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We investigate the electronic structure of a novel Kondo lattice system CeCuX2 (X = As/Sb) employing high resolution depth-resolved photoemission spectroscopy of high quality single crystalline materials. CeCuSb2 and CeCuAs2 represent different regimes of the Doniach phase diagram exhibiting Kondo-like transport properties and CeCuSb2 is antiferromagnetic (TN ~ 6.9 K) while CeCuAs$_2$ does not show long-range magnetic order down to the lowest temperature studied. In this study, samples were cleaved in ultrahigh vacuum before the photoemission measurements and the spectra at different surface sensitivity establish the pnictogen layer having squarenet structure as the terminated surface which is weakly bound to the other layers. Cu 2p and As 2p spectra show spin-orbit split sharp peaks along with features due to plasmon excitations. Ce 3d spectra exhibit multiple features due to the hybridization of the Ce 4f/5d states with the valence states. While overall lineshape of the bulk spectral functions look similar in both the cases, the surface spectra are very different; the surface-bulk difference is significantly weaker in CeCuAs2 compared to that observed in CeCuSb2. A distinct low binding energy peak is observed in the Ce 3d spectra akin to the scenario observed in cuprates and manganites due to the Zhang-Rice singlets and/or high degree of itineracy of the conduction holes. The valence band spectra of CeCuSb$_2$ manifest highly metallic phase. In CeCuAs2, intensity at the Fermi level is significantly small suggesting a pseudogap-type behavior. These results bring out an interesting scenario emphasizing the importance and subtlety of hybridization physics underlying the exoticity of this novel Kondo system.

We investigate the electronic structure of an antiferromagnetic Kondo lattice system CeAgAs2 employing hard x-ray photoemission spectroscopy. CeAgAs2, an orthorhombic variant of HfCuSi2 structure, exhibits antiferromagnetic ground state, Kondo like resistivity upturn and compensation of magnetic moments at low temperatures. The photoemission spectra obtained at different photon energies suggest termination of the cleaved surface at cis-trans-As layers. The depth-resolved data show significant surface-bulk differences in the As and Ce core level spectra. The As 2p bulk spectrum shows distinct two peaks corresponding to two different As layers. The peak at higher binding energy correspond to cis-trans-As layers and is weakly hybridized with the adjacent Ce layers. The As layers between Ce and Ag-layers possess close to trivalent configuration due to strong hybridization with the neighboring atoms and the corresponding feature appear at lower binding energy. Ce 3d core level spectra show multiple features reflecting strong Ce-As hybridization and strong correlation. Intense f0 peak is observed in the surface spectrum while it is insignificant in the bulk. In addition, we observe a features at binding energy lower than the well-screened feature indicating the presence of additional interactions. This feature becomes more intense in the bulk spectra suggesting it to be a bulk property. Increase in temperature leads to a spectral weight transfer to higher binding energies in the core level spectra and a depletion of spectral intensity at the Fermi level as expected in a Kondo material. These results reveal interesting surface-bulk differences, complex interplay of intra- and inter-layer covalency, and electron correlation in the electronic structure of this novel Kondo lattice system.

We investigate the electronic structure of a Kondo lattice system, CeCuSb2 exhibiting significant mass enhancement and Kondo-type behavior. We observe multiple features in the hard x-ray photoemission spectra of Ce core levels due to strong final-state effects. The depth-resolved data exhibit a significant change in relative intensity of the features with the surface sensitivity of the probe. The extracted surface and bulk spectral functions are different and exhibit a Kondo-like feature at higher binding energies in addition to the well and poorly screened features. The core-level spectra of Sb exhibit huge and complex changes as a function of the surface sensitivity of the technique. The analysis of the experimental data suggests that the two non-equivalent Sb sites possess different electronic structures and in each category, the Sb layers close to the surface are different from the bulk ones. An increase in temperature influences the Ce-Sb hybridization significantly. The plasmon-excitation-induced loss features are also observed in all core level spectra. All these results reveal the importance of Ce-Sb hybridizations and indicate that the complex renormalization of Ce-Sb hybridization may be the reason for the exotic electronic properties of this system., Comment: 7 figures

