Electric properties of the twelve-fold vortex structure in hexagonal manganites.

Hexagonal manganites, as a functional ferroelectric (FE) material, receive considerable attention due to their improper ferroelectricity and topological vortex structures. This family exhibits three low-symmetry states accompanied by distinct vortex domain structures. In addition to the FEP63cmand anti-FE (AFE)P-3c1 states accompanied by dual six-fold vortex structures, there is another FEP3c1 state accompanied by a twelve-fold vortex structure. The responses of FE materials to external stimuli, such as external electric fields, are the core ingredients in the physics of FEs and are significant for technological applications. Under external electric fields, the responses of FE materials are determined by special FE domain structures. The electric properties of the FEP63cmand AFEP-3c1 states are very different. However, the electric properties of the FEP3c1 state, which only stabilizes in Ga-substituted In(Mn, Ga)O3, are unclear. The present work studies the electric properties of the FEP3c1 state. The electric-field-driven transition of the FEP3c1 state is found to follow two sequences, i.e. (1) twelve-foldP3c1 → nine-foldP3c1 +P63cm→ three-foldP63cm, and (2) twelve-foldP3c1 → six-foldP3c1 → three-foldP63cm. The variation of average polarization withEfor the FEP3c1 state with the second transition sequence manifests as an unusual triple-hysteresis loop, different from the usual single-hysteresis loop of FE materials. The results are related to the coexistence of the FE and non-FE domain walls in the FEP3c1 state. Furthermore, it is found that the FEP3c1 state at substitution concentration 0.39 exhibits the highest dielectric response. The results advance our understanding of topological vortex structures in hexagonal manganites.

Enhancement of ferroelectricity and homogeneity of orthorhombic phase in Hf0.5Zr0.5O2thin films.

By adoption of a high permittivity ZrO2capping layer (ZOCL), enhanced ferroelectric properties were achieved in the Hf0.5Zr0.5O2(HZO) thin films. For HZO thin film with 10 Å ZOCL, the 2Prvalue can reach as high as ∼43.1µC cm-2under a sweep electric field of 3 MV cm-1. In addition, a reduced coercive field of 1.5 MV cm-1was observed, which is comparable to that of HZO with metallic CL. Furthermore, the homogeneity of ferroelectric orthorhombic phase in HZO films was observed to be clearly increased, as evidenced by nanoscale piezoelectric force microscopy measurements. These results demonstrate that ZOCL is very favorable for high performance ferroelectric HZO films and their future device applications.

Enhanced high temperature ferromagnetism in Bi1-x R x FeO3 (R = Dy, Y) compounds.

In this work we report experimental evidence for the weak high-temperature ferromagnetism in Bi1-x R x FeO3 (R = Dy, Y) compounds by systematic characterizations, excluding the possible side-effects from other iron-based impurities. Remarkable saturated magnetic moment was observed in the Y-substituted samples, Bi1-x Y x FeO3, which is larger than the moment obtained in Bi1-x Dy x FeO3, the Dy-substituted samples with antiferromagnetic background. The physical origin of the weak ferromagnetic transition is discussed and serious lattice distortions have been identified based on the x-ray diffraction and Raman scattering data, although the rhombohedral structure symmetry remains unchanged upon the substitutions. It is believed that the structural distortion suppressed cycloid spin structure is the main factor for the enhanced magnetization in Bi1-x R x FeO3 compounds. Additionally, the Dy3+-Fe3+ antiferromagnetic coupling, which strengthens the antiferromagnetic interaction in Bi1-x Dy x FeO3 compounds, acts as the driving force for the magnetic discrepancy between Bi1-x Y x FeO3 and Bi1-x Dy x FeO3 samples.

MDM4 is targeted by miR-449b-5p to promote the proliferation of endometrial carcinoma.

