Full superconducting gap in the candidate topological superconductor In1−xPbxTe for x=0.2 (original) (raw)
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Superconducting properties and gap structure of the topological superconductor candidate Ti3Sb
Physical Review B
We present a study of the superconducting properties of the candidate topological superconductor Ti3Sb. Electrical transport measurements show zero resistance with a , of ≈ 5.9 K with a transition width Δ ≈ 0.6 K. The superconducting phase boundaries as derived from magneto-transport and magnetic susceptibility measurements agree well. We estimate an upper critical field Bc2(0)≈ 4.5 T. A Ginzburg-Landau (GL) analysis yields values of the coherence length and penetration depth of =6.2 nm and =340 nm, respectively, and a GL parameter ≈ 55, indicating extreme type-II behavior. Furthermore, we observed a step height in the specific heat Δ ≈ 1.61, a value larger than the Bardeen-Cooper-Schrieffer (BCS) value of 1.43, suggesting modest coupling. Measurements of the temperature dependence of the London penetration depth via the tunnel-diode oscillator (TDO) technique down to ≈ 450 mK show a full superconducting gap, consistent with a conventional s-wave gap structure.
Bulk Superconductivity Below 6 K in PdBi2Te3 Topological Single Crystal
Journal of Superconductivity and Novel Magnetism, 2020
We study the structural and bulk superconducting properties of self flux grown PdBi 2 Te 3 single crystal. Phase purity of as grown crystal is confirmed by Rietveld refinement of gently crushed powder XRD of the same. PdBi 2 Te 3 crystallizes in rhombohedral structure with R-3 m space group along with small impurity of Bi. Scanning Electron Microscopy (SEM) images showed layered structure and the elemental analysis by energy dispersive X Ray analysis (EDAX) done on same confirmed the stoichiometry to be near to PdBi 2 Te 3. Characteristic vibrational modes viz. A 1 1g , Eg 2 , A 2 1g are clearly observed in Raman spectrum, and are slightly shifted from that as in case of Bi 2 Te 3. Bulk superconductivity is confirmed by FC and ZFC magnetization measurements (M-T) exhibiting diamagnetic transition with T c onset at around 6K. M-H plots at different temperatures of 2K, 2.5K, 3K, 3.5K, 4K, 4.5K, 5K and 6K showed clear opening of the loop right up to 6K. Both M-T and M-H clearly establish the appearance of bulk type II superconductivity below 6K in studied PdBi 2 Te 3. The lower critical field H c1 and upper critical field H c2 are at 180Oe at 4800Oe respectively at 2K for as grown PdBi 2 Te 3 crystal. Other critical parameters of superconductivity such as coherence length, penetration depth and kappa parameter are also calculated.
Two-band superconductivity in Pb from ab initio calculations
Physical Review B, 2007
We perform first-principles calculations of the band and k-point resolved superconducting gap of Pb in the framework of the density functional theory for superconductors. Without any adjustable parameter or assuption different from s-wave symmetry, we find two different values of the gap on the two sheets of the Fermi surface, which can be related to the different electron-phonon couplings characterizing the electronic states in the corresponding bands. These, in turn, derive from the different orbital character of the electronic states. We also find some intraband gap anisotropy in each Fermi surface sheet. Our calculated gap, critical temperature and total anisotropy of the gap are in good agreement with tunneling experiments. We estimate an Ϸ8% enhancement of T c coming from the gap anisotropy. However, the experimentally found T 3 temperature dependence of the specific heat cannot be found within our assumed anisotropic s-wave gap symmetry.
Two-dimensional topological superconductivity in Pb/Co/Si(111)
Nature communications, 2017
Just like insulators can present topological phases characterized by Dirac edge states, superconductors can exhibit topological phases characterized by Majorana edge states. In particular, one-dimensional topological superconductors are predicted to host zero-energy Majorana fermions at their extremities. By contrast, two-dimensional superconductors have a one-dimensional boundary which would naturally lead to propagating Majorana edge states characterized by a Dirac-like dispersion. In this paper we present evidences of one-dimensional dispersive in-gap edge states surrounding a two-dimensional topological superconducting domain consisting of a monolayer of Pb covering magnetic Co-Si islands grown on Si(111). We interpret the measured dispersive in-gap states as a spatial topological transition with a gap closure. Our method could in principle be generalized to a large variety of heterostructures combining a Rashba superconductor with a magnetic layer in order to be used as a platf...
