Tunable spin polarization and conductance anomalies in mesoscopic one-dimensional systems

The electronic transport properties of mesoscopic one-dimensional (1D) devices have attracted significant interest because of their potential applications and their unique characteristics, some of which – for instance, the “0.7” conductance anomaly in quantum point contacts – have remained unexplained. In this dissertation, we present a comprehensive theoretical model for electronic transport in quasi-1D systems, accounting for many-body effects and neglecting spin–orbit couplings. Then, with this model, we predict that 1D systems can sustain a hierarchy of spin-polarized configurations which emerge above a carrier concentration threshold and are responsible for the 0.7 anomaly. The basis of our theory is an unrestricted three-dimensional Hartree-Fock approach that incorporates the effects of confinement strength, applied magnetic field and temperature. We demonstrate that the spin-polarized states are present in the quantum wire even if no magnetic field is present, provided that the electron concentration in the system is above a confinement-dependent threshold. Our subsequent study of ballistic transport in a quantum point contact reveals that the 0.7 anomaly appears at the threshold concentration for polarization, at a conductance value that is insensitive to temperature due to the capacitive effect exerted by the gates, even though the anomalous shoulder becomes wider with increasing temperature. The 0.7 anomaly is accompanied by another “kink” at ~0.3G0, which results from the singularity of the 1D density of states and disappears with rising temperatures. Our results provide an explanation for the experimental features of the conductance anomaly and underscore the importance of treating the confinement potential in the quasi-1D constriction as three-dimensional.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2017

Author dc:creator

• Sanchez, Alfredo Xavier

Contributors dc:contributor

• Leburton, Jean-Pierre
• Ryu, Shinsei
• Mason, Nadya
• Peng, Jen-Chieh

• quantum point contacts
• nanoelectronics
• mesoscopic physics
• spin polarization
• spintronics

Statement dc:rights

• © 2016 Alfredo X. Sánchez

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/95263

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/95263