T. Tite | Searcharxiv

arXiv2026

Cubic-Zn(1-x)Mn(x)Te optical modes across the phonon and phonon-polariton regimes

Alloying offers a convenient route to tune the physical properties of semiconductors, at the price, however, of local lattice/bond distortions needed to accommodate the lattice mismatch. Being nearly lattice-matched and moreover highly resistant to lattice and bond distortions thanks to a largely covalent bonding, cubic Zn(1-x)Mn(x)Te sets a benchmark to test the sensitivity of lattice vibrations to minimum lattice and bond distortions induced by alloying. We explore experimentally the two transverse optical regimes of cubic Zn(1-x)Mn(x)Te (x<0.7), with ab initio calculations in support: (1) the phonon-polariton regime at quasi-infinite (photon-like) wavelengths averaging over the alloy disorder, probed by forward-Raman scattering, and (2) the purely-mechanical phonon regime down to minimum wavelengths nearly matching the lattice constant zooming into the alloy disorder, achieved by inelastic neutron scattering. The short Zn-Te bond is found to exhibit a compact optical duo distinguishing homo from hetero local bond environments (1 bond: 2 mode), as explained by the percolation model. This deviates from the historical Zn(1-x)Mn(x)Te MREI (modified-random-element-isodisplacement) scheme inspired from classical Raman and infrared studies, in which the optical modes are blind to the bond environment (1-bond: 1-mode). So, the test is positive, reinforcing the status of the percolation scheme as a robust decryptor of (even small) lattice distortions induced by alloying through the lattice dynamics.

cond-mat.mtrl-sci↗

arXiv2004

Isolated modes and percolation in lattice dynamics of (Be,Zn)Se

A mixed II-VI semiconductor Zn[1-x]Be[x]Se possesses non-trivial vibration properties, because its two constituent compounds, ZnSe and BeSe, show very different degree of covalency and hence high elastic contrast. An anomalous Be-Se vibration line has been observed mostly at intermediate Be content in the Raman spectra of thin (Zn,Be)Se films. In order to explain microscopic origins and the detailed composition of these lines, a first-principles calculation of vibration frequencies in a mixed crystal has been done, with frozen-phonon technique and supercell setup within the density functional theory, by the Siesta method, which uses norm-conserving pseudopotentials and strictly localized numerical basis functions. The calculations confirmed an earlier assumption that the anomalous Be-Se line appears due to the formation of continuous chains of a more rigid Be-rich pseudo-continuous phase formed within the more soft Zn-rich host region on crossing the Be-Se bond percolation threshold (~0.19). Different local deformation in percolated and non-percolated regions affect interatomic elastic interactions and split corresponding vibration lines. Besides confirming the percolation model qualitatively, the calculation provides details about vibration patterns in different phonon modes.

cond-mat.mtrl-sci↗