Low superfluid density and possible multigap superconductivity in theBiS2-based layered superconductorBi4O4S3

Abstract

The magnetic penetration depth λ as a function of temperature in Bi4O4S3 was studied by muon-spin-spectroscopy measurements. The superfluid density of Bi4O4S3 is found to be very low. The dependence of λ −2 on temperature possibly suggests the existence of two s-wave type energy gaps with the zero-temperature values of 0.93(3) and 0.09(4) meV. The upturn in the temperature dependence of the upper critical field close to Tc further supports multi-gap superconductivity in Bi4O4S3. The presence of two superconducting energy gaps is consistent with theoretical and other experimental studies. However, a single-gap s-wave model fit with a gap of 0.88(2) meV can not be ruled out completely. The value of λ(T ) at T = 0 K is estimated to be λ(0) = 861(17) nm, one of the largest of all known layered superconductors, reflecting a very low superfluid density.PACS numbers: 74.25.Ha, 76.75.+i Recent years have witnessed a growing interest in superconductivity within layered crystal structure compounds. The recent discovery of superconductivity in the BiS 2 -based compound Bi 4 O 4 S 3 [1, 2] with a transition temperature (T c ) of ≈ 4.5 K has further fostered the research interest in layered superconductors. Exotic superconductivity with higher T c and/or with unconventional pairing mechanism has often been found in materials with a layered crystal structure. In this context, the most familiar examples are the high-T c cuprates and the Fe-based superconductors, where the corresponding CuO 2 or Fe 2 An 2 (An = P, As, Se, Te) layer plays an important role in determining the superconducting properties [3][4][5]. Similarly, the BiS 2 layer is believed to be the basic building block for inducing superconductivity in Bi 4 O 4 S 3 and it is expected that the doping mechanism resembles that of cuprates and Fe-based superconductors. This argument is supported by the discovery of other BiS 2 -based superconductors ReO 1−x F x BiS 2 (Re = La, Ce, Pr, and Nd) with T c values of 10.6, 3.0, 5.5, and 5.6 K, respectively [6][7][8][9].Up to now, only very few theoretical and experimental studies have been performed on Bi 4 O 4 S 3 . The parent phase (Bi 6 O 8 S 5 ) is a band insulator which becomes superconducting after electron doping [1]. A first principles band structure calculation indicates that the superconductivity in Bi 4 O 4 S 3 originates from two Bi 6p orbitals, as they intersect the Fermi surface [10]. A RPA analysis of a two-orbital model for the BiS 2 -based superconductors suggests that the spin fluctuations promote competing A 1g and B 2g superconducting states with similar pairing strengths [11]. Transport measurements under pressure reveal that T c of Bi 4 O 4 S 3 decreases monotonically without distinct change of the normal state metallic behavior [12]. The exact nature of the superconducting state is still debated. Hall, Seebeck coefficients, and magnetoresistance measurements suggest exotic multiband features in Bi 4 O 4 S 3 [13]. Recent measurements of the temperature dependence of the magnetic penetration depth λ us...

Superconductivity in layered BiS2-based compounds

“…λ(T ) is an important parameter that is used to distinguish between different possible superconducting energy gap structures and to help identify the superconducting pairing mechanism. 840 λ(T ) was measured in Bi 4 O 4 S 3 by µSR measurements [30] and using tunnel-diode-oscillator technique [32]. The superfluid density ρ, determined from these measurements, was found to be very low.…”

“…Is the pairing mech- 75 anism similar to that in unconventional superconductors (i.e., Fe-based superconductors, cuprates, etc.) or is pairing more [1,30,15,31,32,33,34, 35] LaO 0.5 F 0.5 BiS 2 2.8 [6,36,8,37,15,38,39,40,41, 42] CeO 0.5 F 0.5 BiS 2 3.0 [8,43,44,27, 45] PrO 0.5 F 0.5 BiS 2 3.5 [8,46,27, 47] NdO 0.5 F 0.5 BiS 2 4.0 [10,8,26,48,49,27, 22] YbO 0.5 F 0.5 BiS 2 5.4 [ [52] likely to be phonon mediated? Herein, we provide a selective review of the large and growing body of literature concerning BiS 2 -based superconductors and related materials.…”

Testing thedx2−y2*-wave pairing symmetry by quasiparticle interference and Knight shift inBiS2Gao1, Zhou2, Huang3 et al. 2014Phys. Rev. B140100View full textAdd to dashboardCite

“…10,11 On the other hand, the strong FS nesting was also proposed to enhance the electron-phonon interaction and make the BiS 2 -based superconductors conventional s-wave superconductors. 9,12,13 On the experimental side, the measured magnetic penetration depth as a function of temperature can be fitted by assuming a fully gapped conventional s-wave pairing symmetry, [14][15][16] thus supporting the electron-phonon interaction as the pairing glue in BiS 2 -based superconductors. However, later neutron scattering experiments suggested that the electron-phonon coupling in LaO 0.5 F 0.5 BiS 2 could be much weaker than previously expected.…”

Electronic structure predictions in Bi-O-S systems

“…Unlike the compounds with a lanthanide oxide spacer layer, some of which display magnetic ordering, Bi-O-S compounds have been shown not to exhibit any magnetic ordering [37], nor any magnetic anomaly in the superconducting state [38].…”

“…The TDO data is well described using a single gap s-wave model, whereas the µSR data point more towards a two-gap s-wave symmetry [38,46].…”