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The first-order ferrimagnet ErCo2 attracts interest not only because of metamagnetism and magnetocaloric effect just above TC ≈ 32–34 K but also because it is closely related with the itinerant metamagnetism of YCo2 and LuCo2. We study the electronic structure of single crystals with hard X-ray photoemission spectroscopy (HAXPES). Magnetization measurements reconfirm the first-order magnetic transition, metamagnetism, and strong magnetic anisotropy. Calculated ErCo2 band structures of the ferrimagnetic and paramagnetic phases are presented in detail. In the ferrimagnetic state, the density of states just below EF is smaller than in the paramagnetic phase. Valence band spectra in the paramagnetic state show strong polarization dependence. Furthermore, the change across the first-order ferrimagnetic transition in the valence band electronic structures is observed. These experimental data are well described by the band structure calculation incorporated with the polarization dependent cross-sections of orbitals. We further discuss possible effects of electron correlation and spin fluctuation

Using the unique characteristics of the free-electron-laser (FEL), we successfully performed high-sensitivity spectral imaging of different materials in the terahertz (THz) and far-infrared (FIR) domain. THz imaging at various wavelengths was achieved using in situ spectroscopy by means of this wavelength tunable and monochromatic source. In particular, owing to its large intensity and directionality, we could collect high-sensitivity transmission imaging of extremely low-transparency materials and three-dimensional objects in the 3&ndash, 6 THz range. By accurately identifying the intrinsic absorption wavelength of organic and inorganic materials, we succeeded in the mapping of spatial distribution of individual components. This simple imaging technique using a focusing optics and a raster scan modality has made it possible to set up and carry out fast spectral imaging experiments on different materials in this radiation facility.

We study the new details of electronic and thermoelectric properties of polycrystalline layered oxychalcogenide systems of (BiO)CuCh (Ch = Se, Te) prepared by using a solid-state reaction. The systems were characterized by using photoemission (PE) spectroscopy and four-probe temperature-dependent electrical resistivity ρ(T). PE spectra are explained by calculating the electronic properties using the generalized-gradient approximation method. PE spectra and ρ(T) show that (BiO)CuSe system is a semiconductor, while (BiO)CuTe system exhibits the metallic behavior that induces the high thermoelectric performance. The calculation of electronic properties of (BiO)CuCh (Ch = S, Se, Te) confirms that the metallic behavior of (BiO)CuTe system is mainly induced by Te 5p states at Fermi energy level, while the indirect bandgaps of 0.68 and 0.40 eV are obtained for (BiO)CuS and (BiO)CuSe systems, respectively. It is also shown that the local symmetry distortion at Cu site strongly stimulates Cu 3d-t2g to be partially...

We have revealed that anisotropic 4f charge distributions caused by the crystalline electric field are responsible for linear dichroism (LD) in 3d core-level photoemission spectra of rare earth compounds. Indeed, we have successfully observed the intrinsic LD for cubic YbB 12 and tetragonal SmCu 2 Si 2 . We have also performed polarization-dependent 4f photoemission in a valence-band region. The observed LDs in the experimental 4f spectra are reduced from those predicted from the theoretical simulations for the localized ions.

We have probed the crystalline electric-field ground states of pure $|J=7/2,{J}_{z}=\ifmmode\pm\else\textpm\fi{}5/2⟩$ as well as the anisotropic $c\text{\ensuremath{-}}f$ hybridization in both valence fluctuating systems $\ensuremath{\alpha}$- and $\ensuremath{\beta}$-${\mathrm{YbAlB}}_{4}$ by linear polarization dependence of angle-resolved core level photoemission spectroscopy. Interestingly, the small but distinct difference between $\ensuremath{\alpha}$- and $\ensuremath{\beta}$-${\mathrm{YbAlB}}_{4}$ was found in the polar angle dependence of linear dichroism, indicating the difference in the anisotropy of $c\text{\ensuremath{-}}f$ hybridization, which may be a key to understanding a heavy Fermi liquid state in $\ensuremath{\alpha}$-${\mathrm{YbAlB}}_{4}$ and a quantum critical state in $\ensuremath{\beta}$-${\mathrm{YbAlB}}_{4}$.

