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postgraduate thesis: Disordered transport in topolotical semimetals

TitleDisordered transport in topolotical semimetals
Authors
Advisors
Advisor(s):Shen, S
Issue Date2018
PublisherThe University of Hong Kong (Pokfulam, Hong Kong)
Citation
Lin, Y. [林跃宇]. (2018). Disordered transport in topolotical semimetals. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR.
AbstractTopological semimetals are novel materials with topologically non-trivial electronic structures. In this study we focus on Weyl semimetals. A Weyl semimetal has a gapless band structure where the conduction band and the valance band are degenerate at a nite number of points. Near each of these band degenerate points, the dispersion is linear in all momentum directions and described by the Weyl equation. These points are called Weyl nodes. A Weyl node acts as a monopole of Berry curvature in momentum space and is assigned with a topological charge of 1. Weyl semimetals posses various exotic transport properties. It has been reported that in the presence of short range Gaussian disorder, a Weyl semimetal has a quantum phase transition from semimetal to metal at a nite critical disorder strength. Above the critical disorder strength, the conductivity of the system increases as disorder strength getting stronger, which is opposite to its behaviour in usual metals. Previous studies mainly focus on a single Weyl node. However, there is a "no-go" theorem saying that the total topological charge must be zero in the Brillouin zone. Thus Weyl nodes must come in pairs with opposite charge. In this thesis we study the disordered quantum transport in a minimal continuum model containing a pair of Weyl nodes. The model allows us to explicitly taking into account internode scatterings e ect. The Green's function technique and the self-consistent Born approximation are used to calculate the density of states and conductivity of the model. A quantum phase transition from semimetal to metal is observed. The density of states and conductivity of the model have similar behavior as in a single Weyl node. We found that the critical disorder strength is reduced as internode scattering become stronger. The conductivity near the nodes is further enhanced above critical disorder strength but its behavior is not qualitatively altered by internode scatterings. Our results can be applied to systems with multiple pairs of Weyl nodes.
DegreeMaster of Philosophy
SubjectTopological dynamics
Semimetals
Dept/ProgramPhysics
Persistent Identifierhttp://hdl.handle.net/10722/255463

 

DC FieldValueLanguage
dc.contributor.advisorShen, S-
dc.contributor.authorLin, Yueyu-
dc.contributor.author林跃宇-
dc.date.accessioned2018-07-05T07:43:39Z-
dc.date.available2018-07-05T07:43:39Z-
dc.date.issued2018-
dc.identifier.citationLin, Y. [林跃宇]. (2018). Disordered transport in topolotical semimetals. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR.-
dc.identifier.urihttp://hdl.handle.net/10722/255463-
dc.description.abstractTopological semimetals are novel materials with topologically non-trivial electronic structures. In this study we focus on Weyl semimetals. A Weyl semimetal has a gapless band structure where the conduction band and the valance band are degenerate at a nite number of points. Near each of these band degenerate points, the dispersion is linear in all momentum directions and described by the Weyl equation. These points are called Weyl nodes. A Weyl node acts as a monopole of Berry curvature in momentum space and is assigned with a topological charge of 1. Weyl semimetals posses various exotic transport properties. It has been reported that in the presence of short range Gaussian disorder, a Weyl semimetal has a quantum phase transition from semimetal to metal at a nite critical disorder strength. Above the critical disorder strength, the conductivity of the system increases as disorder strength getting stronger, which is opposite to its behaviour in usual metals. Previous studies mainly focus on a single Weyl node. However, there is a "no-go" theorem saying that the total topological charge must be zero in the Brillouin zone. Thus Weyl nodes must come in pairs with opposite charge. In this thesis we study the disordered quantum transport in a minimal continuum model containing a pair of Weyl nodes. The model allows us to explicitly taking into account internode scatterings e ect. The Green's function technique and the self-consistent Born approximation are used to calculate the density of states and conductivity of the model. A quantum phase transition from semimetal to metal is observed. The density of states and conductivity of the model have similar behavior as in a single Weyl node. We found that the critical disorder strength is reduced as internode scattering become stronger. The conductivity near the nodes is further enhanced above critical disorder strength but its behavior is not qualitatively altered by internode scatterings. Our results can be applied to systems with multiple pairs of Weyl nodes.-
dc.languageeng-
dc.publisherThe University of Hong Kong (Pokfulam, Hong Kong)-
dc.relation.ispartofHKU Theses Online (HKUTO)-
dc.rightsThe author retains all proprietary rights, (such as patent rights) and the right to use in future works.-
dc.rightsThis work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.-
dc.subject.lcshTopological dynamics-
dc.subject.lcshSemimetals-
dc.titleDisordered transport in topolotical semimetals-
dc.typePG_Thesis-
dc.description.thesisnameMaster of Philosophy-
dc.description.thesislevelMaster-
dc.description.thesisdisciplinePhysics-
dc.description.naturepublished_or_final_version-
dc.date.hkucongregation2018-
dc.identifier.mmsid991044019483203414-

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