Possible High T_{c} Superconductivity in La_{3}Ni_{2}O_{7} under High Pressure through Manifestation of a Nearly Half-Filled Bilayer Hubbard Model.

Inspired by a recent experiment showing that La_{3}Ni_{2}O_{7} exhibits high T_{c} superconductivity under high pressure, we theoretically revisit the possibility of superconductivity in this material. We find that superconductivity can take place, which is somewhat similar to that of the bilayer Hubbard model consisting of the Ni 3d_{3z^{2}-r^{2}} orbitals. Although the coupling with the 3d_{x^{2}-y^{2}} orbitals degrades superconductivity, T_{c} can still be high enough to understand the experiment thanks to the very high T_{c} reached in the bilayer Hubbard model.

Topochemical Synthesis of Ca3 CrN3 H Involving a Rotational Structural Transformation for Catalytic Ammonia Synthesis.

Topochemical reactions have led to great progress in the discovery of new metastable compounds with novel chemical and physical properties. With these reactions, the overall crystal structure of the host material is generally maintained. Here we report a topochemical synthesis of a hexagonal nitride hydride, h-Ca3 CrN3 H, by heating an orthorhombic nitride, o-Ca3 CrN3 , under hydrogen at 673 K, accompanied by a rotational structural transformation. The hydrogen intercalation modifies the Ca-N rock-salt-like atomic packing in o-Ca3 CrN3 to a face-sharing octahedral chain in h-Ca3 CrN3 H, mimicking a "hinged tessellation" movement. In addition, the h-Ca3 CrN3 H exhibited stable ammonia synthesis activity when used as a catalyst.

High-Pressure and High-Temperature Synthesis of Anion-Disordered Vanadium Perovskite Oxyhydrides.

Crystallographic order-disorder phenomena in solid state compounds are of fundamental interest due to intimate relationship between the structure and properties. Here, by using high-pressure and high-temperature synthesis, we obtained vanadium perovskite oxyhydrides Sr1-xNaxVO3-yHy (x = 0, 0.05, 0.1, 0.2) with an anion-disordered structure, which is different from anion-ordered SrVO2H synthesized by topochemical reduction. High-pressure and high-temperature synthesis from nominal composition SrVO2H yielded the anion-disordered perovskite SrVO3-yHy (y ∼ 0.4) with a significant amount of byproducts, while Na substitution resulted in the almost pure anion-disordered perovskite Sr1-xNaxVO3-yHy with an increased amount of hydride anion (y ∼ 0.7 for x = 0.2). The obtained disordered phases for x = 0.1 and 0.2 are paramagnetic with almost temperature-independent electronic conductivity, whereas anion-ordered SrVO2H is an antiferromagnetic insulator. Although we obtained the anion-disordered perovskite under high pressure, a first-principles calculation revealed that the application of pressure stabilizes the ordered phase due to a reduced volume in the ordered structure, suggesting that a further increase of the pressure or reduction of the reaction temperature leads to the anion ordering. This study shows that anion ordering in oxyhydrides can be controlled by changing synthetic pressure and temperature.

Model Construction and a Possibility of Cupratelike Pairing in a New d

Effective models are constructed for a newly discovered superconductor (Nd,Sr)NiO_{2}, which has been considered as a possible nickelate analog of the cuprates. Estimation of the effective interaction, which turns out to require a multiorbital model that takes account of all the orbitals involved on the Fermi surface, shows that the effective interactions are significantly larger than in the cuprates. A fluctuation exchange study suggests occurrence of d_{x^{2}-y^{2}}-wave superconductivity, where the transition temperature should be lowered from the cuprates due to the larger interaction.

Epitaxial Stabilization of SrCu3O4 with Infinite Cu3/2O2 Layers.

We report the epitaxial thin-film synthesis of SrCu3O4 with infinitely stacked Cu3O4 layers composed of edge-sharing CuO4 square planes, using molecular-beam epitaxy. Experimental and theoretical characterizations showed that this material is a metastable phase that can exist by applying tensile biaxial strain from the (001)-SrTiO3 substrate. SrCu3O4 shows an insulating electrical resistivity in accordance with the Cu2+ valence state revealed by X-ray photoelectron spectroscopy. First-principles calculations also indicated that the unoccupied d3z2-r2 band becomes substantially stabilized owing to the absence of apical anions, in contrast to A2Cu3O4Cl2 (A = Sr, Ba) with an A2Cl2 block layer and therefore a trans-CuO4Cl2 octahedron. These results suggest that SrCu3O4 is a suitable parent material for electron-doped superconductivity based on the Cu3O4 plane.

