Antibonding ground state of adatom molecules in bulk Dirac semimetals

Abstract

The ground state of the diatomic molecules in nature is inevitably bonding and its first excited state is antibonding. We demonstrate theoretically that for a pair of distant adatoms placed buried in 3D-Dirac semimetals, this natural order of the states can be reversed and antibonding ground state occurs at the lowest energy of the so-called bound states in the continuum. We propose experimental protocol with use of STM-tip to visualize the topographic map of the local density of states on the surface of the system to reveal the emerging Physics.Introduction.-Three-dimensional Dirac semimetals (3D-DSMs) such as Cd 3 As 2 and Na 3 Bi[1-5] represent novel class of functional materials constituting 3D analogous of gapless graphene [6][7][8]. The band structure of 3D semimetals contains the set of the so-called Dirac points in which conduction and valence bands touch and effective mass becomes zero. Around these points the dispersion of quasiparticles corresponds to those of massless relativistic Dirac particles which result in series of unusual properties of these materials such as linear magnetoresistance, unprecedented Shubnikov-de Haas oscillations and ultrahigh carrier mobility [9][10][11].In this work, we predict one more interesting feature of such materials. Namely, if we consider buried pair of distant adatoms in the bulk of a 3D-DSM as depicted at Fig.1, the ground state of this molecular system formed from bound states in the continuum (BICs) of the adatoms [12][13][14] will be characterized by antibondingtype orbital. This differs from the natural order in diatomic molecules where the ground state is of bondingtype in vast majority of cases and formation of antibonding ground state till now was reported only in systems of artificially fabricated InAs and Ge/Si p-type quantum dots for certain values of the inter-dot separations [15,16]. The behavior we report is a unique effect arising from long-range correlations between distant adatoms mediated by bulk fermions in 3D-DSMs. To detect the predicted effect, we propose to use the experimental approach developed in Ref. [17] for imaging isodensity contours of molecular states by scanning tunneling microscope (STM)-tip, as outlined at Fig.1.The Model.-For theoretical analysis of two adatoms buried inside 3D-DSM, as depicted at Fig.1, we employ an Anderson-like Hamiltonian [18][19][20]

Chiral magnetic chemical bonds in molecular states of impurities in Weyl semimetals

“…Panels (e) and (f) correspond to the case of a Dirac host which was previously considered by some of us in the Ref. 25. One clearly sees the emergence of bonding and antibonding molecular orbitals with σ-type symmetry resulting from the interference between two s-wave atomic orbitals of individual impurities, as it is illustrated in the panel (i).…”

“…One of the aspects of Weyl semimetals which recently received particular attention is the peculiar impurity physics [20][21][22][23][24][25]. In the present work, we clarify the role played by chirality of Weyl quasiparticles in the processes of impurity scattering by investigation of the local density of states.…”

Atomic frustrated impurity states in Weyl metals

“…As a result, a topological Weyl material with unusual characteristics, such as Fermi arcs, chiral anomaly and exotic Hall effects [13][14][15][16][17][18][19], emerges. The peculiar band structure of Weyl systems has dramatic impact on the electronic structure of impurities [20][21][22][23][24][25][26].…”

Majorana molecules and their spectral fingerprints

“…This can result in plethora of intriguing transport signatures [29][30][31][32][33][34][35][36][37][38], such as so-called Majorana oscillations [38]. We demonstrate that, similar to what happens in the system of a pair of QDs placed within a semiconductor [39] or a Dirac-Weyl semimetal host [40,41], the Fano effect in the considered system defines the novel type of molecular binding of QD orbitals, and leads to the formation of a Majorana molecule, characterized by the so-called half-bowtie profiles in the spectral density of states.…”