A team from the physics department of the University of Fribourg has measured surprising properties in a new type of material, properties that pave the way for promising applications in tomorrow's electronics.

Professor Claude Monney's team at Unifr has just published an important result on a “quantum material” consisting of iridium ditelluride (IrTe2). Quantum materials are solids with properties dominated by quantum effects at the electron level. The best-known quantum materials are superconductors and graphene, materials with very special properties that open up new perspectives in many areas.

"Materials like IrTe2 are the next revolution in the field after graphene," explains Dr Christopher Nicholson, a postdoc at Unifr and first author of the study. "They are compounds consisting of one atom of a transition metal - in our case iridium - and two atoms of an element in the same column as Oxygen in the periodic table - in our case tellurium. As with graphene, these compounds are organised in very thin layers, which one can picture like a mille-feuilles.”

This type of compound opens up the possibility of designing materials whose properties can be modified on command, as is achieved for instance in computer hard disks, which are made from materials that can be rearranged by a magnetic field in order to store information. Professor Monney's group has shown that mechanical strain applied to an IrTe2 crystal profoundly alters its microscopic properties. Very large ordered zones develop in the crystal under strain, zones with remarkable quantum properties.  Modifying the properties of a crystal of this type with mechanical strain is both an important fundamental advance and an opening towards practical applications. “Strain changes how the individual layers talk to each other”, explains Christopher Nicholson. “Something that has only recently been realised is that changing this inter-layer coupling can itself induce remarkable effects such as superconductivity, and strain gives us a tuneable knob for these effects."

To characterise the crystal and its response to mechanical strain, the group used two sophisticated pieces of equipment from the physics department, a scanning tunneling microscope to observe the material at the atomic level, and an electron spectrometer to measure the properties of electrons in the material (image, with team member Marie-Laure Mottas).

Article: 

Nicholson, C.W., Rumo, M., Pulkkinen, A. et al. Uniaxial strain-induced phase transition in the 2D topological semimetal IrTe2. Commun Mater 2, 25 (2021). https://doi.org/10.1038/s43246-021-00130-5