When a compound of manganese sulfuride is compressed in diamond anvil cells, it undergoes dramatic transformations. This illustration shows how the interaction between the disulfur (S2 ) molecular and atomic ions (figures 8s) increases from left-to-right until there is enough overlap to make the system metallic. Credit: Dean Smith, Argonne Natl LabResearchers from the University of Nevada, Las Vegas (UNLV) have discovered that a "squishy compound of manganese sulfide (MnS 2) can be compressed in a diamond anvil. They say remarkable things happen."This is a novel type of charge transfer mechanism and it is exciting from the science community's point of view. "We are showing remarkable physical changes over a very short range, in this instance pressure," said Ashkan Salamat (associate professor of physics, UNLV).The researchers explain how MnS 2 (a soft insulator) changes into a metallic form when pressure is increased.Ranga Dias assistant professor of mechanical engineering at Rochester, physics and astronomy says that metals are usually just that: metals. It is very unlikely that they could be made into insulators. It is rare that this material can go from being an insulator to a metallic and back to being an insulator.The transitions also show unprecedented drops in resistance and volume over a very narrow range of pressure changes, all occurring at around 80 degrees Fahrenheit. Salamat believes that the relatively low temperature increases the possibility of the metal transition process being used for technology.The collaboration between Salamat and Dias set new standards for superconductivity at room temperature in previous papers published in Nature and Physical Review Letters. Their work shares a common thread: they explore the "remarkably bizarre" behavior of transition metals and other materials when they are paired together with sulfides and then compress them in a diamond cell anvil.Salamat states that the new phenomenon we are reporting is a fundamental example for responses under high pressure and will be included in physics textbooks. Salamat says that sulfur's behavior when attached to other elements is very fascinating. This has resulted in some amazing breakthroughs."The Dias and Salamat laboratories have made it possible to compress only picoliters (about the same size as a single inkjet particle) of material.Dramatic metal transitions are caused by spin and pressureDias and Salamat explain that the fundamental transitions discussed in this paper involve the interaction of spin states (angular momentum), of individual electrons as pressure is applied.When transition metals and other material are compressed in a diamond annel, bizarre things can occur. Here, Ranga Dias holds an array containing diamond anvil cells. Credit: University of Rochester photo/J. Adam FensterMnS2 is in its normal insulator status. This means that electrons are mostly in unpaired, high spin orbitals. Atoms bounce back and forth when they are in this state. The material is more resistant to an electric charge, as there is less space for individual electrons to pass through it.Salamat says that when pressure is applied, the material is compressed into a metallic state. The electron orbitals "start seeing each other" and immediately come towards each other. This causes pairs of electrons to link up.As pressure increases from 3 gigapascals (435 000 psi to 10 gigapascals), this opens up more room for electrons to move through materials. This is a relative "nudge" when compared to the 182 - 268 gigapascals needed for superconducting material.Dias states that a drop of resistance of this magnitude would be really significant given the pressure range.Even in the final phase, when the MnS2 reverts into an insulator, low resistance is maintained because electrons are still in a "low-spin" state.Future technological advancements and basic materials scienceThe potential applications are still unknown, as is often the case with discoveries in basic science.Salamat claims that a transition metal, which can be shifted from one state to the next at room temperature with very little strain, is likely to prove useful.You could think of a logic switch, or writing hard drive, in which a very, very small variation in strain or voltage could cause something to jump from one electronic state into another. Salamat says that new versions of flash memory or solid state memory could be permutated and adopt a new approach using these materials.These materials can be driven at 300 kelvin by very aggressive maneuvers, which makes them useful for technology.Dylan Durkee is the lead author. He was a former student researcher at Salamat Lab and now works as a graduate student at Dias. Nathan Dasenbrock–Gammon at Rochester and Elliot Snider in Rochester are other coauthors. Keith Lawler and Alexander Smith at UNLV, Christian Childs and Dean Smith at the Argonne National Laboratory, and Simon A.J. Kinder at University of BourgogneContinue reading Researchers create superconducting material at room temperatureFurther information: Dylan Durkee and colleagues, Colossal Density Driven Resistance Response In the Negative Charge Transfer Insulator 2, Physical Review Letters (2021). Information from the Journal: Physical Review Letters, Nature Dylan Durkee, and others, Colossal density-driven resistance response in the Negative Char Transfer Insulator MnS(2021). DOI: 10.1103/PhysRevLett.127.016401
