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Seminars and Colloquia

Physics

Transport properties of topological materials 
 
Thu, Aug 03, 2017,   04:30 PM at Physics Seminar Room 31, 2nd Floor, Main Building

Dr. Chandra Shekhar
Max Planck Institute, Dresden, Germany

Topological materials have newly been identified as a new phase of matter and their properties are highlighted by topology of bands. These materials are further classified into three groups and these are topological insulator, Dirac semimetal, and Weyl semimetal. Topological insulators (TIs) are insulating in bulk (interior) but metallic (conducting) on the surface or edge [1-2]. This conducting surface is originated from the inversion of bulk bands as a result of strong spin-orbit coupling. In materials, not necessarily bulk is always insulating; if it is gapless, materials turn into a semimetal. Other two groups’ topological materials have semimetallic bulk where valence and conduction bands touch at Fermi level at the same point or different points. Depending on whether the bands touching points are doubly degenerate or nondegenerate, such topological material is called a topological Dirac semimetal [3] or a topological Weyl semimetal, [4] respectively. Peculiar properties of topological materials indicate the existence of Majorana, Dirac, and Weyl fermions in condensed matter. My talk will cover different methods of crystal growth and transport properties of different topological materials. For example, many Weyl semimetals show extremely large magnetoresistance and mobility that accompanied by strong quantum oscillations [4]. Interestingly, chiral anomaly and axial gravitational anomaly are a strong evidence of presence of Weyl fermions [5]. A large amplitude of quantum oscillations allows to determine the Berry phase which is a witness for topological Dirac semimetals [3]. Moreover, the bulk transport and the surface transport of topological insulators can be separated by a local transport measurement geometry [2].

References:

[1] Hasan et al., Rev. Mod. Phys. 82 (2010) 3045.

[2] Shekhar, et al. Phys. Rev. B 90 (2014) 165140; Phys. Rev. B 93 (2016) 241106 (R).

[3] Kumar & Shekhare et al., Phys. Rev. B 95 (2017) 121109 (R); Liu, et al., Science 343 (2014) 864.

[4] Shekhar et al., Nat. Phys. 11 (2015) 645; arXiv:1703.03736; arXiv:1703.04527; Weng et al., Phys. Rev. X, 5 (2015) 011029.

[5] Gooth & Shekhar et al., Nature 547 (2017) 324; Arnold & Shekhar et al. Nat. Commun. 7 (2016) 11615

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