The perovskites lead zirconium titanate, PbZr1–x Ti x O3 (0 < x < 1), known as PZT, are solid solutions widely exploited for their strong piezoelectric properties. The utmost technological importance of this class of materials led to considerable activity on piezoelectric films from the experimental and simulation side. In a solid solution like PZT, the distribution of Zr and Ti atoms has no long-range ordering. Thus, these materials are highly challenging to model theoretically but also to investigate experimentally. In this study, we combine infrared (IR) absorption spectroscopy, with a Density Functional Theory method adapted for the calculation of solid solutions. The complexity of PZT material is reproduced through a combination of 2 × 2 × 2 supercells. Using such combination procedure, we show here that ab initio calculations shed light on the interpretation of IR measured absorption spectra for thin films of 5, 10, 45, 90 nm with composition x = 0.75 in PbZr1–x Ti x O3, as well as for pure PbZrO3 and PbTiO3. Furthermore, the simulation on the supercell structure was also performed for multiple compositions 0.5 ≤ x ≤ 1 in both tetragonal and cubic structures, allowing the understanding of the evolution of spectra with temperature (during the tetragonal to cubic phase transition) and with doping. This temperature study reveals the first experimental evidence of polar modes associated with the loss of spontaneous polarization in nanometer size PZT films, deposited on a silicon wafer. This combination of experimental and theoretical methods opens the way for the investigation of other solid solution materials.

Electromagnons (Electroactive spin wave excitations) could prove to be decisive in information technologies but they remain fragile quantum objects, mainly existing at low temperatures. Any future technological application requires overcoming these two limitations. By means of synchrotron radiation infrared spectroscopy performed in the THz energy range and under hydrostatic pressure, we tracked the electromagnon in the cupric oxide CuO, despite its very low absorption intensity. We demonstrate how a low pressure of 3.3 GPa strongly increases the strength of the electromagnon and expands its existence to a large temperature range enhanced by 40 K. Accordingly, these two combined effects make the electromagnon of CuO under pressure a more ductile quantum object. Numerical simulations based on an extended Heisenberg model were combined to the Monte-Carlo technique and spin dynamics to account for the magnetic phase diagram of CuO. They enable to simulate the absorbance response of the CuO electromagnons in the THz range.

The intensive search for alternative noncuprate high-transition-temperature (T c ) superconductors has taken a positive turn recently with the discovery of superconductivity in infinite-layer nickelates. This discovery is expected to be the basis for disentangling the puzzle behind the physics of high T c values in oxides. In the unsolved quest for the physical conditions necessary for inducing superconductivity, we report on a broad-band optical study of a Nd 0.8 Sr 0.2 NiO 2 film measured using optical and terahertz spectroscopy at temperatures above and below the critical temperature T c ∼ 13 K. The normal-state electrodynamics of Nd 0.8 Sr 0.2 NiO 2 can be described by a scattering time at room temperature (τ ≃ 1.3 × 10 −14 s) and a plasma frequency ω p ≃ 5500 cm −1 in combination with an absorption band in the mid-infrared (MIR), characteristics of transition metal oxides, located around ω 0 ∼ 2500 cm −1 and with an amplitude ω p MIR of about 8000 cm −1 . The degree of electronic correlation can be estimated using the ratio ω p 2 /(ω p 2 + (ω p MIR ) 2 ). In the present system, the determined value of 0.32 ± 0.06 indicates a strong electron correlation in the NiO 2 plane with similar strength as cuprates. From 300 to 20 K, we observe a spectral weight transfer between the Drude and MIR band, together with a strong increase in the Drude scattering time, in agreement with DC resistivity measurements. Below T c , a superconducting energy gap 2Δ ∼ 3.3 meV can be extracted from the terahertz reflectivity using the Mattis−Bardeen model.

The intensive search for alternative non-cuprate high-transition-temperature (T c ) superconductors has taken a positive turn recently with the discovery of superconductivity in infinite layer nickelates 1 . This discovery is expected to be the basis for disentangling the puzzle behind the physics of high T c in oxides. In the unsolved quest for the physical conditions necessary for inducing superconductivity, we report an optical study of a Nd 0.8 Sr 0.2 NiO 2 film measured using optical spectroscopy, at temperatures above and below the critical temperature T c ∼ 13 K. The normal-state electrodynamics of Nd 0.8 Sr 0.2 NiO 2 , is described by the Drude model characterized by a scattering time just above T c (τ ∼ 1.7 × 10 −14 s) and a plasma frequency ω p = 8500 cm −1 in combination with an absorption band in the Mid-Infrared (MIR) around ω 0 ∼ 4000 cm −1 . The MIR absorption indicates the presence of strong electronic correlation effect in the NiO 2 plane similarly to cuprates. Below T c , a superconducting energy gap (2∆) of ∼ 3.2 meV is extracted from the Terahertz reflectivity using the the Mattis-Bardeen model. From the Ferrel-Glover-Thinkam Rule applied to the real part of the optical conductivity, we also estimate a London penetration depth of about 490 nm, in agreement with a type-II 2 superconductivity in Nd 0.8 Sr 0.2 NiO 2 Nickelate.