The University of Tennessee, Knoxville

Joint Institute for Advanced Materials

Condensed Matter Seminars


The seminars are held every Friday in the seminar room of the Joint Institute for Advanced Materials (Room 147).

Date Speaker Title
October 20 Niravkumar D. Patel (UT) Magnetic and pairing tendencies in quasi 1D multi-orbital models


October 20

Niravkumar D. Patel (UT)

Magnetic and pairing tendencies in quasi 1D multi-orbital models

The recent discovery of superconductivity under high pressure in the two-leg ladder compound BaFe2S3 [1] opens a broad avenue of research because it represents the first report of pairing tendencies in a quasi-one-dimensional iron-based high-critical-temperature superconductor. Similarly, as in the case of the cuprates, ladders and chains can be far more accurately studied using many-body techniques and model Hamiltonians than their layered counterparts, particularly if several orbitals are active. As a first step, we derive a two-orbital Hubbard model from first principles that describes individual ladders of BaFe2S3 [2]. The model is then studied with the density matrix renormalization group technique [3]. Three main results are found: (i) at half-filling, ferromagnetic order emerges as the dominant magnetic pattern along the rungs of the ladder, and antiferromagnetic order along the legs, in excellent agreement with neutron experiments; (ii) with hole doping, pairs form in the intermediate/strong coupling regime, as found by studying the binding energy of two holes doped on the half-filled system; (iii) projector analysis of the ground state show that same orbital rung and diagonal pairs are most probable. In addition, recently pairing tendencies were also found by our group in a 1D chain of two-orbitals (that can be mapped into a single-orbital two-leg ladder). The analysis of pair-pair correlations show that pairs are formed involving inter-orbital singlets on neighboring sites and different orbitals [4]. In addition, pairing tendencies can be enhanced by increasing the Hund coupling and also by adding an inter-orbital nearest-neighbor antiferromagnetic Heisenberg coupling. These results clearly suggest that magnetic fluctuations are crucial to superconductivity in the iron-based ladder superconductors. These exciting new results pave the way for our understanding of pairing in the iron family of high-Tc materials.


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