Pyrite-type PdSb 2 with a nonsymmorphic cubic structure has been predicted to host six-fold-degenerate exotic fermions beyond the Dirac and Weyl fermions. Though magnetotransport measurements on PdSb 2 suggest its topologically nontrivial character, direct spectroscpic study of its band structure remains absent. Here, by utilizing high-resolution angle-resolved photoemission spectroscopy, we present a systematic study on its bulk and surface electronic structure. Through careful comparison with first-principles calculations, we verify the existence of six-fold fermions in PdSb 2 , which are formed by three doubly degenerate bands centered at the R point in the Brillouin zone. These bands exhibit parabolic dispersion close to six-fold fermion nodes, in sharp contrast to previously reported ones in chiral fermion materials. Furthermore, our data reveal no protected Fermi arcs in PdSb 2 , which is compatible with its achiral structure. Our findings provide a remarkable platform for study of new topological fermions and indicate their potential applications.In high-energy physics, three types of fermions have been predicated to exist in our universe according to the Lanrence invarience, i.e. the Dirac, Weyl and Majorana fermions. Although the existence of Weyl and Majorana fermions as elementary particles is still under hot debate, some quasiparticles constructed out of excitations were theoretically proposed to be able to mimic all three fermions in solids. Very soon after these predictions, Dirac [1-4], Weyl [5-10] and Majorana fermions [11][12][13] were experimentally confirmed to actually exist in topological non-trivial materials. Moreover, rather than the Poincarè symmetry, it is the invariance under crystal symmetry of one of 230 space groups that constrains fermions in solids [14][15][16][17], and thus there might exist some novel fermions beyond elementary particles discussed in highenergy physics. In solids, it is well known that the topological non-trivial four-and two-fold degenerate band crossings correspond to Dirac and Wely fermions, respectively. While, allowed by crystal symmetries, some new exotic fermions showing three-, six-, or eight-fold degeneracy of band crossings have been proposed, which are particularly intriguing since there are no counterparts in high-energy physics due to Poincarè symmetry constrains [14].To date, angle-resolved photoemission spectroscopy (ARPES) experiments have verified several types of exotic fermions beyond the Dirac and Weyl ones. Unique triply degenerate points in the electronic structure of molybdenum phosphide were reported [18]. Moreover, four-, six-(double * Equal contributions † spin-1) and eight-fold (charge-2) degenerate chiral fermions were as well observed in AlPt [19] and CoSi [20-23] families with extremely long surface Fermi arcs, in sharp contrast to Weyl semimetals which have multiple pairs of Weyl nodes with only small separation. In addition, four types of symmetry-stabilized topological fermions have been observed in PdBiSe [24]. The pyrite PdSb 2 ...

We report an unusual pressure-induced superconducting state that coexists with an antiferromagnetic ordering of Eu2+ moments and shows a large upper critical field comparable to the Pauli paramagnetic limit in EuTe2. In concomitant with the emergence of superconductivity with Tc ≈ 3–5 K above Pc ≈ 6 GPa, the antiferromagnetic transition temperature TN(P) experiences a quicker rise with the slope increased dramatically from dTN/dP = 0.85(14) K/GPa for P ≤ Pc to 3.7(2) K/GPa for P ≥ Pc. Moreover, the superconducting state can survive in the spin-flop state with a net ferromagnetic component of the Eu2+ sublattice under moderate magnetic fields μ0H ≥ 2 T. Our findings establish the pressurized EuTe2 as a rare magnetic superconductor possessing an intimated interplay between magnetism and superconductivity.

The interplay between topological electronic structure and superconductivity has attracted tremendous research interests recently as they could induce topological superconductivity (TSCs) which may be used to realize topological qubits for quantum computation. Among various TSC candidates, superconducting BaSn 3 (T c ∼ 4.4 K) has been predicted to be a topological Dirac semimetal (TDS) hosting two pairs of Dirac points along the -A direction. Here, by combining the use of angle-resolved photoemission spectroscopy and ab initio calculations, we identified the predicted topological Dirac fermions and confirmed the TDS nature of the compound. In addition, we observed surface states connecting the Dirac points. Our observations demonstrate BaSn 3 as a superconductor with nontrivial topological electronic structures.

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The van der Waals Fe5–x GeTe2 is a 3d ferromagnetic metal with a high Curie temperature of 275 K. We report herein the observation of an exceptional weak antilocalization (WAL) effect that can persist up to 120 K in an Fe5–x GeTe2 nanoflake, indicating the dual nature with both itinerant and localized magnetism of 3d electrons. The WAL behavior is characterized by the magnetoconductance peak around zero magnetic field and is supported by the calculated localized nondispersive flat band around the Fermi level. The peak to dip crossover starting around 60 K in magnetoconductance is visible, which could be ascribed to temperature-induced changes in Fe magnetic moments and the coupled electronic band structure as revealed by angle-resolved photoemission spectroscopy and first-principles calculations. Our findings would be instructive for understanding the magnetic exchanges in transition metal magnets as well as for the design of next-generation room-temperature spintronic devices.