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

Abstract

We develop theory models for both ballistic and disordered superconducting monolayer black phosphorus devices in the presence of magnetic exchange field and strain. The ballistic case is studied through a microscopic Bogoliubov-de Gennes formalism while for the disordered case we formulate a quasiclassical model. Utilizing the two models, we theoretically study the response of supercurrent to an externally applied magnetic field in two-dimensional black phosphorus Josephson junctions. Our results demonstrate that the response of the supercurrent to a perpendicular magnetic field in ballistic samples can deviate from the standard Fraunhofer interference pattern when the Fermi level and mechanical strain are varied. This finding suggests the combination of chemical potential and strain is an efficient external knob to control the current response in highly sensitive strain-effect transistors and superconducting quantum interference devices. We also study the supercurrent in a superconductor-ferromagnet-ferromagnet-superconductor junction where the magnetizations of the two adjacent magnetized regions are uniform with misaligned orientations. We show that the magnetization misalignment can control the excitation of harmonics higher than the first harmonic sin ϕ (in which ϕ is the phase difference between the superconductors) in supercurrent and constitutes a full spin switching current element. Finally, we discuss possible experimental implementations of our findings. We foresee our models and discussions could provide guidelines to experimentalists in designing devices and future investigations.

Evolution of pair correlation symmetries and supercurrent reversal in tilted Weyl semimetals

“…As recently demonstrated, control of these parameters is possible by, for example, applying strain to the system. [9][10][11] To further shed light on the symmetry profiles of these superconducting correlations, in Figs. 1-3, we present a few representative profiles for the real and imaginary parts of the equal-Pspin and opposite-Pspin components as a function of the momenta k x and k y .…”

“…Such situations can be precisely determined by first-principles calculations; e.g., when the system experiences external strain or is subject to doping and intercalation. A practical example is when a black phosphorus mono- layer is under the application of an external strain, as was recently discussed [9][10][11] . The band-structure parameters were obtained using density-functional-theory computations, and symmetry calculations demonstrated that the momenta coefficients can change sign depending on the strength and direction of the applied in-plane strain.…”

“…4,5 This topological phase results in the band structure in the bulk of Weyl semimetals being gapless, although Fermi arc states connect pairs of Weyl points. [6][7][8][9][10][11] As has been widely discussed, the presence of gapless surface states opens up transport channels free from backscattering. For a conventional type-I WS, the Fermi surface is point-like, where electron and hole states occupy separate energy ranges above or below the Weyl point.…”

“…These intriguing phenomena have motivated a significant wave of interest to the Weyl metal systems both theoretically and experimentally. [7][8][9][10][11]26, When discussing the superconducting state of a Weyl semimetal, the symmetry of the electron-electron coupling potential, ∆, is an important property that gives insight into the nature of the pairing correlations. Moreover, when a relationship exists between the quasiparticle excitations in the Weyl phase and the pair correlations, a more complete understanding of the underlying electronic structure can be obtained.…”

Magnetic Textures and Dynamics in Magnetic Weyl Semimetals

“…Moreover, Weyl semimetals with their Weyl cones tilted to the Fermi surface, namely type-II Weyl semimetals, are also of great interest. [50] Due to their unconventional Fermi surface structure, modification of magnetic quantum oscillations, [51] superconductivity, [52][53][54][55][56][57][58][59][60] optical activity, [61][62][63][64] etc., have been expected and observed in type-II Weyl semimetals.…”