Abstract

The huge increase in the superconducting transition temperature of FeSe induced by an interface to SrTiO3 remains unexplained to date. However, there are numerous indications of the critical importance of specific features of the FeSe band topology in the vicinity of the Fermi surface. Here, we explore how the electronic structure of FeSe changes when located on another lattice matched substrate, namely a Si(001) surface, by first-principles calculations based on the density functional theory. We study non-magnetic (NM) and checkerboard anti-ferromagnetic (AFM) magnetic orders in FeSe and determine which interface arrangement is preferred. Our calculations reveal interesting effects of Si proximity on the FeSe band structure. Bands corresponding to hole pockets at the Γ point in NM FeSe are generally pushed down below the Fermi level, except for one band responsible for a small remaining hole pocket. Bands forming electron pockets centered at the M point of the Brillouin zone become less dispersive, and one of them is strongly hybridized with Si. We explain these changes by a redistribution of electrons between different Fe orbitals rather than charge transfer to/from Si, and we also notice an associated loss of degeneracy between and orbitals.

Highlights

  • Superconductivity (SC) has been found in follows: red (Fe)-based compounds with a quasi-2D structure about a decade and half ago [1]

  • We examine here the electronic structure of FeSe monolayers interfaced to Si with special attention on features considered important for supeconductivity

  • A similar situation occurs if a Tix O2 interlayer is formed between SrTiO3 and FeSe [28]

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Summary

Introduction

Superconductivity (SC) has been found in Fe-based compounds with a quasi-2D structure about a decade and half ago [1]. An example with a simple structure is the tetragonal phase of FeSe possessing a critical temperature Tc = 8 K at an ambient pressure [2]. The critical temperature has been shown to increase dramatically when FeSe with a nanoscale thickness is situated on oxide substrates, up to 100 K when the system becomes truly 2D, for monolayer FeSe on SrTiO3 substrate [3]. Superconducting circuits represent key components for the advancement of quantum computers [4,5]. These are currently operated at temperatures close to absolute zero, but with the help of high-Tc superconductors, the temperature range for quantum circuitry can be increased [6]

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