Interaction-induced topological phase transition and Majorana edge states in low-dimensional orbital-selective Mott insulators

Topological phases of matter are among the most intriguing research directions in Condensed Matter Physics. It is known that superconductivity induced on a topological insulator’s surface can lead to exotic Majorana modes, the main ingredient of many proposed quantum computation schemes. In this context, the iron-based high critical temperature superconductors are a promising platform to host such an exotic phenomenon in real condensed-matter compounds. The Coulomb interaction is commonly believed to be vital for the magnetic and superconducting properties of these systems. This work bridges these two perspectives and shows that the Coulomb interaction can also drive a canonical superconductor with orbital degrees of freedom into the topological state. Namely, we show that above a critical value of the Hubbard interaction the system simultaneously develops spiral spin order, a highly unusual triplet amplitude in superconductivity, and, remarkably, Majorana fermions at the edges of the system.

Improved polaronic transport under a strong Mott–Hubbard interaction in Cu-substituted NiO

We report the origin of improved hole conduction without band-gap collapse in Cu-doped NiO.

Magnetism and magnetic anisotropy in UGa2

We investigate whether first-principles calculations with an improved description of electronic correlations can explain the large magnetic moments and the strong magnetocrystalline anisotropy in the ferromagnetic compound UGa2. The correlations are treated within a static mean-field approximation DFT+U combining the density functional theory (DFT) with an onsite Hubbard interaction U. We find that DFT+U improves the agreement of the magnetic moments with the experiment compared to DFT but worsens the theoretical description of the magnetocrystalline anisotropy.

Спиновые флуктуации и концентрационные магнитные переходы в киральных геликоидальных ферромагнетиках Fe-=SUB=-1-x-=/SUB=-Co-=SUB=-x-=/SUB=-Si

The fluctuation theory is applied to the study of concentration transformations in chiral helicoidal ferromagnetic quasi-binary unordered Fe1-xCoxSi alloys with Dzyaloshinsky-Moriya interaction. The ground state is described on the basis of the LDA + U + SO approximations used in ab initio calculations with additional allowance for concentration fluctuations associated with the difference in the potentials of the intra-atomic Hubbard interaction at the sites occupied by iron and cobalt. Solutions of the obtained equations of the magnetic state for the phases of the long-range and short-range orders with the right and left magnetic chirality are considered. The concentration dependences of the parameters of the intermode interaction are investigated, and the regions of the compositions in which magnetic phase transitions of the first kind induced by thermal fluctuations take place, accompanied by the appearance of fluctuations of the spin helix. It is shown that the transition with a change of the sign of magnetic chirality is accompanied by the appearance of a minimum in the concentration dependence of the mode-mode parameter and the appearance of quantum helicoidal ferromagnetism with a noticeable increase in zero spin fluctuations.

Role of Interactions in the Energy of the Spin Resonance Peak in Fe-Based Superconductors

We consider the spin response within the five-orbital model for iron-based superconductors and study two cases: equal and unequal gaps in different bands. In the first case, the spin resonance peak in the superconducting state appears below the characteristic energy scale determined by the gap magnitude, 2ΔL. In the second case, the energy scale corresponds to the sum of smaller and larger gap magnitudes, ΔL+ΔS. Increasing the values of the Hubbard interaction and the Hund's exchange, we observe a shift of the spin resonance energy to lower frequencies.