OBJECTIVE: Previous studies have shown the involvement of microRNA-449b-5p (miR-449b-5p) and MDM4 in tumor development. This study aims to illustrate the role of miR-449b-5p in inhibiting proliferative capacity of endometrial carcinoma (EC) by targeting MDM4. PATIENTS AND METHODS: Expression levels of miR-449b-5p and MDM4 in tumor tissues and paracancerous ones of EC patients were determined. Relationships between their levels and clinical parameters of EC patients were analyzed. Subsequently, regulatory effects of miR-449b-5p and MDM4 on proliferative capacities in KLE and HEC-1B cells were assessed by cell counting kit-8 (CCK-8) and colony formation assay, respectively. Thereafter, in vivo xenograft models were established in nude mice administrated with KLE cells overexpressing MDM4 or those with miR-449b-5p knockdown. Then, tumor weight and tumor volume were measured after mouse sacrifice. Finally, the interaction between miR-449b-5p and MDM4 was explored by Luciferase assay. RESULTS: It was found that MDM4 was upregulated and miR-449b-5p was downregulated in EC tissues. Highly expressed MDM4 and lowly expressed miR-449b-5p were unfavorable to prognosis in EC patients, manifesting as a larger tumor size, more advanced tumor stage and lower overall survival. Besides, overexpression of MDM4 enhanced in vitro proliferative capacity in EC cells and in vivo tumorigenesis in nude mice bearing EC. Similarly, knockdown of miR-449b-5p yielded similar results. Luciferase assay confirmed that MDM4 was the target gene binding to miR-449b-5p, and its level was negatively correlated with miR-449b-5p level in EC. CONCLUSIONS: MiR-449b-5p and MDM4 are downregulated and upregulated in EC species, respectively. They are closely linked to tumor size, tumor stage and overall survival in EC patients. Through negatively regulating MDM4 level, miR-449b-5p inhibits proliferative capacity in EC cells.

Phase transitions in the classical exchange-anisotropic Kitaev-Heisenberg model.

The Kitaev model on the honeycomb lattice has been receiving substantial attention due to the discovery of quantum spin liquid state associated with this model. Consequently, its classical partners such as the Kitaev-Heisenberg (KH) model and associated phase transitions become concerned. Specifically, an intermediate Kosterlitz-Thouless (KT) phase engaged in the transition from the high-temperature (T) disordered state to the low-T sixfold degenerate state is predicted in the isotropic KH model [Phys. Rev. Lett. 109, 187201 (2012)10.1103/PhysRevLett.109.187201], but so far no sufficient experimental proof has been reported. In this work, we consider an essential extension of this KH model on the honeycomb lattice by including the Kitaev exchange anisotropy that is non-negligible in realistic materials. The associated phase transitions are thus investigated using the Monte Carlo simulations. It is found that such an anisotropy will result in a degradation of the sixfold degeneracy of the ground state in the isotropic KH model down to the fourfold or twofold degenerate ground state, and the finite-T phase transitions will also be modified remarkably. Interestingly, the intermediate KT phase can be suppressed by this Kitaev exchange anisotropy. This work thus provides a more realistic description of the physics ingredient with the KH model and presents a possible explanation on absence of the intermediate phase in real materials where the Kitaev exchange anisotropy can be more or less available.

Knockdown of p66ShcA activates Nrf2 pathway to protect cardiomyocytes from oxidative stress and inflammation induced by H2O2.

OBJECTIVE: Oxidative stress and inflammation are the most common causes of myocardial ischemia and hypoxia. This article focuses on the effect of p66ShcA on H2O2-induced cardiomyocytes. MATERIALS AND METHODS: The p66ShcA knockdown model of H9c2 cells was constructed by plasmid transfection. After treatment of different groups with H2O2, oxidative stress-related factors and inflammatory factors were detected. RESULTS: The expressions of SOD1, SOD2, GPX1, and GPX3 in H2O2 cells were significantly decreased, IL-1ß and IL-6 expression were significantly increased, while p66ShcA siRNA negative group could promote the expression of SOD1, SOD2, GPX1, and GPX3, inhibit the expression of IL-1ß and IL-6 significantly, and activates the Keap1/Nrf2 pathways. CONCLUSIONS: Knockdown of p66ShcA can activate Keap1/Nrf2 pathway, which inhibits H2O2-induced oxidative stress and inflammation in H9c2 cells.

