H.P. van der Meulen

Low-temperature specific heat of REBa2Cu3O7 in magnetic fields up to 5 T (RE = Y, Pr, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu)

Abstract Specific heat measurements have been performed on a series of REBa 2 Cu 3 O 7 -compounds (RE = Y, Pr, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu) in magnetic fields up to 5 T in a temperature range between 1.4 and 40 K. The electronic and lattice contributions to the specific heat of GdBa 2 Cu 3 O 7 have been taken as a reference for the heavy rare-earth compounds in order to deduce the magnetic and crystal-field contributions to the specific heat. The low-temperature data in field of the Dy-, Er-, and Yb-compounds confirm a doublet ground state, that is splitted by the applied field. The crystal-field contributions to the specific heat in these compounds deviate from Schottky behaviour due to anisotropy effects. Values for gJ amount to 2.3, 3.2 and 1.6, respectively.

Emission polarization control in semiconductor quantum dots coupled to a photonic crystal microcavity

We study the optical emission of single semiconductor quantum dots weakly coupled to a photonic-crystal micro-cavity. The linearly polarized emission of a selected quantum dot changes continuously its polarization angle, from nearly perpendicular to the cavity mode polarization at large detuning, to parallel at zero detuning, and reversing sign for negative detuning. The linear polarization rotation is qualitatively interpreted in terms of the detuning dependent mixing of the quantum dot and cavity states. The present result is relevant to achieve continuous control of the linear polarization in single photon emitters.

Double anomaly in the specific heat of superconducting UPt3 and UPt3B0.11

Abstract The specific heat of several poly- and single-crystalline samples of UPt3 and UPt3B0.11 has been measured below 1 K, in order to study the substructure in the anomaly below the superconducting transition. A double anomaly has been observed for Czochralski-grown single-crystalline UPt3 as well as for poly-crystalline UPt3B0.11. The addition of boron increases the transition temperature with roughly 100 mK and does not suppress the second transition.

Blue-to-green single photons from InGaN/GaN dot-in-a-nanowire ordered arrays

Single-photon emitters (SPEs) are at the basis of many applications for quantum information management. Semiconductor-based SPEs are best suited for practical implementations because of high design flexibility, scalability and integration potential in practical devices. Single-photon emission from ordered arrays of InGaN nano-disks embedded in GaN nanowires is reported. Intense and narrow optical emission lines from quantum dot-like recombination centers are observed in the blue-green spectral range. Characterization by electron microscopy, cathodoluminescence and micro-photoluminescence indicate that single photons are emitted from regions of high In concentration in the nano-disks due to alloy composition fluctuations. Single-photon emission is determined by photon correlation measurements showing deep anti-bunching minima in the second-order correlation function. The present results are a promising step towards the realization of on-site/on-demand single-photon sources in the blue-green spectral range operating in the GHz frequency range at high temperatures.

Single-photon emission by semiconductor quantum rings in a photonic crystal

Photon correlation measurements on single InAs/GaAs quantum rings embedded in a photonic crystal lattice demonstrate single-photon emission with g(2)(0) values of 0.4 and photon antibunching between the exciton and biexciton emissions. The measured photon antibunching times of the excitons are longer than that of the biexcitons, resulting in the time asymmetry of the exciton-biexciton photon cross-correlation. Phonon sidebands due to the piezoelectric coupling of excitons to acoustic phonons broaden the emission lines and shift them to lower energies at low excitation intensity.

Phonon Raman scattering in quantum wires

Abstract Phonons in narrow quantum wires of In 0.53 Ga 0.47 As showing strong one-dimensional confinement of carriers have been studied by Raman spectroscopy. A strong enhancement of the Raman intensity of the longitudinal optical phonon of the wires is observed for wire widths decreasing down to 40 nm. For narrower wires (10–30 nm), the Raman intensity falls very rapidly as the surface roughness becomes comparable to the wire width. No changes in the phonon frequency have been observed. The increased Raman intensity is attributed to enhanced resonance effects due to the one-dimensional confinement of carriers. The role of wavevector non-conservation and surface electric fields on the Frohlich scattering efficiency are discussed.

Characteristic temperatures in the heavy-fermion system U(Pt,Pd)3

Abstract A summary is presented of the characteristic temperatures in the series of U(Pt,Pd) 3 heavy-fermion compounds as derived from thermodynamic and transport measurements.

Resonant optical excitation of longitudinal-optical phonons and intermixing in InAs∕AlAs single quantum dots

Excitations of a single InAs∕AlAs self-assembled quantum dot were investigated by photoluminescence excitation spectroscopy. Resonant absorption by longitudinal-optical (LO) phonons of the quantum dot and the barriers is observed. In particular, a resonance at 41meV is attributed to the AlAs-like mode of InAlAs with low Al content. Our results represent a direct optical measure of the intermixing (estimated below 10%) in a single quantum dot. They also demonstrate that all LO phonons of this mixed quantum dot system couple to the exciton states.

Carrier and light trapping in graded quantum-well laser structures

We investigated the carrier and light trapping in GaInAs/AlGaAs single-quantum-well laser structures by means of time-resolved photoluminescence and Raman spectroscopy. The influence of the shape and depth of the confinement potential and of the cavity geometry was studied by using different AlGaAs/GaAs short-period superlattices as barriers. Our results show that grading the optical cavity improves considerably both carrier and light trapping in the quantum well, and that the trapping efficiency is enhanced by increasing the graded confining potential.

PHYSICAL PROPERTIES OF SINGLE-PHASE HIGH-Tc SUPERCONDUCTOR YBa2Cu3O7

Transport and thermodynamical properties as well as structural investigations in the well-characterized 90 K-class high-Tc superconductor YBa2Cu3O7 are presented, especially in relation to the fundamental mechanism of the high-Tc superconductivity. High-precision specific heat measurements around Tc=91.8 K reveal that the value of ΔC/Tc is 48±2 mJ/mol K2. This value results in the fact that the value of ΔC/γTc is 1.33, which is close to 1.43, the weak-coupling BCS value, provided that the coefficient, γ, of the linear term in the specific heat is 36±2 mJ/mol K2.