CM/BIO/ECE Seminar Series

Wednesday, April 5, 2017 4:00pm

Physics Library, Room 223A, Physics Building


Caizhi Xu

Caizhi Xu, University of Illinois at Urbana-Champaign, presents, "Elemental topological Dirac semimetal: α-Sn on InSb(111)," Wednesday, April 5 at 4 p.m. in the Physics Library, Room 223A, Physicsbuilding. Refreshments will be served beginning at 3:30 p.m.

The two-dimensional massless Dirac fermions in graphene lead to many novel electronic properties, such as high carrier mobility and half-integer quantum Hall effect [1]. A three-dimensional (3D) version of this type of fermions has been recently discovered in a class of materials called 3D topological Dirac semimetals (TDSs) [2], which show a number of unusual electronic properties including high carrier mobility, giant magnetoresistance and chiral anomaly [3,4]. They also provide a platform for studying topological phase transitions. However, 3D TDSs are rare. So far, only two of them have been experimentally verified. Our recent work is the realization of 3D TDS phase in a simple elemental material α-Sn under certain type of strain [5]. Using angle-resolved photoemission spectroscopy (ARPES), we have observed a 3D Dirac cone in epitaxially-grown α-Sn films on InSb(111). The nature of this Dirac cone crosses over from 3D to 2D as the film thickness is reduced. First-principles calculations confirm that epitaxial strain is key to the formation of the TDS phase. In addition, when the sign of epitaxial strain is reversed α-Sn can be tuned into a topological insulator. Our results suggest ample opportunities for engineering the electrical properties of α-Sn films through thickness and strain control. Moreover, our work demonstrates that strain engineering offers an effective way to create novel phases in ordinary materials.


[1]       A. H. Castro Neto, et al., "The electronic properties of graphene," Rev. Mod. Phys. 81, 109 (2009).

[2]       Z. K. Liu, et al., "Discovory of a 3D topological Dirac semimetal, Na3Bi," Science 343, 864 (2014).

[3]       T. Liang, et al., "Ultrahigh mobility and giant magnetoresistance in the Dirac semimetal Cd3As2," Nat. Mater. 14, 280 (2014).

[4]       J. Xiong, et al., "Evidence for the chiral anomaly in the Dirac semimetal Na3Bi," Science 350, 413 (2015).

[5]       Caizhi Xu, et al., Physical Review Letters, in press