L. R. Ram Mohan

Piezomodulated electronic spectra of semiconductor heterostructures: GaAs/AlxGa1−xAs quantum well structures

Optical transitions associated with the electronic levels of a single quantum well in GaAs/AlxGa1−xAs heterostructures are observed with exceptional clarity in the piezomodulated reflectivity spectrum measured down to liquid helium temperature. The splitting of such transitions in multiple quantum well structures due to the coupling of the electronic levels in the adjacent wells is illustrated with results on a double quantum well.

Theory of electromagnetic generation of acoustic waves in metals

Abstract The theory of the anomalous skin effect in metals is used in order to study the direct generation of ultrasound by electromagnetic radiation incident on a metal surface, in the absence and in the presence of a magnetic field. The non-monotonic behaviour of the acoustic flux observed experimentally, as a function of the magnetic field can be explained within the framework of the free-electron model assuming that the electrons are scattered diffusely from the metal surface. The reason for this behaviour is traced to the variation of the relative phases of the collision drag force on the bulk ions and that on the surface with increasing magnetic field. The relations between existing theories of direct generation of ultrasound have been investigated within both the free-electron approximation and the effective-mass theory. We conclude that, besides the collision drag force, the Lorentz force and the Bragg reaction force, an additional ‘deformation’ force acts upon the positive ions. We find that the ...

Density isomerism and the Primakoff effect

Abstract We show that the decay width for π 0 →2 γ in nuclear matter could be used as a signal for phase transitions in nuclear matter. The decay width of the π 0 is experimentally measured using pion photoproduction off heavy nuclei by observing the Primakoff peak in the differential cross sections. We present calculations for the differential cross section with corrections to the γ − γ − π 0 vertex arising from the nuclear medium within the nuclear radius when the medium is in the abnormal matter phase.