Magneto-photoluminescence spectroscopy of single InAs/AlAs quantum dots

We present non-resonant, polarization-resolved magneto-photoluminescence measurements up to 12 T on single InAs/AlAs quantum dots. We observe typical g-factors between 1 and 2, very low diamagnetic shifts due to strong exciton localization and low-energy sidebands, which are attributed to the piezoelectric exciton-acoustic phonon interaction.Spanish Ministry of Education/MAT2008- 01555/NANSpanish Ministry of Education/Consolider CSD 2006-19Community of Madrid CAMS-0505-ESP-0200Spanish Ministry of Science and Innovation/Nanoinpho-QD TEC2008-06756-C03-0

Fermi-edge singularities in linear and non-linear ultrafast spectroscopy

We discuss Fermi-edge singularity effects on the linear and nonlinear transient response of an electron gas in a doped semiconductor. We use a bosonization scheme to describe the low energy excitations, which allows to compute the time and temperature dependence of the response functions. Coherent control of the energy absorption at resonance is analyzed in the linear regime. It is shown that a phase-shift appears in the coherent control oscillations, which is not present in the excitonic case. The nonlinear response is calculated analytically and used to predict that four wave-mixing experiments would present a Fermi-edge singularity when the exciting energy is varied. A new dephasing mechanism is predicted in doped samples that depends linearly on temperature and is produced by the low-energy bosonic excitations in the conduction band.Comment: long version; 9 pages, 4 figure

Anomalous heavy-fermion and ordered states in the filled skutterudite PrFe4P12

Specific heat and magnetization measurements have been performed on high-quality single crystals of filled-skutterudite PrFe_4P_{12} in order to study the high-field heavy-fermion state (HFS) and low-field ordered state (ODS). From a broad hump observed in C/T vs T in HFS for magnetic fields applied along the direction, the Kondo temperature of ~ 9 K and the existence of ferromagnetic Pr-Pr interactions are deduced. The {141}-Pr nuclear Schottky contribution, which works as a highly-sensitive on-site probe for the Pr magnetic moment, sets an upper bound for the ordered moment as ~ 0.03 \mu_B/Pr-ion. This fact strongly indicates that the primary order parameter in the ODS is nonmagnetic and most probably of quadrupolar origin, combined with other experimental facts. Significantly suppressed heavy-fermion behavior in the ODS suggests a possibility that the quadrupolar degrees of freedom is essential for the heavy quasiparticle band formation in the HFS. Possible crystalline-electric-field level schemes estimated from the anisotropy in the magnetization are consistent with this conjecture.Comment: 7 pages and 7 figures. Accepted for publication in Phys. Rev.

Specific heat of PbM06S8 in high magnetic field

Contains fulltext : 28491.pdf (publisher's version ) (Open Access

Specific heat of PbMo6S8 in high magnetic field

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Many-body effects in photoluminescence of a two-dimensional electron gas in high magnetic field

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Band structure, photoelectron spectroscopy, and transport properties of SnTaS2

We present band-structure calculations of SnTaS2, an intercalation compound in which the Sn atoms have a very uncommon linear coordination by two S atoms and an unusual formal valency Sn1+. The Sn 5px and 5py states show strong metal-metal bonding in the intercalant planes and the Fermi level is crossed by a very wide band composed of these Sn 5pxpy states. Angle-resolved photoelectron spectra are in agreement with the calculated band structure. SnTaS2 is metallic as is reflected in the measured transport properties (resistivity, Hall effect, thermoelectric power). Low-temperature specific-heat measurements show an anomaly due to superconductivity below 2.8 K. The Sn 4d core levels, measured with photoelectron spectroscopy, show a splitting of 1 eV, indicating the presence of two different types of Sn atoms. This could be due to a valence disproportionation 2Sn+ → Sn0 + Sn2+ and rapid valence fluctuations between Sn0 and Sn2+.