Probing lithium mobility at a solid electrolyte surface.

Solid-state electrolytes overcome many challenges of present-day lithium ion batteries, such as safety hazards and dendrite formation. However, detailed understanding of the involved lithium dynamics is missing due to a lack of in operando measurements with chemical and interfacial specificity. Here we investigate a prototypical solid-state electrolyte using linear and nonlinear extreme-ultraviolet spectroscopies.

Hole Dynamics in Photoexcited Hematite Studied with Femtosecond Oxygen K-edge X-ray Absorption Spectroscopy.

Hematite (α-FeO) is a photoelectrode for the water splitting process because of its relatively narrow bandgap and abundance in the earth's crust. In this study, the photoexcited state of a hematite thin film was investigated with femtosecond oxygen K-edge X-ray absorption spectroscopy (XAS) at the PAL-XFEL in order to follow the dynamics of its photoexcited states. The 200 fs decay time of the hole state in the valence band was observed via its corresponding XAS feature.

Polarization-Resolved Extreme-Ultraviolet Second-Harmonic Generation from LiNbO_{3}.

Second harmonic generation (SHG) spectroscopy ubiquitously enables the investigation of surface chemistry, interfacial chemistry, as well as symmetry properties in solids. Polarization-resolved SHG spectroscopy in the visible to infrared regime is regularly used to investigate electronic and magnetic order through their angular anisotropies within the crystal structure. However, the increasing complexity of novel materials and emerging phenomena hampers the interpretation of experiments solely based on the investigation of hybridized valence states.

Extreme Ultraviolet Second Harmonic Generation Spectroscopy in a Polar Metal.

The coexistence of ferroelectricity and metallicity seems paradoxical, since the itinerant electrons in metals should screen the long-range dipole interactions necessary for dipole ordering. The recent discovery of the polar metal LiOsO was therefore surprising [as discussed earlier in Y. Shi et al.

Femtosecond Charge Density Modulations in Photoexcited CuWO.

Copper tungstate (CuWO) is an important semiconductor with a sophisticated and debatable electronic structure that has a direct impact on its chemistry. Using the PAL-XFEL source, we study the electronic dynamics of photoexcited CuWO. The Cu L X-ray absorption spectrum shifts to lower energy upon photoexcitation, which implies that the photoexcitation process from the oxygen valence band to the tungsten conduction band effectively increases the charge density on the Cu atoms.

Intrinsic 2D Ferromagnetism in VSe Epitaxial Thin Films.

The discoveries of intrinsic ferromagnetism in atomically thin van der Waals crystals have opened a new research field enabling fundamental studies on magnetism at two-dimensional (2D) limit as well as development of magnetic van der Waals heterostructures. Currently, a variety of 2D ferromagnetism has been explored mainly by mechanically exfoliating "originally ferromagnetic (FM)" van der Waals crystals, while a bottom-up approach by thin-film growth technique has demonstrated emergent 2D ferromagnetism in a variety of "originally non-FM" van der Waals materials. Here we demonstrate that VSe epitaxial thin films grown by molecular-beam epitaxy exhibit emergent 2D ferromagnetism with intrinsic spin polarization of the V 3d electrons despite that the bulk counterpart is "originally antiferromagnetic".

Direct observation of the electronic states of photoexcited hematite with ultrafast 2p3d X-ray absorption spectroscopy and resonant inelastic X-ray scattering.

Hematite, α-FeO, is an important semiconductor for photoelectrochemical water splitting. Its low charge carrier mobility and the presence of midgap states provide favourable conditions for electron-hole recombination, hence affecting the semiconductor's photoelectrochemical efficiency. The nature of the excited state and charge carrier transport in hematite is strongly debated.

Magnetic Precursor of the Pressure-Induced Superconductivity in Fe-Ladder Compounds.

The pressure effects on the antiferromagentic orders in iron-based ladder compounds CsFe_{2}Se_{3} and BaFe_{2}S_{3} have been studied using neutron diffraction. With identical crystal structure and similar magnetic structures, the two compounds exhibit highly contrasting magnetic behaviors under moderate external pressures. In CsFe_{2}Se_{3} the ladders are brought much closer to each other by pressure, but the stripe-type magnetic order shows no observable change.

Erratum: Pressure-Induced Mott Transition Followed by a 24-K Superconducting Phase in BaFe_{2}S_{3} [Phys. Rev. Lett. 115, 246402 (2015)].

This corrects the article DOI: 10.1103/PhysRevLett.115.

Pressure-Induced Mott Transition Followed by a 24-K Superconducting Phase in BaFe_{2}S_{3}.

We performed high-pressure study for a Mott insulator BaFe_{2}S_{3}, by measuring dc resistivity and ac susceptibility up to 15 GPa. We found that the antiferromagnetic insulating state at the ambient pressure is transformed into a metallic state at the critical pressure, P_{c}=10  GPa, and the superconductivity with the optimum T_{c}=24  K emerges above P_{c}. Furthermore, we found that the metal-insulator transition (Mott transition) boundary terminates at a critical point around 10 GPa and 75 K.

Pressure-induced superconductivity in the iron-based ladder material BaFe2S3.

All the iron-based superconductors identified so far share a square lattice composed of Fe atoms as a common feature, despite having different crystal structures. In copper-based materials, the superconducting phase emerges not only in square-lattice structures but also in ladder structures. Yet iron-based superconductors without a square-lattice motif have not been found, despite being actively sought out.

Mechanism of enhanced optical second-harmonic generation in the conducting pyrochlore-type Pb2Ir2O7-x oxide compound.

The structural, electronic, and optical properties of pyrochlore-type Pb(2)Ir(2)O(6)O(0.55)('), which is a metal without spatial inversion symmetry at room temperature, were investigated. Structural analysis revealed that the structural distortion relevant to the breakdown of the inversion symmetry is dominated by the Pb-O' network but is very small in the Ir-O network.