Measurement of the acoustic-to-optical phonon coupling in multicomponent systems

In this paper we investigate the acoustic-to-optical up-conversion phonon processes in a multicomponent system. These processes take place during heat transport and limit the efficiency of heat ßow. By combining time-resolved optical and heat capacity experiments we quantify the thermal coupling constant to be g ~ 0.4·1017 W/Km3. The method is based on selective excitation of a part of a multicomponent system, and the measurement of the thermalization dynamics by probing the linear birefringence of the sample with femtosecond resolution. In particular, we study a layered multiferroic organic-inorganic hybrid, in the vicinity of the ferroelectric phase transition. A diverging term of the heat capacity is associated to soft-mode dynamics, in agreement with previous spectroscopy measurements

Charge and sodium ordering in beta-Na0.33V2O3

Polarized Raman and optical spectra for the quasi one-dimensional metallic vanadate beta-Na0.33V2O3 are reported for various temperatures. The spectra are discussed in the light of the sodium and charge ordering transitions occurring in this material, and demonstrate the presence of strong electron-phonon coupling

RIXS interferometry and the role of disorder in the quantum magnet Ba3Ti3-xIrxO9

Motivated by several claims of spin-orbit-driven spin-liquid physics in hexagonal Ba3Ti3-xIrxO9 hosting Ir2O9 dimers, we report on resonant inelastic x-ray scattering (RIXS) at the Ir L3 edge for different x. We demonstrate that magnetism in Ba3Ti3-xIrxO9 is governed by an unconventional realization of strong disorder, where cation disorder affects the character of the local moments. RIXS interferometry, studying the RIXS intensity over a broad range of transferred momentum q, is ideally suited to assign different excitations to different Ir sites. We find pronounced Ir-Ti site mixing. Both ions are distributed over two crystallographically inequivalent sites, giving rise to a coexistence of quasimolecular singlet states on Ir2O9 dimers and spin-orbit-entangled j = 1/2 moments of 5d5 Ir4+ ions. RIXS reveals different kinds of strong magnetic couplings for different bonding geometries, highlighting the role of cation disorder for the suppression of long-range magnetic order in this family of compounds

Coulomb-Blockade Oscillations in Semiconductor Nanostructures

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