Hydrostatic pressure study of paramagnetic-ferromagnetic phase transition in (Ga,Mn)As

The effect of hydrostatic pressure on the paramagnetic - ferromagnetic phase transition has been studied in (Ga,Mn)As. The variation of the Curie temperature (TC) with pressure was monitored by two transport methods: (1) - measurement of zero field resistivity versus temperature {\rho}(T), (2) - dependence on temperature of the Hall voltage hysteresis loop. Two specimens of different resistivity characteristics were examined. The measured pressure-induced changes of TC were relatively small (of the order of 1K/GPa) for both samples, however they were opposite for the two.Comment: 8 pages, 7 figure

Interparticle interactions:Energy potentials, energy transfer, and nanoscale mechanical motion in response to optical radiation

In the interactions between particles of material with slightly different electronic levels, unusually large shifts in the pair potential can result from photoexcitation, and on subsequent electronic excitation transfer. To elicit these phenomena, it is necessary to understand the fundamental differences between a variety of optical properties deriving from dispersion interactions, and processes such as resonance energy transfer that occur under laser irradiance. This helps dispel some confusion in the recent literature. By developing and interpreting the theory at a deeper level, one can anticipate that in suitable systems, light absorption and energy transfer will be accompanied by significant displacements in interparticle separation, leading to nanoscale mechanical motion

Quantum-based realizations of the pascal: status and progress of the EMPIR-project: quantumpascal

The QuantumPascal (QP) project combines the capabilities of 12 European institutions to enable traceable pressure measurements utilizing quantum-based methods that evaluate the number density instead of force per area to target the wide pressure range between 1 Pa and 3 MPa. This article summarizes the goals and results since the project start in June 201

Current Fluctuations in Single Barrier Vertical GaAs/AlAs/GaAs Tunneling Devices

We report the experimental results of the low temperature (T = 4.2 K) low-frequency current fluctuations measurements in the single-barrier resonant tunneling GaAs/AlAs/GaAs device with Siδ-doping in the center of the 10 nm thick AlAs barrier. The dimensions of the device were 200μm by 200μm. For the biasing voltages 0.1 V<|U|<1 V we observed the Fano factors between F = 0.7 and F = 0.95. We explain it by the existence of the trapping centers/imperfections/resonant levels inside the barrier participating in the transport for this range of voltages. Only for the smallest biasing voltages the Fano factor tends to F = 1, expected for a highly nontransparent barrier

Current Fluctuations in Single Barrier Vertical GaAs/AlAs/GaAs Tunneling Devices

We report the experimental results of the low temperature (T = 4.2 K) low-frequency current fluctuations measurements in the single-barrier resonant tunneling GaAs/AlAs/GaAs device with Siδ-doping in the center of the 10 nm thick AlAs barrier. The dimensions of the device were 200μm by 200μm. For the biasing voltages 0.1 V<|U|<1 V we observed the Fano factors between F = 0.7 and F = 0.95. We explain it by the existence of the trapping centers/imperfections/resonant levels inside the barrier participating in the transport for this range of voltages. Only for the smallest biasing voltages the Fano factor tends to F = 1, expected for a highly nontransparent barrier

Stabilization of the Distorted Configuration of the EL2 Defect Induced by the Free Electron Capture in GaAsP

Our results of optical absorption, electronic transport and deep level transient spectroscopy measurements performed on n-type GaAs$\text{}_{1-x}$P$\text{}_{x}$ (x ≈ 0.2) strongly suggest that using both an enlarged-gap material (compared to GaAs) and hydrostatic pressure we can push down the acceptor level of the distorted configuration of the EL2 defect, (EL2*) $\text{}^{–}\text{}^{/}\text{}^{0}$ , sufficiently low into the gap that the distorted configuration of the EL2 defect, EL2*, becomes stabilized

High-Pressure Magnetotransport Measurements of Resonant Tunnelling via X-Minimum Related States in AlAs Barrier

In this paper, we present the results of magnetotransport experiments performed on a single barrier GaAs/AlAs/GaAs heterostructures. Tunnel current was measured as a function of magnetic field for different values of bias voltage and hydrostatic pressure. We observed that the amplitude of the magnetooscillations of tunnel current quenched when the requirements for resonant tunnelling were met and it recovered in out-of-resonance conditions. This effect was observed both for tunnelling through donor states and through X-minimum related quasiconfined conduction band states. The fact that also in the latter case the amplitude was restored suggests that this process involved X$\text{}_{z}$ subbands and took place without a participation of phonons (the so-called k$\text{}_{ǁ}$-conserving process)