Topological phase with a critical-type nodal line state in intermetallic CaPd

Abstract

In recent years, realizing new topological phase of matter has been a hot topic in the fields of physics and materials science. Topological semimetals and metals can conventionally be classified into two types: type-I and type-II according to the tilting degree of the fermion cone. Here, it is the first time to report a new topological metal phase with the critical-type nodal line between type-I and type-II nodal line. The critical-type nodal line shows a unique nontrivial band crossing which is composed of a flat band and a dispersive band and leads to a new fermionic state. We propose intermetallic CaPd can be an existing topological metal for the new fermionic state, characterized with critical-type nodal line in the bulk and drumhead band structure on the surface. Our work not only promotes the concept of critical-type nodal line, but also provides the material realization to study its exotic properties in future experiments. arXiv:1812.10627v1 [cond-mat.mes-hall]

Screening topological materials with a CsCl-type structure in crystallographic databases

“…Recently, they found that the crossing of a flat band and a dispersive band forms a critical-type nodal line which is protected by both mirror symmetry and the coexistence of P and T symmetries in CaPd. Our results are in good agreement with their report (Liu, Jin et al, 2018).…”

“…We can observe from the critical-type nodal-line signature that the flat band is nearly non-dispersive near the nodal line at every k-path in the k z = plane. Such a critical-type nodal line was first proposed by Liu, Jin et al (2018). Recently, they found that the crossing of a flat band and a dispersive band forms a critical-type nodal line which is protected by both mirror symmetry and the coexistence of P and T symmetries in CaPd.…”

“…As a result, the electron-like and hole-like states coexist at each energy level. For critical type, which is formed by a flat band and a dispersive band (Liu, Jin et al, 2018), it has the critical band dispersion between conventional type-I and type-II. Based on these types of band crossing, nodal line can also be termed as type-I, critical-type and type-II, where each point on the nodal line has type-I, critical-type and type-II band crossing, respectively.…”

Emergence of Topological insulator and Nodal line semi-metal states in XX′Bi (X = Na, K, Rb, Cs; X′ = Ca, Sr)

“…Similar gap opening along the nodal line is also observed in several other NLS systems e.g. Cu 3 PdN(~60 meV) 34,35 , ZrSiS(~20 meV) 36,37 , TiB 2 (~25 meV) 38,39 , CaAgBi(~80 meV) 40 , CaPd (~27 meV) 41 and so on. We have also carried out the surface density of states calculation for our material RbCaBi under SOC effect.…”

Realization of Weyl semimetal phases in topoelectrical circuits

“…When the kinetic and potential energy contribute equally, the transition between the Type-I and Type-II phases arises where one of the bands become completely flat with vanishing group velocity. This is the so-called Type-III [36] or Critical-type WSM phase [37]. However, realizing WSM states in condensed matter systems and tailoring their properties are experimentally challenging.…”