P. H. O. Rappl

Experimental investigation of spin-orbit coupling in n-type PbTe quantum wells

The spin-orbit coupling is studied experimentally in two PbTe quantum wells by means of weak antilocalization effect. Using the Hikami-Larkin-Nagaoka model through a computational global optimization procedure, we extracted the spin-orbit and inelastic scattering times and estimated the strength of the zero field spin-splitting energy Δso. The values of Δso are linearly dependent on the Fermi wave vector (kF) confirming theoretical predictions of the existence of large spin-orbit coupling in IV-VI quantum wells originated from pure Rashba effect.

Systematic study of doping dependence on linear magnetoresistance in p-PbTe

We report on a large linear magnetoresistance effect observed in doped p-PbTe films. While undoped p-PbTe reveals a sublinear magnetoresistance, p-PbTe films doped with BaF2 exhibit a transition to a nearly perfect linear magnetoresistance behaviour that is persistent up to 30u2009T. The linear magnetoresistance slope ΔR/ΔB is to a good approximation, independent of temperature. This is in agreement with the theory of Quantum Linear Magnetoresistance. We also performed magnetoresistance simulations using a classical model of linear magnetoresistance. We found that this model fails to explain the experimental data. A systematic study of the doping dependence reveals that the linear magnetoresistance response has a maximum for small BaF2 doping levels and diminishes rapidly for increasing doping levels. Exploiting the huge impact of doping on the linear magnetoresistance signal could lead to new classes of devices with giant magnetoresistance behavior.

Room temperature persistent photoconductivity in p-PbTe and p-PbTe:BaF2

We investigated the persistent photoconductivity effect observed in p-PbTe:BaF2 and undoped p-PbTe films in the temperature range of Tu2009=u2009100–300u2009K. It was observed that the PPC effect scales with temperature and that there is a transition in the relaxation time behavior around ∼150u2009K. We found that the transition is caused by the particular dynamics of the hole carries between the energy barriers that characterize the traps originated from disorder present in the samples. The analysis was performed by comparing the theory of the random potential with the experimental data and revealed the presence of both random local potential fluctuations and localized states, which can be attributed to the presence of disorder due BaF2 doping and Te vacancies.

Investigation of negative photoconductivity in p-type Pb1-xSnxTe film

We investigated the negative photoconductivity (NPC) effect that was observed in a p-type Pb1-xSnxTe film for temperatures varying from 300u2009K down to 85u2009K. We found that this effect is a consequence of defect states located in the bandgap which act as trapping levels, changing the relation between generation and recombination rates. Theoretical calculations predict contributions to the NPC from both conduction and valence bands, which are in accordance with the experimental observations.

Systematic study of transport via surface and bulk states in Bi2Te3 topological insulator

We performed magnetoresistance measurements on Bi2Te3 thin film in the temperature range of T = 1.2–4.0 K and for magnetic fields up to 2 T. The curves exhibited anomalous behavior for temperatures below 4.0 K. Different temperature intervals revealed electrical transport through different conductive channels with clear signatures of weak antilocalization. The magnetoresistance curves were explained using the Hikami–Larkin–Nagaoka model and the 2D Dirac modified model. The comparison between the parameters obtained from the two models revealed the transport via topological surface states and bulk states. In addition, a superconductive like transition is observed for the lowest temperatures and we suggest that this effect can be originated from the misfit dislocations caused by strain, giving rise to a superconductive channel between the interface of the film and the substrate.

Fast photoresponse and high parallel transport in n-type PbTe/PbEuTe quantum wells

We investigated the photoconductivity effect in n-type PbTe/Pb0.88Eu0.12Te quantum wells for a temperature range of 300–10u2009K using infrared light. The measurements revealed that at high temperatures, the photoresponse has small amplitude. As temperature decreases to Tu2009∼u200975u2009K, however, the photoconductivity amplitude increases reaching a maximum value 10 times higher than the original value before illumination. From Hall measurements performed under dark and light conditions, we show that this effect is a result of the carrier concentration increase under illumination. Unexpectedly, for further reduction of temperature, the amplitude starts to decrease again. The electrical resistance profiles indicate that the transport occurs through barriers and the well that behave as two parallel channels. For temperatures below 75u2009K, transport is more effective in the quantum well, where the signal reduction can be associated with the electron-electron scattering due to the increase in the carrier concentration that ...