Scientists at the University of Manchester have developed a new but simple method for creating vertical bundles of alternating superconducting and insulating layers of tantalum disulphide (TaS2). The findings (Important Advances in 2D Material) of the team led by Professor Rahul Nair will accelerate the process of creating such devices – called van der Waals hetero structures – with applications in high-mobility transistors, photovoltaic and optoelectronics.
Van der Waals hetero structures are highly sought after because they have many unique and useful properties not found in natural materials. In most cases, they are prepared by manually stacking one layer on top of another in a time-consuming and labor-intensive process.
The study, published last week in the journal Nano Letters and led by researchers at the National Graphene Institute (NGI), describes the synthesis of a bulk van der Waals heterostructure consisting of alternating 1T and 1H atomic layers of TaS2. 1T and 1H TaS2 are different polymorphs (materials with the same chemical composition, but different atomic arrangement) of TaS2 with completely different properties – the first insulating, the second superconducting at low temperatures.
The new hetero structure was obtained by synthesizing 6R TaS2 (a unique type of TaS2 with alternating 1T and 1H layer structure) by a process known as “phase transition” at high temperature (800 °C). Due to its unique structure, this material exhibits a combination of superconductivity and charge density waves, a rare phenomenon.
Dr. Amritroop Achari, who led the experiment, said: “Our work presents a new concept for the design of bulk heterostructures. The new method enables the direct synthesis of 1T-1H TaS2 bulk heterostructures via a phase transition from readily available 1T TaS2. We believe our work provides a significant advance in science and technology.”
International cooperation
The work was carried out in collaboration with scientists from the NANOlab Center of Excellence at the University of Antwerp in Belgium. Their high-resolution scanning electron microscopy analysis clearly confirmed the alternating 1T-1H 6R TaS2 heterolayer structure for the first time and paved the way for the interpretation of the results.
Professor Milorad Milošević, principal investigator at the University of Antwerp, commented: “This demonstration of an alternating insulating and superconducting layer structure in 6R TaS2 opens many interesting questions related to the anisotropic behavior of this material in an applied magnetic field and now emerging Josephson physics, terahertz emission and others, by analogy with bulk cuprates and iron-based superconductors.”
The findings may therefore have broad implications for the understanding of 2D superconductivity, as well as for the further design of advanced materials for devices based on terahertz and Josephson junctions, the cornerstone of second-generation quantum technology.
