Abstract
Interest in topological states of matter burgeoned over a decade ago with the theoretical prediction and experimental detection of topological insulators, especially in bulk three-dimensional insulators that can be tuned out of it by doping. Their superconducting counterpart, the fully-gapped three-dimensional time-reversal-invariant topological superconductors, have evaded discovery in bulk intrinsic superconductors so far. The recently discovered topological metal β-PdBi2 is a unique candidate for tunable bulk topological superconductivity because of its intrinsic superconductivity and spin-orbit-coupling. In this work, we provide experimental transport signatures consistent with fully-gapped 3D time-reversal-invariant topological superconductivity in K-doped β-PdBi2. In particular, we find signatures of odd-parity bulk superconductivity via upper-critical field and magnetization measurements— odd-parity pairing can be argued, given the band structure of β-PdBi2, to result in 3D topological superconductivity. In addition, Andreev spectroscopy reveals surface states protected by time-reversal symmetry which might be possible evidence of Majorana surface states (Majorana cone). Moreover, we find that the undoped bulk system is a trivial superconductor. Thus, we discover β-PdBi2 as a unique bulk material that, on doping, can potentially undergo an unprecedented topological quantum phase transition in the superconducting state.
Highlights
According to the traditional Landau-Ginzburg paradigm, states of matter are defined by the symmetries broken in thermal equilibrium that are preserved by the underlying Hamiltonian, and phase transitions acquire universal features that only depend on the symmetries involved and the spatial dimension
We have shown that in K-doped β-PdBi2 the bulk superconductivity is unconventional— a necessary condition for 3D topological superconductivity, and that the surface states are helical, a signature of this phase
We recall that sufficient conditions for topological superconductivity in a 3D time-reversal invariant (TRI) material are that the normal state Fermi surfaces enclose an odd number of time-reversal invariant momenta (TRIM) and the fully-gapped bulk superconductivity pairing be odd under inversion
Summary
According to the traditional Landau-Ginzburg paradigm, states of matter are defined by the symmetries broken in thermal equilibrium that are preserved by the underlying Hamiltonian, and phase transitions acquire universal features that only depend on the symmetries involved and the spatial dimension. The sufficient conditions for 3D time-reversal invariant (TRI) topological superconductivity are: One, the normal state Fermi surfaces enclose an odd number of time-reversal invariant momenta, two, the bulk superconductivity is fully gapped, and three, odd-parity[6,7]. Once these conditions are met, the surface states are spanned by robust, helical Majorana surface states. Suppressing the s-wave pairing channel can promote the odd-parity channel[22,23]
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