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Register a new userSignatures for half-metallicity and nontrivial surface states in a Kagome-lattice magnetic Weyl semimetal Co$_3$Sn$_2$S$_2$
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Weyl semimetals with time reversal symmetry breaking are expected to show various fascinating physical behaviors, such as intrinsic giant anomalous Hall effect, chiral anomaly effect in the bulks, and Fermi arcs on the surfaces. Here we report a scanning tunneling microscopy study on the magnetic Weyl semimetal candidate Co$_3$Sn$_2$S$_2$. According to the morphology and local density of states of the surface, we provide assignments to different surface terminations. The measured local density of states reveals a semimetal gap of ~300 mV, which is further verified as the gap in spin-minority bands using spin-resolved tunneling spectra. Additionally, signature for the nontrivial surface states around 50 mV is proposed. This is further confirmed by the observations of standing waves around a step-edge of the sample. Our observations and their comparison with band structure calculations provide direct yet timely evidence for the bulk and surface band structures of the magnetic Weyl semimetal Co$_3$Sn$_2$S$_2$.
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Very recently, the half-metallic compound Co$_3$Sn$_2$S$_2$ was predicted to be a magnetic WSM with Weyl points only 60 meV above the Fermi level ($E_F$). Owing to the low charge carrier density and large Berry curvature induced, Co$_3$Sn$_2$S$_2$ possesses both a large anomalous Hall conductivity (AHC) and a large anomalous Hall angle (AHA), which provide strong evidence for the existence of Weyl points in Co$_3$Sn$_2$S$_2$. In this work, we theoretically studied the surface topological feature of Co$_3$Sn$_2$S$_2$ and its counterpart Co$_3$Sn$_2$Se$_2$. By cleaving the sample at the weak Sn-S/Se bonds, one can achieve two different surfaces terminated with Sn and S/Se atoms, respectively. The resulting Fermi arc related states can range from the energy of the Weyl points to $E_F$-0.1 eV in the Sn-terminated surface. Therefore, it should be possible to observe the Fermi arcs in angle-resolved photoemission spectroscopy (ARPES) measurements. Furthermore, in order to simulate quasiparticle interference (QPI) in scanning tunneling microscopy (STM) measurements, we also calculated the joint density of states (JDOS), which revealed that the QPI patterns arising from Fermi arc related scatterings are clearly visible for both terminals. This work would be helpful for a comprehensive understanding of the topological properties of these two magnetic WSMs and further ARPES and STM measurements.
The search for novel topological phases of matter in quantum magnets has emerged as a frontier of condensed matter physics. Here we use state-of-the-art angle-resolved photoemission spectroscopy (ARPES) to investigate single crystals of Co$_3$Sn$_2$S$_2$ in its ferromagnetic phase. We report for the first time signatures of a topological Weyl loop. From fundamental symmetry considerations, this magnetic Weyl loop is expected to be gapless if spin-orbit coupling (SOC) is strictly zero but gapped, with possible Weyl points, under finite SOC. We point out that high-resolution ARPES results to date cannot unambiguously resolve the SOC gap anywhere along the Weyl loop, leaving open the possibility that Co$_3$Sn$_2$S$_2$ hosts zero Weyl points or some non-zero number of Weyl points. On the surface of our samples, we further observe a possible Fermi arc, but we are unable to clearly verify its topological nature using the established counting criteria. As a result, we argue that from the point of view of photoemission spectroscopy the presence of Weyl points and Fermi arcs in Co$_3$Sn$_2$S$_2$ remains ambiguous. Our results have implications for ongoing investigations of Co$_3$Sn$_2$S$_2$ and other topological magnets.
The band inversion in topological phase matters bring exotic physical properties such as the emergence of a topologically protected surface states. They strongly influence the surface electronic structures of the investigated materials and could serve as a good platform to gain insight into the catalytic mechanism of surface reactions. Here we synthesized high-quality bulk single crystals of the topological semimetal Co$_3$Sn$_2$S$_2$. We found that at room temperature, Co$_3$Sn$_2$S$_2$ naturally hosts the band structure of a topological semimetal. This guarantees the existence of robust surface states from the Co atoms. Bulk single crystal of Co$_3$Sn$_2$S$_2$ exposes their Kagome lattice that constructed by Co atoms and have high electrical conductivity. They serves as catalytic centers for oxygen evolution process (OER), making bonding and electron transfer more efficient due to the partially filled $e_g$ orbital. The bulk single crystal exhibits outstanding OER catalytic performance, although the surface area is much smaller than that of Co-based nanostructured catalysts. Our findings emphasize the importance of tailoring topological non-trivial surface states for the rational design of high-activity electrocatalysts.
In many realistic topological materials, more than one kind of fermions contribute to the electronic bands crossing the Fermi level, leading to various novel phenomena. Here, using momentum-resolved inelastic electron scattering, we investigate the plasmons and their evolution across the phase transition in a type-II Weyl Semimetal MoTe$_2$, in which both Weyl fermions and trivial nonrelativistic fermions contribute to the Fermi surface in the Td phase. One plasmon mode in the 1T phase at high temperature and two plasmon modes in the topological T$_d$ phase at low temperature are observed. Combining with first-priciples calculations, we show that all the plasmon modes are dominated by the interband correlations between the inverted bands of MoTe$_2$. Especially in the T$_d$ phase, since the electronic bands split due to inversion symmetry breaking and spin-orbit coupling, the plasmon modes manifest the interband correlation between the topological Weyl fermions and the trivial nonrelativistic electrons. Our work emphasizes the significance of the interplay between different kinds of carriers in plasmons of topological materials.
Nodal-line metals and semimetals, as interesting topological states of matter, have been mostly studied in nonmagnetic materials. Here, based on first-principles calculations and symmetry analysis, we predict that fully spin-polarized Weyl loops can be realized in the half metal state for the three-dimensional material Li$_3$(FeO$_3$)$_2$. We show that this material has a ferromagnetic ground state, and it is a half metal with only a single spin channel present near the Fermi level. The spin-up bands form two separate Weyl loops close to the Fermi level, which arise from band
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