{"id":1148,"date":"2016-08-22T11:03:57","date_gmt":"2016-08-22T11:03:57","guid":{"rendered":"https:\/\/www.science.nus.edu.sg\/?p=1148"},"modified":"2019-11-06T11:05:16","modified_gmt":"2019-11-06T11:05:16","slug":"a-new-class-of-materials","status":"publish","type":"post","link":"https:\/\/www.science.nus.edu.sg\/blog\/2016\/08\/a-new-class-of-materials\/","title":{"rendered":"A new class of materials"},"content":{"rendered":"<p>22 Aug 2016. NUS physicists and collaborators have developed ultra-thin films of a new class of materials: Weyl semi-metals.<\/p>\n<p>A collaboration between the theory group led by Prof Adam SHAFFIQUE from the Department of Physics at NUS and the experimental group of Prof Michael FUHRER from Monash University produced, for the first time, ultra-thin films of an exciting new class of materials known as Weyl semi-metals. This allows for the verification of its unique electronic properties with theoretical predictions [1].<\/p>\n<p>A Weyl semi-metal is the three-dimensional analogue of graphene. Unlike the usual Schr\u00f6dinger electrons, where the electron velocity increases with energy, graphene electrons move with a large constant velocity in a two-dimensional plane. For Weyl semi-metals, the electrons move with constant velocity in all three dimensions. These electrons also exhibit a property called \u201ctopological band-structure\u201d which makes them more immune to dirt and other imperfections and gives rise to unusual material properties in the presence of magnetic fields.<\/p>\n<p>The newfound ability to grow crystals of this material and control their electronic properties opens up new possibilities for future technological applications. For example, manipulating the topological property of such materials using electric or magnetic fields can create low-power \u201ctopological transistors\u201d that could potentially replace conventional transistors that dissipate large amounts of heat. Theoretical predictions have shown that by bringing Weyl electrons close to a superconductor, they host zero-energy states. These <em>Majoranna<\/em> modes store topological information which can be used to build a quantum computer that is protected from environmental noise.<\/p>\n<p>Prof Shaffique explained that these Na<sub>3<\/sub>Bi samples are sufficiently thin to allow one to change the number of electrons in the film using a back gate. This achievement allows them to analyse and verify the data against theoretical predictions for the conductivity of Weyl semi-metals in the presence of magnetic fields.<\/p>\n<p>Previous theoretical work [2] already predicted that the same mechanism that produces magnetoresistance (a change in electrical resistance due to magnetic fields) in graphene should also be present in Weyl semi-metals. The current experiment validated some of those theoretical ideas, but also raised new questions on the how topological electrons move around in this new class of materials.<\/p>\n<p><img fetchpriority=\"high\" decoding=\"async\" alt=\"18. AShaffique PHY 20160627 1\" src=\"https:\/\/www.science.nus.edu.sg\/wp-content\/uploads\/2019\/11\/18.-AShaffique_PHY_20160627_1.jpg\" width=\"812\" height=\"316\" \/><\/p>\n<p>Figure shows: (a) 20 nm thick sodium bismuth films that were grown and used in this experiment. The crystal structure is shown in the inset. (b) STM images of the thin film show the morphology (main figure) and the atomic scale image of the surface of this material. [Image credit: Jack HELLERSTEDT, Monash University].<\/p>\n<p> <\/p>\n<p><strong>References<\/strong><\/p>\n<p>[1] J. Hellerstedt et al. \u201cElectronic properties of high-quality epitaxial topological dirac semimetal thin films\u201d.\u00a0Nano Letters 16 3210 (2016). DOI: 10.1021\/acs.nanolett.6b00638.<\/p>\n<p>[2] N. Ramakrishnan et al. \u201cTransport and magnetotransport in three-dimensional Weyl semimetals\u201d.\u00a0Phys. Rev. B 92, 245120 (2015). DOI: 10.1103\/PhysRevB.92.245120.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>22 Aug 2016. NUS physicists and collaborators have developed ultra-thin films of a new class of materials: Weyl semi-metals. A…<\/p>\n","protected":false},"author":1,"featured_media":1149,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[23,13],"tags":[],"class_list":["post-1148","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-advanced-materials","category-research-news"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v23.6 (Yoast SEO v23.6) - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>A new class of materials - NUS Faculty of Science<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.science.nus.edu.sg\/blog\/2016\/08\/a-new-class-of-materials\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"A new class of materials\" \/>\n<meta property=\"og:description\" content=\"22 Aug 2016. 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