Investigation on the reported superconductivity in intercalated black phosphorus

Abstract

Superconductivity intrinsic to the intercalated black phosphorus (BP) with a transition temperature T c of 3.8 K, independent of the intercalant, whether an alkali or an alkaline earth element, has been reported recently by R. Zhang et al. (2017). However, the reported T c and the field effect on the superconducting (SC) transition both bear great similarities to those for the pure Sn, which is commonly used for BP synthesis under the vapor transport method. We have therefore decided to determine whether a minute amount of Sn is present in the starting high purity BP crystals and whether it is the culprit for the small SC signal detected. Energydispersive X-ray spectroscopy results confirmed the existence of Sn in the starting high purity BP crystals purchased from the same company as in R. Zhang et al. (2017). We have reproduced the SC transition at 3.8 K in Li-and Na-intercalated BP crystals that contain minute amounts of Sn when prepared by the vapor transport method but not in BP crystals that are free of Sn when prepared by the high-pressure method. We have therefore concluded that the SC transition reported by R. Zhang et al. (2017) is associated with the Sn but not intrinsic to the intercalated BP crystals.

Strain-engineered Majorana zero energy modes and φ0 Josephson state in black phosphorus

“…In general, the intravalley couplings can have different coupling potentials and therefore differing amplitudes in each valley. The observation of intrinsic superconductivity in BP has attracted much attention [49][50][51][52][53][54] as well as controversies 55,56 . Here we assume that the superconductivity can be induced extrinsically in the BP by making use of the proximity effect.…”

Fraunhofer response and supercurrent spin switching in black phosphorus with strain and disorder

“…The consequences of these combinations will be considered in a future work. There are some indications that a BP sheet under pressure and/or with electron doping can be driven into the superconducting phase 4,24-29,47 , although still not conclusively 30,31 . Nonetheless, we assume that singlet superconductivity can be extrinsically induced into a BP sheet by means of the proximity effect when BP is proximity coupled to an s-wave superconducting electrode as shown in Fig.…”

“…Also, it has been found that black phosphorus in both orthorhombic and rhombohedral structures can intrinsically develop superconductivity [21][22][23][24][25][26][27][28][29][30][31] . However, the dominant pairing type in BP has brought up discussions and is still unclear.…”

Control of superconducting pairing symmetries in monolayer black phosphorus

“…Black phosphorus under a pressure of ∼ 10 GPa undergoes an orthorhombic to simple-cubic structural transition and experiences a superconducting phase transition with a critical temperature (T c ) of ∼ 4.8 K, whose origin is still unexplained but could be due to the electronphonon coupling mechanism [27][28][29] . Several works have attempted to provide a theoretical description for the observed superconducting phase in BP [30][31][32][33][34][35][36][37][38][39][40][41] . The effect of strain on the T c of BP was studied from first-principles using the Eliashberg spectral function [33][34][35][36][37] .…”

“…It was found that superconductivity shows a universal critical temperature of 3.8 ± 0.1 K, independent of the synthesized chemical composition 38 . This unusual finding has brought up controversies about the origin of the reported intrinsic superconductivity in BP obtained by doping 39 . The determination of dominant superconducting pairing type(s) in a material is a formidable task.…”