The interplay of Kondo screening and magnetic ordering in strongly correlated materials containing local moments is a subtle problem. Usually the number of conduction electrons per unit cell matches or exceeds the number of moments, and a Kondo-screened heavy Fermi liquid develops at low temperatures. Changing the pressure, magnetic field, or chemical doping can displace this heavy Fermi liquid in favor of a magnetically ordered state. Alternatively, Kondo singlet formation can be suppressed when the number of conduction electrons is small compared to the number of magnetic moments, known as the Kondo exhaustion scenario. Here we report the discovery of such an "exhausted" Kondo lattice material, YbIr3Si7, where the bulk electrical conductivity tends to zero in the antiferromagnetic state below the Neel temperature TN = 4.1 K, as all the free carriers are consumed in the formation of Kondo singlets. By contrast, the surface is conducting, as the Yb3+ ions relax into larger nonmagnetic Yb2+ in the presence of reduced chemical pressure, which shifts the chemical potential.

We study the high Curie temperature ferromagnet (${\mathrm{Cr}}_{0.35}{\mathrm{Sb}}_{0.65}{)}_{2}\mathrm{Te}{}_{3}$ (${T}_{C}=192\phantom{\rule{0.16em}{0ex}}\mathrm{K}$), using $T$-dependent x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and angle-resolved photoemission spectroscopy (ARPES). The $T$-dependent (25--220 K) XAS-XMCD evolution of $\mathrm{Cr}\phantom{\rule{0.16em}{0ex}}3d$ and $\mathrm{Te}\phantom{\rule{0.16em}{0ex}}5p$ unoccupied site- and orbital-projected states shows a systematic modification, which we interpret as due to spin-splitting below $T{}_{C}$. The $T$-dependent XMCD intensity and leading-edge spin-sensitive shifts ${\ensuremath{\gamma}}_{\text{expt}}(T)$ follow bulk magnetization. ARPES measurements with $h\ensuremath{\nu}=78\phantom{\rule{4pt}{0ex}}\mathrm{eV}$ show a metallic state with Sb $5p$ band dispersions at and near Fermi level (${E}_{F}$), consistent with bulk band-structure calculations for ${({\mathrm{Cr}}_{0.33}{\mathrm{Sb}}_{0.67})}_{2}\mathrm{Te}{}_{3}$. However, surface-sensitive ARPES with $h\ensuremath{\nu}=8.4\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ above and below $T{}_{C}$ show linear band dispersions just below ${E}_{F}$, suggesting a remnant of Dirac-type dispersions. Assuming the linear dispersion survives above ${E}_{F}$, it implies a topologically trivial ferromagnet as the estimated Dirac point energy lies above the largest ${\ensuremath{\gamma}}_{\text{expt}}\phantom{\rule{4pt}{0ex}}(T=25\phantom{\rule{0.16em}{0ex}}\mathrm{K})$. The $\mathrm{Cr}\phantom{\rule{0.16em}{0ex}}3d$ XAS-XMCD spectra can be simulated by charge transfer multiplet cluster model calculations with an exchange field ${H}_{\text{ex}}$ which quantitatively reproduces the experimental XMCD. At $T=25\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, the required exchange field ${H}_{\text{ex}}$ of $\ensuremath{\sim}48\phantom{\rule{0.16em}{0ex}}\mathrm{T}$ corresponds to a Zeeman energy $\ensuremath{\zeta}=2.8\phantom{\rule{0.16em}{0ex}}\mathrm{meV}\phantom{\rule{0.16em}{0ex}}<\phantom{\rule{4pt}{0ex}}{T}_{C}=192\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ (= 16.5 meV) $\ensuremath{\ll}{\ensuremath{\gamma}}_{\text{expt}}\ensuremath{\sim}140\phantom{\rule{0.16em}{0ex}}\mathrm{meV}$. The results indicate the role of $\mathrm{Cr}\phantom{\rule{0.16em}{0ex}}3d$ exchange interactions in causing spin-sensitive shifts in $\mathrm{Cr}\phantom{\rule{0.16em}{0ex}}3d$ states, and inducing comparable spin-sensitive shifts via hybridization in $\mathrm{Te}\phantom{\rule{0.16em}{0ex}}5p$ states of ${({\mathrm{Cr}}_{0.35}{\mathrm{Sb}}_{0.65})}_{2}\mathrm{Te}{}_{3}$.

