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Journal of Physics: Condensed Matter - latest papers
Latest articles for Journal of Physics: Condensed Matter
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Effect of Fe doping on the electronic properties of CoSn Kagome semimetal
Quantum phenomena in two-dimensional Kagome materials lead to exotic topological states and complex magnetism. Here, we have investigated the detailed electronic properties of Co FexSn as a function of composition (x) to explore the competing electronic interactions for the origin of complex magnetism and topological properties. We find that the screening effect in the valence electrons increases while the correlation effect decreases with an increase in the Fe doping. Valence fluctuations observed at Co and Fe L edges showed systematic changes in the magnitude of divalent and trivalent states with the increase in x. Fe 3d states are found to be more screened by the conduction electrons than the Co 3d states. A comparison of the theoretical and experimental density of states showed different natures of localized states with strong screening effects on the surface and dominating correlation effects in the bulk for x 0. We have observed localized flat bands on the CoSn (001) surface while quasi-localized flat bands on the Co0.94Fe0.06Sn (001) surface. The distinct character of the bulk and surface band structure is confirmed in the Fe-doped composition. Hence, the bulk-surface interaction present in Co FexSn gives rise to the origin of valence fluctuation, complex magnetism, and topological properties.
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A remarkable match of optical response in the amorphous-crystalline and zinc blende-rock salt phase pairs of GeTe
Despite a large amount of theoretical and experimental work performed so far, the search of phase change materials (PCMs) is done with use of numerical modeling. However, it is not fully clear how and why the phase change translates into the optical contrast. In this work, we argue that a key prerequisite for a material to have a pronounced difference in optical properties between crystalline and glassy phases of PCM is the similar contrast between the observed crystalline and (may be experimentally inaccessible) parent crystalline polymorph of the glassy phase. To illustrate this claim, we report a comparison of dynamic dielectric function of zinc-blende (α-ZnS), CsCl, and rock-salt (NaCl) phases of the binary PCM exemplified by the well known GeTe prototype compound with experimental data and supply a theoretical explanation to the observed behavior based on topological properties of the Fermi surfaces appearing in the protoptypic ‘degenerate’ crystals with A = B having the same local structure as the parent polymorphs and derived from simple analytical model. By this, we arrive to a qualitative rather than purely numeric guidance for possible search of the novel phase-change materials.
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Drastic enhancement of electronic correlations induced by hydrogen insertion in the cerium intermetallic compound CeFeSi
We report a comparative study of two cerium-based intermetallic compounds: CeFeSi with an anti-PbFCl type structure, and CeFeSiH with a ZrCuSiAs type structure. The latter is obtained from CeFeSi through hydrogen insertion. Our results are based on x-rays, transport, thermodynamic and magnetic measurements. While the tetragonal structure with P4/nmm symmetry remains unchanged after hydrogen insertion, the thermodynamic, magnetic, and transport properties change drastically. On the one hand, CeFeSi behaves as a Pauli paramagnet with a small Sommerfeld coefficient, indicating the absence of 4f electron physics. On the other hand, our study shows that CeFeSiH exhibits strong magnetic fluctuations with a magnetic transition at 3.5 K, and coherent Kondo-lattice heavy-fermion features.
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Engineering skyrmion from spin spiral in transition metal multilayers
Skyrmions having topologically protected field configurations with particle-like properties play an important role in various fields of science. Our present study focus on the generation of skyrmion from spin spiral in the magnetic multilayers of 4d/Fe/Ir(111) with 4d = Y, Zr, Nb, Mo, Ru, Rh. Here we investigate the impact of 4d transition metals on the isotropic Heisenberg exchanges and anti-symmetric Dzyaloshinskii–Moriya interactions originating from the broken inversion symmetry at the interface of 4d/Fe/Ir(111) multilayers. We find a strong exchange frustration due to the hybridization of the Fe-3d layer with both 4d and Ir-5d layers which modifies due to band filling effects of the 4d transition metals. We strengthen the analysis of exchange frustration by shedding light on the orbital decomposition of isotropic exchange interactions of Fe-3d orbitals. Our spin dynamics and Monte Carlo simulations indicate that the magnetic ground state of 4d/Fe/Ir(111) transition multilayers is a spin spiral in the ab-plane with a period of 1 to 2.5 nm generated by magnetic moments of Fe atoms and propagating along the a-direction. The spiral wavelengths in Y/Fe/Ir(111) are much larger compared to Rh/Fe/Ir(111). In order to manipulate the skyrmion phase in 4d/Fe/Ir(111), we investigate the magnetic ground state of 4d/Fe/Ir(111) transition multilayers with different external magnetic field. An increasing external magnetic field of ∼12 T is responsible for deforming the spin spiral into a isolated skyrmion which flips into skyrmion lattice phase around ∼18 T in Rh/Fe/Ir(111). Our study predict that the stability of magnetic skyrmion phase in Rh/Fe/Ir(111) against thermal fluctuations is upto temperature T K.
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Theoretical study of the temperature dependence of Auger–Meitner recombination in (Al,Ga)N quantum wells
Non-radiative Auger–Meitner recombination processes in III-nitride based optoelectronic devices operating in the visible spectral range have received significant attention in recent years as they can present a major contribution to the efficiency drop at high temperatures and carrier densities. However, insight into these recombination processes is sparse for III-N devices operating in the ultraviolet wavelength window. In this work we target the temperature dependence of the Auger–Meitner recombination rate in (Al,Ga)N/AlN quantum wells by means of an atomistic electronic structure model that accounts for random alloy fluctuations and connected carrier localisation effects. Our calculations show that in the low temperature regime both the non-radiative Auger–Meitner and radiative recombination rate are strongly impacted by alloy disorder induced carrier localisation effects in these systems. The influence of alloy disorder on the recombination rates is reduced in the high temperature regime, especially for the radiative rate. The Auger–Meitner recombination rate, however, may still be more strongly impacted by alloy disorder when compared to the radiative rate. Our calculations show that while on average radiative recombination slightly increases with increasing temperature, the Auger–Meitner recombination process may, on average, slightly decrease in the temperature range relevant to the thermal efficiency drop (thermal droop). This finding suggests that the considered Auger–Meitner recombination process is unlikely to be directly responsible for the thermal efficiency drop observed experimentally in (Al,Ga)N/AlN quantum well based light emitting devices. Thus, different non-radiative processes, external to the active region, may be the underlying cause of thermal droop in (Al,Ga)N wells.