We present time-resolved high energy x-ray diffraction (tr-HEXRD), time-resolved hard x-ray photoelectron spectroscopy (tr-HAXPES) and time-resolved grazing incidence small angle x-ray scattering (tr-GISAXS) data of the reactive molecular beam epitaxy (RMBE) of $\mathrm{Fe_3O_4}$ ultrathin films on various substrates. Reciprocal space maps are recorded during the deposition of $\mathrm{Fe_3O_4}$ on $\mathrm{SrTiO_3(001)}$, MgO(001) and NiO/MgO(001) in order to observe the temporal evolution of Bragg reflections sensitive to the octahedral and tetrahedral sublattices of the inverse spinel structure of $\mathrm{Fe_3O_4}$. A time delay between the appearance of rock salt and spinel-exclusive reflections reveals that first, the iron oxide film grows with $\mathrm{Fe_{1-\delta}O}$ rock salt structure with exclusive occupation of octahedral lattice sites. When this film is 1.1$\,$nm thick, the further growth of the iron oxide film proceeds in the inverse spinel structure, with both octahedral and tetrahedral lattice sites being occupied. In addition, iron oxide on $\mathrm{SrTiO_3(001)}$ initially grows with none of these structures. Here, the formation of the rock salt structure starts when the film is 1.5$\,$nm thick. This is confirmed by tr-HAXPES data obtained during growth of iron oxide on $\mathrm{SrTiO_3(001)}$, which demonstrate an excess of $\mathrm{Fe^{2+}}$ cations in growing films thinner than 3.2$\,$nm. This rock salt phase only appears during growth and vanishes after the supply of the Fe molecular beam is stopped. Thus, it can be concluded the rock salt structure of the interlayer is a property of the dynamic growth process. The tr-GISAXS data link these structural results to an island growth mode of the first 2-3$\,$nm on both MgO(001) and $\mathrm{SrTiO_3(001)}$ substrates., Comment: 10 pages, 8 figures

Nanoprobe X-ray diffraction (nXRD) using focused synchrotron radiation is a powerful technique to study the structural properties of individual semiconductor nanowires. However, when performing the experiment under ambient conditions, the required high X-ray dose and prolonged exposure times can lead to radiation damage. To unveil the origin of radiation damage, we compare nXRD experiments carried out on individual semiconductor nanowires in their as grown geometry both under ambient conditions and under He atmosphere at the microfocus station of the P08 beamline at the 3rd generation source PETRA III. Using an incident X-ray beam energy of 9 keV and photon flux of 10$^{10}$s$^{-1}$, the axial lattice parameter and tilt of individual GaAs/In$_{0.2}$Ga$_{0.8}$As/GaAs core-shell nanowires were monitored by continuously recording reciprocal space maps of the 111 Bragg reflection at a fixed spatial position over several hours. In addition, the emission properties of the (In,Ga)As quantum well, the atomic composition of the exposed nanowires and the nanowire morphology are studied by cathodoluminescence spectroscopy, energy dispersive X-ray spectroscopy and scanning electron microscopy, respectively, both prior to and after nXRD exposure. Nanowires exposed under ambient conditions show severe optical and morphological damage, which was reduced for nanowires exposed under He atmosphere. The observed damage can be largely attributed to an oxidation process from X-ray induced ozone reactions in air. Due to the lower heat transfer coefficient compared to GaAs, this oxide shell limits the heat transfer through the nanowire side facets, which is considered as the main channel of heat dissipation for nanowires in the as-grown geometry.

