We report a high-pressure single crystal study of the topological superconductor Cu{x}Bi{2}Se{3}. Resistivity measurements under pressure show superconductivity is depressed smoothly. At the same time the metallic behavior is gradually lost. The upper-critical field data B{c2}(T) under pressure collapse onto a universal curve. The absence of Pauli limiting and the comparison of B{c2}(T) to a polar-state function point to spin-triplet superconductivity, but an anisotropic spin-singlet state cannot be discarded completely.

We report a high-pressure single-crystal study of the non-centrosymmetric superconductor YPtBi (Tc = 0.77 K). Magnetotransport measurements show a weak metallic behavior with a carrier concentration n ≃ 2.2 × 10 19 cm −3 . Resistivity measurements up to p = 2.51 GPa reveal superconductivity is promoted by pressure. The reduced upper critical field Bc2(T ) curves collapse onto a single curve, with values that exceed the model values for spin-singlet superconductivity. The Bc2 data point to an odd-parity component in the superconducting order parameter, in accordance with predictions for non-centrosymmetric superconductors.

We report superconductivity at Tc = 1.22 K and magnetic order at TN = 1.06 K in the semimetallic noncentrosymmetric Half Heusler compound ErPdBi. The upper critical field, Bc2, has an unusual quasi-linear temperature variation and reaches a value of 1.6 T for T → 0. Magnetic order is found below Tc and is suppressed at BM ∼ 2.5 T for T → 0. Since Tc ≃ TN , the interaction of superconductivity and magnetism is expected to give rise to a complex ground state. Moreover, electronic structure calculations show ErPdBi has a topologically nontrivial band inversion and thus may serve as a new platform to study the interplay of topological states, superconductivity and magnetic order.

In 3D topological insulators achieving a genuine bulk-insulating state is an important research topic. Recently, the material system (Bi,Sb) 2 (Te,Se) 3 (BSTS) has been proposed as a topological insulator with high resistivity and a low carrier concentration (Ren et al 2011 Phys. Rev. B 84 165311). Here we present a study to further refine the bulk-insulating properties of BSTS. We have synthesized BSTS single crystals with compositions around x = 0.5 and y = 1.3. Resistance and Hall effect measurements show high resistivity and record low bulk carrier density for the composition Bi 1.46 Sb 0.54 Te 1.7 Se 1.3 . The analysis of the resistance measured for crystals with different thicknesses within a parallel resistor model shows that the surface contribution to the electrical transport amounts to 97% when the sample thickness is reduced to 1 μm. The magnetoconductance of exfoliated BSTS nanoflakes shows 2D weak antilocalization with α ≃ −1 as expected for transport dominated by topological surface states.

The low-field magnetic response of the non-centrosymmetric superconductor YPtBi (T c = 0.77 K) is investigated. Ac-susceptibility and dc-magnetization measurements provide solid evidence for bulk superconductivity with a volume fraction of ∼ 70 %. The lower critical field is surprisingly small: B c1 = 0.008 mT (T → 0). Muon spin rotation experiments in a transverse magnetic field of 0.01 T show a weak increase of the Gaussian damping rate σ T F below T c , which yields a London penetration depth λ = 1.6 ± 0.2 µm. The zero-field Kubo-Toyabe relaxation rate σ KT equals 0.129 ± 0.004 µs −1 and does not show a significant change below T c . This puts an upper bound of 0.04 mT on the spontaneous magnetic field associated with a possible odd-parity component in the superconducting order parameter.