Correlation-corrected band topology and topological surface states in iron-based superconductors

Abstract

Iron-based superconductors offer an ideal platform for studying topological superconductivity and Majorana fermions. In this paper, we carry out a comprehensive study of the band topology and topological surface states of a number of iron-based superconductors using a combination of density functional theory (DFT) and dynamical mean field theory. We find that the strong electronic correlation of Fe 3d electrons plays a crucial role in determining the band topology and topological surface states of ironbased superconductors. Electronic correlation not only strongly renormalizes the bandwidth of Fe 3d electrons, but also shifts the band positions of both Fe 3d and As/Se p electrons. As a result, electronic correlation moves the DFT-calculated topological surface states of many iron-based superconductors much closer to the Fermi level, which is crucial for realizing topological superconducting surface states and observing Majorana zero modes as well as achieving practical applications, such as quantum computation. More importantly, electronic correlation can change the band topology and make some iron-based superconductors topologically nontrivial with topological surface states whereas they have trivial band topology and no topological surface states in DFT calculations. Our paper demonstrates that it is important to take into account electronic correlation effects in order to accurately determine the band topology and topological surface states of iron-based superconductors and other strongly correlated materials.

A Gate‐Tunable Ambipolar Quantum Phase Transition in a Topological Excitonic Insulator

“…First proposed in the 1960s, [1][2][3][4] only recently has experimental evidence for the excitonic insulating state been put forth in a small number of 2D electronic systems. [5][6][7][8][9][10][11][12][13][14][15][16][17] Among them, excitonic pairing has been proposed [15,16,18,19] as a contributing mechanism to stabilize the bulk energy gap in WTe 2 monolayers, previously understood as a quasiparticle interference experiments. The presence of a longrange disorder induced Coulomb gap at the Fermi level confirmed the presence of a semimetallic state at high doping.…”

“…First proposed in the 1960s, [ 1–4 ] only recently has experimental evidence for the excitonic insulating state been put forth in a small number of 2D electronic systems. [ 5–17 ] Among them, excitonic pairing has been proposed [ 15,16,18,19 ] as a contributing mechanism to stabilize the bulk energy gap in WTe 2 monolayers, previously understood as a single‐particle band gap in the quantum spin Hall (QSH) state. [ 20–23 ]…”

Theoretical study of the interplay of spin density wave and superconductivity in nickel substitution of the strontium–iron–arsenide (SrFe2−xNixAs2) superconductor in a two-band model

“…According to theories, the parent materials of FebSc are semimetallic, and the density of state close to Fermi's surface is primarily supplied by the iron 3d electrons (orbitals) and all five of the 3d orbitals cross Fermi's surface [21]. Just from the most experimental results and the band structure calculations, the results reveal three iron 3d orbitals (d xy , d yz , and d xz ) provide the primary contribution to the density of states near the Fermi level and they ruffle weakly in the z direction [22].…”