A linearly polarized hard X-ray photoemission system has been developed for studying the ground-state symmetry of strongly correlated materials., An angle-resolved linearly polarized hard X-ray photoemission spectroscopy (HAXPES) system has been developed to study the ground-state symmetry of strongly correlated materials. The linear polarization of the incoming X-ray beam is switched by a transmission-type phase retarder composed of two diamond (100) crystals. The best value of the degree of linear polarization was found to be −0.96, containing a vertical polarization component of 98%. A newly developed low-temperature two-axis manipulator enables easy polar and azimuthal rotations to select the detection direction of photoelectrons. The lowest temperature achieved was 9 K, offering the chance to access the ground state even for strongly correlated electron systems in cubic symmetry. A co-axial sample monitoring system with long-working-distance microscope enables the same region on the sample surface to be measured before and after rotation. Combining this sample monitoring system with a micro-focused X-ray beam by means of an ellipsoidal Kirkpatrick–Baez mirror (25 µm × 25 µm FWHM), polarized valence-band HAXPES has been performed on NiO for voltage application as resistive random access memory to demonstrate the micro-positioning technique and polarization switching.

Layered oxypnictide LaOMnAs shows an antiferromagnetic insulator-to-ferromagnetic metal transition at room temperature with increasing the defect of LaO layer which induces hole doping into the MnAs layers. In order to reveal the details of the transition, we have performed hard-X-ray photoelectron spectroscopy for the insulating LaOMnAs and metallic (LaO) 0.7 MnAs. The spectral changes in the valence band, mainly composed of Mn 3 d states, Mn 2 p core levels, and La 3 d core-levels have been observed across the transition. Our results indicated that Mn 3 d state was significantly influenced by the defect of LaO layer.

In this paper, we show the linearly polarized hard X-ray core-level photoemission spectroscopy of valence fluctuating system β-YbAlB4. Interestingly, we observed subtle but distinct linear dichroisms in Yb2+ 3d5/2 core-level spectra at several angles of β-YbAlB4. Basically linear dichroism in Yb2+ 3d5/2 core-level spectrum is not expected in the ionic picture because Yb2+ 4f orbital is fully occupied. These contradiction indicates the breakdown of ionic picture in β-YbAlB4.

We report the core-level photoemission study of cubic PrBe13, PrIr2Zn20 and PrB6 using linearly polarized hard X-ray. We have successfully observed linear dichroism (LD) in Pr3+ 3d core-level photoemission spectra reflecting the 4f ground-state symmetry for all the compounds. The observed LDs and polarization-dependent spectra are reproduced by ionic-model calculations including the full multiplet theory and the local crystalline electric field (CEF) splitting. We have confirmed that LDs in Pr3+ 3d core-level photoemission spectra are able to determine unambiguously the Pr3+ 4f ground-state symmetry.

We have probed the crystalline electric-field ground states of pure |J=7/2,J_{z}=±5/2⟩ as well as the anisotropic c-f hybridization in both valence fluctuating systems α- and β-YbAlB_{4} by linear polarization dependence of angle-resolved core level photoemission spectroscopy. Interestingly, the small but distinct difference between α- and β-YbAlB_{4} was found in the polar angle dependence of linear dichroism, indicating the difference in the anisotropy of c-f hybridization, which may be a key to understanding a heavy Fermi liquid state in α-YbAlB_{4} and a quantum critical state in β-YbAlB_{4}.

We present a detailed study on the $4f$ ground-state symmetry of the pressure-induced superconductor ${\mathrm{CeCu}}_{2}{\mathrm{Ge}}_{2}$ probed by soft x-ray absorption and hard x-ray photoemission spectroscopy. The revised Ce $4f$ ground states are determined as $|{\mathrm{\ensuremath{\Gamma}}}_{7}\ensuremath{\rangle}=\sqrt{0.45}|{J}_{z}=\ifmmode\pm\else\textpm\fi{}\frac{5}{2}\ensuremath{\rangle}\ensuremath{-}\sqrt{0.55}|\ensuremath{\mp}\frac{3}{2}\ensuremath{\rangle}$ with $\mathrm{\ensuremath{\Sigma}}$-type in-plane rotational symmetry. This gives an in-plane magnetic moment consistent with the antiferromagnetic moment as reported in neutron measurements. Since the in-plane symmetry is the same as that for the superconductor ${\mathrm{CeCu}}_{2}{\mathrm{Si}}_{2}$, we propose that the charge distribution along the $c$ axis plays an essential role in driving the system into a superconducting phase.