Circ-DONSON promotes malignant progression of glioma through modulating FOXO3.

OBJECTIVE: The aim of this study was to investigate the expression level of circ-DONSON in glioma and to explore its effect on glioma metastasis and the underlying mechanism. PATIENTS AND METHODS: Quantitative Real Time-Polymerase Chain Reaction (qRT-PCR) was performed to examine circ-DONSON expression in 40 paired glioma tumor tissues and adjacent tissues. Meanwhile, the relation between circ-DONSON level and clinical parameters of glioma and the prognosis of patients was analyzed. The expression of circ-DONSON in glioma cell lines was analyzed by qRT-PCR as well. In addition, circs-DONSON silencing model was constructed in glioma cell lines. Cell counting kit-8 (CCK-8), cell scratch, and transwell migration assays were performed to investigate the effect of circ-DONSON on biological functions of glioma cells. Finally, the interplay between FOXO3 and circ-DONSON was explored. RESULTS: QRT-PCR results revealed that the expression level of circ-DONSON in glioma tumor tissues was remarkably higher than that of adjacent tissues, and the difference was statistically significant (p<0.05). Compared with patients with low expression of circ-DONSON, significantly higher prevalence of lymph node or distant metastasis and worse prognosis were observed in patients with high expression of circ-DONSON (p<0.05). The proliferation and migration abilities of glioma cells in circ-DONSON silenced group were remarkably suppressed when compared with NC group (p<0.05). Additionally, FOXO3 expression was remarkably down-regulated in glioma cell lines and tissues. FOXO3 expression was negatively correlated with circ-DONSON expression. In addition, cell reverse experiment demonstrated that circ-DONSON and FOXO3 can regulate each other, thereby together affecting the malignant progression of glioma. CONCLUSIONS: Circ-DONSON was remarkably associated with lymph node or distant metastasis, as well as poor prognosis of patients with glioma. Furthermore, it promoted the metastasis of glioma cells via regulating FOXO3.

One-Stop Management with Perfusion for Transfer Patients with Stroke due to a Large-Vessel Occlusion: Feasibility and Effects on In-Hospital Times.

BACKGROUND AND PURPOSE: In-hospital time delays lead to a relevant deterioration of neurologic outcomes in patients with stroke with large-vessel occlusions. At the moment, CT perfusion is relevant in the triage of late-window patients with stroke. We conducted this study to determine whether one-stop management with perfusion is feasible and leads to a reduction of in-hospital times. MATERIALS AND METHODS: In this observational study, we report the first 15 consecutive transfer patients with stroke with externally confirmed large-vessel occlusions who underwent flat panel detector CT perfusion and thrombectomy in the same room. Preinterventional imaging consisted of noncontrast flat panel detector CT and flat panel detector CT perfusion, acquired with a biplane angiography system. The flat panel detector CT perfusion was used to reconstruct a flat panel detector CT angiography to confirm the large-vessel occlusions. After confirmation of the large-vessel occlusion, the patient underwent mechanical thrombectomy. We recorded time metrics and safety parameters prospectively and compared them with those of transfer patients whom we treated before the introduction of one-stop management with perfusion. RESULTS: Fifteen transfer patients underwent flat panel detector CT perfusion and were treated with mechanical thrombectomy from June 2017 to January 2019. The median time from symptom onset to admission was 241 minutes. Median door-to-groin time was 24 minutes. Compared with 23 transfer patients imaged with multidetector CT, it was reduced significantly (24 minutes; 95% CI, 19-37 minutes, versus 53 minutes; 95% CI, 44-66 minutes; P < .001). Safety parameters were comparable between groups. CONCLUSIONS: In this small series, one-stop management with perfusion led to a significant reduction of in-hospital times compared with our previous workflow.

