arXiv subjects

Janusz Sadowski

Publications and source records attributed to Janusz Sadowski.

24 records · Page 2Linked to original sources

arXiv2010

Semiconductor quantum ring as a solid-state spin qubit

The implementation of a spin qubit in a quantum ring occupied by one or a few electrons is proposed. Quantum bit involves the Zeeman sublevels of the highest occupied orbital. Such a qubit can be initialized, addressed, manipulated, read out and coherently coupled to other quantum rings. An extensive discussion of relaxation and decoherence is presented. By analogy with quantum dots, the spin relaxation times due to spin-orbit interaction for experimentally accessible quantum ring architectures are calculated. The conditions are formulated under which qubits build on quantum rings can have long relaxation times of the order of seconds. Rapidly improving nanofabrication technology have made such ring devices experimentally feasible and thus promising for quantum state engineering.

cond-mat.mes-hall↗

arXiv2009

Transport through (Ga,Mn)As nanoislands: Coulomb-blockade and temperature dependence of the conductance

We report on magnetotransport measurements of nanoconstricted (Ga,Mn)As devices showing very large resistance changes that can be controlled by both an electric and a magnetic field. Based on the bias voltage and temperature dependent measurements down to the millikelvin range we compare the models currently used to describe transport through (Ga,Mn)As nanoconstrictions. We provide an explanation for the observed spin-valve like behavior during a magnetic field sweep by means of the magnetization configurations in the device. Furthermore, we prove that Coulomb-blockade plays a decisive role for the transport mechanism and show that modeling the constriction as a granular metal describes the temperature and bias dependence of the conductance correctly and allows to estimate the number of participating islands located in the constriction.

cond-mat.mes-hall↗

arXiv2008

Autocatalytic MBE growth of GaAs nanowires on oxidized Si(100)

GaAs nanowires were grown by molecular beam epitaxy on Si(100) substrates covered with 5 nm SiO2. The growth was performed with As4 at low, close to stoichiometric, As4/Ga flux ratio, using Ga nanodroplets as catalyst. The nanowires are found to be in epitaxial relation to the Si substrate due to contact via pinholes through the SiO2 layer. The nanowires are up to 15 micrometers long and have diameters of about 100 nm, the catalyzing Ga nanodroplets are observed at their tops.

cond-mat.mtrl-sci↗

arXiv2008

GaMnAs: layers, wires and dots

Thin layers of GaMnAs ferromagnetic semiconductor grown by molecular beam epitaxy on GaAs(001) substrates were studied. To improve their magnetic properties the post-growth annealing procedures were applied, using the surface passivation layers of amorphous arsenic. This post growth treatment effectively increases the ferromagnetic-to-paramagnetic phase transition temperature in GaMnAs, and provides surface-rich MnAs layer which can be used for formation of low dimensional structures such as superlattices. If the surface rich MnAs layer consists of MnAs dots, then it is possible to grow Mn-doped GaAs nanowires

cond-mat.mtrl-sci↗

arXiv2007

Electron-electron interaction in 2D and 1D ferromagnetic (Ga,Mn)As

We investigated the magnetotransport in high quality ferromagnetic (Ga,Mn)As films and wires. At low temperature the conductivity decreases with decreasing temperature without saturation down to 20 mK. Here we show, that the conductivity decrease follows a ln($T/T_0$) dependency in 2D films and a $-1/\sqrt{T}$ dependency in 1D wires and is independent of an applied magnetic field. This behavior can be explained by the theory of electron-electron interaction.

cond-mat.mes-hall↗

arXiv2006

All-electrical measurement of spin injection in a magnetic $p$-$n$ junction diode

Magnetic $p$-$n$ junction diodes are fabricated to investigate spin-polarized electron transport. The injection of spin-polarized electrons in a semiconductor is achieved by driving a current from a ferromagnetic injector (Fe), into a bulk semiconductor ($n$-GaAs) via schottky contact. For detection, a diluted magnetic semiconductor ($p$-GaMnAs) layer is used. Clear magnetoresistance was observed only when a high forward bias was applied across the $p$-$n$ junction.

cond-mat.mes-hall↗