Materials Science and Engineering Colloquium – 76207

Materials Science and Engineering Colloquium

Lei Fang, from Northwestern University, will present a talk at the Materials Science and Engineering Colloquium.

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,

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].

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 2×107
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].

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

For further information regarding this event, please contact APAM Department by sending email to or by calling 212-854-4457.

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