Thermoelectric Properties of (Ba,K)Zn2As2 Crystallized in the ThCr2Si2-type Structure.

The compound Ba1-xKxZn2As2 has a low-temperature phase (α-phase) crystallized in the α-BaCu2S2-type structure and a high-temperature phase (ß-phase) crystallized in the ThCr2Si2-type structure. We successfully obtained the ß-phase at room temperature as a metastable state by quenching from above the structural phase transition. This allowed us to determine the thermoelectric properties of the ß-phase from room to high temperature in the range of 0.00 ≤ x ≤ 0.10. The lattice thermal conductivity is quite low, with a value less than 1 W/mK at 773 K, independent of x. The effective suppression may be due to lattice instability in the underdoped region and to randomness in the overdoped region. The maximum dimensionless figure-of-merit ZT was 0.30 at 773 K for x = 0.03 with the power factor of 0.61 mW/mK2, which is relatively high for a ThCr2Si2-type structure. The results demonstrate the effectiveness of quenching for obtaining a low lattice thermal conductivity, thus providing a new method for attaining high thermoelectric performance.

Thermoelectric Properties and Electronic Structures of CuTi2S4 Thiospinel and Its Derivatives: Structural Design for Spinel-Related Thermoelectric Materials.

We report the preparations, thermoelectric and magnetic properties, and electronic structures of Cu-Ti-S systems, namely, cubic thiospinel c-Cu1- xTi2S4 ( x ≤ 0.375), a derivative cubic and Ti-rich phase c-Cu1- xTi2.25S4 ( x = 0.5, 0.625), and a rhombohedral phase r-CuTi2S4. All samples have the target compositions except for r-CuTi2S4, whose actual composition is Cu1.14Ti1.80S4. All of the phases have n-type metallic character and exhibit Pauli paramagnetism, as proven by experiments and first-principles calculations. The Cu and Ti deficiencies in c-Cu1- xTi2S4 and r-CuTi2S4, respectively, decrease the electron-carrier concentration, whereas the "excess" of Ti ions in c-Cu1- xTi2.25S4 largely increases it. For r-CuTi2S4, the reduced carrier concentration increases the electrical resistivity and Seebeck coefficient, leading to the highest thermoelectric power factor of 0.5 mW K-2 m-1 at 670 K. For all of the Cu-Ti-S phases, the thermal conductivity at 670 K is 3.5-5 W K-1 m-1, where the lattice part of the conductivity is as low as 1 W K-1 m-1 at 670 K. As a result, r-CuTi2S4 shows the highest dimensionless thermoelectric figure of merit ZT of 0.2. The present systematic study on the Cu-Ti-S systems provides insights into the structural design of thermoelectric materials based on Cu-M-S (M = transition-metal elements).

Model of the electronic structure of electron-doped iron-based superconductors: evidence for enhanced spin fluctuations by diagonal electron hopping.

We present a theoretical understanding of the superconducting phase diagram of the electron-doped iron pnictides. We show that, besides the Fermi surface nesting, a peculiar motion of electrons, where the next nearest neighbor (diagonal) hoppings between iron sites dominate over the nearest neighbor ones, plays an important role in the enhancement of the spin fluctuation and thus superconductivity. In the highest T(c) materials, the crossover between the Fermi surface nesting and this "prioritized diagonal motion" regime occurs smoothly with doping, while in relatively low T(c) materials, the two regimes are separated and therefore results in a double dome T(c) phase diagram.

Rb(Zn,Cu)4As3 as a New High-Efficiency Thermoelectric Material.

The thermoelectric performance of RbZn4-xCuxAs3 crystallized in the KCu4S3-type structure was investigated. Samples were synthesized via solid-state reactions, followed by hot pressing. Hole carriers were doped by substituting Zn with Cu until x = 0.02, resulting in an increase of the power factor from 0.049 to 0.52 mW/mK2 at T = 797 K. The lattice thermal conductivity was substantially low, with a value of 1.61 W/mK at T = 312 K, independent of doping. This can be attributed to the large vibration of the Rb atoms, as demonstrated by the neutron diffraction analysis. The maximum dimensionless figure of merit, ZT, was 0.53 at T = 797 K, representing the highest value for the 143-Zintl compounds. The result indicated that the 143-Zintl compounds could be a new class of high-performance thermoelectric materials.

