Quantum Griffiths Singularity in Ordered Artificial Superconducting-Islands-Array on Graphene.

Quantum Griffiths phase (QGP) is a novel quantum phenomenon of quantum phase transition in two-dimensional (2D) superconductors, and the emergence of inhomogeneous superconducting rare regions immersed in a metallic matrix is theoretically related to the quantum Griffiths singularity (QGS). However, the theoretical proposal of superconducting rare regions still lacks intuitive experimental verification. Here, we construct an artificial ordered superconducting-islands-array on monolayer graphene with the aid of an anodic aluminum oxide (AAO) membrane. The QGS under both in-plane and out-of-plane magnetic fields is evidenced by the divergent dynamical critical exponent and is in compliance with the direct activated scaling behavior. The phase diagram clearly shows that the QGP is indeed bred in the rare superconducting regions within isolated superconducting islands with a vanished quantum coherence. Our results reveal the universal features of QGP in artificial heterostructured systems and provide a visualized platform for the theoretical proposal of QGS.

Coexistence of Ferromagnetism and Superconductivity at KTaO3 Heterointerfaces.

The coexistence of superconductivity and ferromagnetism is a long-standing issue in superconductivity due to the antagonistic nature of these two ordered states. Experimentally identifying and characterizing novel heterointerface superconductors that coexist with magnetism presents significant challenges. Here, we report the observation of two-dimensional long-range ferromagnetic order in a KTaO3 heterointerface superconductor, showing the coexistence of superconductivity and ferromagnetism. Remarkably, our direct current superconducting quantum interference device measurements reveal an in-plane magnetization hysteresis loop persisting above room temperature. Moreover, first-principles calculations and X-ray magnetic circular dichroism measurements provide decisive insights into the origin of the observed robust ferromagnetism, attributing it to oxygen vacancies that localize electrons in nearby Ta 5d states. Our findings suggest KTaO3 heterointerfaces as time-reversal symmetry breaking superconductors, injecting fresh momentum into the exploration of the intricate interplay between superconductivity and magnetism enhanced by the strong spin-orbit coupling inherent to the heavy Ta in 5d orbitals.

Emergent Intrinsic Ferromagnetism in Two-Dimensional Trigonal Rhodium Oxide.

Two-dimensional (2D) van der Waals single crystals with long-range magnetic order are the precondition and urgent task for developing a 2D spintronics device. In contrast to graphene and transition metal dichalcogenides, the study of 2D single-crystal metal oxides with intrinsic ferromagnetic properties remains a huge challenge. Here, we report a large-size trigonal single-crystal rhodium oxide (SC-Tri-RhO2), with crystal parameters of a = b = 3.074 Å, c = 6.116 Å, and a space group of P3̅m1 (164), exhibiting strong ferromagnetism (FM) at a rather high temperature. Furthermore, theoretical calculations suggest that the ferromagnetism in SC-Tri-RhO2 originates from spin splitting near the Fermi level, and the total magnetic moment is contributed mainly by the Rh atom.

Concentration Phase Separation of Substitution-Doped Atoms in TMDCs Monolayer.

The density and spatial distribution of substituted dopants affect the transition metal dichalcogenides (TMDCs) materials properties. Previous studies have demonstrated that the density of dopants in TMDCs increases with the amount of doping, and the phenomenon of doping concentration difference between the nucleation center and the edge is observed, but the spatial distribution law of doping atoms has not been carefully studied. Here, it is demonstrated that the spatial distribution of dopants changes at high doping concentrations. The spontaneous formation of an interface with a steep doping concentration change is named concentration phase separation (CPS). The difference in the spatial distribution of dopants on both sides of the interface can be identified by an optical microscope. This is consistent with the results of spectral analysis and microstructure characterization of scanning transmission electron microscope. According to the calculation results of density functional theory, the chemical potential has two relatively stable energies as the doping concentration increases, which leads to the spontaneous formation of CPS. Understanding the abnormal phenomena is important for the design of TMDCs devices. This work has great significance in the establishment and improvement of the doping theory and the design of the doping process for 2D materials.

Direct Observation of the Topological Surface State in the Topological Superconductor 2M-WS2.

