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Abstract The vast high entropy alloy (HEA) composition space is promising for discovery of new material phases with unique properties. This study explores the potential to achieve rare‐earth‐free high magnetic anisotropy materials in single‐phase HEA thin films. Thin films of FeCoNiMnCu sputtered on thermally oxidized Si/SiO₂substrates at room temperature are magnetically soft, with a coercivity on the order of 10 Oe. After post‐deposition rapid thermal annealing (RTA), the films exhibit a single face‐centered‐cubic phase, with an almost 40‐fold increase in coercivity. Inclusion of 50 at.% Pt in the film leads to ordering of a singleL1₀high entropy intermetallic phase after RTA, along with high magnetic anisotropy and 3 orders of magnitude coercivity increase. These results demonstrate a promising HEA approach to achieve high magnetic anisotropy materials using RTA. 

Two-dimensional layered transition metal dichalcogenides are potential thermoelectric candidates with application in on-chip integrated nanoscale cooling and power generation. Here, we report a comprehensive experimental and theoretical study on the in-plane thermoelectric transport properties of thin 2H-MoTe2 flakes prepared in field-effect transistor geometry to enable electrostatic gating and modulation of the electronic properties. The thermoelectric power factor is enhanced by up to 45% using electrostatic modulation. The in-plane thermal conductivity of 9.8 ± 3.7 W m−1 K−1 is measured using the heat diffusion imaging method in a 25 nm thick flake. First-principles calculations are used to obtain the electronic band structure, phonon band dispersion, and electron–phonon scattering rates. The experimental electronic properties are in agreement with theoretical results obtained within energy-dependent relaxation time approximation. The thermal conductivity is evaluated using both the relaxation time approximation and the full iterative solution to the phonon Boltzmann transport equation. This study establishes a framework to quantitively compare first-principle-based calculations with experiments in 2D layered materials. 

We report on the synthesis of self-intercalated Nb1+xSe2 thin films by molecular beam epitaxy. Nb1+xSe2 is a metal-rich phase of NbSe2 where additional Nb atoms populate the van der Waals gap. The grown thin films are studied as a function of the Se to Nb beam equivalence pressure ratio (BEPR). X-ray photoelectron spectroscopy and x-ray diffraction indicate that BEPRs of 5:1 and greater result in the growth of the Nb1+xSe2 phase and that the amount of intercalation is inversely proportional to the Se to Nb BEPR. Electrical resistivity measurements also show an inverse relationship between BEPR and resistivity in the grown Nb1+xSe2 thin films. A second Nb-Se compound with a stoichiometry of ∼1:1 was synthesized using a Se to Nb BEPR of 2:1; in contrast to the Nb1+xSe2 thin films, this compound did not show evidence of a layered structure. 

Among group VI transition metal dichalcogenides, MoTe 2 is predicted to have the smallest energy offset between semiconducting 2H and semimetallic 1T′ states. This makes it an attractive phase change material for both electronic and optoelectronic applications. Here, we report fast, nondestructive, and full phase change in Al 2 O 3 -encapsulated 2H-MoTe 2 thin films to 1T′-MoTe 2 using rapid thermal annealing at 900 °C. Phase change was confirmed using Raman spectroscopy after a short annealing duration of 10 s in both vacuum and nitrogen ambient. No thickness dependence of the transition temperatures was observed for flake thickness ranging from 1.5 to 8 nm. These results represent a major step forward in understanding the structural phase transition properties of MoTe 2 thin films using external heating and underline the importance of surface encapsulation for avoiding thin film degradation. 

Abstract Alloyed transition metal dichalcogenides provide an opportunity for coupling band engineering with valleytronic phenomena in an atomically-thin platform. However, valley properties in alloys remain largely unexplored. We investigate the valley degree of freedom in monolayer alloys of the phase change candidate material WSe 2(1-x) Te 2x . Low temperature Raman measurements track the alloy-induced transition from the semiconducting 1H phase of WSe 2 to the semimetallic 1T d phase of WTe 2 . We correlate these observations with density functional theory calculations and identify new Raman modes from W-Te vibrations in the 1H-phase alloy. Photoluminescence measurements show ultra-low energy emission features that highlight alloy disorder arising from the large W-Te bond lengths. Interestingly, valley polarization and coherence in alloys survive at high Te compositions and are more robust against temperature than in WSe 2 . These findings illustrate the persistence of valley properties in alloys with highly dissimilar parent compounds and suggest band engineering can be utilized for valleytronic devices. 

Layered materials enable the assembly of a new class of heterostructures where lattice-matching is no longer a requirement. Interfaces in these heterostructures therefore become a fertile ground for unexplored physics as dissimilar phenomena can be coupled via proximity effects. In this article, we identify an unexpected photoluminescence (PL) peak when MoSe2 interacts with TiSe2. A series of temperature-dependent and spatially resolved PL measurements reveal that this peak is unique to the TiSe2–MoSe2 interface, is higher in energy compared to the neutral exciton, and exhibits exciton-like characteristics. The feature disappears at the TiSe2 charge density wave transition, suggesting that the density wave plays an important role in the formation of this new exciton. We present several plausible scenarios regarding the origin of this peak that individually capture some aspects of our observations but cannot fully explain this feature. These results therefore represent a fresh challenge for the theoretical community and provide a fascinating way to engineer excitons through interactions with charge density waves. 

Applications that use the orbital angular momentum (OAM) of light show promise for increasing the bandwidth of optical communication networks. However, direct photocurrent detection of different OAM modes has not yet been demonstrated. Most studies of current responses to electromagnetic fields have focused on optical intensity–related effects, but phase information has been lost. In this study, we designed a photodetector based on tungsten ditelluride (WTe 2 ) with carefully fabricated electrode geometries to facilitate direct characterization of the topological charge of OAM of light. This orbital photogalvanic effect, driven by the helical phase gradient, is distinguished by a current winding around the optical beam axis with a magnitude proportional to its quantized OAM mode number. Our study provides a route to develop on-chip detection of optical OAM modes, which can enable the development of next-generation photonic circuits. 

Abstract We report the results of polarization‐dependent Raman spectroscopy of phonon states in single‐crystalline quasi‐one‐dimensional NbTe₄and TaTe₄van der Waals materials. The measurements were conducted in the wide temperature range from 80 to 560 K. Our results show that although both materials have identical crystal structures and symmetries, there is a drastic difference in the intensity of their Raman spectra. While TaTe₄exhibits well‐defined peaks through the examined wavenumber and temperature ranges, NbTe₄reveals extremely weak Raman signatures. The measured spectral positions of the phonon peaks agree with the phonon band structure calculated using the density‐functional theory. We offer possible reasons for the intensity differences between the two van der Waals materials. Our results provide insights into the phonon properties of NbTe₄and TaTe₄van der Waals materials and indicate the potential of Raman spectroscopy for studying charge‐density‐wave quantum condensate phases.