arXiv subjects

Adrien Bouhon

Publications and source records attributed to Adrien Bouhon.

45 records · Page 3Linked to original sources

arXiv2017

Bulk topology of line-nodal structures protected by space group symmetries in class AI

We give an exhaustive characterization of the topology of band structures in class AI, using nonsymmorphic space group 33 ($Pna2_1$) as a representative example where a great variety of symmetry protected line-nodal structures can be formed. We start with the topological classification of all line-nodal structures given through the combinatorics of valence irreducible representations (IRREPs) at a few high-symmetry points (HSPs) at a fixed filling. We decompose the total topology of nodal valence band bundles through the local topology of elementary (i.e. inseparable) nodal structures and the global topology that constrains distinct elementary nodal elements over the Brillouin zone (BZ). Generalizing from the cases of simple point nodes and simple nodal lines (NLs), we argue that the local topology of every elementary nodal structure is characterized by a set of poloidal-toroidal charges, one monopole, and one thread charge (when threading the BZ torus), while the global topology only allows pairs of nontrivial monopole and thread charges. We show that all these charges are given in terms of symmetry protected topological invariants, defined through quantized Wilson loop phases over symmetry constrained momentum loops, which we derive entirely algebraically from the valence IRREPs at the HSPs. In particular, we find highly connected line-nodal structures, line-nodal monopole pairs, and line-nodal thread pairs, that are all protected by the unitary crystalline symmetries only. Furthermore, we show symmetry preserving topological Lifshitz transitions through which independent NLs can be connected, disconnected, or linked. Our work constitutes a heuristic approach to the systematic topological classification and characterization of all momentum space line-nodal structures protected by space group symmetries in class AI.

cond-mat.mtrl-sci↗

arXiv2017

Domain walls in a chiral d-wave superconductor on the honeycomb lattice

We perform a fully self-consistent study of domain walls between different chiral domains in chiral $d_{x^2-y^2} \pm id_{xy}-wave superconductors with an underlying honeycomb lattice structure. We investigate domain walls along all possible armchair and zigzag directions and with a finite global phase shift across the domain wall, in addition to the change of chirality. For armchair domain walls we find the lowest domain wall energy at zero global phase shift, while the most favorable zigzag domain wall has a finite global phase shift dependent on the doping level. Below the van Hove singularity the armchair domain wall is most favorable, while at even higher doping the zigzag domain wall has the lowest energy. The domain wall causes a local suppression of the superconducting order parameter, with the superconducting recovery length following a universal curve for all domain walls. Moreover, we always find four subgap states crossing zero energy and well localized to the domain wall. However, the details of their energy spectrum vary notably, especially with the global phase shift across the domain wall.

cond-mat.supr-con↗

arXiv2017

Global band topology of simple and double Dirac-point (semi-)metals

We combine space group representation theory together with scanning of closed subdomains of the Brillouin zone with Wilson loops to algebraically determine global band structure topology. Considering space group #19 as a case study, we show that the energy ordering of the irreducible representations at the high-symmetry points $\{Γ,S,T,U\}$ fully determines the global band topology, with all topological classes characterized through their simple and double Dirac-points.

cond-mat.mtrl-sci↗

arXiv2017

Data Mining for Three-Dimensional Organic Dirac Materials: Focus on Space Group 19

We combined the group theory and data mining approach within the Organic Materials Database that leads to the prediction of stable Dirac-point nodes within the electronic band structure of 3-dimensional organic crystals. We find a particular space group $P2_12_12_1$ ($\#19$) that is conducive to the Dirac nodes formation. We prove that nodes are a consequence of the orthorhombic crystal structure. Within the electronic band structure, two different kinds of nodes can be distinguished: 8-fold degenerate Dirac nodes protected by the crystalline symmetry and 4-fold degenerate Dirac nodes protected by band topology. Mining the Organic Materials Database, we present band structure calculations and symmetry analysis for 6 previously synthesized organic materials. In all these materials, the Dirac nodes are well separated within the energy and located near the Fermi surface, which opens up a possibility for their direct experimental observation.

cond-mat.mtrl-sci↗

arXiv2017

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

A data mining study of electronic Kohn-Sham band structures was performed to identify Dirac materials within the Organic Materials Database (OMDB). Out of that, the 3-dimensional organic crystal 5,6-bis(trifluoromethyl)-2-methoxy-1$H$-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 2-fold degenerate energy levels protected by the monoclinic crystalline symmetry and 2-fold 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 $P2_1/c$ (No. 14, $C^5_{2h}$) by introducing three distinct topological classes.

