Observation of topological nodal fermion semimetal phase in ZrSiS

165

134

We have performed angle-resolved photoemission spectroscopy on HfSiS, which has been predicted to be a topological line-node semimetal with square Si lattice. We found a quasi-two-dimensional Fermi surface hosting bulk nodal lines, alongside the surface states at the Brillouin-zone corner exhibiting a sizable Rashba splitting and band-mass renormalization due to many-body interactions. Most notably, we discovered an unexpected Dirac-like dispersion extending one-dimensionally in k space -the Dirac-node arc -near the bulk node at the zone diagonal. These novel Dirac states reside on the surface and could be related to hybridizations of bulk states, but currently we have no explanation for its origin. This discovery poses an intriguing challenge to the theoretical understanding of topological line-node semimetals. In contrast to conventional semimetals with a finite band-overlap between valence band (VB) and conduction band (CB), topological semimetals are categorized by the band-contacting nature between VB and CB in the Brillouin zone (BZ); point-contact (Dirac/Weyl semimetals) or line-contact (line-node semimetals; LNSMs). The existence of three-dimensional (3D) Dirac semimetals was first confirmed by angle-resolved photoemission spectroscopy (ARPES) of Cd 3 As 2 [9, 10] and Na 3 Bi [11], where the VB and CB contact each other at the point (Dirac point) protected by rotational symmetry of the crystal [12,13]. Recent ARPES studies on noncentrosymmetric transition-metal monopnictides [14][15][16][17] have clarified pairs of bulk Dirac-cone bands and Fermi-arc SSs, supporting their Weyl-semimetallic nature [18,19]. While the existence of Weyl semimetals with point nodes has been confirmed experimentally, the experimental studies of LNSMs with line nodes are relatively scarce [20][21][22][23] despite many theoretical predictions [24][25][26][27][28][29][30].Recently, it was theoretically proposed by Xu et al. that ZrSiO with PbFCl-type crystal structure (space group P 4/nmm) and its isostructural family WHM (W = Zr, Hf, or La; H = Si, Ge, Sn, or Sb; M = O, S, Se and Te; see Fig. 1 . These studies demonstrated the realization of LNSM phase as well as an appearance of nearly-flat SSs around theX point, both were explained on the basis of band calculations.In this Letter, we report the ARPES results on HfSiS. In addition to the overall VB structure which is in support of the LNSM nature of HfSiS, we found new spectral features, such as a large Rashba splitting of SSs atX, a dispersion kink at ∼0.05 eV, and most importantly, unexpected Dirac-like SSs forming a "Dirac-node arc". This is a rare case in the research of topological materials that experiment finds novel SSs that were not predicted by theory.Figure 1(c) shows the ARPES-intensity plot in the VB region as a function of wave vector and binding energy (E B ) measured along theΓX cut at hν = 80 eV (see Supplemental Materials for details of sample preparation [33] and ARPES measurements). One can notice several dispersive bands; holelike bands atΓ (h) with the to...

supporting

confidence: 61%

mentioning

confidence: 99%

Dirac-node arc in the topological line-node semimetal HfSiS

Takane¹,

Wang²,

Souma³

et al. 2016

165

134

“…In general, interactions may destabilize the line-node to create point nodes, fully gapped systems, or when strong, may even invalidate the quasiparticle picture. We will leave questions regarding these phenomena to future work since there exist real materials for which our assumption is valid [33][34][35]. We also note that a version of our stacking construction for gapped phases has also been considered in Ref.…”

mentioning

confidence: 99%

Quasitopological electromagnetic response of line-node semimetals

Ramamurthy

Hughes

2017

Topological semimetals are gapless states of matter which have robust surface states and interesting electromagnetic responses. In this paper, we consider the electromagnetic response of gapless phases in 3 + 1-dimensions with line nodes. We show through a layering approach that an intrinsic 2-form Bµν emerges in the effective response field theory that is determined by the geometry and energy-embedding of the nodal lines. This 2-form is shown to be simply related to the charge polarization and orbital magnetization of the sample. We conclude by discussing the relevance for recently proposed materials and heterostructures with line-node fermi-surfaces.

“…DC conductivities are calculated in hyperhoneycomb lattices with the TNLs 29,30 . Recently, ZrSiS has been observed as a TNLSM experimentally [31][32][33][34][35] . Meanwhile, one can find another type of spinless nodal lines protected by mirror or glide symmetry but not topology.…”

Section: Introductionmentioning

confidence: 99%

“…In general, the protection by the mirror symmetry can coexist with the topological protection. Actually, the nodal lines in ZrSiS are protected also by the glide symmetry 31,32 . We can also realize the WSM phase in spinless systems when either TR or I symmetry is absent [38][39][40][41] .…”

Section: Introductionmentioning

confidence: 99%

Universal phase transition and band structures for spinless nodal-line and Weyl semimetals

Okugawa

Murakami

2017

We study a general phase transition between spinless topological nodal-line semimetal and Weyl semimetal phases. We classify topological nodal lines into two types based on their positions and shapes, and their phase transitions depends on their types. We show that a topological nodalline semimetal becomes the Weyl semimetal by breaking time-reversal symmetry when the nodal lines enclose time-reversal invariant momenta (type-A nodal lines). We also discuss an effect of crystallographic symmetries determining the band structure of the topological nodal-line semimetals. Thanks to protection by the symmetries, the topological nodal-line semimetals can transition into spinless Weyl semimetals or maintain the nodal lines in many crystals after inversion symmetry is broken.