The quantum spin Hall (QSH) effect has attracted extensive research interest because of the potential applications in spintronics and quantum computing, which is attributable to two conducting edge channels with opposite spin polarization and the quantized electronic conductance of 2e2/h. Recently, 2M-WS2, a new stable phase of transition metal dichalcogenides with a 2M structure showing a layer configuration identical to that of the monolayer 1T' TMDs, was suggested to be a QSH insulator as well as a superconductor with a critical transition temperature of around 8 K. Here, high-resolution angle-resolved photoemission spectroscopy (ARPES) and spin-resolved ARPES are applied to investigate the electronic and spin structure of the topological surface states (TSS) in the superconducting 2M-WS2. The TSS exhibit characteristic spin-momentum-locking behavior, suggesting the existence of long-sought nontrivial Z2 topological states therein. We expect that 2M-WS2 with coexisting superconductivity and TSS might host the promising Majorana bound states.

Ferromagnetic CoSe broadband photodetector at room temperature.

Broadband infrared photodetectors based on two-dimensional (2D) materials which are the research focus in the infrared field, have wide applications in remote sensing, thermal imaging, and astronomy observation. In this article, the photodetector based on 2D ferromagnetic material CoSe is studied at room temperature, demonstrating the air-stable, broadband, and up to long wavelength properties. The CoSe material is applied to infrared photodetectors for the first time. The 2D material CoSe is synthesized by using the chemical vapor deposition method. The size of the as-grown CoSe is up to 71.8 µm. The photoresponse of the CoSe photodetector ranges from 450 nm to 10.6 µm. The photoresponsivity of this photodetector is up to 2.58 A W-1 under the 10.6 µm illumination at room temperature. This work provides a new material for broadband photodetector at room temperature and builds a bridge for the magnetoelectronic and broadband photoelectric fields.

Epitaxial growth and characterization of high quality Bi2O2Se thin films on SrTiO3 substrates by pulsed laser deposition.

Recently, Bi2O2Se was revealed as a promising two-dimensional (2D) semiconductor for next generation electronics, due to its moderate bandgap size, high electron mobility and pronounced ambient stability. Meanwhile, it has been predicted that high-quality Bi2O2Se-related heterostructures may possess exotic physical phenomena, such as piezoelectricity and topological superconductivity. Herein, we report the first successful heteroepitaxial growth of Bi2O2Se films on SrTiO3 substrates via pulsed laser deposition (PLD) method. Films obtained under optimal conditions show an epitaxial growth with the c axis perpendicular to the film surface and the a and b axes parallel to the substrate. The growth mode transition to three-dimensional (3D) island from quasi-2D layer of the heteroepitaxial Bi2O2Se films on SrTiO3 (001) substrates is observed as prolonging deposition time of films. The maximum value of electron mobility reaches 160 cm2 V-1 s-1 at room temperature in a 70 nm thick film. The thickness dependent mobility provides evidence that interface-scattering is likely to be the limiting factor for the relatively low electron mobility at low temperature, implying that the interface engineering as an effective method to tune the low temperature electron mobility. Our work suggests the epitaxial Bi2O2Se films grown by PLD are promising for both fundamental study and practical applications.

Synthesis, Crystal Structure, and Physical Properties of Layered LnCrSe2O (Ln = Ce-Nd).

The layered oxyselenides with the formula LnCrSe2O (Ln = Ce-Nd) were synthesized via molten salt methods. The isostructural compounds crystallize in the monoclinic space group of C2/m. The crystal structures feature ∞2[CrSe2O]3- motifs stacked along the a axis, which are separated by Ln3+ ions. The ∞2[CrSe2O]3- layers are composed of [Cr1Se6]9- and [Cr2Se4O2]9- octahedra via corner and edge sharing. Powder X-ray diffraction results confirm the phase purities of the as-synthesized compounds. LnCrSe2O (Ln = Ce-Nd) show typical antiferromagnetic ordering with TN = 125, 120, and 118 K, respectively. Heat capacity measurement for NdCrSe2O indicates that the Debye temperature is 278.4 K. Similar metal-to-semiconductor phase transitions were observed for LnCrSe2O (Ln = Ce-Nd) plates with transition temperatures of 115, 109, and 95 K, respectively. NdCrSe2O also possesses a magnetoresistance effect at low temperature (<25 K) with a significant positive magnetoresistance ∼ 16% at 2 K and 1 T.

Structure Re-determination and Superconductivity Observation of Bulk 1T MoS2.

