Abstract
Weyl semimetal TaAs, congenially accommodating the massless Weyl fermions, furnishes a platform to observe a spontaneous breaking of either the time-reversal or the inversion symmetry and the concurrent genesis of pairs of Weyl nodes with significant topological durability. Former experimental analysis, which reveals that the near-zero spin-polarization of bulk TaAs, experiences a boost in proximity of point-contacts of non-magnetic metals along with the associated tip-induced superconductivity, provides the impetus to study the large-area stacked interfaces of TaAs with noble metals like Au and Ag. The primary outcomes of the present work can be listed as follows: (1) First-principles calculations on the interfacial systems have manifested an increment of the interface-induced spin-polarization and contact-induced transport spin-polarization of TaAs in proximity of noble metals; (2) In contrast to the single interface, for vertically stacked cases, the broken inversion symmetry of the system introduces a z-directional band-dispersion, resulting in an energetically separated series of non-degenerate band crossings. The simultaneous presence of such band-crossings and spin-polarization indicated the coexistence of both broken time reversal and inversion symmetries for metal-semimetal stacked interfaces; (3) quantum transport calculations on different device geometries reveal the importance of contact geometry for spin-transport in TaAs devices. Lateral contacts are found to be more effective in obtaining a uniform spin transport and larger transport spin polarization; (4) the phonon dispersion behaviour of TaAs displays a closure of band-gap with the associated increase of phonon-density of states for the acoustic modes in proximity of lateral contacts of noble metals.
Highlights
Weyl semimetal TaAs, congenially accommodating the massless Weyl fermions, furnishes a platform to observe a spontaneous breaking of either the time-reversal or the inversion symmetry and the concurrent genesis of pairs of Weyl nodes with significant topological durability
Crystalline Weyl semimetal (WSM) systems consist of bulk band crossings, named as Weyl nodes, consisting of non-degenerate three-dimensional bands near Fermi-level, in contrast to the two-dimensional band crossings at Dirac points of G raphene[8,9]
Realization of Weyl nodes is possible, when the time reversal symmetry (TRS) or inversion symmetry (IS) is broken for a Dirac semi-metal[4,5,15,16], where a Dirac node can be considered to be composed of two Weyl nodes of opposite c hirality[17]
Summary
The most fascinating effect of stacked interfaces is the restoration of non-degenerate band-crossings and nodal features along X–U for both the systems, as can be seen from Fig. 4a, b, d and e. B. In Fig. 8, we have plotted a comparison of the percentage of transport spin polarization for different bias voltages, calculated from its absolute value Pt = (I↑- I↓)/( I↑ + I↓) for the electron temperatures 5 K and 300 K for both lateral and vertical contact geometry, where I↑ and I↓ are the spin-up and spin-down currents respectively. The lateral contacts with the metal layer bonded with both Ta and As are more promising in producing a better transport spin polarizations, we intend to obtain the nature of phonon dispersion of TaAs in presence of lateral Au or Ag metal layer, where we have created a smaller system resembling the lateral interface as shown in first column of Fig. 11. In presence of metals, there is an eloquent impact on the phonon dispersion and densities of TaAs, suggesting emergence of phonon-induced correlated behaviour within the system
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