Single-gap superconductivity inβ−Bi2Pd

Abstract

The β-Bi 2 Pd compound has been proposed as another example of a multigap superconductor [Imai et al., J. Phys. Soc. Jpn. 81, 113708 (2012)]. Here, we report on measurements of several important physical quantities capable of showing a presence of multiple energy gaps on our superconducting single crystals of β-Bi 2 Pd with the critical temperature T c close to 5 K. The calorimetric study via a sensitive ac technique shows a sharp anomaly at the superconducting transition, however only a single energy gap is detected. Also other characteristics inferred from calorimetric measurements as the field dependence of the Sommerfeld coefficient and the temperature and angular dependence of the upper critical magnetic field point unequivocally to standard single s-wave gap superconductivity. The Hall-probe magnetometry provides the same result from the analysis of the temperature dependence of the lower critical field. A single-gapped BCS density of states is detected by the scanning tunneling spectroscopy measurements. Then, the bulk as well as the surface sensitive probes evidence a standard conventional superconductivity in this system where the topologically protected surface states have been recently detected by angle-resolved photoemission spectroscopy [Sakano et al., Nat. Commun. 6, 8595 (2015).].

Probing the superconducting gap symmetry of α−PdBi2 : A penetration depth study

“…2,6 Even in the NCS superconduc- tor α-PdBi, ultra-low-temperature scanning tunneling spectra 16 obtained a similar value of ∆(0)/k B T c ≈ 1.9. Clearly, these values are consistent with the parameters reported in our work.…”

“…However, later experiments using muon-spin relaxation (µSR) 5 and calorimetric studies 6 have shown a single isotropic BCS-like gap in β-PdBi 2 with negligible contribution from the topologically protected surface states.…”

“…It has been suggested that for Type-II superconductors, the surface Andreev bound states consisting of Majorana Fermions are expected to decay into the bulk within a few coherence lengths ξ. Using the value of ξ≈20 nm for β-PdBi 2 from calorimetric measurements, 6 , and ξ≈66 nm for α-PdBi from STS measurements, 16 these states should have a spatial extent of ∼100 nm from the surface. Given our fitted value of λ(0)≈140 nm, our penetration depth measurements is able to measure field penetration from ∼140 nm inwards, with Angstrom resolution.…”

Unconventional superconductivity in the strong-coupling limit for the heavy fermion system CeCoIn5

“…For instance, Fig. 2 (a) shows the temperature-evolution of the ac-measured heat capacity [12] at 0 and 5.5 T applied along the c-axis. At zero field, on cooling from the normal state the C/T signal jumps suddenly (in less than 40 mK) at 2.25 K towards the low-temperature superconducting state.…”

Evolution of the topologically protected surface states in superconductorβ-Bi2Pd from the three-dimensional to the two-dimensional limit

“…More recently, two members of the Bi-Pd family of superconductors have been found to exhibit topologically protected surface states with Rashba-like spin splitting. While the superconducting state of noncentrosymmetric BiPd appears to be topologically trivial [43][44][45], the pairing symmetry of centrosymmetric β-Bi 2 Pd remains to be elucidated [46][47][48][49][50][51][52]. Despite the fact that spin-and angleresolved photoemission spectroscopy (ARPES) has revealed the presence of notrivial surfaces states at the Fermi level [46], no Andreev bound states associated with Majorana fermions have been observed in pointcontact spectroscopy [48].…”