We performed a detailed microscopic analysis of the inter-layer magnetic couplings for bilayer CrI3. As the first step toward understanding the recent experimental observations and utilizing them for device applications, we estimated magnetic force response as well as total energy. Various van der Waals functionals unequivocally point to the ferromagnetic ground state for the low-temperature structured bilayer CrI3 which is further confirmed independently by magnetic force response calculations. The calculated orbital-dependent magnetic forces clearly show that eg-t2g interaction is the key to stabilize this ferromagnetic order. By suppressing this ferromagnetic interaction and enhancing antiferromagnetic orbital channels of eg-eg and t2g-t2g, one can realize the desirable antiferromagnetic order. We showed that high-temperature monoclinic stacking can be the case. Our results provide unique information and insight to understand the magnetism of multi-layer CrI3 paving the way to utilize it for applications.

Thermoelectrics directly converts waste heat into electricity and is considered a promising means of sustainable energy generation. While most of the recent advances in the enhancement of the thermoelectric figure of merit (ZT) resulted from a decrease in lattice thermal conductivity by nanostructuring, there have been very few attempts to enhance electrical transport properties, i.e., the power factor. Here we use nanochemistry to stabilize bulk bismuth telluride (BiTe) that violates phase equilibrium, namely, phase-pure n-type KBiTe. Incorporated potassium and tellurium in BiTe far exceed their solubility limit, inducing simultaneous increase in the electrical conductivity and the Seebeck coefficient along with decrease in the thermal conductivity. Consequently, a high power factor of ∼43 μW cm K and a high ZT > 1.1 at 323 K are achieved. Our current synthetic method can be used to produce a new family of materials with novel physical and chemical characteristics for various applications.

To understand the superconductivity recently discovered in Nd0.8Sr0.2NiO2, we carried out LDA+DMFT (local density approximation plus dynamical mean-field theory) and magnetic force response calculations. The on-site correlation in Ni-3d orbitals causes notable changes in the electronic structure. The calculated temperature-dependent susceptibility exhibits the Curie-Weiss behavior, indicating the localized character of its moment. From the low-frequency behavior of self-energy, we conclude that the undoped phase of this nickelate is Fermi-liquid-like contrary to cuprates. Interestingly, the estimated correlation strength by means of the inverse of quasi-particle weight is found to increase and then decrease as a function of hole concentration, forming a dome-like shape. Another remarkable new finding is that magnetic interactions in this material become two-dimensional by hole doping. While the undoped NdNiO2 has the sizable out-of-plane interaction, hole dopings strongly suppress it. This two-dimensionality is maximized at the hole concentration δ ≈ 0.25. Further analysis as well as the implications of our new findings are presented. arXiv:1909.05824v2 [cond-mat.supr-con]

Fe₃GeTe₂ is found to have antiferromagnetic ground state spin order in its stoichiometric phase. It is a defect and doping that make this material ferromagnetic.