We report on a PET system that has been recently completed after the last several years of development work. The PET system is a sub-component of PET/EPR hybrid imaging system for investigating tumor hypoxia in small animal, and will be deployed to replace the current PET subsystem of the PET/EPR imager. The new PET system possesses several superior features over the existing system for small animal imaging: the axial field-of-view is increased 4 times from $\sim 25$ mm to $\sim 106 \mathrm{~mm}$, and constituent scintillator pixel size is reduced from 3.0 mm to 1.0 mm to achieve sub-millimeter image resolution. The PET system is modularized and built by using 14 detector modules (DM). Each DM consists of 8 detector units (DU) in a row, and each DU in turn is a 12 x 12 array of $1 \mathrm{x} 1 \mathrm{x} 10 \mathrm{~mm}^{3}$ LYSO crystals coupled to a Hamamastu 14161-3050HS-04 MPPC array. The PET system employs a new signal readout method to efficiently handle a greatly increased number of detector outputs by combining a conventional resistive network (RN) and a strip-line (SL) method. Due to the highly multiplexing feature of the readout, each DM generates the total of 6 outputs only (2 SLs and 4 RNs) for digitization. After the evaluation test, BASP-10011 readout board (Brightonix Imaging, Korea) was adopted for high throughput and performance data acquisition needed for routine animal imaging studies, and was incorporated into the PET system. Following successful development and integration of all components, we started to conduct phantom imaging for performance evaluation of the PET system before installing it inside the EPR magnets. $\mathrm{A}^{22} \mathrm{Na}$ point source image shows 0.8 mm FWHM resolution in both transverse and axial direction. Image of a NEMA image quality phantom was acquired to assess the imaging performance of the PET system. We present the completed PET system and initial results on phantom imaging. More thorough performance results from on-going systematic evaluation will be reported at the conference.

We study the high Curie temperature ferromagnet (Cr0.35Sb0.65)2Te 3 (TC=192 K ), using T -dependent x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and angle-resolved photoemission spectroscopy (ARPES). The T -dependent (25-220 K) XAS-XMCD evolution of Cr 3 d and Te 5 p unoccupied site- and orbital-projected states shows a systematic modification, which we interpret as due to spin-splitting below T C . The T -dependent XMCD intensity and leading-edge spin-sensitive shifts gammaexpt(T ) follow bulk magnetization. ARPES measurements with h nu =78 eV show a metallic state with Sb 5 p band dispersions at and near Fermi level (EF), consistent with bulk band-structure calculations for (Cr0.33Sb0.67)2Te 3 . However, surface-sensitive ARPES with h nu =8.4 eV above and below T C show linear band dispersions just below EF, suggesting a remnant of Dirac-type dispersions. Assuming the linear dispersion survives above EF, it implies a topologically trivial ferromagnet as the estimated Dirac point energy lies above the largest gammaexpt(T =25 K ) . The Cr 3 d XAS-XMCD spectra can be simulated by charge transfer multiplet cluster model calculations with an exchange field Hex which quantitatively reproduces the experimental XMCD. At T =25 K , the required exchange field Hex of similar to 48 T corresponds to a Zeeman energy zeta =2.8 meV C=192 K (= 16.5 meV) <exptsimilar to 140 meV . The results indicate the role of Cr 3 d exchange interactions in causing spin-sensitive shifts in Cr 3 d states, and inducing comparable spin-sensitive shifts via hybridization in Te 5 p states of (Cr0.35Sb0.65)2Te 3 .

