The interaction between aligned dipoles is long-ranged and highly anisotropic: it changes from repulsive to attractive depending on the relative positions of the dipoles. We report on the observation of the attractive component of the dipolar coupling between excitonic dipoles in stacked semiconductor bilayers. We show that the presence of a dipolar exciton fluid in one bilayer modifies the spatial distribution and increases the binding energy of excitonic dipoles in a vertically remote layer. The binding energy changes are explained by a many-body polaron model describing the deformation of the exciton cloud due to its interaction with a remote dipolar exciton. The results open the way for the observation of theoretically predicted new and exotic collective phases, the realization of interacting dipolar lattices in semiconductor systems as well as for engineering and sensing their collective excitations. * These authors have equal contributions † hubert@pdi-berlin.de expansion and an interaction-driven phase transition between a gas and a state of self-bound, self-ordered liquid droplets, stabilized by the balance between attraction and repulsion and quantum fluctuations [2][3][4][5].

We report on the electrical generation of surface acoustic waves (SAWs) on doped semiconductor substrates. This is implemented by using interdigital transducers (IDTs) placed on piezoelectric ZnO films sputtered onto evaporated thin metal layers. Two material systems are investigated, namely ZnO/Au/GaAs and ZnO/Ni/InP. The rf-field applied to the transducer is electrically screened by the highly conductive metal film underneath the ZnO film without any extra ohmic losses. As a result, absorption of the rf-field by the mobile carriers in the lossy doped region underneath the IDT is avoided, ensuring efficient SAW generation. We find that the growth temperature of the ZnO film on the metal layer affects its structure and, thus, the efficiency of SAW generation. With this technique, the SAW active layers can be placed close to doped layers, expanding the application range of SAWs in semiconductor devices.

For radioactive thin specimens in high pressure or high temperature environments, the conventional approach for high precision elastic modulus measurements is not easy. Radiation damage to transducer’s bonds or the substantial changes in specimen dimensions induced by temperature, pressure, and phase transitions, reduce the intrinsic accuracy of the time-of-flight acoustic measurements. We describe here an alternative approach in which the surface acoustic-wave (SAW) velocity is measured directly with a fixed propagation distance, independent of specimen dimensions. Then, using the known relationship between SAW and shear velocities, it is possible to obtain the shear modulus with a high accuracy without measuring the bulk shear wave. Laser ultrasonics was used combining a pulsed laser source with a heterodyne interferometer. The proposed technique is validated for Al, Au, Ta, and Pb 0.8% Ca, TA6V4 without phase transitions, and for Sn and Co through the phase transitions.

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