Physical Review B, 2018
The temperature dependence of the London penetration depth ∆λ(T) in the superconducting doped topological crystalline insulator Sn1−xInxTe was measured down to 450 mK for two different doping levels, x ≈ 0.45 (optimally doped) and x ≈ 0.10 (underdoped), bookending the range of cubic phase in the compound. The results indicate no deviation from fully gapped BCS-like behavior, eliminating several candidate unconventional gap structures. Critical field values below 1 K and other superconducting parameters are also presented. The introduction of disorder by repeated particle irradiation with 5 MeV protons does not enhance Tc, indicating that ferroelectric interactions do not compete with superconductivity.
Robust odd-parity superconductivity in the doped topological insulator NbxBi2Se3
Physical Review B, 2017
We present resistivity and magnetization measurements on proton-irradiated crystals demonstrating that the superconducting state in the doped topological insulator NbxBi2Se3 (x = 0.25) is surprisingly robust against disorder-induced electron scattering. The superconducting transition temperature Tc decreases without indication of saturation with increasing defect concentration, and the corresponding scattering rates far surpass expectations based on conventional theory. The lowtemperature variation of the London penetration depth ∆λ(T) follows a power law (∆λ(T) ∼ T 2) indicating the presence of symmetry-protected point nodes. Our results are consistent with the proposed robust nematic Eu pairing state in this material.
Science Bulletin, 2019
Connate topological superconductor (TSC) combines topological surface states with nodeless superconductivity in a single material, achieving effective p-wave pairing without interface complication. By combining angle-resolved photoemission spectroscopy and in-situ molecular beam epitaxy, we studied the momentum-resolved superconductivity in β-Bi 2 Pd film. We found that the superconducting gap of topological surface state (Δ TSS ~ 3.8 meV) is anomalously enhanced from its bulk value (Δ b ~ 0.8 meV). The ratio of 2Δ TSS /k B T c ~ 14.2, is substantially larger than the BCS value. By measuring β-Bi 2 Pd bulk single crystal as a comparison, we clearly observed the upward-shift of chemical potential in the film. In addition, a concomitant increasing of surface weight on the topological surface state was revealed by our first principle calculation, suggesting that the Dirac-fermion-mediated parity mixing may cause this anomalous superconducting enhancement. Our results establish β-Bi 2 Pd film as a unique case of connate TSCs with a highly enhanced topological superconducting gap, which may stabilize Majorana zero modes at a higher temperature.
Unusual nature of fully gapped superconductivity in In-doped SnTe
Physical Review B, 2013
The superconductor Sn1−xInxTe is a doped topological crystalline insulator and has become important as a candidate topological superconductor, but its superconducting phase diagram is poorly understood. By measuring about 50 samples of high-quality, vapor-grown single crystals, we found that the dependence of the superconducting transition temperature Tc on the In content x presents a qualitative change across the critical doping xc ≃ 3.8%, at which a structural phase transition takes place. Intriguingly, in the ferroelectric rhombohedral phase below the critical doping, Tc is found to be strongly enhanced with impurity scattering. It appears that the nature of electron pairing changes across xc in Sn1−xInxTe.
Pressure-induced superconductivity in topological parent compound Bi 2 Te 3
Proceedings of the National Academy of Sciences, 2010
We report a successful observation of pressure-induced superconductivity in a topological compound Bi 2 Te 3 with T c of ∼3 K between 3 to 6 GPa. The combined high-pressure structure investigations with synchrotron radiation indicated that the superconductivity occurred at the ambient phase without crystal structure phase transition. The Hall effects measurements indicated the hole-type carrier in the pressure-induced superconducting Bi 2 Te 3 single crystal. Consequently, the first-principles calculations based on the structural data obtained by the Rietveld refinement of X-ray diffraction patterns at high pressure showed that the electronic structure under pressure remained topologically nontrivial. The results suggested that topological superconductivity can be realized in Bi 2 Te 3 due to the proximity effect between superconducting bulk states and Dirac-type surface states. We also discuss the possibility that the bulk state could be a topological superconductor.