induced strain. 8The ABO 3 perovskite structure supports both magnetic and polar ground states. The diverse array of physical properties can be controlled via tilting of the BO 6 octahedra 9 through the B-O-B overlap, and by ordering of cations on both the A 10, 11 and B sites 12 . Thin film heterostructures of ABO 3 materials afford new properties arising from strain and internal interfaces 6 . Recent theoretical work [13][14][15][16] has proposed that specific combinations of cation order and tilting, originally elucidated for HRTEM defect analysis of bulk materials 17 , can impose polarity on (ABO 3 :A′BO 3 ) 1:1 heterostructures where both components adopt the Pnma structure. This involves out-of-phase octahedral tilting along two pseudocubic a p perovskite subcell directions denoted a -and in-phase tilting along th...

Second Harmonic Generation induced by the electric field of a strong nearly single-cycle terahertz pulse with the peak amplitude of 300 kV/cm is studied in a classical inorganic ferroelectric thin film of (Ba0.8Sr0.2)TiO3. The dependences of the SHG intensity on the polarization of the incoming light is revealed and interpreted in terms of electric polarization induced in the plane of the film. As the THz pulse pumps the medium in the range of phononic excitations, the induced polarization is explained as a dynamical change of the ferrolectric order parameter. It is estimated that under action of the THz pulse the ferroelectric order parameter acquires an in-plane component up to 6% of the net polarization.

Two types of low-voltage electroswitchable nonlinear photonic crystals were fabricated providing spatial-frequency control of second harmonic generation radiation of visible light. A two-dimensional photonic crystal was fabricated by focused ion beam etching of a ferroelectric BaSrTiO3 thin film and switched by an electric field applied by an interdigital electrode system, which simultaneously acted as a one-dimensional photonic crystal. The fabricated device operated at a second harmonic wavelength around 400nm with an efficiency incomparably higher than in the case of linear optics.

Regular surface domain gratings were created in strontium barium niobate crystals by local poling with an AFM-tip. Piezoresponse force microscopy was utilized to subsequently image the domain patterns and to investigate their temporal and thermal stability. The gratings were examined by means of nonlinear diffraction in reflection geometry using a Ti-sapphire laser (800 nm) as pump source. The well-resolved second harmonic diffraction patterns were recorded for various angles of incidence of the fundamental wave. The origin of the observed nonlinear diffraction is discussed.

The photoexcitation and relaxation of carriers is studied in WSe 2 nanolayers on Si/SiO 2 substrate by optical pump-probe technique. The excitation wavelength falls in the vicinity of the band edge. The thickness variation of WSe 2 layers acts as tuning of band gap of the layers. In this way, a band edge spectroscopy is carried out using the constant excitation wavelength. It is shown that the relaxation time constants increase with the thickness increase, while the amplitude of transient reflectivity changes nonmonotonically. A model is suggested describing the amplitude behavior.