[LA-SiGMA] LASiGMA Seminar - Dr. Peter Armitage, 3:30pm at Louisiana State University

[shelley lee]

Dear All,

 

Dr. Peter Armitage of John Hopkins University will be giving a seminar
September 18th at 3:30 pm in 1008B in the Digital Media Center at the
Louisiana State University. The title of his talk is "How to Kill a
Topological Insulator? "

 

Abstract:

Topological insulators (TIs) are states of matter characterized by an
inverted band structure driven by strong spin-orbit coupling  (SOC). They
have a variety of unusual properties including robust surface states (SS)
that are protected by topological properties of the bulk wave functions. Of
particular interest is the quantum phase transition that separates a TI from
a conventional insulator.   Such a transition between different topological
classes can only occur when the bulk band gap closes.  In this work, we have
utilized time-domain terahertz spectroscopy  (TDTS) to investigate the low
frequency conductivity in (Bi1-xInx)2Se3 through this transition by tuning
SOC through In substitution.  Above a thickness dependent doping threshold
we observe a sudden collapse in the transport lifetime that indicates the
destruction of the topological phase.  We associate this with the doping
where the states from opposite surfaces hybridize.   As a function of
thickness this threshold asymptotically approaches the doping x ~ 0.06 of a
maximum in the mid-infrared absorption, which can be identified with the
band gap closing and change in topological class.  The correlation length
associated with the quantum phase transition appears as the evanescent
length of the surface states.  Our work shows the fundamental role that
finite size effects play in this transition though the `bulk-boundary
correspondence' of topological systems.

 

Biography:

N. Peter Armitage has been on the faculty of the Department of Physics and
Astronomy at Johns Hopkins University since 2006. He received his bachelor's
degree in Physics from Rutgers University in 1994 and his Ph.D. from
Stanford University in 2001.   He is a physicist whose research centers on
material systems which exhibit coherent quantum effects at low temperatures,
like superconductors and "quantum" magnetism.   Like waves on the sea, their
behavior is intrinsically collective and is not easily reduced to the
properties of individual particles - i.e., they are emergent.  Dr.
Armitage's principal scientific interest is understanding how is it that
large ensembles of strongly interacting, but fundamentally simple particles
like electrons in solids act collectively to exhibit complex emergent
quantum phenomena.  He is exploiting (and developing) recent technical
breakthroughs using very low frequency microwave and THz range radiation to
probe these systems at their natural frequency scales. The material systems
of interest require new measurement techniques as many of their relevant
frequencies fall between the range of usual optical and electronic methods.
He has been the recipient of a DARPA Young Faculty Award, an NSF Career
Award, a Sloan Research Fellowship, was a three time Kavli Frontiers Fellow,
the winner of the first William Spicer Award from the Stanford Synchrotron
Radiation Laboratory, and was the winner of  the 2005 William L. McMillan
Award from the University of Illinois for "outstanding contributions in
condensed matter physics."

 

The seminar will be a live broadcast from Louisiana State University, and
can be viewed live at the sites listed below:

 

UNO - Liberal Arts Building 234

Xavier - Qatar Pavilion Conference Room 226

LATech - PML 1015, Center for Instructional Technology, at the Wyly Tower

 

The seminar will also be accessible via adobe connect. Connection
information will follow early next week.

 

Please see attached flyer and let me know if you have any questions.

 

Regards,

 

Shelley Lee

Project Coordinator

225-578-0465

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