In this paper we attempt to understand the role of tin and carbon in magnetic interactions in Mn$_3$SnC. Mn$_3$SnC exhibits a time dependent magnetic configuration and a complex magnetic ground state with both ferromagnetic and antiferromagnetic orders. Such a magnetic state is attributed to presence of distorted Mn$_6$C octahedra with long and short Mn--Mn bonds. Our studies show that C deficiency increases the tensile strain on the Mn$_6$C octahedra which elongates Mn--Mn bonds and strengthens ferromagnetic interactions while Sn deficiency tends to ease out the strain resulting in shorter as well as longer Mn--Mn bond distances in comparison with stoichiometric Mn$_3$SnC. Such a variation strengthens both, ferromagnetic and antiferromagnetic interactions. Thus the structural strain caused by both Sn and C is responsible for complex magnetic ground state of Mn$_3$SnC., Comment: Accepted in JMMM

The interface of two dissimilar materials is well known for surprises in condensed matter, and provides avenues for rich physics as well as seeds for future technological advancements. We present some exciting magnetization (M) and remnant magnetization ($\mu$) results, which conclusively arise at the interface of two highly functional materials, namely the graphitic shells of a carbon nanotube (CNT) and $\alpha$-Fe$_2$O$_3$, a Dzyaloshinskii-Moriya Interaction (DMI) driven weak ferromagnet (WFM) and piezomagnet (PzM). We show that the encapsulation inside CNT leads to a very significant enhancement in M and correspondingly in $\mu$, a time- stable part of the remanence, exclusive to the WFM phase. Up to 70% of in-field magnetization is retained in the form of $\mu$ at the room temperature. Lattice parameter of CNT around the Morin transition of the encapsulate exhibits a clear anomaly, confirming the novel interface effects. Control experiments on bare $\alpha$-Fe$_2$O$_3$ nanowires bring into fore that the weak ferromagnets such as $\alpha$-Fe$_2$O$_3$ as are not as weak, as far as their remanence and its stability with time is concerned, and encapsulation inside CNT leads to a substantial enhancement in these functionalities.

Conversion of Si to a direct bandgap semiconductor for optoelectronic application is a great challenge for many decades. It is proposed that embedment of suitable sized quantum dots into silicon matrix may be exploited to convert silicon to a direct bandgap semiconductor. The other bottleneck to this outstanding issue is the identification of local excitons, a signature of direct bandgap property and their comportment within the dots that can be utilized in engineering optoelectronic devices, quantum communications, etc. We studied the core level spectra of Si/Ge quantum huts embedded Si employing high resolution photoemission spectroscopy. Inverted quantum huts (IQHs) of Ge (13.3nm x 6.6nm) were grown on a Si buffer layer deposited on Si(001) surface using molecular beam epitaxy method and the photoemission experiments were carried out at different locations of the IQH structures exposed via controlled sputtering and annealing processes. We discover distinct features in the Ge 3$d$ core level spectra at the lower binging energy side of the bulk 3$d$ peak in contrast to the scenario of core level satellites often observed due to photoemission final state effects. The energy of these features are found to be sensitive to the location of the IQH structure probed revealing different core hole screening by the excitons located at different parts of IQHs. These results reveal local character of the excitons in the IQHs necessary for type I photoluminescence and establish core level spectroscopy as a direct probe of local excitons. These finding are expected to help amalgamation of microelectronics and solid state photonics important for optoelectronic applications., Comment: 3 figures

We demonstrate that a single zone furnace with a modified synthesis chamber design is sufficient to obtain metal (Fe, Co or Ni) filled carbon nanotubes (CNT) with high filling efficiency and controlled morphology. Samples are formed by pyrolysis of metallocenes, a synthesis technique that otherwise requires a dual zone furnace. Respective metallocene in all three cases are sublimed in powder form, a crucial factor for obtaining high filling efficiency. While Fe@CNT is routinely produced using this technique, well-formed Ni@CNT or Co@CNT samples are reported for the first time. This is achieved by sublimation of nickelocene (or cobaltocene) in combination with 'camphor'. These samples exhibit some of the highest saturation magnetization (Ms) values, at least an order of magnitude higher than that reported for Ni or Co filled CNT, by aerosol assisted pyrolysis. The results also elucidate on why Ni or Co@CNT are relatively difficult to obtain by pyrolyzing powder metallocene alone. Overall, a systematic variation of synthesis parameters provides insights for obtaining narrow length and diameter distribution and reduced residue particles outside filled CNT - factors which are important for device related applications. Finally, the utility of this technique is demonstrated by obtaining highly aligned forest of Fe2O3@CNT, wherein Fe2O3 is a functional magnetic oxide relevant to spintronics and battery applications.