It now seems within reach of experiment the excitonic insulator, a quantum state of matter theorized half a century ago and long pursued by physicists. Researchers from the Nanoscience Institute of the Modena National Research Council have foreseen the possibility of “observing it experimentally” and “unequivocally” in molybdenum sulphide at pressures and temperatures that can be reached in the laboratory. According to Italian scientists – whose study was conducted in collaboration with the University of Modena and Reggio Emilia and is published in the Pnas magazine the result provides a strategy for realizing this elusive state of matter of possible impact for future quantum technologies.


“The state of excitonic insulator – explains Daniele Varsano of Cnr-Nano – it occurs when particles called excitons spontaneously form in a material composed of an electron and a hole – the hole left by the electron that moves in the crystal – which remain bound because they have opposite electric charge “.” Making it in real materials has stimulated in recent years an intense research activity, motivated both by the interest in fundamental physics ch and from potential applications in future quantum technologies. But his experimental observation remains elusive because it is masked by other phenomena “adds Varsano.

Now the Cnr-Nano researchers, through simulations based on quantum mechanics, have shown that molybdenum sulphide, which in conditions of atmospheric pressure is a conventional insulating material, under the effect of strong pressures and low temperatures creates a new quantum phase characterized by the spontaneous and permanent generation of excitons. “The transition from conventional to excitonic insulator is due solely to the behavior of the electrons of the molybdenum sulphide without any deformation of the crystal lattice structure, unlike what happens in other materials in which high pressures cause lattice distortions that prevent the recognition of a possible excitonic state “argues Massimo Rontani of Cnr-Nano.

Rontani adds that “the study also demonstrates that the new state is obtained for pressure and temperature values ​​accessible in modern laboratories, thus indicating a way for the experimental observation of the excitonic insulator”. The simulations that led to these results, “incredibly computationally demanding”, were developed within MaX-Materials at Exascale, the European infrastructure of excellence for applied supercomputing to new materials, coordinated by Cnr-Nano of Modena. “The advances achieved in parallel computing technologies now make it possible to validate theories and predict behaviors of matter that were impossible to study until a few years ago, and to propose experiments to discover properties of matter that are still unobserved” finally underlines Varsano.

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