Breakdown of induced p± ip pairing in a superconductor-semiconductor hybrid

Superconductor-semiconductor hybrids are platforms for realizing effective p-wave superconductivity. Spin-orbit coupling, combined with the proximity effect, causes the two-dimensional semiconductor to inherit p ± ip intraband pairing [1–3], and application of magnetic field can then result in transitions to the normal state [4– 6], partial Bogoliubov Fermi surfaces [7], or topological phases with Majorana modes [8–13]. Experimentally probing the hybrid superconductorsemiconductor interface is challenging due to the shunting effect of the conventional superconductor. Consequently, the nature of induced pairing remains an open question. Here, we use the circuit quantum electrodynamics architecture to probe induced superconductivity in a two dimensional Al-InAs hybrid system. We observe a strong suppression of superfluid density and enhanced dissipation driven by magnetic field, which cannot be accounted for by the depairing theory of an s-wave superconductor. These observations are explained by a picture of independent intraband p ± ip superconductors giving way to partial Bogoliubov Fermi surfaces, and allow for the first characterization of key properties of the hybrid superconducting system. In the ongoing effort to conclusively identify Majorana modes in superconductor-semiconductor hybrids, there has been a great deal of research on states at the boundaries of one-dimensional systems [14–23]. Due to the bulk-boundary correspondence, the presence of these states should be controlled by bulk system parameters such as density and mobility, which have so far been inaccessible to experimental probes. We use a resonant microwave circuit to extract these properties in a twodimensional system [24, 25]. Our results indicate that the InAs has a strongly renormalized chemical potential, which poses a difficulty for schemes where the density must be controlled under the aluminum, but is beneficial for recently-proposed routes to Majorana physics that are closely related to the emergence of Bogoliubov Fermi arcs [26]. The basic picture of proximity effect in Al-InAs is presented in Fig. 1. An aluminum layer with a spindegenerate Fermi-surface is strongly coupled to a highmobility InAs two-dimensional electron gas. InAs has a pair of spin-orbit coupled Fermi surfaces which results in p ± ip intraband pairing of the form ∆(kx ± iky)/|k| for pure Rashba spin-orbit interaction, where k is the momentum at the Fermi surface labeled by ± [1, 11]. This pairing holds a special importance because a state with single, chiral px + ipy pairing is topologically nontrivial, and therefore capable of hosting Majorana modes [28]. Application of an in-plane magnetic field probes the nature of the induced pairing. For weak spin-orbit coupling, interband s-wave pairing quickly emerges [11, 29], and the system eventually transitions to an isotropic normal state [6]. In contrast, strong spin-orbit coupling makes the p ± ip pairing robust. Application of magnetic field then generates anisotropic suppression of the induced gap, and eventually the emergence of Bogoliubov Fermi surfaces [7]. Bogoliubov Fermi surfaces, however, may be subject to an instability that was explored in re-