2H MoS2 has been intensively studied because of its layer-dependent electronic structures and novel physical properties. Though the metastable 1T MoS2 with a [MoS6 ] octahedron was observed over the microscopic area, the true crystal structure of 1T phase has not been strictly determined. Moreover, the true physical properties have not been demonstrated from experiments owing to the challenge for the preparation of pure 1T MoS2 crystals. 1T MoS2 single crystals were successfully synthesized and the crystal structure of 1T MoS2 re-determined from single-crystal X-ray diffraction. 1T MoS2 crystallizes in the space group P3‾ m1 with a cell of a=b=3.190(3) Šand c=5.945(6) Å. The individual MoS2 layer consists of MoS6 octahedra sharing edges with each other. More surprisingly, the bulk 1T MoS2 crystals undergo a superconducting transition of Tc =4 K, which is the first observation of superconductivity in pure 1T MoS2 phase.

Enhanced Superconductivity in Restacked TaS2 Nanosheets.

Since interface superconductivity was discovered at the interface between two insulating layers LaAlO3 and SrTiO3, such interface-induced superconducting systems have been a research hotspot in superconductivity. Here, we report homogeneous interfaces formed by stacking chemically exfoliated monolayer TaS2 nanosheets randomly. Enhanced superconductivity of Tc = 3 K is observed, compared with 0.8 K of parent 2H-TaS2. The measurement of heat capacity shows the increase of electronic specific-heat coefficient γ of restacked TaS2 nanosheets compared to parent 2H-TaS2 crystals. Density functional theory calculations indicate that increase and delocalization of electron states near the Fermi surface due to the homogeneous interfaces effects could account for the enhanced superconductivity.

Synthesis, Structure, and Properties of Clathrate Si30.3(8) P15.7(8) Se7.930(3).

The new clathrate single crystal Si30.3(8) P15.7(8) Se7.930(3) was synthesized through a solid-state reaction, and it was characterized to have a unit cell parameter a=19.7614(1) Šand belong to space group Fm3‾ . In this clathrate structure, a Se1-Si3 bond forms in place of the tetrakaidecahedron structure, and pental dodecahedral cages composed of Si and P atoms encapsulate Se2, Se3, and Se4 guest atoms. Similar structures are observed in partial Te- and Ge-substituted compounds. Theoretical calculations based on an ordered formula Si32 P14 Se7 showed a semiconducting electronic structure with a band gap of 0.711 eV. A photoelectric response was observed in this compound at room temperature. Across the whole temperature range, this material exhibited a weak temperature-dependent diamagnetic signal, and no phase transition or thermal anomaly was observed in heat capacity measurements.

Phosphatase and Tensin Homolog (PTEN) Represses Colon Cancer Progression through Inhibiting Paxillin Transcription via PI3K/AKT/NF-κB Pathway.

The tumor suppressor gene phosphatase and tensin homolog (PTEN) is frequently mutated in colon cancer. However, the potential contribution of loss of PTEN to colon cancer progression remains unclear. In this study, we demonstrated that PTEN overexpression or knockdown in Lovo colon cancer cells decreased or increased paxillin expression, respectively. Moreover, paxillin reversed PTEN-mediated inhibition of Lovo cell invasion and migration. Overexpression of PTEN in an orthotropic colon cancer nude mice model inhibited tumor formation and progression. In addition, PTEN protein level was negatively correlated with that of paxillin in human colon cancer tissues. Mechanistically, we identified three NF-κB binding sites on paxillin promoter and confirmed that paxillin was a direct transcriptional target of NF-κB. Our findings reveal a novel mechanism by which PTEN inhibits the progression of colon cancer by inhibiting paxillin expression downstream of PI3K/AKT/NF-κB pathway. Thereby, PTEN/PI3K/AKT/NF-κB/paxillin signaling cascade is an attractive therapeutic target for colon cancer progression.

Thymoquinone Pretreatment Overcomes the Insensitivity and Potentiates the Antitumor Effect of Gemcitabine Through Abrogation of Notch1, PI3K/Akt/mTOR Regulated Signaling Pathways in Pancreatic Cancer.

