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UID:DSC-16565
DTSTART;TZID=Europe/Berlin:20191030T110000
SEQUENCE:1572476856
TRANSP:OPAQUE
DTEND;TZID=Europe/Berlin:20191030T120000
URL:https://www.dresden-science-calendar.de/calendar/de/detail/16565
LOCATION:MPI-CPfS\, Nöthnitzer Straße 4001187 Dresden
SUMMARY:Smith: Polarized mid-infrared spectroscopy as a potential tool for 
 investigating Weyl semimetals 
CLASS:PUBLIC
DESCRIPTION:Speaker: Prof. Leigh M. Smith\nInstitute of Speaker: University
  of Cincinnati\, OH\, USA\nTopics:\nChemie\n Location:\n  Name: MPI-CPfS (
 Seminarraum 1+2\, Nöthnitzer Straße 40\, 01187 Dresden)\n  Street: Nöth
 nitzer Straße 40\n  City: 01187 Dresden\n  Phone: \n  Fax: \nDescription:
  Time-integrated and femtosecond transient spectroscopies have been used f
 or years to probe electronic states in semiconductors\, understanding the 
 band structure\, intra- and inter-band transitions\, and interactions with
  phonons\, nanostructures and defects. We use polarized Raman spectroscopy
  and polarized transient reflectivity (TR) to investigate the band-to-band
  transitions and relaxation dynamics in tellurium which has a 0.35 eV gap.
  Tellurium is a chiral material with complex nested conduction and valence
  bands\, and which has recently been shown by ARPES to exhibit spin textur
 es resulting from a Weyl node near the H6 conduction band minimum. TR spec
 tra show transitions between the H4\, H5 and H6 VBs and the H6 CB\, while 
 the dynamics shows evidence for scattering of carriers to indirect valleys
 . Weyl semimetals occur when the gap collapses (usually because of strong 
 spin-orbit coupling) causing band crossings and inversions over limited pa
 rts of the Brillouin zone\, while well defined gaps are seen elsewhere. Be
 cause the gap collapses only partially\, mid-infrared pulses in principle 
 can interrogate transitions from bands near the Fermi energy to higher lyi
 ng states in the same region of k space. We use resonant Raman scattering\
 , polarized transient reflectivity\, and polarized photothermal and photog
 alvanic spectroscopies in a device to investigate the electronic structure
  of the Type-II Weyl semimetal NbIrTe4. This material has broken inversion
  symmetry which results in 16 Weyl nodes which are less than 100 meV from 
 the Fermi energy. In principle\, the chiral Weyl nodes should couple stron
 gly with circularly polarized light. We use linear- and circular-polarized
  mid-infrared to visible spectroscopies ranging from 0.3 to 3 eV to show t
 here is some evidence for band-to-band electronic transitions\, and also t
 hat the nanoflakes couple strongly to circularly polarized light\, particu
 larly at low energies approaching the Weyl nodes. Some possible insights a
 re gained by comparison of these very preliminary results with DFT calcula
 tions of the phonon modes and band structure. The potential for extensions
  of these measurements to low temperatures\, magnetic and electric fields\
 , and other new materials will be discussed. We acknowledge the support of
  the NSF through grants DMR 1507844\, DMR 1531373 and ECCS 1509706. Peide 
 Ye (Purdue Univ) supplied the Tellurium nanoflakes\, Stephen Wilson (UCSB)
  supplied the NbIrTe4 single crystals\, Fuchun Zhang (Kavli Institute\, Be
 ijing) and Congcong Le (now at MPI Dresden) have provided theoretical supp
 ort. _____________________________________________________________________
 ____________ Leigh M. Smith is Professor and Head of the Department of Phy
 sics. He has been at the University of Cincinnati since 1990. He received 
 his BA in Mathematics and Physics at the University of Virginia\, PhD in C
 ondensed Matter Physics from the University of Illinois at Urbana-Champaig
 n\, and was Postdoctoral Fellow at the IBM T.J. Watson Research Center. He
  has been Visiting Faculty at the Danish Technical University and Australi
 an National University.
DTSTAMP:20261103T091122Z
CREATED:20191015T220629Z
LAST-MODIFIED:20191030T230736Z
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