Generation and Detection of Spin Currents in Semiconductor Nanostructures with Strong Spin-Orbit Interaction

Storing, transmitting, and manipulating information using the electron spin resides at the heart of spintronics. Fundamental for future spintronics applications is the ability to control spin currents in solid state systems. Among the different platforms proposed so far, semiconductors with strong spin-orbit interaction are especially attractive as they promise fast and scalable spin control with all-electrical protocols. Here we demonstrate both the generation and measurement of pure spin currents in semiconductor nanostructures. Generation is purely electrical and mediated by the spin dynamics in materials with a strong spin-orbit field. Measurement is accomplished using a spin-to-charge conversion technique, based on the magnetic field symmetry of easily measurable electrical quantities. Calibrating the spin-to-charge conversion via the conductance of a quantum point contact, we quantitatively measure the mesoscopic spin Hall effect in a multiterminal GaAs dot. We report spin currents of 174 pA, corresponding to a spin Hall angle of 34%

Characterization of spin-orbit interactions of GaAs heavy holes using a quantum point contact

We present transport experiments performed in high quality quantum point contacts embedded in a GaAs two-dimensional hole gas. The strong spin-orbit interaction results in peculiar transport phenomena, including the previously observed anisotropic Zeeman splitting and level-dependent effective g-factors. Here we find additional effects, namely the crossing and the anti-crossing of spin-split levels depending on subband index and magnetic field direction. Our experimental observations are reconciled in an heavy hole effective spin-orbit Hamiltonian where cubic- and quadratic-in-momentum terms appear. The spin-orbit components, being of great importance for quantum computing applications, are characterized in terms of magnitude and spin structure. In the light of our results, we explain the level dependent effective g-factor in an in-plane field. Through a tilted magnetic field analysis, we show that the QPC out-of-plane g-factor saturates around the predicted 7.2 bulk value

Tunneling, Spin Dynamics and Interference at the Fractional Quantum Hall Edge

The quantum Hall effect, the first topological quantum phase of matter ever observed, remains today an important framework for the advancement of fundamental physics. With the advent of the topological model of quantum computation and the prediction of nonabelian braiding statistics in the ν=5/2 state, it further gained technological relevance as a potential platform for proof-of-concept demonstration of an intrinsically noise-resistant qubit. Both for enabling technological advances and answering fundamental questions, it is essential to understand transport of fractional quasiparticles across narrow constrictions. The edges of fractional quantum Hall (FQH) fluids are predicted to form strongly interacting chiral one-dimensional systems, resulting in unique dynamics of the tunneling processes coupling them. We investigate the validity of the existing theory in relatively simple, well-understood states, closing a gap in the available literature. Our data agree partially with the theoretical model, with an effective quasiparticle charge of e/3 obtained in a nonlinear regression analysis in parts of the parameter space. The phenomenology is more complex than anticipated, highlighting the need for further theoretical efforts. As the material system which can be grown with the highest purity, GaAs is the platform of choice for research into the fractional quantum Hall effect. The presence of spinful nuclei with a sizeable hyperfine interaction of the conduction electrons is both a blessing and a curse, resulting in a considerable enrichment of transport phenomena in the fractional quantum Hall effect whenever two ground states of opposite spin are energetically close. Well documented in extended areas of 2DEG, those effects have so far not been thoroughly explored in confined systems. We study the dynamic interaction of a quantum point contact with its nuclear environment, and show that neighboring structures can be coupled by the diffusion of nuclear spins. Lastly, we report studies of electronic interferometers designed to probe braiding statistics in fractional quantum Hall states. More than ten years after the publication of first theoretical proposals and experimental efforts, path interference of quasiparticles has proven difficult to realize. We set limits on the dimensions of conventional geometries susceptible of probing braiding statistics and introduce a new promising design, reporting indications of the Aharonov-Bohm effect in the ν=4/3 state. The insights we provide open questions with respect to fundamental aspects of the dynamics of edge states and to properties of unconventional interferometers geometries, motivating extensive theoretical investigations. Further, we propose new experimental approaches to the study of fractional quantum Hall edge states, potentially guiding further experimental work. Finally, our report of a signature of path interference in a fractional state together with a first characterization of more advanced gating techniques is an encouraging step towards the successful demonstration of noncommutative braiding statistics

Generation and detection of spin currents in semiconductor nanostructures with strong spin-orbit interaction

Storing, transmitting, and manipulating information using the electron spin resides at the heart of spintronics. Fundamental for future spintronics applications is the ability to control spin currents in solid state systems. Among the different platforms proposed so far, semiconductors with strong spin-orbit interaction are especially attractive as they promise fast and scalable spin control with all-electrical protocols. Here we demonstrate both the generation and measurement of pure spin currents in semiconductor nanostructures. Generation is purely electrical and mediated by the spin dynamics in materials with a strong spin-orbit field. Measurement is accomplished using a spin-to-charge conversion technique, based on the magnetic field symmetry of easily measurable electrical quantities. Calibrating the spin-to-charge conversion via the conductance of a quantum point contact, we quantitatively measure the mesoscopic spin Hall effect in a multiterminal GaAs dot. We report spin currents of 174 pA, corresponding to a spin Hall angle of 34%

Quasiparticle tunneling in the lowest Landau level

ISSN:1098-0121ISSN:0163-1829ISSN:1550-235XISSN:0556-2805ISSN:2469-9969ISSN:1095-379

Aharonov-Bohm rings with strong spin-orbit interaction: the role of sample-specific properties

We present low-temperature transport experiments on Aharonov–Bohm (AB) rings fabricated from two-dimensional hole gases in p-type GaAs/AlGaAs heterostructures. Highly visible h/e (up to 15%) and h/2e oscillations, present for different gate voltages, prove the high quality of the fabricated devices. Like in previous work, a clear beating pattern of the h/e and h/2e oscillations is present in the magnetoresistance, producing split peaks in the Fourier spectrum. The magnetoresistance evolution is presented and discussed as a function of temperature and gate voltage. It is found that sample specific properties have a pronounced influence on the observed behaviour. For example, the interference of different transverse modes or the interplay between h/e oscillations and conductance fluctuations can produce the features mentioned above. In previous work they have occasionally been interpreted as signatures of spin–orbit interaction (SOI)-induced effects. In the light of these results, the unambiguous identification of SOI-induced phase effects in AB rings remains still an open and challenging experimental task.ISSN:1367-263

Quantum dot thermometry at ultra-low temperature in a dilution refrigerator with a 4 He immersion cell

Experiments performed at a temperature of a few millikelvins require effective thermalization schemes, low-pass filtering of the measurement lines, and low-noise electronics. Here, we report on the modifications to a commercial dilution refrigerator with a base temperature of 3.5 mK that enable us to lower the electron temperature to 6.7 mK measured from the Coulomb peak width of a quantum dot gate-defined in an [Al]GaAs heteostructure. We present the design and implementation of a liquid He-4 immersion cell tight against superleaks, implement an innovative wiring technology, and develop optimized transport measurement procedures. Published under license by AIP Publishing