György Papp

Spin filtering in a magnetic-electric barrier structure

The spin-dependent tunnelling of two-dimensional electrons through a magnetic barrier can be substantially enhanced by the addition of an electric barrier. The spin polarization is found to be strongly dependent on the incident wave vector parallel to the barrier, the incident electron energy, and the height of the electric barrier. The conductance for the spin-up and spin-down electrons can be tuned with this electrical barrier.

Snake states and Klein tunneling in a graphene Hall bar with a pn-junction

The Hall (RH) and bend (RB) resistances of a graphene Hall bar structure containing a pn-junction are calculated when in the ballistic regime. The simulations are done using the billiard model. Introducing a pn-junction—dividing the Hall bar geometry in two regions—leads to two distinct regimes exhibiting very different physics: (1) both regions are of n-type and (2) one region is n-type and the other p-type. In regime (1), a “Hall plateau”—an enhancement of the resistance—appears for RH. On the other hand, in regime (2), we found a negative RH, which approaches zero for large B. The bend resistance is highly asymmetric in regime (2) and the resistance increases with increasing magnetic field B in one direction while it reduces to zero in the other direction.

Wood degradation caused by UV-laser of 248 nm wavelength

Methods and materials Krypton fluoride (KrF) excimer laser of 248 nm wavelength is used to study the degradation of wood. All of the samples were irradiated by 5000 pulses selected from the pulse train of the laser operated with 10 Hz repetition frequency. The pulses had 15 ns duration and 20 mJ energy. We studied the effect of UV-laser irradiation on eight wood species by IR spectroscopic methods. The samples were chosen from four kinds of soft wood (Scotch pine, spruce, larch, Douglas-fir) and from four kinds of hard wood (Black locust, beech, ash, silver maple). Within these groups 4-4 samples were chosen so that the different issues (heartwood, sapwood, eartywood, latewood) represented all species. Diffuse reflected infrared spectra were recorded before and after irradiation using a Bio-Rad Digilab FTS-65A/896 FTIR-spectrometer. The spectra were baseline corrected using a linear algorithm and were normalized to the band between 1352 cm -~ and t406 cm-k The spectrum of the untreated sample was subtracted from the spectrum of the irradiated one, to obtain the difference spectrum.