Spin magnetization and electron localization in semiconductor quantum wires and quantum point contacts
2012 (English)Conference paper (Other academic)
The physics of low-dimensional semiconductor structures such as quantum wires (QW) and quantum point contacts (QPCs) has developed into an important part of nanotechnology, especially in connection with spintronics and quantum information. In our current studies we focus on electronic states, effects of electron interactions and conductance anomalies in semiconductor quantum point contacts and wires with different geometries to a model GaAs/AlGaAs device . Using the local spin density approximation (LSDA) we recover spin-polarized states in the middle of a conventional QPC results in the 0.7 (2e2/h) conductance anomaly as well as spin-split states near the two edges of the QPC that may be associated with the conductance anomaly in the vicinity of 0.25 (2e2/h). Effects of spontaneous magnetization might be also used for spintronics applications such as spin filters and all-electric QPC spin-polarizer. These systems are physically rich and constantly bring new experimental data such as the unusual conductance behavior in the case of shallow confinement potential in a low electron density regime, the anomalous properties of the 2DEG around the pinch-off regime and the formation of bound states with Kondo physics involved. This leads to the study of ballistic transport in low-dimensional semiconductor-based nanostructures in the ultralow electron density domain where the interaction-induced localization of electrons takes place. By means of LSDA we have shown that the localization of electrons within the barrier embedded in the wire and that the localization is highly dependent on the sharpness and length of the potential barrier. For a shallow barrier-free wire we retraced the structural transitions at low densities from a single chain of localized states to double and triple chains (Wigner spin lattices). We have found that the double chain appears as a double zig-zag co nfiguration  . Localized electrons may have interesting applications for semiconductor nanodevices. Indeed the formation of bound state and spin binding within QPC confinement potential opens possibilities to store information and to realize qubits in quantum circuits. We have studied the electron transport in a quantum wire in the presence of bias between source and drain . Our work has confirmed that spontaneous spin splitting does occur within the wire and it is responsible for both the 0.25 and 0.85 plateaus. We have also shown that the 0.25 plateau consists of two regions, one that is spin polarized, and another that is degenerate with a conductance that remains essentially the same at both sides of the transition. This result is of potential interest for semiconductor spintronics since it opens a new possibility for spin manipulation by electric field.  K.-F. Berggren and I.I. Yakimenko. J. Phys.: Condens. Matter 20, 164203 (2008).  E. Welander, K.-F. Berggren, I. I. Yakimenko. Phys. Rev. B 82, 073307 (2010).  H. Lind, I. I. Yakimenko, K.-F. Berggren. Phys. Rev. B 83, 075308 (2011).
Place, publisher, year, edition, pages
National CategoryPhysical Sciences
IdentifiersURN: urn:nbn:se:liu:diva-81995OAI: oai:DiVA.org:liu-81995DiVA: diva2:557265
Spin-Related Phenomena in Mesoscopic Transport, Nordita, Stockholm, 3-28 September 2012