Scientists have discovered a material that can become an insulator or a conductor, depending on the applied pressure.
The ability of a material to conduct current is determined by the movement of free electrons, which is why metals are good conductors. In insulators, electrons are "locked" much more strongly, and it takes more energy to make them move than the applied voltage normally carries. However, physicists at the University of Rochester and the University of Nevada have found a compound that behaves in a completely non-standard way. Their article was published in the journal Physical Review Letters.
Ashkan Salamat and his colleagues studied the conductive properties of metal sulfides, focusing on manganese disulfide. Under normal conditions, it is a mild insulator. However, placing it on a diamond "anvil" and creating a great pressure, the scientists noticed that the substance changed into a metallic state and abruptly lost the previously high electrical resistance. With an increase in pressure up to 12 gigapascals (about 12 thousand atmospheres), the resistance dropped hundreds of millions of times.
In this case, a further increase in pressure (up to 36 gigapascals) led to the reverse transition, and MnS2 became an insulator again. “Usually metals remain metals; it is highly unlikely that they could be turned into insulators, says Ranga Dias, one of the authors of the work. "It is extremely rare that this material passes from insulator to metal and back to insulator."
Scientists have shown how high pressure causes manganese disulfide to "switch" into a conductive state. Under these conditions, individual atoms move closer together, so that their outer electrons can interact and pair. As a result, a space appears in the crystal lattice through which charges can move. Finally, with even more pressure, the grating became too "thick".
The authors emphasize that the transitions of manganese disulfide occur at room temperature and relatively moderate pressure. As a rule, this requires the use of cryogenic conditions and an order of magnitude stronger compression. Recall that by creating a pressure of about 500 gigapascals, even metallic hydrogen can be obtained - the form in which it exists in the bowels of giant planets.