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SUMMARY: High-fidelity description of spectral functions in correlated mat
 erials - Mark van Schilfgaarde\, King's College London
DTSTART:20201015T130000Z
DTEND:20201015T140000Z
UID:TALK152179@talks.cam.ac.uk
CONTACT:Jan Behrends
DESCRIPTION:Many-body phenomena such quantum criticality\, non-Fermi liqui
 d behavior\, and perhaps most importantly\, unconventional superconductivi
 ty\, have largely stayed within the province of model theories. But models
  must rely on educated guesses for their form\, and the means of discrimin
 ating between model assumptions is limited. As a result the field has rema
 ined without a firm foundation for decades. A key reason is that multiple 
 energy scales are operative: the high energy scales that control the low-e
 nergy fluctuations cannot be integrated out without model assumptions. Ab 
 initio methods could in principle supplant model Hamiltonians\; however\, 
 these low-energy phenomena cannot be reliably explained unless both one-pa
 rticle and two-particle response functions are described with very high fi
 delity. Limitations to their fidelity has largely precluded them from real
 izing this possibility.\nTo manage electron correlations\, Green's functio
 n methods have proven to be powerful tools in the theorist's toolbox. Ab i
 nitio Green's function methods have traditionally divided into two tracks:
  low-order many-body perturbation theory (MBPT)\, applicable to systems wi
 th weak or moderate correlations\, and where the independent particle pict
 ure is no longer adequate\, nonperturbative Dynamical Mean Field Theory (D
 MFT)\, added to density functional theory. Each has advantages\, but also 
 limitations. In this talk I show recent progress in joining MBPT with DMFT
  to characterize one- and two-particle spectral functions with much higher
  fidelity than either separately. In many correlated materials including m
 ost unconventional superconductors\, spin fluctuations drive low-energy co
 rrelations that give rise to exotic phenomena.\nMBPT\, and augmenting it w
 ith DMFT when needed\, yield a broadly applicable frame- work for electron
 ic structure that describe spectral functions of many kinds of systems wit
 h high fidelity. This talk focuses on several unconventional superconducto
 rs where MBPT and DMFT must be combined. It shows the promise of these new
  methods as reliable predictors of unconventional superconductivity\, and 
 a basis to identify the dominant mechanisms in a manner that is not possib
 le with models.
LOCATION:Details of video conferencing will be distributed nearer the time
 .
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