Large secondharmonic generation and linear electrooptic effect in trigonal selenium and tellurium
Abstract
Trigonal selenium and tellurium crystalize in helical chainlike structures and thus possess interesting properties such as nontrivial band topology, gyrotropic effects, and nonlinear optical responses. By performing systematic densityfunctionaltheory calculations with the generalized gradient approximation plus scissors correction, we study their linear and nonlinear optical (NLO) properties. We find that both materials exhibit large secondharmonic generation (SHG) and linear electrooptic (LEO) effect. In particular, tellurium has the huge SHG coefficient (χ_{x}^{x x (2 )}) in the photon energy range of 0 ∼3 eV with the maximum magnitude being about 16 times larger than that of GaN, a widely used NLO material. Tellurium is also found to possess the gigantic static SHG coefficient χ_{x}^{y z (2 )}, which is up to 100 times larger than that of GaN. On the other hand, selenium exhibits the large LEO coefficient r_{x x x}(0 ) , which is more than six times larger than that of GaN. Thus, tellurium and selenium may find valuable applications in NLO and LEO devices such as frequency conversion, electrooptical switches, and light signal modulators. Interestingly, our calculations also reveal that for each material, the χ_{x}^{x x (2 )} values for the two helical structures are equal but the χ_{x}^{y z (2 )} values differ in sign, suggesting that the SHG spectroscopy is a useful probe of their chirality. The calculated static and optical dielectric constants as well as SHG coefficients at the CO_{2} laser frequency are in good agreement with the available experiments. Finally, much stronger NLO responses of selenium and tellurium compared with the semiconductors with similar band gaps are attributed to their quasionedimensional structures with directional covalent bonding and lonepair electrons. These findings will help the search for new materials with large NLO coefficients.
 Publication:

Physical Review B
 Pub Date:
 July 2019
 DOI:
 10.1103/PhysRevB.100.035202
 arXiv:
 arXiv:1904.01927
 Bibcode:
 2019PhRvB.100c5202C
 Keywords:

 Physics  Computational Physics;
 Condensed Matter  Materials Science;
 Physics  Optics
 EPrint:
 Phys. Rev. B 100, 035202 (2019)