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<p class="MsoNormal"><b><span style="font-size:16.0pt">The location for today’s MOS seminar has been changed to
</span></b><b><span style="font-size:20.0pt;color:red">24-115.</span></b><b><span style="font-size:16.0pt"><o:p></o:p></span></b></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<div>
<p class="MsoNormal"><b><span style="font-size:11.0pt">Christine Brooks</span></b><span style="font-size:11.0pt"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Administrative Assistant<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Massachusetts Institute of Technology<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Department of Chemistry<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">77 Massachusetts Ave, 6-333<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Cambridge, MA 02139<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">p: 617.253.7239<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">e: <a href="mailto:cbrooks@mit.edu">cbrooks@mit.edu</a><o:p></o:p></span></p>
</div>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="color:black">From: </span></b><span style="color:black">Christine Brooks <cbrooks@mit.edu><br>
<b>Date: </b>Tuesday, February 26, 2019 at 9:36 AM<br>
<b>To: </b>mos <mos@mit.edu><br>
<b>Cc: </b>speclab-all <speclab-all@mit.edu>, ptsogroup <ptsogroup@mit.edu><br>
<b>Subject: </b>TODAY - Modern Optics and Spectroscopy Seminar with Xiaoyang Zhu (Columbia University)<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:14.0pt">There will be a Modern Optics and Spectroscopy Seminar held
<b>today at 12pm </b>in <b><span style="color:red">5-234</span></b></span><o:p></o:p></p>
<p class="MsoNormal"><b><span style="font-size:14.0pt;color:red"> </span></b><o:p></o:p></p>
<p class="MsoNormal"><b><span style="font-size:14.0pt;color:red">**Please note </span>
</b><b><span style="font-size:14.0pt">updated <span style="color:red">location**</span></span></b><o:p></o:p></p>
<p class="MsoNormal"><b><span style="font-size:14.0pt"> </span></b><o:p></o:p></p>
<p class="MsoNormal" style="margin-bottom:6.0pt"><b><span style="font-size:16.0pt">Xiaoyang Zhu<br>
Columbia University</span></b><i><span style="font-size:14.0pt"><br>
<br>
</span></i><b><i><span style="font-size:16.0pt">“Ferroelectric polarons and spectroscopic view of the “perfect” semiconductor”</span></i></b><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:10.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="layout-grid-mode:char;vertical-align:baseline"><i><span style="font-family:"Times New Roman",serif;color:black">Lead halide perovskites have been demonstrated as high performance materials in solar cells and light-emitting devices.
These materials are characterized by coherent band transport expected from crystalline semiconductors, but dielectric responses and phonon dynamics typical of liquids. Here we explain the essential physics in this class of materials based their dielectric
functions and dynamic symmetry breaking on nano scales. We show that the dielectric function in the THz region may lead to dynamic and local ordering of polar nano domains by an extra electron or hole, resulting a quasiparticle which we call a ferroelectric
large polaron, a concept similar to solvation in chemistry. Compared to a conventional large polaron, the collective nature of polarization in a ferroelectric large polaron may give rise to order(s)-of-magnitude larger reduction in the Coulomb potential. Using
two-dimensional optical Kerr effect (2D-OKE) spectroscopy, we directly probe the energetics and local phonon responses of ferroelectric polarons. The ferroelectric polaron may explain the defect tolerance and low recombination rates of charge carriers in lead
halide perovskites, as well as providing a design principle for the “perfect” semiconductor for optoelectronics.</span><span style="color:black"> </span></i><o:p></o:p></p>
<p class="MsoNormal"> <br>
<br>
<br>
<o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:14.0pt">Refreshments will be served immediately following the seminar!</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal"><b><span style="font-size:11.0pt">Christine Brooks</span></b><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Administrative Assistant</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Massachusetts Institute of Technology</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Department of Chemistry</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt">77 Massachusetts Ave, 6-333</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Cambridge, MA 02139</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt">p: 617.253.7239</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt">e: <a href="mailto:cbrooks@mit.edu">cbrooks@mit.edu</a></span><o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
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