Magnetic Stress-Driven Metal-Insulator Transition in Strongly Correlated Antiferromagnetic CrN.

Traditionally, the Coulomb repulsion or Peierls instability causes the metal-insulator phase transitions in strongly correlated quantum materials. In comparison, magnetic stress is predicted to drive the metal-insulator transition in materials exhibiting strong spin-lattice coupling. However, this mechanism lacks experimental validation and an in-depth understanding. Here we demonstrate the existence of the magnetic stress-driven metal-insulator transition in an archetypal material, chromium nitride. Structural, magnetic, electronic transport characterization, and first-principles modeling analysis show that the phase transition temperature in CrN is directly proportional to the strain-controlled anisotropic magnetic stress. The compressive strain increases the magnetic stress, leading to the much-coveted room-temperature transition. In contrast, tensile strain and the inclusion of nonmagnetic cations weaken the magnetic stress and reduce the transition temperature. This discovery of a new physical origin of metal-insulator phase transition that unifies spin, charge, and lattice degrees of freedom in correlated materials marks a new paradigm and could lead to novel device functionalities.

Reversal of Band-Ordering Leads to High Hole Mobility in Strained p-type Scandium Nitride.

Low hole mobility of nitride semiconductors is a significant impediment to realizing their high-efficiency device applications. Scandium nitride (ScN), an emerging rocksalt indirect band gap semiconductor, suffers from low hole mobility. Utilizing the ab initio Boltzmann transport formalism including spin-orbit coupling, here we show the dominating role of ionized impurity scattering in reducing the hole mobility in ScN thin films. We suggest a route to increase the hole mobility by reversing band ordering through strain engineering. Our calculation shows that the biaxial tensile strain in ScN lifts the split-off hole band above the heavy hole and light hole bands, leading to a lower hole-effective mass and increasing mobility. Along with the impurity scattering, the Fröhlich interaction also plays a vital role in the carrier scattering mechanism due to the polar nature of ScN. Increased hole mobility in ScN will lead to higher efficiencies in thermoelectric, plasmonics, and neuromorphic computing devices.