In order to investigate the mechanism of the formation of laser induced periodic surface structures (LIPSS), in situ observation of LIPSS formation on Si wafers under the irradiation of intense THz pulses with a center wavelength of $\sim 72 \pmb{\mu m}$ emitted from a free electron laser (THz-FEL) was performed. When the number N of the irradiated THz pulse is less than $\pmb{50\sim 70}$ , fine LIPSS with a period of $\pmb{3\sim 4\mu \mathrm{m}}$ almost parallel to the polarization of the THz pulses were observed. For $\mathrm{N} > 250$ , coarse structures with a period of $30\sim 40\mu \mathrm{m}$ emerged.

We found the irradiation of focused linearly polarized terahertz (THz)-waves emitted from THz free-electron laser (THz-FEL) engraved fine periodic stripe structures on the surfaces of single-crystal Si wafers. The experiments were performed at several wavelengths ranging from 50 to 82 μm with a macro-pulse fluence up to 32 J/cm2. The engraved structures are considered equivalent to the laser-induced periodic surface structures (LIPSS) produced by the irradiation of a femtosecond (fs)-pulsed laser in the near-infrared (NIR) region. However, the minimum period of ∼1/25 of the wavelength in the present case of THz-FEL is surely much smaller than those reported so far by use of fs-lasers and no more explicable by the so far proposed mechanisms. The finer LIPSS confirmed by longer-wavelength laser excitation by means of THz-FEL motivates investigation into the universal mechanism of LIPSS formation, which has been under a hot debate for decades.

We have investigated an insulating origin of the layered Mn oxypnictide (LaO)MnPn with half-filled Mn 3 d bands by choosing pnictogen atoms from P to Sb and introduction of hole carriers. Metallic states are found in (LaO)MnAs and (LaO)MnSb at higher hole doping.

We report experimentally observed linear dichroism in angle-resolved core-level photoemission spectra of PrIr2Zn20 and PrB6 in cubic symmetry. The different anisotropic 4f charge distributions between the compounds due to the crystalline-electric-field splitting are responsible for the difference in the linear dichroism, which has been verified by spectral simulations with the full multiplet theory for a single-site Pr3+ ion in cubic symmetry. The observed linear dichroism and polarization-dependent spectra in two different photoelectron directions for PrIr2Zn20 are reproduced by theoretical analysis for the Gamma_3 ground state, whereas those of the Pr 3d and 4d core levels indicate the Gamma_5 ground state for PrB6., 6 pages, 4 figures

We have developed a linear polarization-dependent hard X-ray photoemission (HAXPES) measurement system, by which the orbital contribution in the valence bands as well as the conduction electrons in solids can be revealed. Our experimental set up, recent progress and a few examples of the linear polarization dependence of HAXPES spectra are shown. It is also shown that the polarization dependence of the core-level spectra is fairly explained by theoretical calculations of photoelectron angular distributions for single atoms.

Photoluminescence properties of hydrothermal method-grown zinc oxide (ZnO) are evaluated in the extreme ultraviolet (EUV) region. The prominent fluorescence peak observed at 380 nm is characterized by a double exponential decay profile, where the 1.6 ns fast decay component is attributed to free excitons while the 15 ns slow decay component is assigned to trapped carriers. The response time of ZnO is improved to 70 ps by intentional iron (Fe) ion doping accomplished through the removal of the platinum lining in the growth chamber. This response time-improved ZnO will have promising applications in EUV lithography and X-ray free electron laser (XFEL) research.

Researchers report sub-angstrom fundamental-wavelength lasing at the SPring-8 Angstrom Compact Free-Electron Laser in Japan. The output has a maximum power of more than 10 GW, a pulse duration of 10−14 s and a lasing wavelength of 0.634 A.

We investigated the interaction of rare-gas clusters with intense EUV–FEL pulses in the 51–62-nm region by using the SPring-8 Compact SASE Source (SCSS) test facility in Japan. For this purpose, we developed a pulsed cluster source consisting of a solenoid-type pulsed valve and a liquid helium cryostat. The interaction of giant xenon clusters with intense FEL pulses was investigated by detecting photoions using a momentum imaging spectrometer. We observed the emission of energetic highly charged ions when xenon cluster beam (〈 N 〉 ∼ 10,000) was irradiated by intense FEL pulses of wavelength 62 nm.