Effect of region-wide use of prehospital stroke triage scale on management of patients with acute stroke.

BACKGROUND: Prehospital stroke triage scales help with the decision to transport patients with suspected stroke to suitable hospitals. OBJECTIVE: To explore the effect of the region-wide use of the Japan Urgent Stroke Triage (JUST) score, which can predict several types of stroke: large vessel occlusion (LVO), intracranial hemorrhage (ICH), subarachnoid hemorrhage (SAH), and cerebral infarction other than LVO (CI). METHODS: We implemented the JUST score and conducted a retrospective and prospective multicenter cohort study at 13 centers in Hiroshima from April 1, 2018, to March 31, 2020. We investigated the success rate of the first request to the hospital, on-scene time, and transport time to hospital. We evaluated the door-to-puncture time, puncture-to-reperfusion time, and 90-day outcome among patients with final diagnoses of LVO. RESULTS: The cohort included 5141 patients (2735 before and 2406 after JUST score implementation). Before JUST score implementation, 1269 strokes (46.4%) occurred, including 140 LVO (5.1%), 394 ICH (14.4%), 120 SAH (4.4%), and 615 CI (22.5%). The JUST score was used in 1484 (61.7%) of the 2406 patients after implementation, which included 1267 (52.7%) cases of stroke (186 LVO (7.7%), 405 ICH (16.8%), 109 SAH (4.5%), and 567 CI (23.6%)). Success rate of the first request to the hospital significantly increased after JUST score implementation (76.3% vs 79.7%, p=0.004). JUST score implementation significantly shortened the door-to-puncture time (84 vs 73 min, p=0.03), but the prognosis remained unaltered among patients with acute LVO. CONCLUSIONS: Use of prehospital stroke triage scales improved prehospital management and preparation time of intervention among patients with acute stroke.

Possible pairing mechanism switching driven by structural symmetry breaking in BiS2-based layered superconductors.

Investigation of isotope effects on superconducting transition temperature (Tc) is one of the useful methods to examine whether electron-phonon interaction is essential for pairing mechanisms. The layered BiCh2-based (Ch: S, Se) superconductor family is a candidate for unconventional superconductors, because unconventional isotope effects have previously been observed in La(O,F)BiSSe and Bi4O4S3. In this study, we investigated the isotope effects of 32S and 34S in the high-pressure phase of (Sr,La)FBiS2, which has a monoclinic crystal structure and a higher Tc of ~ 10 K under high pressures, and observed conventional-type isotope shifts in Tc. The conventional-type isotope effects in the monoclinic phase of (Sr,La)FBiS2 are different from the unconventional isotope effects observed in La(O,F)BiSSe and Bi4O4S3, which have a tetragonal structure. The obtained results suggest that the pairing mechanisms of BiCh2-based superconductors could be switched by a structural-symmetry change in the superconducting layers induced by pressure effects.

Two-orbital model explains the higher transition temperature of the single-layer Hg-cuprate superconductor compared to that of the La-cuprate superconductor.

In order to explore the reason why the single-layered cuprates, La(2-x)(Sr/Ba)(x)CuO4 (T(c)≃40 K) and HgBa2CuO(4+δ) (T(c)≃90 K) have such a significant difference in T(c), we study a two-orbital model that incorporates the d(z2) orbital on top of the d(x2-y2) orbital. It is found, with the fluctuation exchange approximation, that the d(z2) orbital contribution to the Fermi surface, which is stronger in the La system, works against d-wave superconductivity, thereby dominating over the effect of the Fermi surface shape. The result resolves the long-standing contradiction between the theoretical results on Hubbard-type models and the experimental material dependence of T(c) in the cuprates.

Strain-induced creation and switching of anion vacancy layers in perovskite oxynitrides.

Perovskite oxides can host various anion-vacancy orders, which greatly change their properties, but the order pattern is still difficult to manipulate. Separately, lattice strain between thin film oxides and a substrate induces improved functions and novel states of matter, while little attention has been paid to changes in chemical composition. Here we combine these two aspects to achieve strain-induced creation and switching of anion-vacancy patterns in perovskite films. Epitaxial SrVO3 films are topochemically converted to anion-deficient oxynitrides by ammonia treatment, where the direction or periodicity of defect planes is altered depending on the substrate employed, unlike the known change in crystal orientation. First-principles calculations verified its biaxial strain effect. Like oxide heterostructures, the oxynitride has a superlattice of insulating and metallic blocks. Given the abundance of perovskite families, this study provides new opportunities to design superlattices by chemically modifying simple perovskite oxides with tunable anion-vacancy patterns through epitaxial lattice strain.

