[en] It has recently been shown that at T < 270 K a persistent inversion from n- to p-type can be induced by illumination in a 200-nm-thick surface layer of lowly-doped commercial germanium wafers [1]. The presence of photo-generated holes is detected by the appearance of a fast relaxing component in TF-μSR measurements, caused by cyclic muonium charge state transitions Mu"−_T + h"+ leftrightharpoons Mu"0_T. For a quantitative determination of the photo-induced hole carrier concentration we use a Monte-Carlo simulation to generate muon decay histograms for different hole capture rates (forward reaction), and ionization rates (reverse reaction due to thermal activation) [2]. The hole carrier concentration is determined by comparing simulated and experimental relaxation rates. These results have been used to estimate the photo-induced hole concentration in low-energy μSR experiments [1]

No abstract available

[en] Full text: The controlled manipulation of the charge carrier concentration in nanometer-thin layers is the basis of current semiconductor technology and of fundamental importance for device applications. Here we demonstrate the persistent inversion from n- to p-type in a 200-nm-thick surface layer of germanium wafers by illumination. The inversion with a half-life >12 h is induced at T=220 K, and disappears after warming above 280 K. The increase of the hole carrier concentration in the surface layer is detected by low-energy muon spin rotation. We propose accumulation of photo-generated electrons in empty surface acceptor states as the origin of the inversion, and that thermal activation at T∼280 K liberates the electrons from the surface states. (author)

No abstract available

[en] Heterostructures consisting of magnetic/superconducting layers juxtaposed to each other are ideal systems to investigate the interplay of the two order parameters and to study possible interlayer coupling. Recently, so called giant proximity effects have been reported in Josephson devices consisting of HTS electrodes and a barrier of a cuprate in the pseudogap or AF state. Low energy μSR offers the unique possibility to measure on a nanometer scale local field distributions and identify superconducting and magnetic fractions. We used polarized low energy muons to investigate the local properties of single, bi- and tri-layers composed of superconducting YBa₂Cu₃O_7-δ and semiconducting PrBa₂Cu₃O_7-δ. Zero field measurements show that the PBCO layers (thickness 50-75 nm) display in all structures the known AF ordering. However, measurements of the field profile B(z) in the Meissner state show that below the critical temperature of YBCO, supercurrents flow without dissipation over the 50 nm thick AF barrier. The measurements indicate that a finite superfluid density may be induced in the AF layer adjacent to the superconducting layer.

No abstract available

[en] For classical superconductors the interaction with light results in a reduction of the energy gap due to excess of quasiparticles. Surprisingly, this is very different for cuprate superconductors where it was found that illumination with light increases the charge carrier density. Systematic investigations in YBa₂Cu₃O_7-δ showed that T_c is increased by this effect which is most pronounced at the heavily underdoped side of the phase diagram. Up to now studies of photo-induced processes have been restricted to investigations of transport properties and critical temperatures. Using low energy μSR changes in the Meissner screening profile caused by illumination were directly investigated. We will show that the photo-persistent effect in underdoped YBa₂Cu₃O_7-δ is related to an increase of the superfluid density close to the surface. We are also able to show that the oxygen ordering is a crucial ingredient of the photo-induced effect.

No abstract available