Previously, we reported a PET/EPR hybrid imaging system aiming to study and improve the efficacy of PET hypoxic tumor imaging using EPR oxygen imaging as a ground truth. Encouraged by the successful results with this exploratory system, we launched a PET subsystem development for the next generation PET/EPR scanner that has more suitable features for small animal imaging. The distinctive features of the new PET system include an ~4 times larger axial field-of-view (~106 mm) to allow whole body imaging of rodents, and a potentially sub-millimeter resolution by use of ~1 mm width LYSO scintillators. We devised a new signal multiplexing method to efficiently handle the significantly increased number of silicon photomultiplier outputs of this new system. The design of the detector module (DM) of the system has undergone several iterations. In the final design, the DM consists of 8 detector units (DU) on a 175mm x 20 mm printed circuit board, and each DU is made of a 12x12 LYSO crystals (1x1x10 mm 3 ) coupled to a Hamamatsu 14161-3050HS-04 MPPC array (4x4 3.2 mm pitch). The new signal multiplexing method produces only 6 outputs for each DM: two outputs for coincidence time and DU identification, and four outputs for pixel crystal identification within a DU. Fourteen (14) DMs have been developed and successfully assembled into a PET ring whose inner and outer diameters are 60 mm and 115 mm, respectively. Evaluation tests were conducted by using a Brightonix BASP-10011 data acquisition board that provides high-throughput 16 12-bit 80 MSPS analog-to-digital converter (ADC) and 16 time-to-digital converter (TDC) channels. The initial results indicate that when using the BASP-10011 resulting DM performance properties were as good as those obtained by using the CAEN 5742 waveform sampler operating at 0.7 GSPS. At the meeting, we will present the development of the PET system employing the BASP-10011 DAQ and its performance measurement result.

Corundum oxide Ti2O3 shows the metal-insulator transition around 400-600 K accompanying the nearest Ti3+-Ti3+ bond (a1ga1g singlet state) formation along the c axis. In order to clarify the hole-doping effect for the a1ga1g singlet bond in Ti2O3, we investigated Ti 3d orbital anisotropy between corundum-type Ti2O3 and ilmenite-type MgTiO3 using linear dichroism of soft x-ray absorption spectroscopy of the Ti L2,3 edge. From the linear dichroic spectral weight in MgyTi2-yO3, we confirmed that the a1ga1g state is dominant not only in y = 0.01 (almost Ti2O3), but also in y = 0.29, indicating that the Ti-Ti bond survives against a certain level of hole doping. In y = 0.63 corresponding to 46% hole doping per Ti, the 3d orbital symmetry changes from a1g to e pi g.

We present a comprehensive study of CaCu$_3$Ru$_4$O$_{12}$ using bulk sensitive hard and soft x-ray spectroscopy combined with local-density approximation (LDA) + dynamical mean-field theory (DMFT) calculations. Correlation effects on both the Cu and Ru ions can be observed. From the Cu $2p$ core level spectra we deduce the presence of magnetic Cu$^{2+}$ ions hybridized with a reservoir of itinerant electrons. The strong photon energy dependence of the valence band allows us to disentangle the Ru, Cu, and O contributions and thus to optimize the DMFT calculations. The calculated spin and charge susceptibilities show that the transition metal oxide CaCu$_3$Ru$_4$O$_{12}$ must be classified as a Kondo system and that the Kondo temperature is in the range of 500-1000 K.

Electron quasiparticles play a crucial role in simplifying the description of many-body physics in solids with surprising success. Conventional Landau's Fermi-liquid and quasiparticle theories for high-temperature superconducting cuprates have, however, received skepticism from various angles. A path-breaking framework of electron fractionalization has been established to replace the Fermi-liquid theory for systems that show the fractional quantum Hall effect and the Mott insulating phenomena; whether it captures the essential physics of the pseudogap and superconducting phases of cuprates is still an open issue. Here, we show that excitonic excitation of optimally doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ with energy far above the superconducting-gap energy scale, about 1 eV or even higher, is unusually enhanced by the onset of superconductivity. Our finding proves the involvement of such high-energy excitons in superconductivity. Therefore, the observed enhancement in the spectral weight of excitons imposes a crucial constraint on theories for the pseudogap and superconducting mechanisms. A simple two-component fermion model which embodies electron fractionalization in the pseudogap state well explains the change, pointing toward a novel route for understanding the electronic structure of superconducting cuprates.