BACKGROUND: The gemcitabine-insensitivity remains the main challenge for pancreatic cancer treatment. Thymoquinone, the predominant bioactive ingredient of Nigella sativa, has been shown to possess promising anti-cancer and chemo-sensitizing effects on pancreatic cancer, however, its meticulous mechanism is still indistinct. AIM: The objective of the present study was to investigate the potency of thymoquinone in combination with gemcitabine in inducing apoptosis and preventing the development of gemcitabine-insensitivity in pancreatic cancer cells. METHODS: The anti-tumor effects of thymoquinone and gemcitabine were analyzed via evaluation of alterations of cell viability, tumor weight, apoptosis-related proteins, caspase-3, -9 activities and NF-κB DNA binding activity in pancreatic cancer cells in vitro and PANC-1 cells orthotopic xenograft in vivo. RESULTS: Thymoquinone pretreatment following gemcitabine treatment synergistically caused an increase in pancreatic cancer cells apoptosis and tumor growth inhibition both in vitro and in vivo. The novel combinational regimen also contributes to alterations of multiple molecular signaling targets, such as the suppression of Notch1, NICD accompanying with up-regulation of PTEN, the inactivation of Akt/mTOR/S6 signaling pathways, and the suppression of phosphorylation and nuclear translocation of p65 induced by TNF-α. Thymoquinone pretreatment and gemcitabine also induced down-regulation of anti-apoptotic Bcl-2, Bcl-xL, XIAP and up-regulation and activation of pro-apoptotic molecules including Caspase-3, Caspase-9, Bax and increased release of cytochrome c. CONCLUSIONS: This novel modality of thymoquinone pretreatment can enhance the anti-cancer activity of gemcitabine and may be a promising option in the treatment of pancreatic cancer.

Effect of local structure distortion on superconductivity in Mg- and F-codoped LaOBiS2.

La1-xMgxO1-2xF2xBiS2 (x = 0.1-0.35) were synthesized, and their superconductive properties were investigated. The superconducting transition temperature (Tc) increased below the codoping level (x ≤ 0.25). La1-xMgxOBiS2 (x = 0-0.2) and La1-xMgxO0.6F0.4BiS2 (x = 0.1-0.3) were further prepared to explore the effect of Mg(2+). We found that the introduction of Mg(2+) and F(-) leads to local structure distortion. Larger distortion is beneficial for superconductivity in LaOBiS2, which was further confirmed by the results in La1-xCaxO1-2xF2xBiS2 (x = 0.2, 0.3).

Synthesis, structural, and transport properties of Cr-doped BaTi2As2O.

The interplay between unconventional superconductivity and the ordering of charge/spin density wave is one of the most vital issues in both condensed matter physics and material science. The Ti-based compound BaTi2As2O, which can be seen as the parent phase of superconducting BaTi2Sb2O, has a layered structure with a space group P4/mmm, similar to that of cuprate and iron-based superconductors. This material exhibits a charge density wave (CDW) ordering transition revealed by an anomaly at around 200 K in transport measurements. Here, we report the synthesis and systematical study of the physical properties in Cr-doped BaTi(2-x)Cr(x)As2O (x = 0-0.154) and demonstrate that the transition temperature of the CDW ordering is suppressed gradually by the doped Cr element. The magnetization measurements confirm the evolution of the CDW ordering transition. These observed behaviors are similar to that observed in iron-based superconductors, but no superconductivity emerges down to 2 K. In addition, the first-principles calculations are also carried out for well-understanding the nature of experimental observations.

Health economics in Africa from 1991 to 2020: A systematic review.

This systematic review was conducted to identify, evaluate and characterize the overall progress of health economics research conducted for Africa. Health economics studies carried out from 1991 to 2020 for Africa were retrieved from the EconLit database using relevant searching strategies. According to the methodology of Preferred Reporting Items for Systematic Review and Meta-Analysis, qualified journal papers were included. Using bibliometrics, we ran a series of analyses on authorship, studied countries, affiliations, and countries of origin, journals, and research topics. A total of 2935 studies were screened, and 178 were included in this review. We observed that the determinants of illness is the most researched topics. The United States, World Bank, University of California Berkeley, are respectively the most influential countries, world organizations, and academic institutions in the field of health economics of Africa. HIV/AIDs is still the leading health issue in highly cited health economics studies in Africa. Health Policy and Planning is the most productive and academically influential journal, and Kenya is the most studied country by health economists among all African countries. African health systems are vulnerable compared to developed countries, as many of them are underfunded. The academic strength in Africa is much weaker than that of leading health economics counties. Even within the continent, the academic development and the attention it receives are uneven. More influential health economics studies of Africa should be published in addition to the disease focus of HIV/AIDS.

Design of a Greenhouse Solar-Assisted Heat Pump Dryer for Kelp (Laminaria japonica): System Performance and Drying Kinetics.

