R. von Baltz

The origin of the photo-emf in ferroelectric and non-ferroelectric materials

A photo-emf arises from an optical excitation that is either asymmetric in k-space or occurs at asymmetries in real space, as is shown by a discussion of the Boltzmann transport equation. Excitation asymmetric in k-space leads to the photogalvanic effect. A photo-current is impressed with unpolarized light in the bulk of ferro- and pyroelectric crystals, and with polarized light even in non-pyroelectric piezoelectric crystals. Photon drag and optical rectification are outlined in connection with the photogalvanic effects. Excitation at asymmetries in real space leads to a barrier photo-emf, if both electrons and holes are mobile and if the electric and chemical potentials are not spatially constant in the unilluminated semiconductor. The Dember effect as being based on one mobile charged species only, does not represent a photo-emf. Anomalous photovoltages of a magnitude larger than the band gap, in particular in polytype zinc sulfide, that have been accounted for by a battery of barrier photo cells, are ...

The bulk photovoltaic effect in ferro- and piezoelectric materials

Abstract Under fixed illumination intensity I, a photovoltaic cell can be characterized by its short circuit current (-density) js and its open circuit voltage Vo. In the following, we shall restrict ourselves to the discussion of steady state phenomena where Vo is identical with the emf of the cell.

Acoustic plasmons in a two-component Fermi system

The dispersion and line width of the longitudinal collective modes of a two-component degenerate Fermi-system (T=0) are obtained from the zeros of the dielectric function ε(q,ω). The basis of our theory are kinetic equations for the distribution function including elastic electron-impurity scattering. Our results area) there is only one acoustic branchb) this mode is overdamped forq→0, andc) acoustic plasmons contribute only little to the energy loss-function (or the screened electron-ion and electron-electron potential).

Distance between quantum states and the motion of wave packets

A definition of the distance between two quantum states is given which is independent of the (global) phase of the wavefunction. For example, wave packets for the harmonic oscillator and a particle in a box potential are investigated.

On the intrinsic bulk photovoltaic effect: Performing the sum over intermediate states

By using a different approach as proposed recently, we perform an analytical summation of virtual transitions to all Bloch bands in terms of derivatives of Bloch functions. This alternative discussion about the existence of an intrinsic bulk photovoltaic effect confirms our previous results. We also would like to emphasize that the bulk photovoltaic effect may be used as a sensitive tool investigating the electronic structure of a solid.

Dielectric function of one-dimensional peirls insulator

Abstract We use Penns model to calculate the complex dielectric functional and reflectivity of a quasi-one-dimensional insulator. A brief comparison with KCP is made.

Bulk photovoltaic effect in pure pyro- and piezoelectrics

Abstract We present an exact expression for the bulk photovoltaic response coefficient of a pure noncentrosymmetric crystal. Our theory may explain experimental results obtained for ferroelectric BaTiO 3 and piezoelectric Te and GaP.

A model calculation to explain the existence of bulk photo-currents in ferroelectrics

Abstract We present a quantum mechanical calculation of the bulk photovoltaic current in ferroelectrics which leads to the correct order of magnitude compared with experimental data. Our theory is based on the model of “asymmetric” transition probabilities which has been recently proposed by Glass to explain the anomalous photovoltaic effect in LiNbO3.

Band structure investigation of the bulk photovoltaic effect in n-GaP

Abstract A band structure investigation of the bulk photovoltaic tensor for n-Gap is presented. It is based on a second-order quantum mechanical response formalism and the known electronic structure of GaP. The good agreement between experimental data and our numerical results demonstrates that the intrinsic bulk photovoltaic effect in GaP is related to an optically induced nonlinear interference phenomenon.

Use of Micro-Computers in Theoretical Physics Courses

When teaching physics nowadays, usage of PC’s offers a powerful tool to make students acquainted with realistic systems and models of theoretical physics. Hereto we give two examples: Dynamics of a Laser and Eigenstates of a Quantum Particle in a Potential.