Papers by Alejandro Martín Lobos
ABSTRACT Yb2M3Ga9 (M = Rh, Ir) are intermediate valence systems which exhibit anisotropic magneti... more ABSTRACT Yb2M3Ga9 (M = Rh, Ir) are intermediate valence systems which exhibit anisotropic magnetic susceptibilities. This anisotropy can be explained by crystal field level splitting that is similar in magnitude to the Kondo temperature. To examine this picture further, we have performed inelastic neutron scatting experiments on polycrystalline samples at 12 and 300 K for Yb2Rh3Ga9 as well as measurements of the 4f occupation number of both Yb2Rh3Ga9 and Yb2Ir3Ga9. The inelastic neutron scattering spectrum indicates an inelastic response at low temperature and a quasielastic response at high temperature. These data are consistent with theoretical calculations based on an approach within the non-crossing approximation including the effects of crystal field level splitting.
Physical Review B, 2008
We studied the intensity of resonant Raman scattering due to optical phonons in a planar II-VI ty... more We studied the intensity of resonant Raman scattering due to optical phonons in a planar II-VI type semiconductor microcavity in the regime of strong coupling between light and matter. Two different sets of independent experiments were performed at near outgoing resonance with the middle polariton (MP) branch of the cavity. In the first, the Stokes-shifted photons were kept at exact resonance with the MP, varying the photonic or excitonic character of the polariton. In the second, only the incoming light wavelength was varied, and the resonant profile of the inelastic scattered intensity was studied when the system was tuned out of the resonant condition. Taking some matrix elements as free parameters, both independent experiments are quantitatively described by a model which incorporates lifetime effects in both excitons and photons, and the coupling of the cavity photons to the electron-hole continuum. The model is solved using a Green's function approach which treats the exciton-photon coupling nonperturbatively.
Physical Review B, 2008
The physical properties including magnetic susceptibility, magnetization, specific heat, and dyna... more The physical properties including magnetic susceptibility, magnetization, specific heat, and dynamic susceptibility Љ͑E͒ are reported for single crystals of the cubic UM 2 Zn 20 ͑M=Co,Rh͒ materials. Maxima in the thermodynamic data at T max ϳ 10 K for both compounds and a broad peak in Љ͑E͒ at 5 K in UCo 2 Zn 20 of width ⌫ = 5 meV indicate a heavy-fermion state characterized by a Kondo temperature T K ϳ 20-30 K arising from weak hybridization of f-and conduction-electron states. Anderson impurity model fits to the data in the Kondo limit including crystalline electric-field effects corroborate an ionic-like uranium electronic configuration in UM 2 Zn 20 .
Physical Review B, 2005
The intermediate valence compounds Yb 2 M 3 Ga 9 (M = Rh, Ir) exhibit an anisotropic magnetic sus... more The intermediate valence compounds Yb 2 M 3 Ga 9 (M = Rh, Ir) exhibit an anisotropic magnetic susceptibility. We report measurements of the temperature dependence of the 4f occupation number, n f (T), for Yb 2 M 3 Ga 9 as well as the magnetic inelastic neutron scattering spectrum S mag (∆E) at 12 and 300 K for Yb 2 Rh 3 Ga 9 . Both n f (T) and S mag (∆E) were calculated for the Anderson impurity model with crystal field terms within an approach based on the non-crossing approximation. These results corroborate the importance of crystal field effects in these materials; they also suggest that Anderson lattice effects are important to the physics of Yb 2 M 3 Ga 9 .
Physical Review B, 2005
Magnetic susceptibility, heat capacity, and electrical resistivity measurements have been carried... more Magnetic susceptibility, heat capacity, and electrical resistivity measurements have been carried out on single crystals of the intermediate valence compounds Yb2Rh3Ga9 and Yb2Ir3Ga9. These measurements reveal a large anisotropy due apparently to an interplay between crystalline electric field (CEF) and Kondo effects. The temperature dependence of magnetic susceptibility can be modelled using the Anderson impurity model including CEF within an approach based on the Non-Crossing Approximation.
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Papers by Alejandro Martín Lobos