PUBLICATIONS

Subsequently, a selection of research papers are listed where GTPack was applied. If you would like to have your paper added to the list, please get in touch with us.

Magnetic and Electronic Properties of Complex Oxides from First‐Principles

M. Hoffmann, A. Ernst, W. Hergert, V. N. Antonov, W. A. Adeagbo, R. M. Geilhufe, H. Ben Hamed, Phys. Status Solidi B, accepted (2020)

The theoretical treatment of complex oxide structures requires a combination of efficient methods to calculate structural, electronic, and magnetic properties, due to special challenges such as strong correlations and disorder. In terms of a multi‐code approach, we combine various complementary first‐principles methods based on density functional theory to exploit their specific strengths. Pseudopotential methods, known for giving reliable forces and total energies, are used for structural optimization. The optimized structure serves as input for the Green’s function and linear muffin‐tin orbital methods. Those methods are powerful for the calculation of magnetic ground states and spectroscopic properties. Within the multi‐code approach, disorder is investigated by means of the coherent potential approximation within a Green’s function method or by construction of special quasirandom structures in the framework of the pseudopotential methods. Magnetic ground states and phase transitions are studied using an effective Heisenberg model treated in terms of a Monte Carlo method, where the magnetic exchange parameters are calculated from first‐principles. We demonstrate the performance of the multi‐code approach with different examples, including defect formation, strained films and surface properties.

Hund nodal line semimetals: The case of a twisted magnetic phase in the double-exchange model

R. M. Geilhufe, F. Guinea, and V. Juričić, Phys. Rev. B, 99, 020404(R) (2019)

We propose a class of topological metals, which we dub Hund nodal line semimetals, arising from the strong Coulomb interaction encoded in the Hund’s coupling between itinerant electrons and localized spins. We here consider a particular twisted spin configuration, which is realized in the double-exchange model which describes the manganite oxides. The resulting effective tetragonal lattice of electrons with hoppings tied to the local spin features an antiunitary nonsymmorphic symmetry that, in turn, together with another nonsymmorphic but unitary glide-mirror symmetry, protects crossings of a double pair of bands along a high-symmetry line on the Brillouin zone boundary. We also discuss the stability of Hund nodal line semimetals with respect to symmetry breaking arising from various perturbations of the twisted phase. Our results motivate further studies of other realizations of this state of matter, for instance, in different spin backgrounds, properties of its drumhead surface states, as well as its stability to disorder and interactions among the itinerant electrons.

Symmetry analysis of odd- and even-frequency superconducting gap symmetries for time-reversal symmetric interactions

R. M. Geilhufe and A. V. Balatsky, Phys. Rev. B, 97, 024507 (2018)

Odd-frequency superconductivity describes a class of superconducting states where the superconducting gap is an odd function in relative time and Matsubara frequency. We present a group theoretical analysis based on the linearized gap equation in terms of Shubnikov groups of the second kind. By discussing systems with spin-orbit coupling and an interaction kernel which is symmetric under the reversal of relative time, we show that both even- and odd-frequency gaps are allowed to occur. Specific examples are discussed for the square lattice, the octahedral lattice, and the tetragonal lattice. For irreducible representations that are even under the reversal of relative time the common combinations of s- and d-wave spin singlet and p-wave spin triplet gaps are revealed, irreducible representations that are odd under reversal of relative time give rise to s- and d-wave spin triplet and p-wave spin singlet gaps. Furthermore, we discuss the construction of a generalized Ginzburg-Landau theory in terms of the associated irreducible representations. The result complements the established classification of superconducting states of matter.

Three-dimensional organic Dirac-line materials due to nonsymmorphic symmetry: A data mining approach

R. M. Geilhufe, A. Bouhon, S. S. Borysov, and A. V. Balatsky, Phys. Rev. B., 95, 041103(R), 2017

A data mining study of electronic Kohn-Sham band structures was performed to identify Dirac materials within the Organic Materials Database. Out of that, the three-dimensional organic crystal 5,6-bis(trifluoromethyl)-2-methoxy-1H-1,3-diazepine was found to host different Dirac-line nodes within the band structure. From a group theoretical analysis, it is possible to distinguish between Dirac-line nodes occurring due to twofold degenerate energy levels protected by the monoclinic crystalline symmetry and twofold degenerate accidental crossings protected by the topology of the electronic band structure. The obtained results can be generalized to all materials having the space group P21/c (No. 14) by introducing three distinct topological classes.