In order to solve a series of problems with kelp drying including long drying time, high energy consumption, low drying efficiency, and poor quality of dried kelp, this work proposes the design of a novel greenhouse double-evaporator solar-assisted heat pump drying system. Experiments on kelp solar-assisted heat pump drying (S-HP) and heat pump drying (HP) under the condition of irradiance of 100-700 W/m2 and a temperature of 30, 40, or 50 °C were conducted and their results were compared in terms of system performance, drying kinetics, and quality impact. The drying time was reduced with increasing irradiance or temperature. The coefficient of performance (COP) and specific moisture extraction rate (SMER) of S-HP were 3.590-6.810, and 1.660-3.725 kg/kW·h, respectively, roughly double those of HP when the temperatures are identical. The Deff of S-HP and HP were 5.431 × 10-11~11.316 × 10-11 m2/s, and 1.037 × 10-11~1.432 × 10-11 m2/s, respectively; additionally, solar radiation greatly improves Deff. The Page model almost perfectly described the changes in the moisture ratio of kelp by S-HP and HP with an inaccuracy of less than 5%. When the temperature was 40 °C and the irradiance was above 400 W/m2, the drying time of S-HP was only 3 h, and the dried kelp maintained the green color with a strong flavor and richness in mannitol. Meanwhile, the coefficient of performance was 6.810, the specific moisture extraction rate was 3.725 kg/kWh, and the energy consumption was 45.2%, lower than that of HP. It can be concluded that S-HP is highly efficient and energy-saving for macroalgae drying and can serve as an alternate technique for the drying of other aquatic products.

Two-Dimensional Superconductivity at the Titanium Sesquioxide Heterointerface.

The study of exotic superconductivity in two dimensions has been a central theme in the solid state and materials research communities. Experimentally exploring and identifying exotic, fascinating interface superconductors with a high transition temperature (Tc) are challenging. Here, we report an experimental observation of intriguing two-dimensional superconductivity with a Tc of up to 3.8 K at the interface between a Mott insulator Ti2O3 and polar semiconductor GaN. At the verge of superconductivity, we also observe a striking quantum metallic-like state, demonstrating that it is a precursor to the two-dimensional superconductivity as the temperature is decreased. Our work shows an exciting opportunity to exploit the underlying, emergent quantum phenomena at the heterointerfaces via heterostructure engineering.

Absence of superconductivity in LiCu2P2.

We successfully synthesized the copper-based pnictide LiCu(2)P(2), which was reported as a superconductor with T(c) = 3.7 K before. The temperature dependence of resistivity and DC magnetization was measured on both polycrystalline and single-crystalline LiCu(2)P(2). However, our repeatable synthesizing and measurements showed no superconducting transition either in resistivity or DC magnetization above 2 K. A metallic behavior can be seen in resistivity, and a Curie-Weiss behavior was observed in DC magnetization from 2 to 300 K. We have also carried out the Hall effect and MR measurements on the sample, from which we conclude that the LiCu(2)P(2) has a single-band character. We also synthesized the polycrystalline Li(1-x)Cu(2)P(2), LiCu(2-x)P(2), and Li(1+x)Cu(2-x)P(2) with different stoichiometries, and observed no superconductivity in all the samples.

Critical Current Density and Vortex Dynamics in Pristine and Irradiated KCa2Fe4As4F2.

We report the critical current density (Jc) and vortex pinning properties in single crystals of a novel iron-based superconductor (IBS) KCa2Fe4As4F2 with large Jc in the pristine state, before and after introduction of artificial defects by swift-particle irradiation. The effects of 2.6 GeV U and 3 MeV proton irradiations in KCa2Fe4As4F2 single crystals on transition temperature Tc and Jc, including its dose dependence, are systematically studied. Jc~8 MA/cm2 under a self-field at 2 K in the pristine crystal is strongly enhanced up to 19.4 and 17.5 MA/cm2 by irradiation of 2.6 GeV U-ions and 3 MeV protons, respectively. Suppression of Tc and dose dependence of Jc in KCa2Fe4As4F2 is different from that in a representative IBS of (Ba,K)Fe2As2, which can be explained by considering the presence of embedded defects in pristine KCa2Fe4As4F2. The vortex dynamics in the pristine and proton irradiated KCa2Fe4As4F2 single crystals are also investigated from the analyses of the field dependence of Jc and the normalized magnetic relaxation rate. In addition to the contribution of embedded defects, weak collective pinning is considered for comprehensive analyses. Vortex dynamics in KCa2Fe4As4F2 is similar to those in (Ba,K)Fe2As2 to some extent, and different from that in anisotropic Li0.8Fe0.2OHFeSe. Large anisotropy, due to the presence of insulating blocking layers in KCa2Fe4As4F2, which leads to much lower irreversibility field (Hirr) compared with 122-type IBSs, strongly affect the vortex dynamics.