Controlling the anomalous Hall effect (AHE) is crucial for advancing spintronic devices. In this work, we investigate how constant-volume biaxial strain affects the intrinsic anomalous Hall conductivity (AHC) of hexagonal close-packed (hcp) cobalt. The calculations combine first-principles density functional theory (DFT) with a Wannier-based tight-binding model. Our results reveal a non-monotonic AHC response to applied strain. The conductivity reaches a maximum under small compressive strain and is suppressed more rapidly by larger compressive strain than by equivalent tensile strain. We examine microscopically how strain shifts the energy position of anti-crossing band features near the Fermi level. This shift drives a redistribution of the Berry curvature hotspots. These results confirm constant-volume biaxial strain as a viable approach to tuning the intrinsic AHE in hcp cobalt.

In this study, we investigated the effect of the Se/In flux ratio on the structural and optical properties of In2Se3 thin films grown on a Si(111) substrate via molecular beam epitaxy. All films were epitaxially grown at 300 degrees C with Se/In flux ratios of 3.6, 5, and 7. X-ray diffraction and Raman spectroscopy revealed that films grown at flux ratios of 3.6 and 7 contained a mixture of hexagonal gamma- and beta-In2Se3 phases, whereas the film grown at a ratio of 5 was single-phase gamma-In2Se3 with improved structural uniformity and ordering. Photoluminescence measurements revealed a dominant emission peak at 1.95 eV, attributed to gamma-In2Se3, with the high intensity observed for the 5-ratio sample. A secondary lower-energy peak at 1.44 eV, associated with beta-In2Se3, was detected in the 3.6 and 7 ratio samples. These results demonstrate that the combined influence of the nominal Se/In supply ratio and growth kinetics plays an important role in determining phase composition, structural uniformity, and optical emission in In2Se3 thin films, providing valuable insights for phase-engineered epitaxial growth in optoelectronic applications.

The ultrathin tungsten (W) layer has been utilized as a spin-generating source for memory application in magnetic heterostructures. We investigate the spin Hall conductivity (SHC, sigma xz y) of W-N compounds, focusing on WN and W2N, employing first-principles calculations. We evaluate the SHC, formation energy (Delta F), and phonon frequencies for all cases. Three possible structures, including NaCl, hexagonal, and NbO type, are considered for WN. While the SHC of WN in NaCl and a hexagonal structure are substantial, the thermodynamic average of WN is -194( h/e) S/cm, much smaller than pure W. However, W2N, whose stability is confirmed by phonon calculations, shows a large SHC of sigma xz y =-966( h/e) S/cm with a spin Hall angle (theta SH) of -0.44, in good agreement with the experiment, enhanced by 18% over beta-W. Most of the spin Berry curvature, responsible for such large sigma xzy, stems from the [110] (kx = ky) plane and is analyzed from a symmetry perspective using representations of group theory.

We report the high-quality growth of CdTe(111) films on GaAs(111)B substrates despite a significant lattice mismatch of 14.6 %, achieved using molecular beam epitaxy (MBE). The quality of the CdTe films was found to be highly dependent on the pre-treatment of the GaAs substrates. Notably, the best crystallinity was achieved on Te-treated GaAs(111)B substrates at elevated temperatures. CdTe films were successfully epitaxially grown along the [111] direction on Te-treated GaAs(111)B substrates over a wide temperature range of 50 to 320 degrees C, with improved crystallinity observed at higher temperatures. The optimal growth temperature for high-quality CdTe films was determined to be between 270 and 320 degrees C. Additionally, film crystallinity was found to improve with increasing thickness due to strain relaxation. When the CdTe film thickness approached approximately 500 nm, photoluminescence measurements showed a significant reduction in defect-related emissions, suggesting improved optical quality.

Spin Hall effect (SHE) is the conversion of charge current to spin current. Non-magnetic heavy transition metals (TMs) are expected to have large spin Hall conductivity (SHC) thanks to their large spin-orbit coupling (SOC). Among transition metals, beta-W with A15 structure, has been reported to be among the materials that have large SHC, and SHCs of its alloys are even greater. In this work, SHCs of beta-W and its alloys with Ta have been theoretically studied by the combination of the first principles calculation with the tight binding method. Two possible configurations of Ta in W sites are considered and the relative energetics between the configurations are calculated to estimate the thermodynamic average of SHCs using Boltzmann transport distribution. We find that SHC of Ta in the bcc site is much enhanced but gives less contribution to the thermodynamic average of SHC due to the large difference in total energy of the two configurations.

