Electronic phase diagram in a new BiS₂-based Sr_1−xLa_xFBiS₂system

Abstract

Abstract. In this paper, we systematically study the electron doping effect in a new BiS 2 -based system Sr 1−x La x FBiS 2 (0 ≤ x ≤ 0.7) through multiple techniques of X-ray diffraction, electrical transport, magnetic susceptibility, and Hall effect measurements. The parent compound SrFBiS 2 is found to possess a semiconducting-like ground state, with thermally activation energy E g ∼ 38 meV. By the partial substitution of La for Sr, superconductivity emerges when x > 0.3, reaching its maximal superconducting transition temperature T c ∼ 3.5 K at x = 0.55. In the normal state of superconducting samples, it is clearly seen that there exists a crossover from metallic to semiconducting state below a temperature T min , which shifts to lower temperatures with increasing La content. Based on these measurements, the associated electronic phase diagram of Sr 1−x La x FBiS 2 system has thus been established.

Effect of yttrium substitution on the superconducting properties ofLa1−xYxO0

“…2(a). Often, the systematic chemical substitution studies of the same systems have different phase diagrams [4,6,8,12,15,16]. Sometimes T c does not change and seems to be independent of substituent concentrations until a solubility limit emerges, even though both parent compounds are stable and can be synthesized [13].…”

“…A layered structure is also observed for these materials, composed of superconducting BiS 2 and blocking oxide layers. Subsequent studies demonstrated that superconductivity is induced in general by electron doping in the blocking layers, as with the systems LnO 1−x F x BiS 2 (Ln = La, Ce, Pr, Nd, Yb) and La 1−x M x OBiS 2 (M = Ti, Zr, Hf, Th) [13] layer [14,15]. The parent compounds, AOBiS 2 (A = La, Ce, Th) [6,13] and SrFBiS 2 [14][15][16], are bad metals and show semiconducting-like behavior; however, theoretical studies employing the tight-binding model and density functional calculations predicted that electron doping in the BiS 2 system increases the density of states at the Fermi level [17,18], making electron doping a crucial tuning parameter for superconductivity.…”

“…Subsequent studies demonstrated that superconductivity is induced in general by electron doping in the blocking layers, as with the systems LnO 1−x F x BiS 2 (Ln = La, Ce, Pr, Nd, Yb) and La 1−x M x OBiS 2 (M = Ti, Zr, Hf, Th) [13] layer [14,15]. The parent compounds, AOBiS 2 (A = La, Ce, Th) [6,13] and SrFBiS 2 [14][15][16], are bad metals and show semiconducting-like behavior; however, theoretical studies employing the tight-binding model and density functional calculations predicted that electron doping in the BiS 2 system increases the density of states at the Fermi level [17,18], making electron doping a crucial tuning parameter for superconductivity. The pairing mechanism in both Bi 4 O 4 S 3 and LaO 0.5 F 0.5 BiS 2 has also been investigated; recent studies of the temperature dependence of the penetration depth by the tunnel diode oscillator technique revealed evidence for fully gapped, strongly-coupled s-wave superconductivity in the Bi 4 O 4 S 3 compound [19], and an s-wave character for LaO 0.5 F 0.5 BiS 2 was indicated in muon-spin spectroscopy measurements [20].…”

Effect of hydrostatic pressures on the superconductivity of new BiS 2 based REO 0.5 F 0.5 BiS 2 (RE=La, Pr and Nd) superconductors

“…According to some theoretical studies, the fundamental electronic properties are attributed to the BiS 2 layers [1][2][3][4][5][6][7][8][9][10]. The band structure can be described as the valance band being consisting of S 3p and O 2p orbitals and the conduction band is mainly attributed to Bi6p xy and S 3p [13][14][15]. The electron doping is achieved through the O À 2 site F À 1 substitution.…”

Proximity to Fermi-surface topological change in superconductingLaO0.54F0.46BiS2

“…Well-known examples are cuprate and iron-pnictide superconductors, where the relationship between the superconductivity and charge/spin degrees of freedom in the superconducting planes are still in hot debate [1,2]. Recent discovery of a series of Bi-dichalcogenide layered superconductors [3][4][5][6][7][8][9][10][11][12], Bi 4 O 4 (S,Se) 3 and (Ln,Sr)(O,F)Bi(S,Se) 2 where Ln denotes lanthanoid atoms, has provided a new field of two-dimensional superconductivity with manifested spin-orbital coupling [13,14]. Among them, LaO 1−x F x BiS 2 exhibits the maximum superconducting transition temperature (T c ) of 10.6 K at x ∼ 0.5 upon pressure [4].…”