Experimental Realization of Type-II Dirac Fermions in a PdTe2 Superconductor

Abstract

A Dirac fermion in a topological Dirac semimetal is a quadruple-degenerate quasi-particle state with a relativistic linear dispersion. Breaking either time-reversal or inversion symmetry turns this system into a Weyl semimetal that hosts double-degenerate Weyl fermion states with opposite chiralities. These two kinds of quasi-particles, although described by a relativistic Dirac equation, do not necessarily obey Lorentz invariance, allowing the existence of so-called type-II fermions. Recent theoretical discovery of type-II Weyl fermions evokes the prediction of type-II Dirac fermions in PtSe 2 -type transition metal dichalcogenides, expecting an experimental confirmation. Here, we report an experimental realization of type-II Dirac fermions in PdTe 2 by angle-resolved photoemission spectroscopy combined with ab-initio band calculations. Our experimental finding makes the first example that has both superconductivity and type-II Dirac fermions, which turns the topological material research into a new phase.

The study on quantum material WTe2

“…TaIrTe 4 [55] and LaAlGe [56] were also demonstrated to hold type-II Weyl fermions. Recently, the band structure with highly tilted cone has also been found in type-II Dirac semi-metals [57][58][59][60][61].…”

Pd3Te2: an s-wave superconductor with Pd atom coordinated by five Te atoms

“…PdTe 2 is a layered compound forming by the stacking of layers composed of {PdTe 6 } octahedral as in PdTe. More recently, Noh et al reported the existence of type-II Dirac fermions in PdTe 2 by angle-resolved photoemission spectroscopy combined with ab initio band calculations [9].…”

Band Structure Perfection and Superconductivity in Type‐II Dirac Semimetal Ir1−xPtxTe2

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Recent levels of interest in topological semimetals (TSMs) have stimulated a fruitful avenue of research in materials science. [12][13][14][15] The concept of broken Lorentz invariance also results in a new system termed type-II DSM, in which the Dirac cones are tilted significantly along specific momentum directions, [16][17][18][19][20][21][22][23] leading to a modulated effective mass and the potential for new applications. [12][13][14][15] The concept of broken Lorentz invariance also results in a new system termed type-II DSM, in which the Dirac cones are tilted significantly along specific momentum directions, [16][17][18][19][20][21][22][23] leading to a modulated effective mass and the potential for new applications.

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“…[24][25][26][27] In particular, intrinsic topological superconductivity (TSC) [28][29][30][31][32][33] could be induced in type-II DSMs due to a finite density of states around the Dirac points, potentially hosting Majorana modes [28][29][30][31][32][33][34][35][36][37] with possible applications in topological quantum computations. [16,[18][19][20][21] These materials are group-10 transition-metal dichalcogenides (TMDC), with crystal structures belonging to the 3 l P m space group, offering similar electronic structures consisting of type-II Dirac dispersions protected by C 3v symmetry. [16,[18][19][20][21] These materials are group-10 transition-metal dichalcogenides (TMDC), with crystal structures belonging to the 3 l P m space group, offering similar electronic structures consisting of type-II Dirac dispersions protected by C 3v symmetry.…”

“…[38,39] Materials made of type-II DSMs have been recently discovered in the 1T-PtSe 2 family, i.e., PtSe 2 , PtTe 2 , and PdTe 2 . [16,17] However, these materials are limited by the problem that the Dirac points are far below the Fermi level, and there are several trivial bands crossing the Fermi surface, [16][17][18][19][20][21] which constrains the use of these materials in transport studies and for future applications. [16,17] However, these materials are limited by the problem that the Dirac points are far below the Fermi level, and there are several trivial bands crossing the Fermi surface, [16][17][18][19][20][21] which constrains the use of these materials in transport studies and for future applications.…”