The superconductivity of cuprates, which has been a mystery ever since its discovery decades ago, is created through doping electrons or holes into a Mott insulator. There, however, exists an inherent electron-hole asymmetry in cuprates. The layered crystal structures of cuprates enable collective charge excitations fundamentally different from those of three-dimensional metals, i.e., acoustic plasmons. Acoustic plasmons have been recently observed in electron-doped cuprates by resonant inelastic X-ray scattering (RIXS); in contrast, there is no evidence for acoustic plasmons in hole-doped cuprates, despite extensive measurements. This contrast led us to investigate whether the doped holes in cuprates La_2-xSr_xCuO_4 are conducting carriers or are too incoherent to induce collective charge excitation. Here we present momentum-resolved RIXS measurements and calculations of collective charge response via the loss function to reconcile the aforementioned issues. Our results provide unprecedented spectroscopic evidence for the acoustic plasmons and long sought conducting p holes in hole-doped cuprates.

In this work, we systematically report the synthesis, structure, and magnetism of a compound of filled anti-Mn3Si5 type La3MnAs5. It crystallizes in a hexagonal structure with the space group of P63/mcm (193). The structure consists of face-sharing MnAs6 octahedral chains along the c axis, which are well separated by a large distance of 8.9913 angstrom, demonstrating a strong one-dimensional (1D) structural character. Physical property measurements indicate that La3MnAs5 is a ferromagnetic metal with TC similar to 112 K. Due to the short-range intrachain spin coupling, the susceptibility deviates from the Curie-Weiss behavior in a wide temperature window and the magnetic entropy corresponding to the ferromagnetic transition is significantly lower than that expected from the fully saturated state. The magnetic critical behavior studies show that La3MnAs5 can be described by the three-dimensional Heisenberg model. The orbital hybridization between the 1D MnAs6 chain and intermediate La atom near the Fermi level reveals that the itinerant electrons play a key role in transmitting spin interaction among the MnAs6 spin chains. Our results indicate that La3MnAs5 is a rare ferromagnetic metal with well-separated spin chains, which provides a good opportunity to study the mechanism of interchain spin coupling via itinerant electrons.

Resonant inelastic x-ray scattering (RIXS) studies across the Ce M-5 edge have been carried out to investigate the electronic structure of the ferromagnetic CeAgSb2 Kondo system. The RIXS spectra exhibit energy loss features corresponding to final states usually observed by combining photoemission and inverse photoemission spectroscopy. At low energy loss, a clear signature of the spectral features corresponding to the spin-orbit interaction is also observed. Polarization dependence provides evidence for the S-1(0) symmetry singlet ground state by a total suppression of the f(0) final state. A simplified single-impurity Anderson model combined with full multiplet theory allows an accurate description of the spin-charge excitations. The RIXS data also reveal a strong temperature T dependence of the fluorescencelike structure. We conjecture that this behavior reflects the T dependence of the Kondo resonance.

We present X-ray spectroscopic evidence for the evolution of valence-specific spin states and tetragonal distortions in single-layer cobaltates. Measurements of Co $L_3$-edge resonant inelastic X-ray scattering reveal the $t_{2g}$ electronic structure of Co for hole-doped La$_{2-x}$Sr$_x$CoO$_4$ ($x$ = 0.5, 0.7 and 0.8). As the Sr-doping $x$ increases, the tetragonal splitting of the $t_{2g}$ states of high-spin Co$^{2+}$ decreases, whereas that of low-spin Co$^{3+}$ increases and the fraction of high-spin Co$^{3+}$ increases. The results enable us to clarify the origin of the change of magnetic anisotropy and in-plane resistivity in a mixed-valence cobaltate caused by the interplay of spin-orbit coupling and tetragonal distortion.

