Type-II topological metals

Abstract

Topological metals (TMs) are a kind of special metallic materials, which feature nontrivial band crossings near the Fermi energy, giving rise to peculiar quasiparticle excitations. TMs can be classified based on the characteristics of these band crossings. For example, according to the dimensionality of the crossing, TMs can be classified into nodal-point, nodal-line, and nodal-surface metals. Another important property is the type of dispersion. According to degree of the tilt of the local dispersion around the crossing, we have type-I and type-II dispersions. This leads to significant distinctions in the physical properties of the materials, owing to their contrasting Fermi surface topologies. In this article, we briefly review the recent advances in this research direction, focusing on the concepts, the physical properties, and the material realizations of the type-II nodal-point and nodal-line TMs.

Mitrofanovite Pt3Te4: A Topological Metal with Termination-Dependent Surface Band Structure and Strong Spin Polarization

“…Topological metals are materials with nontrivial band crossings or band inversions near the Fermi energy, giving rise to peculiar quasiparticle excitations. − They can be classified based on the dimensionality and degeneracy of their band crossings . Prominent examples include Dirac, Weyl, nodal-line, and nodal-surface metals .…”

“…Topological metals are materials with nontrivial band crossings or band inversions near the Fermi energy, giving rise to peculiar quasiparticle excitations. − They can be classified based on the dimensionality and degeneracy of their band crossings . Prominent examples include Dirac, Weyl, nodal-line, and nodal-surface metals . In topological metals, bulk superconductivity can also coexist with topologically nontrivial states, as demonstrated for PbTaSe 2 enabling the intriguing perspective of Majorana Fermions in solid-state physics.…”

Photonic Type-III Nodal Loop and Topological Phase Transitions at Bilayer Metasurfaces

“…Consequently, a ring-like degeneracy (type-III NL) is obtained in the Brillouin zone, as shown in Figure 1. In addition, the NL has the nearly k-independent degenerating frequency, f NL , distinguished significantly from the so-called hybrid type of loop degeneracy with strong k-dependence (Li et al, 2020;Xiong et al, 2020). We employ microwave near-field scanning measurements to observe the type-III NL at the metasurface and confirm its existence.…”

“…In terms of the dispersion of degenerating bands, NL can be classified into type-I and type-II configurations with the former meaning the cross between positive and negative bands and the latter representing the cross between positive (negative) bands (Li et al, 2020). There is also a hybrid configuration, where the dispersion of at least one band is strongly momentum-dependent and changes the dispersion sign over the closed-loop in k-space (Li et al, 2020;Xiong et al, 2020). Such classifications are applicable likewise to both DPs and WPs and have been investigated extensively in 2D/3D photonics (Pyrialakos et al, 2017;Wang et al, 2017;Hu et al, 2018;Mann et al, 2018).…”

Topological properties of subsystem-symmetry-protected edge states in an extended quasi-one-dimensional dimerized lattice

“…Symmetries of a system can be used to classify the topology of electronic band structures. Based on topological classification [10][11][12][13][14][15][16], a diversity of new and interesting materials can be categorized into topological insulating [1,[17][18][19][20], topological superconducting [2,[21][22][23][24], topological semi-metal [25][26][27][28], and topological metal [29][30][31][32][33][34][35] states in one, two, or three dimensions.…”