Association of elective cesarean delivery with metabolic measures in childhood: A prospective cohort study in China.

BACKGROUND AND AIMS: Cesarean delivery may increase the risk of childhood obesity, a precursor of metabolic syndrome (MetS). We aimed to investigate the association of elective cesarean delivery (ElCD) with MetS and its components in a Chinese birth cohort. METHODS AND RESULTS: This cohort included 1467 children (737 delivered by ElCD and 730 by spontaneous vaginal delivery [SVD]) who were followed up at the age of 4-7 years in 2013. MetS was defined as the presence of ≥3 components: central obesity, hypertriglyceridemia, low high-density lipoprotein (HDL), high fasting glucose, and hypertension. Of the 1467 children, 93 (6.3%) were categorized as having MetS: 50 (6.8%) delivered by ElCD and 43 (5.9%) by SVD. After multivariable adjustment, ElCD was not associated with MetS (adjusted odds ratio [AOR] 1.15, 95% confidence interval [CI] 0.74, 1.78) or certain components including hypertriglyceridemia, low HDL, and high fasting glucose but was associated with central obesity (AOR 1.33, 95% CI 1.02, 1.72) and hypertension (AOR 1.50, 95% CI 1.15, 1.96), as well as higher levels of total cholesterol (3.43 vs. 3.04 mmol/L; P < 0.001), low-density lipoprotein-cholesterol (1.77 vs. 1.67 mmol/L, P = 0.002), fasting glucose (5.08 vs. 5.02 mmol/L, P = 0.022), systolic (97.57 vs. 94.69 mmHg, P < 0.001)/diastolic blood pressure (63.72 vs. 62.24 mmHg, P < 0.001), and BMI (15.46 vs. 14.83 kg/m2, P < 0.001) than SVD. CONCLUSIONS: ElCD is not associated with MetS in early to middle childhood but is associated with its components including central obesity and hypertension, as well as various continuous indices.

Effects of Ambient Gases on the Electrical Performance of Solution-Processed C8-BTBT Thin-Film Transistors.

We performed a systematic study of the influence of environmental conditions on the electrical performance characteristics of solution-processed 2,7-dioctyl [1] benzothieno[3,2-b][1]-benzothiophene (C8-BTBT) thin-film transistors (TFTs). Four environmental exposure conditions were considered: high vacuum (HV), O2, N2, and air. The devices exposed to O2 and N2 for 2 h performed in a manner similar to that of the device kept in HV. However, the device exposed to air for 2 h exhibited significantly better electrical properties than its counterparts. The average and highest carrier mobility of the 70 air-exposed C8-BTBT TFTs were 4.82 and 8.07 cm2V-1s-1, respectively. This can be compared to 2.76 cm2V-1s-1 and 4.70 cm2V-1s-1, respectively, for the 70 devices kept in HV. Furthermore, device air stability was investigated. The electrical performance of C8-BTBT TFTs degrades after long periods of air exposure. Our work improves knowledge of charge transport behavior and mechanisms in C8-BTBT OTFTs. It also provides ideas that may help to improve device electrical performance further.

Flexible, Fatigue-Free, and Large-Scale Bi3.25La0.75Ti3O12 Ferroelectric Memories.

