Takahiro Iwagaki | Searcharxiv

arXiv2026

Correlated topological-polarization surface states in the narrow-gap insulator FeSb2

Strong electron correlations and band topology each generate rich quantum phases, but conflicting elemental requirements have largely kept them apart. Topological polarization offers a route to unite them, producing polar surface states from bonding charge without spin-orbit coupling and thereby extending band topology to correlated 3d transition-metal compounds. Here we demonstrate that epitaxial thin films of the narrow-gap insulator FeSb2 host metallic polar surface states of topological-polarization origin, governed by the strong correlations of the bulk. Nonreciprocal surface transport emerges only below the onset temperature of a correlation-driven reconstruction of the bulk Fe 3d orbital occupation, providing direct evidence of bulk-edge correspondence in a correlated topological system. Moreover, electrostatic gating drives this correlated surface across a quantum phase transition into a ferromagnetic or possibly altermagnetic state. Our results establish topological polarization as a design principle for correlated topological phases in a broad range of materials.

cond-mat.str-el↗

arXiv2026

Emergent Cooperative Superstructures via Order-Disorder Kinetics in Molecule-Intercalated NbSe2

The design of quantum states at heterointerfaces has enabled a variety of emergent phenomena. Among them, molecular intercalation superlattices have attracted attention as tunable hybrid materials, formed by inserting organic molecules into van der Waals crystals, where molecular structure and chemistry provide new degrees of freedom. Traditionally, the intercalated molecules have been regarded as inactive spacers, while possible molecular ordering and its impact on the host lattice have remained largely unexplored. Here, we report the discovery of a cooperative superstructure (CSS) phase in molecule intercalated NbSe2, where ordering of the guest molecules induce a concomitant superstructure in the NbSe2 host lattice, characterized by a moiré structure due to incommensurability between the molecular layer and the inorganic lattice. Synchrotron X-ray diffraction reveals the emergence of CSS phase, accompanied by crystal symmetry lowering. Complementary resistivity and thermal-quench measurements show that the transition is governed by unusually slow order-disorder kinetics, so that the CSS phase can be selectively accessed under standard laboratory cooling rates. This kinetic behavior arises from slow molecular dynamics coupled to the host lattice, contrasting with fast charge or magnetic ordering in inorganic solids. Our findings establish molecular ordering as a route for engineering heterointerfaces, enabling thermally programmable superstructures.

cond-mat.mtrl-sci↗