Domain walls in insulating materials may be orders of magnitude more conducting than the bulk, allowing one to design the material functionality by their patterning. Studies of inhomogeneities such as domain walls in the presence of strong electronic interactions is a very challenging problem. A particularly interesting case is that of Mott insulators, where electrons are trapped solely by their mutual repulsion. In a prototypical material TaS₂ the electrons are localized in star-of-David shaped unit cells ordered hexagonally. The order is interrupted along the domain walls where the inter-star distances are modified. For small changes in the distances, the domain wall is just as insulating as the interior of the domains, while if the stars are brought very close together the domain wall should turn into a good conductor. We uncovered a further possibility: the Mott insulating state can still be disrupted in the wall by the kinetic energy gain, but without this leading to a true metallization. We show that in TaS₂ the conducting band is gapped due to the structural dimerization along the domain walls. The study was published in the paper Mottness collapse without metallization in the domain wall of the triangular-lattice Mott insulator 1T−TaS₂ in Physical Review Letters.

Domenske stene v izolatorskih snoveh so lahko za velikostne rede bolj prevodne kot notranjost domen, zato lahko na lastnosti materiala vplivamo s strukturiranjem vzorca. Proučevanje domenskih sten in drugih nehomogenosti je v prisotnosti močnih interakcij med elektroni zelo zahtevno. Zlasti so zanimivi Mottovi izolatorji, v katerih so elektroni ujeti zgolj zaradi njihovega medsebojnega odboja. V tantalovem disulfidu, TaS₂, so elektroni lokalizirani znotraj osnovnih celic v obliki Davidovih zvezd, ki tvorijo trikotno mrežo. Ureditev je prekinjena vzdolž domenskih sten, kjer so razdalje med zvezdami spremenjene. Če je sprememba le majhna, so domenske stene ravno tako izolativne kot notranjost domen, če pa je razmik zadosti zmanjšan, naj bi domenska stena postala dober prevodnik. V našem delu smo razkrili še tretjo možnost: Mottovo izolatorsko stanje se lahko vzdolž domenske stene poruši zaradi povečane kinetične energije, ne da bi to vodilo k nastanku pravega kovinskega stanja. Pokazali smo, da ima prevodni pas domenskih sten v TaS₂ energijsko režo zaradi strukturne dimerizacije vzdolž stene. Rezultati raziskave z naslovom Mottness collapse without metallization in the domain wall of the triangular-lattice Mott insulator 1T−TaS₂ so bili objavljeni v reviji Physical Review Letters.