The α-type organic conductors constitute the second solid-state system in which massless Dirac fermions were discovered, following graphene, and, like graphene, they provide a single material platform encompassing many aspects of Dirac physics and topological properties. Although research on these materials initially developed independently within the field of organic conductors, a series of physical phenomena closely related to those in graphene and inorganic topological systems have recently been successively observed in α-(ET)₂I₃ and α-(BETS)₂I₃. In this article, we review recent developments in organic Dirac systems from the perspective of general topological properties, focusing in particular on symmetry-broken quantum Hall states and the dimensional crossover to three-dimensional topological semimetal or insulator phases at low temperatures.

We propose a new approach to searching for wave-like dark matter (DM) by monitoring the direct excitation of superconducting qubits, quantum two-level systems originally developed for quantum computation. We show that superconducting qubits can serve as highly sensitive quantum sensors for DM detection. In particular, a broad class of wave-like DM models induces an effective electric field that can drive transitions from the ground state to the excited state of a qubit. Our proposal is to search for such excitations as a signature of wave-like DM. We outline the theoretical foundation of this detection scheme and summarize recent experimental progress toward its realization. We demonstrate that qubit-based searches can probe regions of parameter space that have not been explored previously.

In ferromagnets, electric current generally induces a transverse Hall voltage in proportion to the net magnetization. While such a property is usually not expected in antiferromagnets, recent theoretical studies predicted that non-coplanar antiferromagnetic order with finite scalar spin chirality (i.e., a solid angle spanned by neighboring spins) can induce a large “topological” Hall effect even without net magnetization or external magnetic field. Here, we report its experimental realization in intercalated van der Waals magnets CoTa₃S₆ and CoNb₃S₆. The present results indicate that the scalar spin chirality mechanism offers a promising route to the realization of giant spontaneous Hall response even in compensated antiferromagnets.

The heavy-fermion superconductor CeRh₂As₂, characterized by local inversion symmetry breaking at the Ce sites, exhibits an exceptionally high upper critical field and a magnetic-field-induced multiphase superconducting state. In this article, we review our recent microscopic investigations of this compound using nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR). Our measurements reveal that both the low-field and high-field superconducting phases possess a spin-singlet nature, providing compelling evidence for a magnetic-field-induced transition from even- to odd-parity superconducting state, which is driven by the sublattice degree of freedom. Furthermore, zero-field NQR measurements unveiled a rare antiferromagnetic transition occurring inside the superconducting state. A comparative study with the non-magnetic reference compound LaRh₂As₂, which exhibits conventional fully-gapped s-wave superconductivity, demonstrates that the strong electron correlation originating from the Ce 4f electrons is indispensable for realizing these exotic states. These findings highlight that the interplay between local inversion symmetry breaking and strong electron correlations provides a novel platform for exploring unconventional superconductivity and multiple characteristic orders.