In this study, the effect of elastic biaxial strain on electronic structure and the anomalous Hall conductivity (AHC) of alpha-Fe has been systematically studied by using the combination of a first principles calculation with the tight binding method through the Wannier function. It is found that applying strain in cubic structure of alpha-Fe results in the reduction of crystal symmetry and gives the modification on the bands near Fermi level, which causes a significant change in the AHC of strained systems. The AHC of strained alpha-Fe is found to be sensitive with applying strain, which shows the large enhancement of AHC at +2% tensile strain with AHC value is up to 929 Omega(-1) cm(-1) (increases more than 30%) compared with the unstrained one, while slightly reduces when applying compressive strain. The modification of AHC is found to be related to the change of Berry curvature contributed from the spin orbit coupling (SOC) induced energy gap near Fermi level. (c) 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

In this work, intrinsic spin Hall conductivity of β‐W and its alloy with V has been theoretically studied by the combination of ab initio method with the tight binding method. Both two possible configurations of V in β‐W structure are fully considered and their total energy difference used to estimate the thermodynamic average SHC of alloy by using Maxwell‐Boltzmann distribution. It is found that due to the small total energy difference between two configurations, there is a significant contribution to the thermodynamic average SHC of the alloy from both configurations, which results in the average SHC of alloy being enhanced up to 12.3% compared with the pristine β‐W. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

We report the temperature dependences of the dielectric function ε = ε1 + iε2 and critical point (CP) energies of the uniaxial crystal GaSe in the spectral energy region from 0.74 to 6.42 eV and at temperatures from 27 to 300 K using spectroscopic ellipsometry. The fundamental bandgap and strong exciton effect near 2.1 eV are detected only in the c-direction, which is perpendicular to the cleavage plane of the crystal. The temperature dependences of the CP energies were determined by fitting the data to the phenomenological expression that incorporates the Bose–Einstein statistical factor and the temperature coefficient to describe the electron–phonon interaction. To determine the origin of this anisotropy, we perform first-principles calculations using the mBJ method for bandgap correction. The results clearly demonstrate that the anisotropic dielectric characteristics can be directly attributed to the inherent anisotropy of p orbitals. More specifically, this prominent excitonic feature and fundamental bandgap are derived from the band-to-band transition between s and pz orbitals at the Γ-point.

A combination of a first-principles electronic structure and Boltzmann transport calculations was used to study the electronic and thermoelectric properties of Ga-doped ZnO (GZO). Band structure of GZO showed rigid-like behavior with that of pristine ZnO; however, the only difference was seen in the position of Fermi level due to an additional electron. Therefore, the thermoelectric properties of GZO were found to show similar behavior with pristine ZnO. We suggest that it is possible to control the carrier concentration of the doped system by controlling the Ga concentration, which can optimize the power factor of GZO.

The effect of C dopant on the electronic structure and thermoelectric properties of SnSe has been studied using density functional theory (DFT) and by solving the Boltzmann transport equation (BTE). We found that the substitution of C into the Sn site creates a strongly localized defect state with a sharp density for the state peak. This strong modification of band structure reduces the band gap from 0.61 eV to 0.42 eV. It was found that the maximal Seebeck coefficient can be enhanced up to 17.1% and the maximal temperature reduces from 525 K to 280 K. These behaviors can be understood using the Mott equation and Goldsmid – Sharp relation.

High-temperature ferromagnetism in materials composed of non-magnetic constituents is one of the most intriguing aspects in condensed matter physics as well as materials science. Beyond oxide compounds where the ferromagnetism is mainly induced by dilute magnetic dopants, a variety of unusual ferromagnetic materials, mostly fabricated artificially to control the magnetic and electronic properties, have been investigated for spintronic device applications. The unexpected ferromagnetism, attributed to strain and structural defects or proximity and interfacial effects, is now extended to quantum materials, despite prevailing controversy on its physical origin. Recently, the ferromagnetism observed in topological materials with high mobility arising from the linear energy dispersion invokes new interest in the field of spintronics. Here, we report experimental verification of peculiar high-temperature ferromagnetism in β-Ag2Se topological semimetal, composed of non-magnetic constituents. We have fabricated stoichiometric Ag2Se (S-Ag2Se) and Ag-vacant Ag2Se (V-Ag2Se) samples. Contrary to non-magnetic behavior of S-Ag2Se, V-Ag2Se shows distinct ferromagnetic response up to room temperatures. First-principles calculations demonstrate that the ferromagnetic ordering occurs only in V-Ag2Se if there is finite Hubbard U, which can be explained by self-trapped magnetic polaron model with strong p-d hybridization. High-temperature ferromagnetism, especially in topological materials, allows exploring a significant new direction in material engineering for spintronic applications.

