Materials Science and Engineering Colloquium
Date: February 04, 2015 from 10:30 am to 11:30 am EST
Location: Columbia University
Morningside Campus
S.W. Mudd, Room 214
Contact: For further information regarding this event, please contact APAM Department by sending email to or by calling 212-854-4457.
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High Mobility Charge Carriers in Two-dimensional Semimetal [Pb2BiS3][AuTe2]
and Huge Critical Current Density in Iron-based Superconductor SmFeAsO0.8F0.15

Lei Fang

Department of Chemistry, Northwestern University, Evanston, IL

Materials Science Division, Argonne National Laboratory, Lemont, IL


   Studying two-dimensional (2D) materials is a mainstream in material science due to the unique properties, emerging physics, and great impacts on next-generation microelectronic devices. Currently, materials discovery is a compelling mission in 2D materials research. Inspired by the discovery of quantum spin Hall insulator state in HgTe quantum wells, our research focuses on novel electronic states in heterostructure-like materials with strong spin-orbit coupling. In this talk, I will first introduce our recent research on layered material [Pb2BiS3][AuTe2] which is composed of insulating layer [Pb2BiS3] and conductive sheet [AuTe2]. This naturally formed heterostructure exhibits a multiband electronic structure featuring high hole mobility of 1360 cm2/Vs. The insulating layer [Pb2BiS3] and the weak interlayer coupling lead to an extremely large anisotropy Г≈104, comparable to that of benchmark 2D materials graphite and Bi2Sr2CaCu2O8. The weak interlayer coupling also endows this material with a highly cleavable property and enables nano crystals with a thickness smaller than 10 nm via exfoliation. More strikingly, this material exhibits linear band dispersions which coincide with the half branch Dirac cone of graphene. Ultrahigh Fermi velocities 106 m/s and light effective mass 0.046 me of carriers were found.  Our results provide a novel candidate for a monolayer platform to investigate emerging electronic properties at the atomic sale [1].

   The second part of my talk focuses on the newly discovered iron-based superconductors. Due to the relatively high superconducting transition temperature (TC) and critical current density (JC), iron-based superconductors have prompted great enthusiasm for electricity distribution and high superconducting magnet applications. SmFeAsO1-xFx is of particular interest as it has the highest TC (57 K) among these materials. However, the knowledge of application potential of SmFeAsO1-xFx remains limited because of the lack of sizeable single crystals for study. To meet this challenge, we fabricated micro Hall magnetometer array and micro calorimeter to characterize micrometer-sized SmFeAsO0.8F0.15 crystals which incorporate columnar nano defects via particle irradiation. A record high JC of 2x107 A/cm2 was observed at 5 K and self-fields. We also observed a notable reduction of the thermodynamic anisotropy, from 8 to 4 upon irradiation. The huge JC, low anisotropy and high TC of SmFeAsO0.8F0.15 strongly suggest that this material may be the best iron-based superconductor for application [2].

   At the end of my talk, I will briefly discuss my future directions on 2D electronic materials with highlights on synergistic research between design, theoretical calculations, synthesis and advanced characterizations. Particularly, I will introduce my 2D materials database which contains more than 1000 novel inorganic systems. This database can be used for structure mining to pursue powerful electronic and energy materials.



[1] L. Fang, et. al. to appear in JACS.

[2] L. Fang, et al. Nat. Commun. doi: 10.1038/ncomms 3655 (2013).

Host: Irving Herman