Hourglass Dirac chain metal in rhenium dioxide

Abstract

Nonsymmorphic symmetries, which involve fractional lattice translations, can generate exotic types of fermionic excitations in crystalline materials. Here we propose a topological phase arising from nonsymmorphic symmetries—the hourglass Dirac chain metal, and predict its realization in the rhenium dioxide. We show that ReO2 features hourglass-type dispersion in the bulk electronic structure dictated by its nonsymmorphic space group. Due to time reversal and inversion symmetries, each band has an additional two-fold degeneracy, making the neck crossing-point of the hourglass four-fold degenerate. Remarkably, close to the Fermi level, the neck crossing-point traces out a Dirac chain—a chain of connected four-fold-degenerate Dirac loops—in the momentum space. The symmetry protection, the transformation under symmetry-breaking, and the associated topological surface states of the Dirac chain are revealed. Our results open the door to an unknown class of topological matters, and provide a platform to explore their intriguing physics.

From Type-II Triply Degenerate Nodal Points and Three-Band Nodal Rings to Type-II Dirac Points in Centrosymmetric Zirconium Oxide

“…3(c). Though the two nodal ring are touched together here, they are not nodal chain [51][52][53] as the two nodal rings are in the same plane and the touching is accident. Remarkably, beyond the critical strain, the two nodal rings would merge together to produce four droplet-shaped nodal rings [see Fig.…”

Hourglass Weyl loops in two dimensions: Theory and material realization in monolayer GaTeI family

“…In this way, the Weyl and Dirac semimetals were discovered [5][6][7][8][9][10][11], which have twofold and fourfold degenerate band crossing points, and around these points, the low-energy electrons resemble the Weyl and Dirac fermions and can exhibit fascinating physical effects like their counterparts in high energy physics [12][13][14]. Moving forward, it was realized that crystalline solids may host more types of emergent fermions beyond the Weyl/Dirac paradigm [15][16][17][18][19]. For example, in a three-dimensional (3D) material, besides 0D nodal point, band crossings may also take the form of 1D nodal loops [20][21][22][23][24][25][26][27][28][29] or even 2D nodal surfaces [30][31][32][33][34].…”

Experimental discovery of nodal chains

“…

Three-dimensional (3D) topological nodal points [1][2][3][4][5][6], such as Weyl and Dirac nodes have attracted wide-spread interest across multiple disciplines and diverse material systems. Unlike nodal points that contain little structural variations, nodal lines [7][8][9] can have numerous topological configurations in the momentum space, forming nodal rings [10][11][12][13], nodal chains [14][15][16][17][18] and potentially nodal links [19][20][21] and nodal knots [22,23]. However, nodal lines have much less development for the lack of ideal material platforms [24][25][26].

…”