Ideal type-II Weyl phonons in wurtzite CuI

Abstract

Weyl materials exhibiting topologically nontrivial touching points in band dispersion pave the way to exotic transport phenomena and novel electronic devices.Here, we demonstrate the signature of ideal type-II Weyl phase in phonon dispersion of solids through first-principles investigations. Type-II phononic Weyl phase is manifested in noncentrosymmetric wurtzite CuI by six pairs of Weyl points (WPs) in the = 0.0 plane. On the iodine-terminated surface of the crystal, very clean surface arcs are readily detectable. Each pair of WPs connected by open surface arcs is well separated by a large distance of 0.26 Å −1 , ten times larger than that in TaAs. The opposite chirality of WPs with quantized Berry curvature produces Weyl phonon Hall effect, in analogy to valley Hall effect of electrons. Such ideal type-II Weyl phase are readily observable in experiment, providing a unique platform to study novel thermal transport properties distinct from type-I Weyl phase.

Prediction of crossing nodal-lines and large intrinsic spin Hall conductivity in topological Dirac semimetal Ta3As family

“…2. Similar to the case of Cu 3 PdN and Mackay-Terrones crystal, the band crossings can be understood from the argument of codimension [16][17][18][19][20][21] . In general, the four bands without SOC effects near the Dirac points can be described by two identical 2 × 2 Hamiltonians, which are written as…”

“…According to the distribution and degeneracy of crossing nodal points, TSMs can usually be divided into three categories: Dirac semimetals, Weyl semimetals, and nodal line semimetals (NLSMs) [15][16][17][18][19][20][21][22][23] . The Weyl points are discrete points in momentum space where the conduction bands and valence bands cross each other.…”

Ideal type-II Weyl points in topological circuits

“…Unfortunately, the realization of ideal type-II WPs has been hindered by the lack of an experimental platform with enough flexibility to produce strongly tilted dispersion bands [ 8 ]. To the best of our knowledge, ideal type-II WPs have only been theoretically predicted in certain condensed matter systems without experimental validation [ 3 , 29 , 30 ].…”

“…Using site-resolved transmission measurement and mapping out the band structures, we confirm the existence of two key signatures of type-II WPs: (i) a strongly tilted band structure with two group velocities in the same direction, and (ii) the existence of topological surface states in an incomplete bandgap. Unlike previous proposals [ 3 , 29 , 30 ], our design utilizes a macroscopic circuit system. In this experimental platform, lattice sites can be wired in an arbitrary manner with arbitrary numbers of connections per node and long-range connections, and the hopping strengths are independent of the distance between the nodes [ 6 ].…”

Hourglass Weyl and Dirac nodal line phonons, and drumhead-like and torus phonon surface states in orthorhombic-type KCuS

“…Very recently, topological phonons in solid-state materials have been studied theoretically and experimentally. A series of three-dimensional (3D) materials with rich topological phononic states have been proposed: (1) different types of nodal point phonons, including the single and high degenerate Weyl point phonons, [34][35][36][37][38][39] ideal type-2 Weyl point phonons, [40][41][42] unconventional triangular Weyl point phonons, 43 Dirac point phonons, 44 three-fold degenerate point phonons, 45 and six-fold nodal point phonons; 46 (2) different types of nodal line phonons, including nodal-ring phonons, 47 Weyl nodal straight line phonons, 48 helical nodal line phonons, 49 periodic cage-like network phonons, 50 type-3 nodal-line phonons, 51 Weyl nodal line phonons, [52][53][54] hourglass nodal-net phonons; 55 and (3) multiple nodal surface phonons. 56 Among them, double Weyl point phonons in parity-breaking FeSi 34 and phononic helical nodal lines in MoB 2 49 have been verified via inelastic X-ray scattering.…”