Flexible, fatigue-free, large-scale, and nonvolatile memory is an emerging technological goal in a variety of fields, including electronic skins, wearable devices, and other flexible electronics. Perovskite oxide films deposited on rigid substrates (e.g., Si and SrTiO3) at 500-700 °C and >1.0 Pa oxygen ambience have been widely used in electronic industries. However, their applications in flexible electronics are challenging, if not impossible. Here, the Bi3.25La0.75Ti3O12 ferroelectric films with SrRuO3 or Pt electrodes were prepared on the two-dimensional mica substrates, and then the flexible Pt/SrRuO3/Bi3.25La0.75Ti3O12/Pt memories have been achieved through reducing the mica to ∼10 µm thickness. These memories show the saturated polarization of Ps ∼ 20 µC/cm2, and either the <1% bending strain or a normal light illumination hardly overcomes the potential barrier among different polarizations which originate from the noncentral symmetry of the atomic structure. As a result, they can undergo 109 write/erase cycles and/or 10000 times bending with 1.4 mm in radius without any fatigue or damage. Furthermore, they can withstand the operation at 20-200 °C or under light illumination. In short, these flexible oxide memories provide comprehensive performance for industrial applications.

Parent Artery Reconstruction for Large or Giant Cerebral Aneurysms Using the Tubridge Flow Diverter: A Multicenter, Randomized, Controlled Clinical Trial (PARAT).

BACKGROUND AND PURPOSE: Although flow diverters have been reported with favorable clinical and angiographic outcomes in various literatures, randomized trials determining their true effectiveness and safety are still in lack. The Parent Artery Reconstruction for Large or Giant Cerebral Aneurysms Using the Tubridge Flow Diverter (PARAT) trial was designed to evaluate the safety and efficacy of the Tubridge flow diverter in the treatment of large or giant aneurysms in comparison with Enterprise stent-assisted coiling. MATERIALS AND METHODS: This prospective, multicenter, randomized trial was conducted at 12 hospitals throughout China. Enrolled adults with unruptured large/giant intracranial aneurysms were randomly assigned (1:1) to receive either Enterprise stent-assisted coiling or Tubridge flow diverter implantation. The primary end point was complete occlusion at 6-month follow-up, while secondary end points included technical success, mortality, target vessel-related stroke, aneurysm bleeding, in-stent stenosis, parent artery occlusion, and the frequency of all adverse events. RESULTS: Among 185 enrolled subjects, 41 withdrew before procedure initiation. Overall, 82 subjects underwent Tubridge implantation, and 62 subjects were primarily treated with stent-assisted coiling. The results of 6-month follow-up imaging included complete occlusion rates of 75.34% versus 24.53% for the Tubridge and stent-assisted coiling groups, respectively, with a calculated common odds ratio of 9.4 (95% confidence interval, 4.14-21.38; P < .001). There was a higher, nonsignificant frequency of complications for Tubridge subjects. Multivariate analysis showed a decreased stroke rate at the primary investigational site, with a marginal P value (P = .051). CONCLUSIONS: This trial showed an obviously higher rate of large and giant aneurysm obliteration with the Tubridge FD over Enterprise stent-assisted coiling. However, this higher obliteration rate came at the cost of a nonsignificantly higher rate of complications. Investigational site comparisons suggested that a learning curve for flow-diverter implantation should be recognized and factored into trial designs.

Helical and skyrmion lattice phases in three-dimensional chiral magnets: Effect of anisotropic interactions.

In this work, we study the magnetic orders of a classical spin model with anisotropic exchanges and Dzyaloshinskii-Moriya interactions in order to understand the uniaxial stress effect in chiral magnets such as MnSi. Variational zero temperature calculations demonstrate that various helical orders can be developed depending on the interaction anisotropy magnitude, consistent with experimental observations at low temperatures. Furthermore, the uniaxial stress induced creation and annihilation of skyrmions can be also qualitatively reproduced in our Monte Carlo simulations. Our work suggests that the interaction anisotropy tuned by applied uniaxial stress may play an essential role in modulating the magnetic orders in strained chiral magnets.

Magnetic impurity doping induced spin-glass state and short-range zigzag order in the honeycomb iridate Na2IrO3.