The spin–orbit torque (SOT) resulting from a spin current generated in a nonmagnetic transition metal layer offers a promising magnetization switching mechanism for spintronic devices. To fully exploit this mechanism, in practice, materials with high SOT efficiencies are indispensable. Moreover, new materials need to be compatible with semiconductor processing. This study introduces W–Ta and W–V alloy layers between nonmagnetic β-W and ferromagnetic CoFeB layers in β-W/CoFeB/MgO/Ta heterostructures. We carry out first-principles band structure calculations for W–Ta and W–V alloy structures to estimate the spin Hall conductivity. While the predicted spin Hall conductivity values of W–Ta alloys decrease monotonically from −0.82 × 10 3 S/cm for W 100 at% as the Ta concentration increases, those of W–V alloys increase to −1.98 × 10 3 S/cm for W 75 V 25 at% and then gradually decrease. Subsequently, we measure the spin Hall conductivities of both alloys. Experimentally, when β-W is alloyed with 20 at% V, the absolute value of the spin Hall conductivity considerably increases by 36% compared to that of the pristine β-W. We confirm that the W–V alloy also improves the SOT switching efficiency by approximately 40% compared to that of pristine β-W. This study demonstrates a new material that can act as a spin current-generating layer, leading to energy-efficient spintronic devices.

The complex dielectric function epsilon = epsilon(1) + i epsilon(2) of monolayer tungsten disulfide (WS2) is investigated for the energy range from 1.5 to 6.0 eV and temperatures from 41 to 300 K. Measurements were performed under ultra-high vacuum conditions to avoid degradation and overlayer contamination. Fourteen critical-point (CP) energies were observed and their origins in Brillouin-zone were identified by band structure calculations. At low temperature the A and B excitonic peaks split into four CPs, which is understood as the neutral and charged exciton states of monolayer WS2. At low temperatures the CP energies show blue shifts with enhanced structure due to the reduction of electron-phonon interaction. The temperature dependence of these data was obtained by a phenomenological expression with Bose-Einstein statistical factor.

We investigate analytically the anisotropic dielectric properties of single-crystal α-SnS near the fundamental absorption edge by considering atomic orbitals. Most striking is the excitonic feature in the armchair- (b-) axis direction, which is particularly prominent at low temperatures. To determine the origin of this anisotropy, we perform first-principles calculations using the GW0 Bethe–Salpeter equation including the electron–hole interaction. The results show that the anisotropic dielectric characteristics are a direct result of the natural anisotropy of p orbitals. In particular, this dominant excitonic feature originates from the py orbital at the saddle point in the Γ–Y region.

We investigated the magnetocrystalline anisotropy (MCA) of MnPt(0 0 1) film and MnPt/MgO(0 0 1) using ab initio electronic structure calculations. We found that the magnetic ground state of the MnPt film strongly depends on thickness (n). In bulk and in film with n >= 7 monolayers; AFM-II is the magnetic ground state. However, as the film thickness reduces, the magnetic ground state shifts from AFM-II to AFM-III. We employ layer-by-layer Heisenberg model to explain thickness dependent ground state transition. AFM-III state in the Mn-terminated film shows large perpendicular MCA(PMCA), which further enhances on a MgO(0 0 1) substrate. We conclude that the interface plays a key role for the enhancement of PMCA on the substrate.

The anomalous Hall effect (AHE) is commonly observed phenomena in magnetic systems, where 3d ferromagnetic metals are epitomic exampels[1-4]. In last decade, the intrinsic anomalous Hall effect (AHE) is well formulated in the framework of Berry phase formalism. In this study, the role of elasticity on AHE in fcc Ni has been investigated using first-principles calculations, where Wannier functions are fully exploited. Different lattice distortions along the (001), (110), and (111) are taken into account while volume is kept constant. The resulting AHE, more specifically, the Berry curvature for different lattice strains are discussed, where exhaustive analysis in Brillouine zone is provided regarding level degeneracies, changes in momentum matrices, and so forth.

The effect of strain on the electronic structure and the thermoelectric properties of higher manganese silicide (HMS) Mn 4 Si 7 was studied by using density functional theory (DFT) and by solving Boltzmann transport equation (BTE). We found that tensile strain reduced the band gap while compressive strain did not affect the band gap much. The electrical conductivity shows highly anisotropic with the in-plane direction being more dominant while the Seebeck coefficient does not change much, which leads to the the power factor along the in-plane direction being higher compared with that along the out-of-plane direction. The anisotropy of the electrical conductivity was due to a change of the band dispersion in the valence-band maximum (VBM). It was suggested that compressive strain can improve the power factor of Mn 4 Si 7 .