First-principles study on the origin of large thermopower in hole-doped LaRhO(3) and CuRhO(2).

Based on first-principles calculations, we study the origin of the large thermopower in Ni-doped LaRhO(3) and Mg-doped CuRhO(2). We calculate the band structure and construct the maximally localized Wannier functions from which a tight binding Hamiltonian is obtained. The Seebeck coefficient is calculated within the Boltzmann's equation approach using this effective Hamiltonian. For LaRhO(3), we find that the Seebeck coefficient remains nearly constant within a large hole concentration range, which is consistent with the experimental observation. For CuRhO(2), the overall temperature dependence of the calculated Seebeck coefficient is in excellent agreement with the experiment. The origin of the large thermopower is discussed.

Theoretical aspects of charge correlations in θ-(BEDT-TTF)2X.

A review is given on the theoretical studies of charge correlations in θ-(BEDT-TTF)2X. Various studies show that within a purely electronic model on the θ-type lattice with on-site U and nearest neighbor Vp and Vc interactions, the diagonal stripe, c-axis three-fold, and the vertical stripe charge correlations are favored in the regime Vp Vc , respectively. In the realistic parameter regime of Vp ∼Vc , there is competition between the c-axis three fold state and diagonal stripe state. Since these are different from the experimentally observed a-axis three fold and the horizontal stripe charge correlations, additional effects have to be included in order to understand the experiments. The electron-lattice coupling, which tends to distort the lattice into the θ d -type, is found to favor the horizontal stripe state, suggesting that the occurrence of this stripe ordering in the actual materials may not be of purely electronic origin. On the other hand, distant electron-electron interactions have to be considered in order to understand the a-axis three fold correlation, whose wave vector is close to the nesting vector of the Fermi surface. These studies seem to suggest that the minimal model to understand the charge correlation in θ-(BEDT-TTF)2X may be more complicated than expected. Future problems regarding the competition between different types of charge correlations are discussed.

Unconventional pairing in doped band insulators on a honeycomb lattice: the role of the disconnected Fermi surface and a possible application to superconducting ß-MNCl (M=Hf, Zr).

We investigate the possibility of realizing unconventional superconductivity in doped band insulators on the square and honeycomb lattices. The latter lattice is found to be a good candidate due to the disconnectivity of the Fermi surface. We propose applying the theory to the superconductivity in doped layered nitride ß-MNCl (M= Hf, Zr). Finally, we compare two groups of superconductors with disconnected Fermi surface, ß-MNCl and the iron pnictides, which have high critical temperature Tc, despite some faults against superconductivity are present.

Simple aspiration with balloon catheter technique (simple ABC technique) against proximal internal carotid artery occlusion in cases of cardiogenic cerebral embolism.

Background In cases of acute ischemic stroke, manual aspiration of the thrombus is commonly performed with a balloon guiding catheter placed in the cervical segment of the internal carotid artery (ICA). However, most manual aspirations using a balloon guiding catheter are combined with inner catheters, as in the direct aspiration first pass technique (ADAPT). We experienced some cases of acute ischemic stroke with proximal ICA occlusion due to cardiogenic thrombus where we obtained sufficient recanalization by simple manual aspiration from inflated Optimo 9F balloon catheters (Tokai Medical Products, Japan) placed in the origin of the cervical segment of the ICA without any inner catheter or stent retriever. We perform by preference this procedure, named the simple Aspiration with Balloon Catheter (simple ABC) technique. Herein, we report two recent cases and discuss this procedure. Case presentation Case 1: An 80-year-old man with paroxysmal atrial fibrillation developed left ICA occlusion. We performed the simple ABC technique and obtained a large amount of dark red and white thrombus. Puncture-to-reperfusion time was 14 minutes with Thrombolysis in Cerebral Infarction (TICI) grade 3. Case 2: A 69-year-old man with chronic atrial fibrillation developed left internal carotid occlusion. We performed the simple ABC technique and obtained a large amount of dark red thrombus. Puncture-to-reperfusion time was 15 minutes with TICI grade 2b. Conclusion The simple ABC technique is useful to deal with a large amount of thrombus, shortens procedure time, enables less invasive thrombectomy, and can shift immediately to subsequent procedures such as delivering a stent retriever or ADAPT.