We developed a method to experimentally quantify the fourth-order multipole moment of the rare-earth 4f orbital. Linear dichroism (LD) in the Er 3d5/2 core-level photoemission spectra of cubic ErCo2 was measured using bulk-sensitive hard X-ray photoemission spectroscopy. Theoretical calculation reproduced the observed LD, and the result showed that the observed result does not contradict the suggested \(\Gamma _{8}^{3}\) ground state. Theoretical calculation further showed a linear relationship between the LD size and the size of the fourth-order multipole moment of the Er3+ ion, which is proportional to the expectation value \(\langle O_{4}^{0} + 5O_{4}^{4}\rangle \), where \(O_{n}^{m}\) are the Stevens operators. These analyses indicate that the LD in 3d photoemission spectra can be used to quantify the average fourth-order multipole moment of rare-earth atoms in a cubic crystal electric field.

Single-pass free-electron lasers based on self-amplified spontaneous emission1,2,3,4 are enabling the generation of laser light at ever shorter wavelengths, including extreme ultraviolet5, soft X-rays and even hard X-rays6,7,8. A typical X-ray free-electron laser is a few kilometres in length and requires an electron-beam energy higher than 10 GeV (refs 6, 8). If such light sources are to become accessible to more researchers, a significant reduction in scale is desirable Here, we report observations of brilliant extreme-ultraviolet radiation from a 55-m-long compact self-amplified spontaneous-emission source, which combines short-period undulators with a high-quality electron source operating at a low acceleration energy of 250 MeV. The radiation power reaches saturation at wavelengths ranging from 51 to 61 nm with a maximum pulse energy of 30 µJ. The ultralow emittance (0.6π mm mrad) of the electron beam from a CeB6 thermionic cathode9 is barely degraded by a multiple-stage bunch compression system that dramatically enhances the beam current from 1 to 300 A. This achievement expands the potential for generating X-ray free-electron laser radiation with a compact 2-GeV machine. Free-electron lasers can produce powerful pulses of radiation at very short wavelengths, even in the hard-X-ray region. In general, however, they comprise facilities several kilometres in length. A 55-m-long laser could open up the technology to a broader range of researchers.

X-ray photoemission spectra of Mn 1− x Cr x Au 2 ( x = 0, 0.05, and 0.13) are presented and compared with theoretical total and partial density of state (DOS) curves. Site- and spin-decomposed partial DOS and magnetism of these materials are also discussed.

CeRh3B2 is a ferromagnet with exceptionally high Curie temperature ( T C = 115 K) among the Ce compounds with no transition metal magnetic element. Magnetic circular dichroism of soft X-ray photoabsorption (XMCD) has revealed that the orbital angular momentum of Ce 4f electron is quenched to some extent. In addition, preferential occupation of the Ce 4f orbital pointing to the c-axis has been confirmed by the soft X-ray photoabsorption measurements with different geometries. On the other hand, resonant photoemission around the Ce 3d → 4f photoabsorption edge has been adopted in order to disentangle the Ce 4f and Rh 4d components in the valence band. The Rh 4d spectrum is qualitatively consistent with the band structure calculation. Although the Ce 4f spectrum has a peak near the Fermi level, the spectral shape is qualitatively different from that of the typical Kondo materials and is rather similar to that of itinerant Ce 4f systems.

Soft and hard X-ray photoelectron spectroscopy (SX- and HAXPES) has been performed for strongly correlated transition-metal oxides and rare-earth compounds in order to reveal the bulk electronic structures and/or the bulk Fermi surfaces. The variation of the bulk V 3 d spectrum for Sr 1 - x Ca x VO 3 depending on x and the feature of the Fermi surfaces for Sr 2 - x Ca x RuO 4 is consistent with other bulk-sensitive measurements and band structure calculations, respectively. It has been demonstrated for rare-earth compounds that the application of the HAXPES enables us to obtain more reliable information on the bulk electronic structures and valences.

Accurate synchronization of pulses from an extreme ultraviolet free electron laser (EUV-FEL) and optical pulses from a Ti:sapphire laser is demonstrated. By using an indium (In)-doped zinc oxide (ZnO) crystal, pulses from these sources can be synchronized with ~ 3 -ps accuracy, an improvement of over three orders of magnitude compared to the widely-used cerium-doped yttrium aluminum garnet (Ce:YAG) scintillator. This dramatic improvement in response time will be valuable for pump-probe experiments using FEL and other ultrafast sources, and is expected to create new possibilities for time-resolved short wavelength spectroscopy.

The pulse energy of an extreme-ultraviolet free-electron laser (EUV-FEL) has been directly measured using a cryogenic radiometer installed in an experimental station. The laser provided 21.0, 18.0, and 19.5 μ J / pulse at wavelengths of 51, 55, and 61 nm, respectively. The contribution of higher harmonics was estimated by measuring the attenuation of the average pulse energy with increasing Ar gas pressure in a gas cell. The ratio of the intensity of the higher harmonics to that of the fundamental was estimated to be about 1%.

