Bauer, Florian (2014): Microscopic Origin of the 0.7Anomaly in Quantum Point Contacts. Dissertation, LMU München: Faculty of Physics 

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Abstract
A Quantum point contact (QPC) is a one dimensional constriction, separating two extended electron systems allowing transport between them only though a short and narrow channel. The linear conductance of QPCs is quantized in units of the conductance quantum G_Q=2e^2/h, where e is the electron charge and h is Planck's constant. Thus the conductance shows a staircase when plotted as a function of gatevoltage which defines the width of the channel. In addition measured curves show a shoulderlike step around 0.7G_Q. In this regime QPCs show anomalous behaviour in quantities like electrical or thermal conductance, noise, and thermopower, as a function of external parameters such as temperature, magnetic field, or applied voltage. These phenomena, collectively known as the 0.7anomaly in QPCs are subject of controversial discussion. This thesis offers a detailed description of QPCs in the parameter regime of the 0.7anomaly. A model is presented which reproduces the phenomenology of the 0.7anomaly. We give an intuitive picture and a detailed description of the microscopic mechanism leading to the anomalous behavior. Further, we offer detailed predictions for the behavior of the 0.7anomaly in the presence of spinorbit interactions. Our best theoretical results were achieved using an approximation scheme within the functional renormalization group (fRG) which we developed to treat inhomogeneous interacting fermi systems. This scheme, called the coupled ladder approximation (CLA), allows the flow of the twoparticle vertex to be incorporated even if the number of interacting sites N, is large, by reducing the number of independent variables which represent the twoparticle vertex from O(N^4) to O (N^2).
Item Type:  Thesis (Dissertation, LMU Munich) 

Keywords:  quantum point contacts, 0.7 anomaly, conductance quantisation, 
Subjects:  600 Natural sciences and mathematics 600 Natural sciences and mathematics > 530 Physics 
Faculties:  Faculty of Physics 
Language:  English 
Date Accepted:  29. August 2014 
1. Referee:  Delft, Jan von 
Persistent Identifier (URN):  urn:nbn:de:bvb:19178928 
MD5 Checksum of the PDFfile:  fa03faacd483f58256b881790d60598a 
Signature of the printed copy:  0001/UMC 22720 
ID Code:  17892 
Deposited On:  18. Feb 2015 15:03 
Last Modified:  01. Aug 2016 09:41 