Direct evidence of two superconducting gaps in FeSe0.5Te0.5: SnS-Andreev spectroscopy and the lower critical field

Abstract

We present direct measurements of the superconducting order parameter in nearly optimal FeSe0.5Te0.5 single crystals with critical temperature TC ≈ 14 K. Using intrinsic multiple Andreev reflection effect (IMARE) spectroscopy and measurements of lower critical field, we directly determined two superconducting gaps, ∆L ≈ 3.3 − 3.4 meV and ∆S ≈ 1 meV, and their temperature dependences. We show that a two-band model fits well the experimental data. The estimated electron-boson coupling constants indicate a strong intraband and a moderate interband interaction.

Light-induced enhancement of superconductivity in iron-based superconductor FeSe0.5Te0.5

“…1c) and other measurements 29,[31][32][33][34] . The simultaneously obtained large gap energy, 2Δ L (0) = 8.0 meV, provides a considerably large value of the ratio 2Δ L =k B T c~5 .8, exceeding the weak-coupling limit of 3.53, in accordance with previous Andreev spectroscopy 55,56 and the magnetic penetration depth measurement by muon spin rotation technique 57 . One may also consider the effect of the charge density fluctuation (CDF) that also contributes to THG 58 .…”

Doping-dependent switch from one- to two-component superfluidity in coupled electron-hole van der Waals heterostructures

“…However, in system B, when it switches from one-component to two-component superfluidity, two peaks associated with the gaps bb and tt will appear in the spectral function at negative frequencies [41]. Other experimental techniques that can be used to detect the presence or absence of the second gap tt are Andreev reflection spectroscopy [42,43] and scanning tunneling microscopy (STM) [44].…”

A doping-dependent switch from one- to two-component superfluidity at temperature above 100K in coupled electron-hole Van der Waals heterostructures

“…However in system B, when it switches from one-component to two-components superfluidity, two peaks associated with the gaps ∆ bb and ∆ tt will appear in the spectral function at negative frequencies [36]. Other experimental techniques that can be used to detect the presence or absence of the second gap ∆ tt are Andreev reflection spectroscopy [37,38] and scanning tunneling microscopy (STM) [39].…”