Based on the modified Heisenberg-Kitaev model, the effects of magnetic substitution on the magnetic properties of the honeycomb-lattice iridate [Formula: see text] [Formula: see text] are studied using Monte Carlo simulations. It is observed that the long-range zigzag state of the original system is rather fragile and can be replaced by a spin-glass state even for small substitution, well consistent with the experimental observation in Ru-substituted samples (Mehlawat et al 2015 Phys. Rev. B 92 134412). Both the disordered Heisenberg and Kitaev interactions caused by the magnetic ion-doping are suggested to be responsible for the magnetic phase transitions in the system. More interestingly, a short-range zigzag order is suggested to survive above the freezing temperature even at high magnetic impurity doping levels.

A correlation study between IgH gene rearrangement and orbital lymphoma removal operation prognosis.

OBJECTIVE: To explore the relationship between IgH gene rearrangement and orbital MALT (mucose-associated lymphoid tissue) lymphoma removal operation prognosis, and to quantify the effect of IgH gene rearrangement on primary orbital MALT lymphoma prognosis. PATIENTS AND METHODS: Fifty-eight patient cases with primary orbital MALT lymphoma were included in this study. Orbital lymphoma specimens were embedded in paraffin for sectioning. IgH gene rearrangement was detected using PCR. The correlation between IgH gene rearrangement and the patient recurrence and survival rates were determined using statistical analysis. The aforementioned rates were calculated and a survival curve was determined. p-values lower than 0.05 was considered statistically significant. RESULTS: We found that the 5-year disease-free survival rate was 90.8% in patients with orbital MALT lymphoma (mean value 56.7 months, range 52-60 months). The use of IgH gene rearrangement detection methods found that the non-recurrence rate of primary orbital MALT lymphoma cases was 79.3%. Survival analysis revealed that IgH gene rearrangement was significantly correlated with recurrence of orbital MALT lymphoma (p<0.001). CONCLUSIONS: IgH gene rearrangement detection can be improved by the combined usage of multiple primer pairs, especially family specific primers. In the future, detection of IgH gene rearrangement may be used as a novel marker to predict the prognosis of patients with primary orbital MALT lymphoma.

Preliminary Experience with Stent-Assisted Coiling of Aneurysms Arising from Small (<2.5 mm) Cerebral Vessels Using The Low-Profile Visualized Intraluminal Support Device.

BACKGROUND AND PURPOSE: The Low-Profile Visualized Intraluminal Support (LVIS) stent is a new device recently introduced for the treatment of wide-neck intracranial aneurysms. This single-center study presents the authors' preliminary experience using the LVIS stent to treat saccular aneurysms with parent arteries smaller than 2.5 mm. MATERIALS AND METHODS: Aneurysms with a LVIS stent used in a small parent vessel (<2.5 mm in diameter) between October 2014 and April 2016 were included. Procedure-related complications, angiographic results, clinical outcomes, and midterm follow-up data were analyzed retrospectively. RESULTS: A total of 22 patients was studied, including 5 ruptured and 17 unruptured aneurysms. Most of the aneurysms were located in the anterior circulation (90.9%). Stent placement in the parent arteries measuring 1.7-2.4 mm in diameter (mean, 2.1 mm) was successful in 100% of cases. Procedure-related complication developed in 1 patient (4.5%) who presented with aneurysm rupture. No permanent morbidity and mortality occurred. Immediate angiographic outcome showed complete occlusion in 8 aneurysms (36.4%), neck residual in 8 (36.4%), and residual aneurysm in 6 (27.3%). All patients underwent angiographic follow-up at a mean of 8.3 months, which revealed complete occlusion in 18 (81.8%) patients, neck remnant in 3 (13.6%), and residual sac in 1 (4.5%). No recanalization of the target aneurysm was observed. There was 1 case with asymptomatic in-stent stenosis. CONCLUSIONS: Our preliminary results show that the deployment of LVIS stents in small vessels is feasible, safe, and effective in the midterm. Larger studies with long-term follow-up are needed to validate our promising results.

The crucial role of Mn spiral spin order in stabilizing the Dy-Mn exchange striction in multiferroic DyMnO3.

