Experimental observation of drumhead surface states in SrAs3

Abstract

the topological nodal-line semimetal (tnS) is a unique class of materials with a one dimensional line node accompanied by a nearly dispersionless two-dimensional surface state. However, a direct observation of the so called drumhead surface state within current nodal-line materials is still elusive. Here, using high-resolution angle-resolved photoemission spectroscopy (ARPES) along with firstprinciples calculations, we report the observation of a topological nodal-loop (tnL) in SrAs 3 , whereas caAs 3 exhibits a topologically trivial state. our data reveal that surface projections of the bulk nodalpoints are connected by clear drumhead surface states in SrAs 3. furthermore, our magneto-transport and magnetization data clearly suggest the presence (absence) of surface states in SrAs 3 (caAs 3). notably, the observed topological states in SrAs 3 are well separated from other bands in the vicinity of the fermi level. RAs 3 where R = Ca, Sr, thus, offers a unique opportunity to realize an archetype nodal-loop semimetal and establish a platform for obtaining a deeper understanding of the quantum phase transitions. Experimental discoveries of non-trivial topological states in semimetals such as the Dirac 1-4 , Weyl 5-8 , and nodal-line 9-12 semimetals have greatly expanded the family of available topological materials beyond topological insulators 13-18. In the case of the node line/loop semimetals the valence and conduction bands touch along lines/loops in the Brillouin zone and disperse linearly in directions perpendicular to these lines. The density of states at the Fermi energy in an NLS is greater than that of a Dirac or Weyl semimetal, providing a more favorable condition for investigating exotic non-trivial phases and realistic material platforms for developing applications. Note that, the NLSs are not robust against spin-orbit coupling or other perturbations and require crystal symmetries for their protection. To date, several structural classes of NLSs such as PbTaSe 2 19 , LaN 20 , Cu 3 PdN 21 , and ZrSiS-type 10,11,22-27 materials have been reported with associated space group symmetries that protect the nodal-line state. However, the nodal-loop states in PbTaSe 2 19 , and Cu 3 PdN 21 lie in the vicinity of other metallic bands, LaN requires multiple symmetries for protection, while in the ZrSiX-type systems the topological states lie above the Fermi level. It is highly desirable, therefore, to find materials which require minimum symmetry protections without the presence of other nearby bands that interfere in isolating topological features within the electronic spectrum. It has been recently shown that time-reversal symmetry (TRS) with a center of inversion symmetry (CIS) is sufficient, in principle, to protect a nodal-line state 28-30. APn 3 (A = Ca, Sr, Ba, Eu; Pn = P, As) family of compounds has been identified as a potential material class to host such a minimal symmetry protected NLS when SOC is excluded 29,30. Among these, CaP 3 and CaAs 3 are the only members of this series to have a triclinic cryst...

Supercurrent diode effect and finite momentum superconductivity

“…In both cases, an upturn of in-plane critical field has been observed and attributed to the Rashba spin splitting. Other candidates include transition metal dichacodegnide MoTe 2 in the low-symmetry T d structure [34][35][36], and half-heusler superconductors such as YPtBi with tetrahedral point group [37][38][39][40]. These two classes of materials have strong spin-orbit interaction and small Fermi energy, which enhances the supercurrent diode effect.…”

Diabolical touching point in the magnetic energy levels of topological nodal-line metals

“…Topological nodal-line metals, including CaP 3 , provide an experimental platform to make Landau-Dirac points a reality, owing to an interplay of magnetic symmetries and breakdown. Future investigations should determine if a similar Landau-Dirac phenomenology exists for two other topological nodal-line material candidates, which host more complicated Fermi surfaces than the present study: (a) SrAs 3 , a cousin of CaP 3 with a similar crystalline structure and an experimentally-evidenced, [61][62][63] nodal-line degeneracy, and (b) the square-net compound ZrSiS, for which breakdown has been experimentally demonstrated [64]. Other platforms for Landau-Dirac points plausibly exist, owing to the diversity of magnetic space groups [65], as well as the qualitatively-distinct forms of breakdown in varied solid-state systems [31-35, 45-50, 66].…”

Magnetic Generation and Switching of Topological Quantum Phases in a Trivial Semimetal α−EuP3

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