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제목: Emergent Physics in 3D Correlated Topological Semimetals 

 

연사: 양   범  정 박사님 (RIKEN)

 

일시: 2013. 12. 26(목) 오후 4:00

 

장소: 제1과학관 물리학과 2층 라운지세미나실

 

 

초록: Recently, there has been a surge of research interests in the physics of the 3D semimetal, which is so-called the Weyl semimetal. The Weyl semimetal is composed of several Fermi points around which the electron shows the linear dispersion relation in all three momentum directions. Because of the nontrivial topological property of the Fermi point, the Weyl semi-metal shows several topologically nontrivial properties such as the Fermi Arc and quantum Hall effects. In this talk, I’d like to introduce the novel physical properties of the 3D interacting Weyl semimetal and its associated quantum critical phenomena. My talk is composed of two parts. The first part is about the emergent topological phenomena in pyrochlore iridates, one promising candidate material supporting Weyl semimetals. Due to the recent development of thin film and artificial superstructure growth technique, it is possible to control the dimensionality of the system, smoothly between the two-dimensions (2D) and three-dimensions (3D). In this work we unveil the dimensional crossover of emergent topological phenomena in correlated topological materials. In particular, by focusing on the thin film of pyrochlore iridate antiferromagnets grown along the [111] direction, we demonstrate that it can show giant anomalous Hall conductance, which is proportional to the thickness of the film, even though there is no Hall effect in 3D bulk material. In addition, we uncover the emergence of a new topological phase, whose nontrivial topological properties are hidden in the bulk insulator but manifest only in thin films. This shows that the thin film of topological materials is a new platform to search for unexplored novel topological phenomena.


The second part of my talk is about the quantum criticality of the topological phase transition associated with the Weyl semimetal. Topological phase transitions in condensed matters accompany emerging singularities of the electronic wave function, often manifested by gap-closing points in the momentum space. In conventional topological insulators in three dimensions (3D), the low energy theory near the gap-closing point can be described by relativistic Dirac fermions coupled to the long range Coulomb interaction, hence the quantum critical point of topological phase transitions provides a promising platform to test the novel predictions of quantum electrodynamics. Here we show that a new class of quantum critical phenomena emanates in topological materials breaking either the inversion symmetry or the time-reversal
symmetry. At the quantum critical point, the theory is described by the emerging low energy fermions, dubbed the anisotropic Weyl fermions, which show both the relativistic and Newtonian dynamics simultaneously. The interplay between the anisotropic dispersion and the Coulomb interaction brings about a new screening phenomenon distinct from the conventional Thomas-Fermi screening in metals and logarithmic screening in Dirac fermions.

 

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