A team led by IMDEA Nanociencia has successfully synthesized and characterized two-dimensional islands of NbTe₂ with a type-1H hexagonal crystal structure, a metastable phase not observed in the bulk material. The research, published in the journal ACS Nano, utilized techniques such as molecular beam epitaxy on graphene and tunneling microscopy, confirming the structure and metallic nature of this phase.
Measurements taken at low temperatures revealed a charge density modulation with a periodic 4 × 4 pattern, related to an instability in the crystal lattice vibrations. "This was not what we expected from this material, because in three dimensions it has a type-1T structure, not this hexagonal 1H phase," explains Manuela Garnica, the study's lead author.
The finding demonstrates how a material's properties can change when confined to two dimensions and that tellurium can give rise to electronic states distinct from its equivalents with selenium or sulfur. Charge density waves illustrate the collective reorganization of electrons. "This work adds a new piece to the scientific debate on how matter reorganizes itself on a two-dimensional scale and helps us better understand these materials at a fundamental level," notes the researcher.
The team plans to study the material at even lower temperatures, around 1 K, to explore the potential existence of superconductivity and its competition with the electronic charge reorganization. The research is supported by IMDEA Nanociencia's accreditation as a Severo Ochoa Center of Excellence.
