In: Physical Review B, 2008, vol. 78, no. 13, p. 134111
We investigated with synchrotron x-ray diffraction and reflectometry the formation of structural domains in the near-surface region of single crystalline SrTiO₃ (001) substrates with Y0.6Pr0.4Ba₂Cu₃O₇/La2/3Ca1/3MnO₃ superlattices grown on top. We find that the antiferrodistortive cubic to tetragonal transition, which occurs at...
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In: Physical Review Letters, 2008, vol. 101, no. 9, p. 097010
Muon spin rotation experiments were performed on the pnictide high temperature superconductor SmFeAsO1-xFx with x=0.18 and 0.3. We observed an unusual enhancement of slow spin fluctuations in the vicinity of the superconducting transition which suggests that the spin fluctuations contribute to the formation of an unconventional superconducting state. An...
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In: Physical Review Letters, 2008, vol. 101, no. 9, p. 097011
We present far-infrared ellipsometric measurements of polycrystalline samples of the pnictide superconductor RFeAsO0.82F0.18 (R=Nd and Sm). We find evidence that the electronic properties are strongly anisotropic such that the optical spectra are dominated by the weakly conducting c-axis response similar to the cuprate high-temperature superconductors....
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In: Physical Review Letters, 2008, vol. 100, p. 177004
We present broadband infrared ellipsometry measurements of the c-axis conductivity of underdoped RBa₂Cu₃O₇₋δ (R=Y, Nd, and La) single crystals. Our data show that separate energy scales are underlying the redistributions of spectral weight due to the normal state pseudogap and the superconducting gap. Furthermore, they provide evidence that these gaps do not...
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In: Physical Review Letters, 2008, vol. 100, no. 16, p. 166401
The charge dynamics in weakly hole doped high temperature superconductors is studied in terms of the accurate numerical solution to a model of a single hole interacting with a quantum lattice in an antiferromagnetic background, and accurate far-infrared ellipsometry measurements. The experimentally observed two electronic bands in the infrared spectrum can be identified in terms of the interplay...
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In: Physical Review Letters, 2007, vol. 99, no. 26, p. 266801
We used infrared spectroscopic ellipsometry to investigate the electronic properties of LaTiO₃/SrTiO₃ superlattices (SLs). Our results indicated that, independent of the SL periodicity and individual layer thickness, the SLs exhibited a Drude metallic response with sheet carrier density per interface ≈3×10¹⁴ cm⁻². This is probably due to the leakage of d electrons at...
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In: Science, 2008, vol. 319, p. 597-600
Electronic phases with symmetry properties matching those of conventional liquid crystals have recently been discovered in transport experiments on semiconductor heterostructures and metal oxides at millikelvin temperatures. We report the spontaneous onset of a one-dimensional, incommensurate modulation of the spin system in the high-transition-temperature superconductor...
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In: Physical Review B: Condensend Matter and Materials Physics, 2007, vol. 76, no. 15, p. 155125
We have studied the temperature dependence of spectroscopic ellipsometry spectra of an electrically insulating, nearly stoichiometric YTiO₃ single crystal with ferromagnetic Curie temperature TC=30 K. The optical response exhibits a weak but noticeable anisotropy. Using a classical dispersion analysis, we identify three low-energy optical bands at 2.0, 2.9, and 3.7 eV....
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In: Europhysics Letters, 2007, vol. 80, no. 2, p. 27005
By muon spin rotation we investigated the magnetic properties of a series of highly Na-doped NaxCoO₂ single crystals with 0.78(1) ≼ x ≼ 0.97(1). Our data provide evidence for an intrinsically inhomogeneous magnetic state which can be described in terms of hole-doping (Na vacancy)-induced magnetic clusters that percolate at 1−x≳0.04 until they yield a bulk...
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In: Physical Review B, 2006, vol. 74, p. 104513
The phonon spectra of YBa₂Cu₄O₈ polycrystalline samples with different isotope substitution for Ba, Cu, and O have been studied using far-infrared ellipsometry and Raman scattering. The observed isotope shifts of Raman- and infrared-active phonons provide insight into their relative Ba, Cu, and O normal mode content. This allows us to examine mode eigenvectors obtained from lattice...
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