Abstract
Multifold degenerate points in the electronic structure of metals lead to exotic behaviors. These range from twofold and fourfold degenerate Weyl and Dirac points, respectively, to sixfold and eightfold degenerate points that are predicted to give rise, under modest magnetic fields or strain, to topological semimetallic behaviors. The present study shows that the nonsymmorphic compound PdSb2 hosts six-component fermions or sextuplets. Using angle-resolved photoemission spectroscopy, crossing points formed by three twofold degenerate parabolic bands are directly observed at the corner of the Brillouin zone. The group theory analysis proves that under weak spin-orbit interaction, a band inversion occurs.
Highlights
Multifold degenerate points in the electronic structure of metals lead to to lead to exotic transport properties, such as large carrier mobility,[11,12] anomalous exotic behaviors
The present study shows that the nonsymmorphic compound PdSb2 hosts six-component fermions or sextuplets
Condensed matter systems can realize novel fermions which have otherwise no counterpart in high energy angle-resolved photoemission spectroscopy, crossing points formed by three physics[21] because the former do not need twofold degenerate parabolic bands are directly observed at the corner of the to follow certain symmetries which are Brillouin zone
Summary
Condensed matter systems can exhibit quasiparticle excitations in both nonsymmorphic[22,23] and symmorphic crystal which mimic the wavefunctions of exotic fermions predicted in structures,[23] nonsymmorphic operations are essential for high energy physics.[1]. The band dispersion near this point (along the X3−R−X3 direction) is measured with 65 eV p-polarized photon (Figure 2e), which reveals the presence of two concentric electron pockets centered at R. These pockets coincide with each other at the upper sixfold degenerate point, which appears at ≈0.25 eV binding energy. ARPES measurements provide a clear experimental signature of six component fermions in PdSb2 This investigation will stimulate further studies in identifying novel fermions with quadratic band crossings, which can exhibit unusual physical properties that are distinctly different from that of Dirac and Weyl fermions. PdSb2 is an interesting test bed to understand the superconducting instabilities of exotic fermions, which could open new routes toward unconventional superconducting states of matter
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