Zusammenfassung (Englisch)
When considering quantization effects in 1D in the context of materials with strong spin-orbit interaction, new research fields have opened up as, for example, the high-topical field of topological quantum computation. Therein, the coupling of a high-mobility 2D electron gas with large spin-orbit interaction to an s-wave superconductor presents a fundamental part. In these experiments, quantum ...
Zusammenfassung (Englisch)
When considering quantization effects in 1D in the context of materials with strong spin-orbit interaction, new research fields have opened up as, for example, the high-topical field of topological quantum computation. Therein, the coupling of a high-mobility 2D electron gas with large spin-orbit interaction to an s-wave superconductor presents a fundamental part. In these experiments, quantum point contacts are employed to measure the quantized conductance doubling. Furthermore, to follow the theoretical recipe for the creation of a spinless p-wave superconductor in which a single isolated Majorana state arises, quantum point contacts generate the required 1D subband structure.
As a second example, the physics of quantum point contacts has fueled a variety of device applications and concepts, merging under the roof of spinorbitronics. One goal is the realization of a spin-transistor. Realizing the proposed spin-transistor generally entails two main manufacturing challenges: Firstly, using ferromagnetic electrodes for the generation and read-out of the spin-polarized current, one is usually subjected to the conductance mismatch. Secondly, spin-dephasing mechanisms inside the transistor channel impede a loss-free transmission of spin-information. An elegant, ballistic and all-electric spin-transistor concept has been recently presented, wherein these obstacles are readily eliminated. Therein, two serial quantum point contacts, which are implemented in a 2D electron gas, are employed as a spin injector and spin detector by adjusting the strength of lateral spin-orbit coupling inside the 1D channel.
Given the examples outlined above, it is interesting to note that the key requirements for topological quantum computation and the spinorbitronic device application are very similar: Achieving large spin-orbit coupling in a highly mobile electron system with a clean semiconductor surface. In this regard, InAs/InGaAs-based heterostructures offer inherent advantages in their material properties, like a low effective mass, a large Landé g-factor, as well as large Rashba spin-orbit interaction, making them attractive candidates for these device applications.
To harvest the undeniable potential of this semiconductor system, material specific challenges have to be met. This thesis focuses on those perspectives of the InAs-based material system which would qualify it as a reliable platform for the realization of reliable 1D spinorbitronic devices.
For this purpose, we studied the electric transport behavior in one and two dimensions in the InGaAs/InAlAs-based material system, which offers high electron mobility and in principle gives access to high spin-orbit interaction. In our initial 1D transport measurements with electrically defined quantum point contacts, we found severe conductance instabilities near depletion of the 1D channel, which furthermore led to a significant hysteretic behavior with impeded ballisticity. In a systematic study of the electric transport in different InGaAs/InAlAs layouts, we identified energy states at the InGaAs surface, together with ionized deep level donor states inside the InAlAs barrier layers to limit the field-effect control of the transport properties in one and two dimensions. On the basis of the obtained results – all merging in a conclusive charge transfer model which we developed in the course of this thesis – we eventually achieved reliable control of the electric transport characteristics and accomplished to significantly enlarge the charge density range in the 2DEG accessible via external gating. In the course of this evaluation, we reveal a top-gate voltage field regime, in which we create a metastable charge configuration state in the system that yielded a giant and surprising magnification of Rashba-type spin-orbit interaction. We provide an interpretation for the origin of this effect by means of self-consistent band structure calculations.
Übersetzung der Zusammenfassung (Deutsch)
Die vorliegende Arbeit beschäftigt sich mit dem Potential InAs-basierter Materialsysteme als Entwicklungsplattform für zuverlässige und robuste 1D-Spinorbitronik-Bauelemente.
Im Fokus dabei stehen Untersuchungen des Feldeffekt-gesteuerten elektrischen Transportverhaltens ein- und zweidimensionaler InGaAs/InAlAs-Systeme. Basierend auf den Erkenntnissen dieser Transportstudie, deren Ergebnisse in ...
Übersetzung der Zusammenfassung (Deutsch)
Die vorliegende Arbeit beschäftigt sich mit dem Potential InAs-basierter Materialsysteme als Entwicklungsplattform für zuverlässige und robuste 1D-Spinorbitronik-Bauelemente.
Im Fokus dabei stehen Untersuchungen des Feldeffekt-gesteuerten elektrischen Transportverhaltens ein- und zweidimensionaler InGaAs/InAlAs-Systeme. Basierend auf den Erkenntnissen dieser Transportstudie, deren Ergebnisse in einem in sich schlüssigen Umladungsmodel zusammengeführt werden, kann zudem mittels Bandstrukturrechnungen die beobachtete Vervielfachung der Rashba Spin-Bahn-Kopplungsstärke während des Bestehens einer metastabilen Ladungsanordnung im System diskutiert und nachvollzogen werden.
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