cond-mat.mtrl-sci↗

arXiv2016

From chiral d-wave to nodal line superconductivity in the harmonic honeycomb lattices

Motivated by the recent realization of the three-dimensional hyperhoneycomb and stripyhoneycomb lattices in lithium iridate (Li$_2$IrO$_3$), we study the possible spin-singlet superconducting states on the whole series of harmonic honeycomb lattices. Beginning with an isolated out-of-plane twist making the honeycomb lattice three-dimensional, we find that the chiral d$\pm$id state, well-known from the honeycomb lattice, is realized in the largest members of the series at low to intermediate doping. Along the twist, four chiral edge states form a two-dimensional dispersive band. Reducing the distance between the twists to form the smaller members of the harmonic honeycomb lattices, the degeneracy between the d-wave states is lifted, which finally destroys the chiral state. By analyzing the hyper- and stripyhoneycomb lattices and generalizing using the $D_{2h}$ point group of all the harmonic honeycomb lattices, we show that the superconducting state often belongs to the trivial irreducible representation. This state has nodal lines at low to intermediate doping, which is possible because the full lattice symmetry allows sign changes between different sets of bonds. We also find time-reversal symmetry broken states, which are either fully gapped or feature nodal points, in certain parts of the phase diagram. Finally, we draw a comparison between the states classified in terms of the $D_{2h}$ symmetries and those observed on the $D_{6h}$ honeycomb lattice.

cond-mat.supr-con↗

arXiv2016

Gap opening and large spin-orbit splitting in MX2 (M=Mo,W X=S,Se,Te) from the interplay between crystal field and hybridizations: insights from ab-initio theory

By means of first-principles density functional calculations, we study the maximally localized Wannier functions for the 2D transition metal dichalcogenides MX2 (M=Mo,W X=S,Se,Te). We found a M^+4-like ionic charge and a single occupied d-band. The center of the d-like maximally localized Wannier function associated with this band is distributed among three M sites. Part of the energy gap is opened by the crystal field splitting induced by the X^-2-like atoms. We extract the hopping parameters for the Wannier functions and provide a perspective on tight-binding model. From the analysis of the tight binding model, we have found an inversion of the band character between the Gamma and the K points of the Brillouin zone due to the M-M hybridization. The consequence of this inversion is the closure of the gap. The M-X hybridization is the only one that tends to open the gap at every k-point, the change in the M-X and M-M hybridization is the main responsible for the difference in the gap between the different dichalcogenide materials. The inversion of the bands gives rise to different spin-orbit splitting at Gamma and K point in the valence band. The different character of the gap at Gamma and K point offers the chance to manipulate the semiconductive properties of these compounds. For a bilayer system, the hybridizations between the out of plane orbitals and the hybridizations between the in plane orbitals split the valence band respectively at the Gamma and K point. The splitting in the valence band is opened also without spin-orbit coupling and comes from the M-M and X-X hybridization between the two monolayers.

cond-mat.mtrl-sci↗

arXiv2014

Current inversion at the edges of a chiral $\boldsymbol{p}$-wave superconductor

Motivated by Sr$_2$RuO$_4$, edge quasiparticle states are analyzed based on the self-consistent solution of the Bogolyubov-de Gennes equations for a topological chiral $p$-wave superconductor. Using a tight-binding model of a square lattice for the dominant $γ$-band we explore the non-trivial geometry and band structure dependence of the edge states and currents. As a peculiar finding we show that for high band fillings currents flow in reversed direction comparing straight and zigzag edges. We give a simple explanation in terms of the positions of the zero-energy bound states using a quasi-classical picture. We also show that a Ginzburg-Landau approach can reproduce these results. Moreover, the band filling dependence of the most stable domain wall structure is discussed.

cond-mat.supr-con↗

arXiv2010

Influence of the domain walls on the Josephson effect in Sr$_2$RuO$_4$

A detailed theoretical interpretation of the Josephson interference experiment between Sr$_2$RuO$_4$ and Pb reported by Kidwingira \textit{et al} is given. Assuming chiral p-wave pairing symmetry a Ginzburg-Landau theory is derived in order to investigate the structure of domain walls between chiral domains. It turns out that anisotropy effects of the Fermi surface and the orientation of the domain walls are essential for their internal structure. Introducing a simple model for a Josephson junction the effect of domain walls intersecting the interface between Sr$_2$RuO$_4$ and Pb is discussed. It is shown that characteristic deviations of the Fraunhofer interference pattern for the critical Josephson current as a function of the magnetic field occurs in qualitative agreement with the experimental finding. Moreover the model is able also to account for peculiar hysteresis effects observed in the experiment.

cond-mat.supr-con↗