The electronic structures of rare-earth-filled skutterudites have been investigated by high-resolution photoemission spectroscopy. In order to reveal their bulk nature, the bulk-sensitive photoemission spectroscopy with soft X-ray (hv∼800 – 1100 eV) and hard X-ray (hv∼8000 eV) is a very powerful tool since the rare-earths' valence and electronic structures on the surface are often different from those in the bulk. Our experimental results clearly show the coexistence of the strongly mixed-valence state and the heavy-fermion state in SmOs4Sb12 and the quasi-particle peak near the Fermi level in PrFe4P12 induced by the hybridization between the rare-earth 4f and conduction electrons.

We have carried out soft and hard X-ray spectroscopy of Sm-based filled skutterudites SmFe 4 P 12 and SmOs 4 Sb 12 . Sm 3d–4f resonant photoemission and Sm 3d–4f X-ray absorption spectra suggest that SmOs 4 Sb 12 has much more strongly mixed Sm valence state than SmFe 4 P 12 in the bulk. On the other hand, the Sm trivalent state is dominant on the surface of SmOs 4 Sb 12 .

Ultraviolet photoelectron spectroscopy (UPS) was performed on Ni Mn based Heusler-type intermetallic compounds, including the mother material for the ferromagnetic shape memory. Although UPS is relatively surface-sensitive, it is useful to explore the compositional dependence of the electronic states. Significant changes in the band structure are found between Ni 2 MnGa and Ni 2 MnIn, that are interpreted in terms of the increase of the hybridization between the neighboring transition metal 3d states. An increase of the band filling is found in going from Ni 2 MnIn to Ni 2 MnSn, which is interpreted by the increase of the number of 5p electrons in changing from In to Sn.

We have studied electronic structures of VO 2 by soft and hard X-ray synchrotron core-level photoelectron spectroscopy. In our measurements, temperature and photon energy dependences of the V 2p core-level spectra are observed. Remarkable spectral changes are observed across the metal-insulator transition (MIT) at T = 340 K . A clear shoulder structure is observed on the lower binding energy side of the V 2 p 3 / 2 peak in the metallic phase. This shoulder structure, being stronger for larger h ν , is interpreted as the well-screened feature by bulk conduction electrons.

The electronic states of Nd 0.45 Sr 0.55 MnO 3 in the two-dimensional metal phase have been revealed by the high-resolution Mn 2 p – 3 d resonant photoemission. The vanishingly weak intensity at E F indicates an anomalous metal due to the two-dimensionality of the electronic states.

Sm-based filled skutterudites SmFe 4 P 12 and SmOs 4 Sb 12 have been investigated by soft and hard X-ray photoemission spectroscopy (PES). Bulk-sensitive Sm 3d–4f resonant PES and surface-sensitive valence-band PES spectra suggest in the bulk that SmOs 4 Sb 12 has much more strongly mixed Sm valence state than SmFe 4 P 12 . A significant Sm divalent peak in the vicinity of the Fermi level ( E F ) has been observed in SmOs 4 Sb 12 , indicating that the Sm 4f states contribute to the electronic states at E F .

Magnetic circular dichroism in the soft-X-ray absorption spectra in the Mn 2p → 3d excitation region has been measured for Nd1−xSrxMnO3 ( x = 0.40 , 0.47 , 0.50 ). Small but clear differences in XAS and MCD spectra are found with respect to x compositions. We will discuss the total moment estimated from both XAS–MCD spectra and magnetization measurement.

Physical review / B 89(12), 121111 (2014). doi:10.1103/PhysRevB.89.121111, We present genuine bulk Ir 5d jeff states of layered perovskite iridates obtained by hard-x-ray photoemissionspectroscopy (HAXPES) with s- and p-polarized lights. HAXPES spectra of Sr2 IrO4 and Ba2 IrO4 are wellreproduced by the quasiparticle density of states calculated by the local density approximation with dynamical mean-field theory (LDA + DMFT). It is demonstrated that the insulating nature of the iridates is triggered by antiferromagnetic correlation (Slater type) combined with electron correlation (Mott type). The extremely-low-energy bulk-sensitive photoemission spectroscopy reveals “bad metallic” states in the paramagnetic phase of the iridates, suggesting strongly renormalized metallic states above the Neel temperature as predicted by the LDA + DMFT., Published by APS, College Park, Md.

