Intertwining exotic quantum order and nontrivial topology is at the frontier of condensed matter physics [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] . A charge density wave (CDW) like order with orbital currents has been proposed as a powerful resource for topological states in the context of the quantum anomalous Hall effect 5,6 and for the hidden matter in the pseudogap phase of cuprate superconductors 7,8 . However, the experimental realization of such topological charge order is challenging. Here we use high-resolution scanning tunnelling microscopy (STM) to discover a topological charge order in a kagome superconductor 21-25 KV3Sb5. Through both lattice-sensitive topography and electronic-sensitive spectroscopic imaging, we observe a 2×2 superlattice, consistent with the star of David deformation in the underlying kagome lattice. Spectroscopically, an energy gap opens at the Fermi level, across which the charge modulation exhibits an intensity reversal, signaling a charge ordering. The strength of charge modulations further displays a clockwise or anticlockwise chiral anisotropy, which we demonstrate can be switched by an applied magnetic field. Our observations and theoretical analysis point to a topological charge order in the frustrated kagome lattice, which not only leads to a giant anomalous Hall effect, but can also be a strong precursor of unconventional superconductivity.

The theoretical proposal of chiral fermions in topological semimetals has led to a significant effort towards their experimental realization. In particular, the Fermi surfaces of chiral semimetals carry quantized Chern numbers, making them an attractive platform for the observation of exotic transport and optical phenomena. While the simplest example of a chiral fermion in condensed matter is a conventional |C|=1 Weyl fermion, recent theoretical works have proposed a number of unconventional chiral fermions beyond the standard model which are protected by unique combinations of topology and crystalline symmetries. However, materials candidates for experimentally probing the transport and response signatures of these unconventional fermions have thus far remained elusive. In this Letter, we propose the RhSi family in space group No. 198 as the ideal platform for the experimental examination of unconventional chiral fermions. We find that RhSi is a filling-enforced semimetal that features near its Fermi surface a chiral double sixfold-degenerate spin-1 Weyl node at R and a previously uncharacterized fourfold-degenerate chiral fermion at Γ. Each unconventional fermion displays Chern number ±4 at the Fermi level. We also show that RhSi displays the largest possible momentum separation of compensative chiral fermions, the largest proposed topologically nontrivial energy window, and the longest possible Fermi arcs on its surface. We conclude by proposing signatures of an exotic bulk photogalvanic response in RhSi.

Topological matter is known to exhibit unconventional surface states and anomalous transport owing to unusual bulk electronic topology. In this study, we use photoemission spectroscopy and quantum transport to elucidate the topology of the room temperature magnet Co 2 MnGa. We observe sharp bulk Weyl fermion line dispersions indicative of nontrivial topological invariants present in the magnetic phase. On the surface of the magnet, we observe electronic wave functions that take the form of drumheads, enabling us to directly visualize the crucial components of the bulk-boundary topological correspondence. By considering the Berry curvature field associated with the observed topological Weyl fermion lines, we quantitatively account for the giant anomalous Hall response observed in our samples. Our experimental results suggest a rich interplay of strongly correlated electrons and topology in this quantum magnet.The discovery of topological phases of matter has led to a new paradigm in physics, 30 which not only explores the analogs of particles relevant for high energy physics, but also 31 offers new perspectives and pathways for the application of quantum materials [1][2][3][4][5][6][7][8][9][10]. To 32 date, most topological phases have been discovered in non-magnetic materials [6][7][8], which 33 severely limits their magnetic field tunability and electronic/magnetic functionality. Iden-34 tifying and understanding electronic topology in magnetic materials will not only provide 35 indispensable information to make their existing magnetic properties more robust, but also 36 has the potential to lead to the discovery of novel magnetic response that can be used to ex-37 plore future spintronics technology. Recently, several magnets were found to exhibit a large 38 anomalous Hall response in transport, which has been linked to a large Berry curvature in 39 their electronic structures [11][12][13][14][15]. However, it is largely unclear in experiment whether the 40 Berry curvature originates from a topological band structure, such as Dirac/Weyl point or 41 line nodes, due to the lack of spectroscopic investigation. In particular, there is no direct vi-42 sualization of a topological magnetic phase demonstrating a bulk-boundary correspondence 43 with associated anomalous transport. 44Here we use angle-resolved photoemission spectroscopy (ARPES), ab initio calculation 45 and transport to explore the electronic topological phase of the ferromagnet Co 2 MnGa [10]. 46In our ARPES spectra we discover a line node in the bulk of the sample. Taken together with 47 our ab initio calculations, we conclude that we observe Weyl lines protected by crystalline 48 mirror symmetry and requiring magnetic order. In ARPES we further observe drumhead 49 surface states connecting the bulk Weyl lines, revealing a bulk-boundary correspondence in a 50 magnet. Combining our ARPES and ab initio calculation results with transport, we further 51 find that Berry curvature concentrated by the Weyl lines accounts for the giant intrinsic 52 anomal...