arXiv subjects

Ilteris K. Turan

Publications and source records attributed to Ilteris K. Turan.

4 recordsLinked to original sources

arXiv2026

Magnetic exchange interactions in the molecular orbital spin system NaV2O5 from a distributed moment point of view

The magnetism in NaV2O5 results from doping of the narrow split-off conduction band of V2O5, which becomes half-filled and leads to a Mott-insulating splitting of spin resolved bands with anti-ferromagnetic order of the spins along the zigzag chains. In the Pmmn structure the spin of this S = 1/2 system is equally shared between two vanadium atoms, residing in a molecular orbital type state. While below 34 K a charge disproportionation occurs into V4+ and V5+, the situation above this temperature is less clear and amounts to a fluctuating moment with equal probability of occupancy of each V. While traditionally described as a quarter-filled ladder system with electron spin localized on the rungs of the ladder, we here take a distributed moment approach in terms of the spin density lumped into individual atomic magnetic sites, including the small induced moments on the oxygen atoms. Exchange interactions are calculated between these sites using a linear response approach based on quasiparticle-self-consistent GW band structures. Surprisingly we find the exchange interactions between the small magnetic moments induced on the vanadyl and bridge oxygen sites to be of the same order of magnitude and even larger than the exchange interactions between vanadium atoms. Their role in the critical temperature is found to be crucial. The spin wave spectra obtained from this classical Heisenberg type Hamiltonian extracted from first-principles contains unusual optic spin wave type collective excitations of high energy.

cond-mat.str-el↗

arXiv2026

Electronic band structure and exciton properties of $Pna2_1$ CaSnN$_2$

The electronic band structure of CaSnN$_2$ in the wurtzite-based $Pna2_1$ structure is calculated using the Quasiparticle Self-consistent (QS)GW$^{BSE}$ method, including ladder diagrams in the screened Coulomb interaction W$^{BSE}$ and is found to have a direct gap of 2.59 eV at Γ, which corresponds to blue light wavelength of 478 nm and makes it an attractive candidate for sustainable blue light-emitting diodes (LEDs), avoiding Ga and In. The valence band splitting is analyzed in terms of symmetry labeling, and the effective mass tensor is calculated for several bands at Γ. The valence band maximum has a1 symmetry and gives allowed transitions to the conduction band minimum for light polarized along the {\bf c}-direction. While this is unfavorable for light emission with transverse electric (TE) or s-polarization from the basal plane, this would not be an impediment if another surface other than the basal plane is used. Furthermore, the crystal field splitting between the $a_1$ and $b_1$ states, corresponding to polarizations along {\bf c} and {\bf a} respectively, reverses under an applied uniaxial tensile strain of 3.7% along the {\bf c} direction, which might occur under biaxial compressive strain in the basal plane. The optical dielectric function, including electron-hole interaction effects is also reported, and the excitons are analyzed, including several dark excitons.

cond-mat.mtrl-sci↗

arXiv2025

Electronic structure and exchange interactions in altermagnetic MnGeP$_2$ in the quasiparticle-self-consistent $GW$ approach

The QS$GW$ method is used to study the electronic band structure, optical dielectric function, and exchange interactions in chalcopyrite, $I\bar{4}2d$, structure MnGeP$_2$. The material is found to be an antiferromagnetic semiconductor with the lowest direct gap of 2.44 eV at the $Γ$ point and an indirect gap of 1.87 eV. The material is an altermagnet, with the two magnetic atoms of opposite spin related by a two-fold rotation operation perpendicular to the main 4-fold rotation inversion axis. The spin splittings along a low symmetry line like $PN$ are sizable, while at k-points on the diagonal mirror planes or on the twofold symmetry axes, the spin splitting is zero. The exchange interactions are calculated using a linear response approach. The antiferromagnetic exchange-interaction between nearest neighbors in the primitive unit cell is dominating and found to be slightly decreasing upon carrier doping. The transverse spin susceptibilities, which provide interatomic site exchange interactions after averaging over the muffin-tin spheres, are calculated from the $GW$ band structure and wave functions. From these exchange interactions, the spin wave spectra are obtained along the high symmetry lines and the Néel temperature is calculated using the mean-field and Tyablikov (RPA) estimations. The dielectric function and the optical absorption spectra are calculated, including excitonic effects, using the Bethe-Salpeter equation. The exchange interactions around Mn$_{\rm Ge}$ defect sites are also studied. While we find it can generate ferromagnetic interactions with neighboring spins, we did not find evidence of producing an overall ferromagnetic phase. If Mn antisites are introduced by exchanging Mn with a nearby Ge, the interactions stay largely antiferromagnetic. Adding Mn antisites leads to a metallic band structure.

cond-mat.mtrl-sci↗

arXiv2025

Metal-organic chemical vapor deposition of MgGeN2 films on GaN and sapphire

MgGeN2 films were synthesized using metal-organic chemical vapor deposition on GaN/c-sapphire templates and c-plane sapphire substrates. Energy-dispersive X-ray spectroscopy was used to estimate the cation composition ratios. To mitigate magnesium evaporation, the films were grown at pyrometer temperature 745 °C with a wafer rotation speed of 1000 rpm. Growth rates were determined by fitting energy-dispersive X-ray spectroscopy spectra to film thicknesses using NIST DTSA-II software. The thickness estimates determined by this method were consistent with scanning transmission electron microscopy measurements done for selected samples. Scanning electron microscopy images revealed faceted surfaces indicative of a tendency toward three-dimensional growth. X-ray diffraction spectra confirmed that the films were highly crystalline and exhibited preferential orientation in alignment with the substrate. Atomic force microscopy measurements show that film thicknesses are consistent across samples grown on both GaN templates and sapphire substrates, with typical roughnesses around 10 nm. Transmittance spectra of films grown on double-side-polished sapphire substrates yielded band gaps of 4.28 +- 0.06 eV for samples exhibiting close-to-ideal stoichiometry. Comparison of the measured spectra with ab initio calculations are in good agreement both near the band gap and at higher energies where excitation is into higher-lying bands. These findings provide insight into the growth and characterization of MgGeN2, contributing to the development of this material for potential applications in optoelectronics and power electronics.

cond-mat.mtrl-sci↗