ReO${}_{3}$ is a remarkable transition metal oxide in that it has the highest conductivity of all oxides, comparable even with that of silver. Using state of the art bulk-sensitive angle-resolved photoelectron spectroscopy, the authors are able to observe clear dispersions of the Re 5$d$ and O 2$p$ derived bands as well as the momentum splitting of the Fermi surface due to the Re 5$d$ spin-orbit interaction. The experimental results are compared quantitatively to density functional theory band structure calculations, thereby providing a deeper understanding of the material class of the 5$d$ oxides.

Herein we show that nonresonant inelastic x-ray scattering involving an s core level is a powerful spectroscopic method to characterize the excited states of transition metal compounds. The spherical charge distribution of the s core hole allows the orientational dependence of the intensities of the various spectral features to produce a spatial charge image of the associated multiplet states in a straightforward manner, thereby facilitating the identification of their orbital character. In addition, the s core hole does not add an extra orbital angular momentum component to the multiplet structure so that the well-established Sugano-Tanabe-Kamimura diagrams can be used for the analysis of the spectra. For α-MnS we observe the spherical charge density corresponding to its high-spin 3d^{5} (^{6}A_{1}) ground state configuration and we were able to selectively image its excited states and identify them as t_{2g} (^{5}T_{2}) and e_{g} (^{5}E) with an energy splitting 10Dq of 0.78 eV.

We report on the development of a high-resolution and highly efficient beamline for soft X-ray resonant inelastic X-ray scattering (RIXS) located at the Taiwan Photon Source. This beamline adopts an optical design that uses an active grating monochromator (AGM) and an active grating spectrometer (AGS) to implement the energy compensation principle of grating dispersion. Active gratings are utilized to diminish defocus, coma and higher-order aberrations, as well as to decrease the slope errors caused by thermal deformation and optical polishing. The AGS is mounted on a rotatable granite platform to enable momentum-resolved RIXS measurements with scattering angles over a wide range. Several high-precision instruments developed in-house for this beamline are described briefly. The best energy resolution obtained from this AGM–AGS beamline was 12.4 meV at 530 eV, achieving a resolving power of 4.2 × 10 4 , while the bandwidth of the incident soft X-rays was kept at 0.5 eV. To demonstrate the scientific impact of high-resolution RIXS, we present an example of momentum-resolved RIXS measurements on a high-temperature superconducting cuprate, i.e. La 2– x Sr x CuO 4 . The measurements reveal the A 1 g buckling phonons in superconducting cuprates, opening a new opportunity to investigate the coupling between these phonons and charge-density waves.

Quantum phase transitions play an important role in shaping the phase diagram of high-temperature cuprate superconductors. These cuprates possess intertwined orders which interact strongly with superconductivity. However, the evidence for the quantum critical point associated with the charge order in the superconducting phase remains elusive. Here, we reveal the short-range charge orders and the spectral signature of the quantum fluctuations in La2-xSrxCuO4 (LSCO) near the optimal doping using highresolution resonant inelastic x-ray scattering. On performing calculations through a diagrammatic framework, we discover that the charge correlations significantly soften several branches of phonons. These results elucidate the role of charge order in the LSCO compound, providing evidence for quantum critical scaling and discommensurations associated with charge order.

