Solid State Physics Laboratory

About: Solid State Physics Laboratory is a facility organization based out in Delhi, India. It is known for research contribution in the topics: Quantum dot & Dielectric. The organization has 1754 authors who have published 2597 publications receiving 50601 citations.

Enhanced Interactions between Dipolar Polaritons

Abstract: Nonperturbative coupling between cavity photons and excitons leads to the formation of hybrid light-matter excitations, termed polaritons. In structures where photon absorption leads to the creation of excitons with aligned permanent dipoles, the elementary excitations, termed dipolar polaritons, are expected to exhibit enhanced interactions. Here, we report a substantial increase in interaction strength between dipolar polaritons as the size of the dipole is increased by tuning the applied gate voltage. To this end, we use coupled quantum well structures embedded inside a microcavity where coherent electron tunneling between the wells creates the excitonic dipole. Modifications of the interaction strength are characterized by measuring the changes in the reflected light intensity when polaritons are driven with a resonant laser. The factor of 6.5 increase in the interaction-strength-to-linewidth ratio that we obtain indicates that dipolar polaritons could constitute an important step towards a demonstration of the polariton blockade effect, and thereby to form the building blocks of many-body states of light.

Comparison of etch characteristics of KOH, TMAH and EDP for bulk micromachining of silicon (110)

Abstract: Bulk micromachining in Si (110) wafer is an essential process for fabricating vertical microstructures by wet chemical etching. We compared the anisotropic etching properties of potassium hydroxide (KOH), tetra-methyl ammonium hydroxide (TMAH) and ethylene di-amine pyro-catechol (EDP) solutions. A series of etching experiments have been carried out using different etchant concentration and temperatures. Etching at elevated temperatures was found to improve the surface quality as well as shorten the etching time in all the etchants. At 120°C, we get a smooth surface (Ra = 21.2 nm) with an etching rate 12.2 μm/min in 40wt% KOH solution. At 125°C, EDP solution (88wt%) was found to produce smoothest surface (Ra = 9.4 nm) with an etch rate of 1.8 μm/min. In TMAH solution (25wt%), the best surface roughness was found to be 35.6 nm (Ra) at 90°C with an etch rate of 1.18 μm/min. The activation energy and pre-exponential factor in Arrhenius relation are also estimated from the corresponding etch rate data.

The order parameters and in nematic p-alkyl-p' -cyano-biphenyls : polarized Raman measurements and the influence of molecular association

Abstract: Values for the order parameters and from polarized Raman measurements are reported for the homologous series of nemaric alkylcyanobiphenyls. With increasing chain length a change of behaviour is observed from «low» -values to higher values corresponding to the Maier-Saupe mean-fied theory. In addition, correlation factors describing the anti-parallel molecular association in these compounds have been derived from permittivity measurements. A tentative qualitative model is given in which the low -values are attributed to this association. This leads to a certain proportion of «dimers», for which the long molecular axis is not parallel to the direction of the Raman-vibration anymore. In addition, steric interactions can be expected to lead to non-parallelism of the long axis of a dimer and of a neighbouring monomer. For specific parameters of the dimer, the combination of these two effects can lead to a marked broadening of f(β), and thus to low or negative values for En fonction de la longueur des chaines, on observe une augmentation de correspondant a la theorie de champ moyen de Maier et Saupe. Evaluation des facteurs de correlation decrivant l'association moleculaire antiparallele en vue de mesures de permittivite

Physical-properties of liquid-crystalline materials in relation to their applications

Abstract: A short review is given of successively the diamagnetic susceptibility, the refractive index, the dielectric permittivity, the elastic constants and the viscosity coefficients of nematic liquid crystals. Emphasis is on typical results that have been obtained, and the possibilities and problems connected with a molecular interpretation. In particular an attempt is made to distinguish in the macroscopic quantity the influence of the molecular properties involved, of the direct temperature dependence, and of the dependence on the orientational order (indirect temperature dependence).