Momentum-Dependent Hybridization Gap and dispersive in-gap state of The Kondo Semiconductor SmB6

We report the temperature-dependent three-dimensional angle-resolved photoemission spectra of the Kondo semiconductor SmB$_6$. We found a difference in the temperature dependence of the peaks at the X and $\Gamma$ points, due to hybridization between the Sm 5d conduction band and the nearly localized Sm 4f state. The peak intensity at the X point has the same temperature dependence as the valence transition below 120 K, while that at the $\Gamma$ point is consistent with the magnetic excitation at Q=(0.5,0.5,0.5) below 30 K. This suggests that the hybridization with the valence transition mainly occurs at the X point, and the initial state of the magnetic excitation is located at the $\Gamma$ point.Comment: 5 pages, 3 figure

Optical study of charge instability in CeRu2Al10 in comparison with CeOs2Al10 and CeFe2Al10

The anisotropic electronic structure responsible for the antiferromagnetic transition in CeRu2Al10 at the unusually high temperature of T0=28 K was studied using optical conductivity spectra, Ce 3d x-ray photoemission spectra, and band calculation. It was found that the electronic structure in the ac plane is that of a Kondo semiconductor, whereas that along the b axis has a nesting below 32 K (slightly higher than T0). These characteristics are the same as those of CeOs2Al10 [ S. Kimura et al. Phys. Rev. Lett. 106 056404 (2011)]. The c-f hybridization intensities between the conduction and 4f electrons of CeRu2Al10 and CeOs2Al10 are weaker than that of CeFe2Al10, showing no magnetic ordering. These results suggest that the electronic structure with one-dimensional weak c-f hybridization along the b axis combined with two-dimensional strong hybridization in the ac plane causes charge-density wave (CDW) instability, and the CDW state then induces magnetic ordering

Revealing the higher-order spin nature of the Hall effect in non-collinear antiferromagnet Mn3Ni0.35Cu0.65N\mathrm{Mn_3Ni_{0.35}Cu_{0.65}N}

Ferromagnets generate an anomalous Hall effect even without the presence of a magnetic field, something that conventional antiferromagnets cannot replicate but noncollinear antiferromagnets can. The anomalous Hall effect governed by the resistivity tensor plays a crucial role in determining the presence of time reversal symmetry and the topology present in the system. In this work we reveal the complex origin of the anomalous Hall effect arising in noncollinear antiferromagnets by performing Hall measurements with fields applied in selected directions in space with respect to the crystalline axes. Our coplanar magnetic field geometry goes beyond the conventional perpendicular field geometry used for ferromagnets and allows us to suppress any magnetic dipole contribution. It allows us to map the in-plane anomalous Hall contribution and we demonstrate a 120$^\circ$ symmetry which we find to be governed by the octupole moment at high fields. At low fields we subsequently discover a surprising topological Hall-like signature and, from a combination of theoretical techniques, we show that the spins can be recast into dipole, emergent octupole and noncoplanar effective magnetic moments. These co-existing orders enable magnetization dynamics unachievable in either ferromagnetic or conventional collinear antiferromagnetic materials

Preparation and evaluation of Mn3GaN1-x thin films with controlled N compositions

Thin films of antiperovskite Mn3GaN1-x were grown on MgO (001) substrates by reactive magnetron sputtering, and their structural, magnetic, and magneto-optical properties were systematically investigated. It was found that the combination of the deposition rate and the N2 gas partial pressure could produce epitaxial films with a wide range of N composition (N-deficiency) and resulting c/a values (0.93 - 1.0). While the films with c/a = 0.992 - 1.0 were antiferromagnetic, the films with c/a = 0.93 - 0.989 showed perpendicular magnetic anisotropy (PMA) with the maximum PMA energy up to 1.5×106 erg/cm3. Systematic dependences of the energy spectra of the polar Kerr signals on the c/a ratio were observed, and the Kerr ellipticity was as large as 2.4 deg. at 1.9 eV for perpendicularly magnetized ferromagnetic thin films with c/a = 0.975. These results highlight that the tetragonal distortion plays an important role in magnetic and magneto-optical properties of Mn3GaN1-x thin films

Phase Selective Growth and Characterization of Vanadium Dioxide Films on Silicon Substrates

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Temperature-Dependent Raman and Ultraviolet Photoelectron Spectroscopy Studies on Phase Transition Behavior of VO2 Films with M1 and M2 Phases

International audienceStructural and electronic phase transitions behavior of two polycrystalline VO2 films, one with pure M1 phase and the other with pure M2 phase at room temperature, were investigated by temperature-controlled Raman spectroscopy and ultraviolet photoelectron spectroscopy (UPS). We observed characteristic transient dynamics in which the Raman modes at 195 cm−1 (V-V vibration) and 616 cm−1 (V-O vibration) showed remarkable hardening along the temperature in M1 phase film, indicating the rearrangements of V-V pairs and VO6 octahedra. It was also shown that the M1 Raman mode frequency approached those of invariant M2 peaks before entering rutile phase. In UPS spectra with high energy resolution of 0.03 eV for the M2 phase film, narrower V3d band was observed together with smaller gap compared to those of M1 phase film, supporting the nature of Mott insulator of M2 phase even in the polycrystalline film. Cooperative behavior of lattice rearrangements and electronic phase transition was suggested for M1 phase film

Anomalous Superconducting-Gap Structure of Slightly Overdoped Ba(Fe1-xCox)(2)As-2

We observed the anisotropic superconducting-gap (SC-gap) structure of a slightly overdoped superconductor, Ba(Fe1-xCox)2As2 (x = 0.1), using three-dimensional (3D) angle-resolved photoemission spectroscopy. Two hole Fermi surfaces (FSs) observed at the Brillouin zone center and an inner electron FS at the zone corner showed a nearly isotropic SC gap in 3D momentum space. However, the outer electron FS showed an anisotropic SC gap with nodes or gap minima around the M and A points. The different anisotropies obtained the SC gap between the outer and inner electron FSs cannot be expected from all theoretical predictions with spin fluctuation, orbital fluctuation, and both competition. Our results provide a new insight into the SC mechanisms of iron pnictide superconductors. © 2014 The Physical Society of Japan.