Bulk-sensitive hard x-ray photoemission spectroscopy (HAXPES) reveals for as-grown epitaxial films of half-metallic ferromagnetic CrO2(100) a pronounced screening feature in the Cr 2p3/2 core level and an asymmetry in the O 1s core level. This gives evidence of a finite, metal-type Fermi edge, which is surprisingly not observed in HAXPES. A spectral weight shift in HAXPES away from the Fermi energy is attributed to single-ion recoil effects due to high energy photoelectrons. In conjunction with inverse PES the intrinsic correlated Mott-Hubbard-type electronic structure is unravelled, yielding an averaged Coulomb correlation energy Uav ~ 3.2 eV., Comment: Manuscript 12 pages, 4 figures; Supplemental material 7 pages, 5 figures

We carried out time-of-flight mass spectrometry for neon clusters that were exposed to intense free electron laser pulses with the wavelength of 62 nm, which induce optical transition from the ground state (2s 2 2p 6 ) to an excited state (2s 2 2p 5 nl ) in the Ne atoms. In contrast to Ne + ions produced by two-photon absorption from isolated Ne atoms, the Ne + ion yield from Ne clusters shows a linear dependence on the laser intensity (I). We discuss the ionization mechanisms which give the linear behaviour with respect to I and expected features in the electron emission spectrum. (Some figures may appear in colour only in the online journal)

Hard and soft x-ray photoelectron spectroscopy was performed for core and valence electrons in V${}_{3}$Si. The recoil effects on the photoelectron emission were observed not only in the case of the Si 2$p$ core level, but also for the valence band, although such effects were not observed for the V 2$p$ and V 3$p$ core levels. The valence-band results are compared with the results of the theoretical model calculation based on the tight-binding cluster approximation and harmonic approximation for lattice vibrations. The Si 2$p$ core-level results interpreted as due to the single nucleus recoil effects are consistent with the interpretation of those of the valence electrons calculated on these approximations. From the ${E}_{\mathrm{B}}$ dependence of the valence-band recoil shifts, useful information is obtained on the Si 3$p$ partial density of states near the Fermi level.

UBe13 is a typical heavy-fermion superconductor compound. The energy band structure and the Fermi surface for UBe13 are calculated by the relativistic linear APW method. The Fermi surface is found to consist of two hole sheets and one electron sheet. These sheets of the Fermi surface are all small in size and closed in topology. The generalized gradient approximation is also applied to the energy-band calculation of UBe13. These results are compared with those of the conventional LDA calculation.

The metal-insulator (MI) transition in LiV${}_{2}$O${}_{4}$ has been studied by optical measurements in infrared regions at low temperatures and under high pressures. At 40 K, the metal phase under ambient pressure changes gradually into the insulating state under pressures above 7 GPa, where the newly opened $2\ensuremath{\Delta}$ gap is estimated to be $\ensuremath{\sim}$0.4 eV. At pressures higher than 8 GPa, the precursor of the structural phase transition is observed as a redshift of the transverse optical phonon peak in the far-infrared (FIR) region with decreasing temperatures. The behavior of this pressure-induced MI transition is observed not only at low temperatures but also at room temperature. At 300 K, a decrease in conduction carriers with pressure is also detected as a gradual suppression in the Drude response of the FIR region below 0.1 eV, with a ten- to 20-fold decrease in the optical conductivity. Extensive investigation of the optical response revealed a successive transformation of the electronic state in a region between the metal and the insulator phases in the pressure-temperature phase diagram. The redshift is only observed near the boundary to the insulator phase (boundary 2), where a complete homogeneous structural change appears to occur. On the contrary, an inhomogeneous structural change is realized in the intermediate phase between the metal and insulator phases, between boundaries 1 and 2, accompanied by a topographic localization or a short-range alternation of the valence.

An accident in a nuclear power plant, which can be caused by an unpredictable event such as an explosion, fire, and earthquake, has severe and far-reaching consequences. Therefore, it is crucial to carefully and constantly monitor the plant and precisely detect any radiation source. Radiation contamination in laboratories and in the environment due to nuclear fallout is among the issues that require an immediate solution. Radiation detection has become increasingly important because of the increasing number of nuclear power plants that have been established to replace conventional power plants, as part of the effort to suppress carbon dioxide emission. For these purposes, this chapter will discuss the principle and method of mapping flying radiations. Visual mapping of intensity and direction of