Precise quantitative delineation of tumor hypoxia is essential in radiation therapy treatment planning to improve the treatment efficacy by targeting hypoxic sub-volumes. We developed a combined imaging system of positron emission tomography (PET) and electron para-magnetic resonance imaging (EPRI) of molecular oxygen to investigate the accuracy of PET imaging in assessing tumor hypoxia. The PET/EPRI combined imaging system aims to use EPRI to precisely measure the oxygen partial pressure in tissues. This will evaluate the validity of PET hypoxic tumor imaging by (near) simultaneously acquired EPRI as ground truth. The combined imaging system was constructed by integrating a small animal PET scanner (inner ring diameter 62 mm and axial field of view 25.6 mm) and an EPRI subsystem (field strength 25 mT and resonant frequency 700 MHz). The compatibility between the PET and EPRI subsystems were tested with both phantom and animal imaging. Hypoxic imaging on a tumor mouse model using $^{18}$F-fluoromisonidazole radio-tracer was conducted with the developed PET/EPRI system. We report the development and initial imaging results obtained from the PET/EPRI combined imaging system.

We present the development of a PET insert system for potential simultaneous PET/MR imaging using a 9.4 T small animal MRI scanner to test our system. The detectors of the system adopt a strip-line based multiplexing readout method for SiPM signals. In this readout, multiple SiPM outputs in a row share a common strip-line. The position information about a hit SiPM is encoded in the propagation time difference of the signals arriving at the two ends of the strip-line. The use of strip-lines allows us to place the data acquisition electronics remotely from the detector module to greatly simplify the design of the detector module and minimize the mutual electromagnetic interference. The prototype is comprised of 14 detector modules, each of which consists of an 8x4 LYSO scintillator array (each LYSO crystal is 3x3x10 mm(3)) coupled to two units of Hamamatsu MPPC arrays (4x4, 3.2 mm pitch) that are mounted on a strip-line board. On the strip-line board, outputs of the 32 SiPMs are routed to 2 strip-lines so that 16 SiPM signals share a strip-line. The detector modules are installed inside a plastic cylindrical supporting structure with an inner and outer diameter of 60 mm and 115 mm, respectively, to fit inside a Bruker BioSpec 9.4 T MR scanner. The axial field of view of the prototype is 25.4 mm. The strip-lines were extended by using 5-meter cables to a sampling data acquisition (DAQ) board placed outside the magnet. The detectors were not shielded in the interest of investigating how they may affect and be affected by the MRI. Experimental tests were conducted to evaluate detection performance, and phantom and animal imaging were carried out to assess the spatial resolution and the MR compatibility of the PET insert. Initial results are encouraging and demonstrate that the prototype insert PET can potentially be used for PET/MR imaging if appropriate shielding will be implemented for minimizing the mutual interference between the PET and MRI systems.

We report our study about the growth and characterization of Bi2Te3 thin films on top of Y3Fe5O12 (111), Tm3Fe5O12 (111), Fe3O4 (111), and Fe3O4 (100) single-crystal substrates. Using molecular-beam epitaxy, we were able to prepare the topological insulator/ferromagnetic insulator heterostructures with no or minimal chemical reaction at the interface. We observed the anomalous Hall effect on these heterostructures and also a suppression of the weak antilocalization in the magnetoresistance, indicating a topological surface-state gap opening induced by the magnetic proximity effect. However, we did not observe any obvious x-ray magnetic circular dichroism (XMCD) on the Te M-45 edges. The results suggest that the ferromagnetism induced by the magnetic proximity effect via van der Waals bonding in Bi2Te3 is too weak to be detected by XMCD, but still can be observed by electrical transport measurements. This is in fact not inconsistent with reported density-functional calculations on the size of the gap opening.

We have successfully grown centimeter-sized layered $R$SrNiO$_4$ single crystals under high oxygen pressures of 120 bar by the floating zone technique. This enabled us to perform neutron scattering experiments where we observe close to quarter-integer magnetic peaks below $\sim$77 K that are accompanied by steep upwards dispersing spin excitations. Within the high-frequency Ni-O bond stretching phonon dispersion, a softening at the propagation vector for a checkerboard modulation can be observed. Together with our spin wave simulations these observations reveal that this Ni$^{3+}$ system exhibits charge disproportionation with charges segregating into a checkerboard pattern within a nano phase separation scenario rather than showing a Jahn-Teller effect.