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Eu1-xHoxMnO3 with x<0.5 has an orthorhombic perovskite structure, where the partial substitution of europium by holmium increases the orthorhombic distortion and changes the low-temperature magnetic structure from canted antiferromagnetic to the multiferroic ground state with cycloidal spin arrangement for x>0.2. We employ polarized, temperature-dependent Raman spectroscopy to study the lattice dynamics and spin-phonon coupling (SPC) effects for the two representative compositions x=0.1 and x=0.3. We observe an enhancement of phonon frequencies by Ho3+ substitution and we use the Ag(4) mode as a measure to evaluate the orthorhombic distortion angle θ. SPC manifests itself as mode-specific softening for T<100 K, induced by the magnetic ordering of Mn3+ spins. Furthermore, we present evidence that the hitherto elusive Raman peak at ≈650cm-1 is a phonon of B3g symmetry and ascribe it to the B3g(1) out-of-phase MnO6-breathing mode. We show that this mode has the strongest SPC effect of all observed phonon modes, a fact which we explain by the participation of the apical O(1) ions, modulating the Mn-O(1)-Mn bond whose SPC contribution was hitherto not accessible. Finally, we present a quantitative evaluation of the SPC contribution by the antiferromagnetic plane-to-plane coupling through the Mn-O(1)-Mn bonds and discriminate if from the in-plane ferromagnetic Mn-O(2)-Mn part. [ABSTRACT FROM AUTHOR]

The low-temperature electronic properties of rare-earth intermetallics are substantially influenced by the symmetry and magnitude of the crystal electric field. The direct spectroscopic analysis of crystal-field splitting can be challenging, especially in low-dimensional systems, because it requires both high spectral resolution and pronounced sensitivity. We demonstrate the eligibility of electronic Raman spectroscopy for this purpose by the direct determination of the 4ƒ level splitting in ultrathin ordered CePt5 films down to ≈ 1.5 nm thickness on Pt(111). Crystal-field excitations of Ce 4ƒ electrons give rise to Raman peaks at energy losses up to ≈ 25 meV. Three distinct peaks occur which we attribute to inequivalent Ce sites, located (i) at the interface to the substrate, (ii) next to the Pt-terminated film surface, and (iii) in the CePt5 layers in between. The well-resolved Raman signatures allow us to identify a reduced crystal-field splitting at the interface and an enhancement at the surface, highlighting its strong dependence on the local atomic environment. [ABSTRACT FROM AUTHOR]

The vibrational properties of the Au-induced (√3x √3)R 30° reconstruction of the Si(111) surface are investigated by polarized surface Raman spectroscopy and density-functional theory. The Raman measurements are performed in situ at room temperature as well as 20 K, and they reveal the presence of vibrational eigenmodes in the spectral range from 20 to 450 cm-1. In particular, two peaks of E symmetry at 75 and 183 cm-1 dominate the spectra. No substantial difference between room- and low-temperature spectra is observed, suggesting that the system does not undergo a phase transition down to 20 K. First-principles calculations are performed based on the structural models discussed in the literature. The thermodynamically stable conjugate honeycomb-chained-trimer model (CHCT) [Surf. Sci. 275, L691 (1992)] leads to phonon eigenvalues compatible with the experimental observations in the investigated spectral range. On the basis of the phonon eigenfrequencies, symmetries, and Raman intensities, we assign the measured spectral features to the calculated phonon modes. The good agreement between measured and calculated modes provides a strong argument in favor of the CHCT model. [ABSTRACT FROM AUTHOR]

Ordered submonolayers of adsorbate atoms on semiconductor surfaces constitute a playground for electronic correlation effects, which are tightly connected to the local atomic arrangement and the corresponding vibration eigenmodes. We report on a study of the vibration eigenmodes of Au-covered Si(111) surfaces with (5 × 2) reconstruction using polarized Raman spectroscopy and first-principles calculations. Upon Au coverage, the vibration eigenmodes of the clean reconstructed Si(111)- (7 × 7) surface are quenched and replaced by new eigenmodes, determined by the Au- (5 × 2) reconstruction. Several polarization-dependent surface eigenmodes emerge in the spectral range from 25 to 120 cm-1, with the strongest ones at 29, 51, and 106 cm-1. In our first-principles calculations we have determined the vibration frequencies, the corresponding elongation patterns, and the Raman intensities for two different structure models currently discussed in the literature. The best agreement with the experimental results is achieved for a model with 0.7 monolayer coverage and seven Au atoms per unit cell, proposed by S. G. Kwon and M. H. Kang [Phys. Rev. Lett. 113, 086101 (2014)]. [ABSTRACT FROM AUTHOR]