DyMnO3 hosts the less addressed duality of multiferroicity, owing to the Dy-Mn exchange striction and inverse Dzyaloshinskii-Moriya interaction between Mn spin pairs. Although the duality in DyMnO3 has been discussed earlier, there remains a question whether the Mn magnetic sublattice is necessarily multiferroic for generating the Dy-Mn exchange striction. In this work, we investigate the multiferroicity of Dy(Mn1-xFex)O3 (0 ≤ x ≤ 0.1) through detailed magnetic and ferroelectric characterization. It is found that Fe-doping continuously suppresses the independent Dy spin order but instead promotes the Dy-Mn(Fe) coupling. This coupling benefits the Dy-Mn(Fe) exchange striction which remarkably enhances the ferroelectric polarization at a low doping level (x ≤ 0.015), beyond which the Mn spiral spin order breaks down leading to collapse of the macroscopic polarization at x ≥ 0.05. This work discloses the crucial role of Mn spiral spin order in stabilizing the Dy-Mn exchange striction and thus highlights the duality of multiferroicity in DyMnO3.

Long-Term Outcome of Tubridge Flow Diverter(S) in Treating Large Vertebral Artery Dissecting Aneurysms-A Pilot Study.

BACKGROUND AND PURPOSE: The experience of flow diverters (FDs) in treating large vertebral artery-dissecting aneurysms (VADAs) is still limited. This study was conducted to present our long-term outcome of VADAs treated with a Tubridge flow diverter (TFD), a new device developed in China. MATERIALS AND METHODS: The clinical and angiographic data of six patients harboring large VADAs and treated with TFDs were prospectively collected and analyzed. RESULTS: A total of nine TFDs were successfully implanted in six patients. Angiographic follow-up images were available for all patients at a median of 26.0 (18.5, 37.5) months after treatment. Five of the six VADAs were completely occluded, and the last was improved (near complete occlusion). In-stent stenosis was detected in one case and was handled appropriately by angioplasty and stenting. All covered branches and parent arteries remained patent. There were no complications or new neurological deficits observed in any of the patients. At the latest clinical follow-up (36.5 (26.0, 44.5) months), all patients achieved 0 in the modified Rankin scale score. CONCLUSIONS: Our preliminary experience suggests that the Tubridge flow diverter might be an alternative treatment for large and recurrent dissecting aneurysms derived from the vertebral artery.

Ashkin-Teller criticality and weak first-order behavior of the phase transition to a fourfold degenerate state in two-dimensional frustrated Ising antiferromagnets.

We study the thermal phase transition of the fourfold degenerate phases (the plaquette and single-stripe states) in the two-dimensional frustrated Ising model on the Shastry-Sutherland lattice using Monte Carlo simulations. The critical Ashkin-Teller-like behavior is identified both in the plaquette phase region and the single-stripe phase region. The four-state Potts critical end points differentiating the continuous transitions from the first-order ones are estimated based on finite-size-scaling analyses. Furthermore, a similar behavior of the transition to the fourfold single-stripe phase is also observed in the anisotropic triangular Ising model. Thus, this work clearly demonstrates that the transitions to the fourfold degenerate states of two-dimensional Ising antiferromagnets exhibit similar transition behavior.

Electronic structure of organometal halide perovskite CH3NH3BiI3 and optical absorption extending to infrared region.

The electronic structure and optical absorption spectrum of organometal halide perovskite compound CH3NH3BiI3 as a substituting candidate of well-concerned CH3NH3PbI3 not only for environmental friendly consideration are studied using the first principles calculations. It is revealed that a Bi replacement of Pb in CH3NH3PbI3 does not change seriously the band edge structure but the bandgap becomes narrow. Consequently, CH3NH3BiI3 exhibits not only stronger visible light absorption than CH3NH3PbI3 does but more strong absorption in the infrared region, which is however absent in CH3NH3PbI3. It is suggested that CH3NH3BiI3 may be one of even more promising alternatives to CH3NH3PbI3 for spectrum-broad and highly-efficient solar cells.