Microscopic Origins of Optical Second Harmonic Generation in Noncentrosymmetric–Nonpolar Materials

Abstract

We use a symmetry-based structural analysis combined with an electronic descriptor for bond covalency to explain the origin of the second-order nonlinear optical response (second harmonic generation, SHG) in noncentrosymmetric nonpolar ATeMoO6 compounds (where A = Mg, Zn, or Cd). We show that the SHG response has a complex dependence on the asymmetric geometry of the AO6 and AO4 functional units and the orbital character at the valence band edge, which we are able to distinguish using an A–O bond covalency descriptor. The degree of covalency between the divalent A-site cation and the oxygen ligands dominates over the geometric contributions to the SHG arising from the acentric polyhedra, and this can be understood from considerations of the local static charge density distribution. The use of a local dipole model for the polyhedral moieties (AO4/AO6, MoO4, and TeO4) can account for a nonzero SHG response, even though the materials exhibit nonpolar structures; however, it is insufficient to explain the change in the magnitude of the SHG response upon A-cation substitution. The atomic scale and electronic structure understanding of the macroscopic SHG behavior is then used to identify hypothetical HgTeMoO6 as a candidate telluromolybdate with an enhanced nonlinear optical response.

A -cation control of magnetoelectric quadrupole order in A(TiO)Cu4(PO4)4Kimura1, Toyoda2, Babkevich3 et al. 2018Phys. Rev. B258530View full textAdd to dashboardCite

“…1(c) because it seems to be directly mediated by the A-cation. As shown in Table I For more discussion, we quantify the degree of A-O hybridization using a bond covalency defined as C A,O = −|C MA − C MO | (in eV) [40,41]. |C MA | and |C MO | are the band center of mass for A orbital (Pb 6s, Ba 5p, and for PbTCPO.…”

RbMgCO3F: A New Beryllium-Free Deep-Ultraviolet Nonlinear Optical Material

“…As pointed out in our previous work, however, large SAMD does not necessitate a large NLO response, since three dipolar moments in P6̅ 2m align along the principal directions of a Reuleaux triangle located on the B 2+ cation site and macroscopically cancel. 18 The moderate SHG intensity in RbMgCO 3 F is attributable to the increased SAMD in the achiral NCS material, which, although indicating a greater number of inversion symmetry lifting distortions in the structure, acts to constructively cancel an induced polarization arising from the oscillating electric field of an incident photon. The extent to which this occurs in RbMgCO 3 F is examined in the inset of Figure 6, which depicts the electron localization function (ELF) in the (001) plane.…”

The Large Second‐Harmonic Generation of LiCs2PO4 is caused by the Metal‐Cation‐Centered Groups

“…[1a] In contrast, Li et al [2a] considered this theory as insufficient for LCPO,s uggesting that the SHG effect arises from the preferred spatial orientation of nonbonding O2p orbitals.Qualitatively,the SHG phenomenon is discussed by considering either bond dipole moments of covalent bonds (e.g.,t he P À Ob onds in LCPO) [1a, 3] or specific acentric atom displacements. [4] Thev alence electronic density distribution of anon-centrosymmetric material is determined not only by covalent bonds but also by ionic bonds (e.g., the Li À Oa nd CsÀOb onds in LCPO). Therefore,t he possibility that ionic bonds can also contribute to the SHG response cannot be excluded.…”