Applicability of Carotid Artery Stenting for Patients 80 Years or Older: A Single-Center Experience.

BACKGROUND: A meta-analysis found that for internal carotid artery stenosis procedures in elderly patients, the risk of perioperative stroke is significantly greater for carotid artery stenting (CAS) than for carotid endarterectomy. We retrospectively examined characteristics and perioperative results of CAS for patients 80 years and older at a single medical center. METHODS: A total of 97 patients with internal carotid artery stenosis underwent CAS using the dual-protection (simultaneous flow reversal and distal filter) and blood-aspiration method. We divided patients into 2 groups, octogenarian and non-octogenarian. We evaluated patient background, captured visible debris, in-stent protrusion, major adverse events (i.e., major stroke and death), and hyperintense spots on diffusion-weighted images after CAS. RESULTS: The success rate of the CAS procedure was 100% with no major adverse events within 30 days. We found vulnerable plaque in 50% (15/30 patients) and 26.9% (18/67 patients) of octogenarian and non-octogenarian groups, respectively (P = 0.047). Diffusion-weighted images revealed small hyperintense spots in 20% (6/30 patients) and 18.0% (12/67 patients) of the octogenarian and non-octogenarian groups, respectively (P = 0.785). Visible debris was observed in 43.3% (13/30 patients) and 22.4% (15/67 patients) of the octogenarian and non-octogenarian groups, respectively (P = 0.004). CONCLUSIONS: The plaque of carotid stenosis in octogenarians is often vulnerable, but using a dual protection and blood aspiration method, we safely performed CAS in octogenarian patients.

Factors Related to Frailty Associated with Clinical Deterioration After Meningioma Surgery in the Elderly.

BACKGROUND: Older patients are increasingly presenting for surgery with intracranial meningioma because of progress with diagnostic imaging and longer life expectancy. However, older patients have many problems, such as comorbidities and reduced physiological capacity reflected in the frailty index. This study examines the factors affecting clinical deterioration after surgery in older patients, particularly factors associated with frailty. METHODS: Two hundred sixty-five patients older than 65 years underwent surgical resection of meningioma at Hiroshima University and related hospitals between 2000 and 2016. Karnofsky Performance Status (KPS) scores before and after surgery were evaluated. Factors related to the deterioration of KPS were analyzed with multivariate logistic regression modeling, including body mass index and serum albumin. RESULTS: KPS score deteriorated compared with preoperative score in 56 patients at discharge and in 40 patients at 3 months later, and 2 patients died within 1 year after surgery. Multivariate logistic regression analysis in addition to preoperative body mass index and serum albumin indicated skull base tumor location (odds ratio [OR], 4.67; 95% confidence interval [CI], 2.02-10.8) and serum albumin (OR, 2.38; 95% CI, 1.06-5.34) were risk factors for deterioration of KPS score at discharge. Age (OR, 0.91; 95% CI, 0.85-0.98), skull base tumor location (OR, 4.32; 95% CI, 1.45-12.9), tumor size (OR, 1.03; 95% CI, 1.00-1.05), and serum albumin (OR, 3.53; 95% CI, 1.29-9.61) were significant risk factors for perioperative intracranial complications. CONCLUSIONS: Skull base tumor location and serum albumin correlated with deterioration of clinical status after surgery.

Retreat from Stress: Rattling in a Planar Coordination.

Thermoelectric devices convert heat flow to charge flow, providing electricity. Materials for highly efficient devices must satisfy conflicting requirements of high electrical conductivity and low thermal conductivity. Thermal conductivity in caged compounds is known to be suppressed by a large vibration of guest atoms, so-called rattling, which effectively scatters phonons. Here, the crystal structure and phonon dynamics of tetrahedrites (Cu,Zn)12 (Sb,As)4 S13 are studied. The results reveal that the Cu atoms in a planar coordination are rattling. In contrast to caged compounds, chemical pressure enlarges the amplitude of the rattling vibration in the tetrahedrites so that the rattling atom is squeezed out of the planar coordination. Furthermore, the rattling vibration shakes neighbors through lone pairs of the metalloids, Sb and As, which is responsible for the low thermal conductivity of tetrahedrites. These findings provide a new strategy for the development of highly efficient thermoelectric materials with planar coordination.