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SUMMARY:Part I: Strong Coupling Theory of Superconductivity and Ferroelect
 ric Quantum Criticality in Metallic SrTiO 3 \;                     Part II
 : Reducing the Sign Problem with Complex-path Quantum Monte Carlo: The Cas
 e of Superconductivity with Repulsion
DTSTART:20261008T090000Z
DTEND:20261008T100000Z
DTSTAMP:20261101T115700Z
UID:indico-event-9459@scitalks.tifr.res.in
DESCRIPTION:Speakers: Sudip Kumar Saha\n\nIn the first part\, I will discu
 ss superconductivity in doped SrTiO₃ (STO)\, where the pairing mechanism
  remains unresolved. Several experiments  have observed an enhancement of
  Tc near a ferroelectric quantum critical  point (QCP) associated with th
 e softening of a transverse optical (TO) phonon mode. This suggests that c
 ritical ferroelectric fluctuations play an  important role in pairing in 
 STO. Using strong-coupling Eliashberg theory\, we have shown that a linear
  Rashba-type coupling between electrons and  he soft TO mode captures the
  main features of the experimentally observed superconducting phase diagra
 m\, while an additional nonlinear  (quadratic) coupling is needed for agr
 eement with its finer features. In the second part\, I will turn to the a
 pplication of complex-path quantum  Monte Carlo (QMC) to superconducting 
 systems with repulsive interactions. Here\, repulsion generates complex we
 ights\, leading to strong phase cancellations and a severe sign problem in
  conventional QMC. To address this challenge\, we deform the path integral
  contour into the complex plane using holomorphic flow\, which preserves t
 he partition function while guiding the sampling manifold toward steepest-
 descent regions and reducing the sign problem. As a first step\, I have ap
 plied this approach to a simplified Morel–Anderson interaction\, neglect
 ing spatial and dynamical fluctuations. I will show that this method drama
 tically reduces the sign problem and enables calculations at much lower te
 mperatures. This work provides a foundation for extending this method to m
 ore realistic systems with both spatial and temporal fluctuations.\n\nhttp
 s://scitalks.tifr.res.in/event/9459/
LOCATION:AG80 and on Zoom
URL:https://scitalks.tifr.res.in/event/9459/
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