TY - JOUR AB - Structural strain severely impacts material properties, such as the linear and nonlinear optical response. Moreover, strain plays a key role, e.g., in the physics of ferroelectrics and, in particular, of their domain walls. μ-Raman spectroscopy is a well-suited technique for the investigation of such strain effects as it allows to measure the lattice dynamics locally. However, quantifying and reconstructing strain fields from Raman maps requires knowledge on the strain dependence of phonon frequencies. In this paper, we have analyzed both theoretically and experimentally the phonon frequencies in the widely used ferroelectrics lithium niobate and lithium tantalate as a function of uniaxial strain via density functional theory and μ-Raman spectroscopy. Overall, we find a good agreement between our ab initio models and the experimental data performed with a stress cell. The majority of phonons show an increase in frequency under compressive strain, whereas the opposite is observed for tensile strains. Moreover, for E-type phonons, we observe the lifting of degeneracy already at moderate strain fields (i.e., at ±0.2%) along the x and y directions. This paper, hence, allows for the systematic analysis of three-dimensional strains in modern-type bulk and thin-film devices assembled from lithium niobate and tantalate. AU - Singh, Ekta AU - Pionteck, Mike N. AU - Reitzig, Sven AU - Lange, Michael AU - Rüsing, Michael AU - Eng, Lukas M. AU - Sanna, Simone ID - 47993 IS - 2 JF - Physical Review Materials KW - Physics and Astronomy (miscellaneous) KW - General Materials Science SN - 2475-9953 TI - Vibrational properties of LiNbO3 and LiTaO3 under uniaxial stress VL - 7 ER - TY - JOUR AU - Neufeld, Sergej AU - Bocchini, Adriana AU - Schmidt, Wolf Gero ID - 22310 JF - Physical Review Materials SN - 2475-9953 TI - Potassium titanyl phosphate Z- and Y-cut surfaces from density-functional theory ER - TY - JOUR AU - Riedl, T. AU - Kunnathully, V. S. AU - Trapp, A. AU - Langer, T. AU - Reuter, Dirk AU - Lindner, J. K. N. ID - 21797 JF - Physical Review Materials SN - 2475-9953 TI - Strain-driven InAs island growth on top of GaAs(111) nanopillars ER - TY - JOUR AU - Riedl, T. AU - Kunnathully, V. S. AU - Trapp, A. AU - Langer, T. AU - Reuter, D. AU - Lindner, J. K. N. ID - 15714 JF - Physical Review Materials SN - 2475-9953 TI - Strain-driven InAs island growth on top of GaAs(111) nanopillars ER - TY - JOUR AU - Riedl, Thomas AU - Kunnathully, V. S. AU - Trapp, A. AU - Langer, T. AU - Reuter, Dirk AU - Lindner, Jörg ID - 34093 IS - 1 JF - Physical Review Materials KW - Physics and Astronomy (miscellaneous) KW - General Materials Science SN - 2475-9953 TI - Strain-driven InAs island growth on top of GaAs(111) nanopillars VL - 4 ER - TY - JOUR AU - Baron, Elias AU - Goldhahn, Rüdiger AU - Deppe, Michael AU - As, Donat Josef AU - Feneberg, Martin ID - 23831 JF - Physical Review Materials SN - 2475-9953 TI - Influence of the free-electron concentration on the optical properties of zincblende GaN up to 1×1020cm−3 ER - TY - JOUR AU - Baron, Elias AU - Goldhahn, Rüdiger AU - Deppe, Michael AU - As, Donat Josef AU - Feneberg, Martin ID - 13966 JF - Physical Review Materials SN - 2475-9953 TI - Influence of the free-electron concentration on the optical properties of zincblende GaN up to 1×1020cm−3 ER - TY - JOUR AU - Mamiyev, Z. AU - Lichtenstein, T. AU - Tegenkamp, C. AU - Braun, Christian AU - Schmidt, Wolf Gero AU - Sanna, S. AU - Pfnür, H. ID - 13406 IS - 6 JF - Physical Review Materials SN - 2475-9953 TI - Plasmon spectroscopy: Robust metallicity of Au wires on Si(557) upon oxidation VL - 2 ER - TY - JOUR AB - In recent years, Raman spectroscopy has been used to visualize and analyze ferroelectric domain structures. The technique makes use of the fact that the intensity or frequency of certain phonons is strongly influenced by the presence of domain walls. Although the method is used frequently, the underlying mechanism responsible for the changes in the spectra is not fully understood. This inhibits deeper analysis of domain structures based on this method. Two different models have been proposed. However, neither model completely explains all observations. In this work, we have systematically investigated domain walls in different scattering geometries with Raman spectroscopy in the common ferroelectric materials used in integrated optics, i.e., KTiOPO4, LiNbO3, and LiTaO3. Based on the two models, we can demonstrate that the observed contrast for domain walls is in fact based on two different effects. We can identify on the one hand microscopic changes at the domain wall, e.g., strain and electric fields, and on the other hand a macroscopic change of selection rules at the domain wall. While the macroscopic relaxation of selection rules can be explained by the directional dispersion of the phonons in agreement with previous propositions, the microscopic changes can be explained qualitatively in terms of a simplified atomistic model. AU - Rüsing, Michael AU - Neufeld, Sergej AU - Brockmeier, Julian AU - Eigner, Christof AU - Mackwitz, P. AU - Spychala, K. AU - Silberhorn, Christine AU - Schmidt, Wolf Gero AU - Berth, Gerhard AU - Zrenner, Artur AU - Sanna, S. ID - 4769 IS - 10 JF - Physical Review Materials SN - 2475-9953 TI - Imaging of 180∘ ferroelectric domain walls in uniaxial ferroelectrics by confocal Raman spectroscopy: Unraveling the contrast mechanism VL - 2 ER - TY - JOUR AU - Braun, Christian AU - Hogan, Conor AU - Chandola, Sandhya AU - Esser, Norbert AU - Sanna, Simone AU - Schmidt, Wolf Gero ID - 13415 IS - 5 JF - Physical Review Materials SN - 2475-9953 TI - Si(775)-Au atomic chains: Geometry, optical properties, and spin order VL - 1 ER - TY - JOUR AB - The optical properties of pristine and titanium-doped LiNbO3 are modeled from first principles. The dielectric functions are calculated within time-dependent density-functional theory, and a model long-range contribution is employed for the exchange-correlation kernel in order to account for the electron-hole binding. Our study focuses on the influence of substitutional titanium atoms on lithium sites. We show that an increasing titanium concentration enhances the values of the refractive indices and the reflectivity. AU - Friedrich, Michael AU - Schmidt, Wolf Gero AU - Schindlmayr, Arno AU - Sanna, Simone ID - 10021 IS - 3 JF - Physical Review Materials SN - 2475-9953 TI - Optical properties of titanium-doped lithium niobate from time-dependent density-functional theory VL - 1 ER -