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Condensed Matter Seminars

ics Condensed Matter
Thursday, March 29, 2018
11:00 AM
Physics Building, Room 313
Adriana Moreo [Host: Despina Louca]
University of Tennessee
"New Directions in Theoretical Studies of High Tc Superconductors"

The discovery of high critical temperature superconductivity in iron-based pnictides and chalcogenides brought to the  forefront the need to develop efficient theoretical procedures to treat multiorbital models of interacting electrons. Among the many challenges, we need to clarify the role that the orbital degree of freedom plays in pairing and how its interaction with magnetic and lattice degrees of freedom leads to the stabilization of exotic phases such as the nematic state. Theoretical studies in the strong and weak coupling limits cannot address the physically relevant intermediate regime, with a mixture of itinerant and localized degrees of freedom. Traditional numerical methods, such as Lanczos or quantum Monte Carlo, have either a too rapidly growing Hilbert space with increasing size or sign problems. For this reason, it is necessary to develop new models and techniques, and also better focus on systems where both experiments and accurate theory can be used in combination to reach a real understandingof iron pairing tendencies. Examples of recent advances along these directions that will be discussed in this talk include:
i) The development of spin-fermion models [1] that allow studies in the difficult nematic regime with a finite
short-range antiferromagnetic correlation length above the ordering critical temperatures. This type of studies
also allow the inclussion of doping, quenched disorder, and the study of transport and real-frequency responses;
ii) The application of the Density Matrix Renormalization Group (DMRG) approach to multi-orbital Hubbard
models in chain and ladder structures [2] triggered by the discovery of superconductivity at high pressure in ladder
iron-based compounds such as BaFe2S3 and BaFe2Se3. In this context,
the recently reported [2] pairing tendencies unveiled at intermediate Hubbard U will be discussed;
iii) Results for a newly developed multi-orbital spin-fermion model for the CuO2 planes in high Tc cuprates.[3]

 [1] S.Liang {\it et al.}, Phys.Rev.Lett.{\bf 109}, 047001 (2012) and Phys. Rev. Lett. {\bf 111} 047004 (2013); Phys. Rev. B{\bf 92} 104512 (2015); C. Bishop {\it et al.}, Phys. Rev. Lett. {\bf 117} 117201 (2016); Phys. Rev. B{\bf 96} 035144 (2017). [2] N.D. Patel {\it et al.}, Phys. Rev. B{\bf 96}, 024520(2017). See also  N.D. Patel {\it et al.}, Phys. Rev. B{\bf 94}, 075119(2016). [3] Mostafa Hussein et al., in preparation.

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