Structure Responsible for the Superconducting State in La3Ni2O7 at High-Pressure and Low-Temperature Conditions.

Very recently, a new superconductor with Tc = 80 K has been reported in nickelate (La3Ni2O7) at around 15-40 GPa conditions (Nature, 621, 493, 2023), which is the second type of unconventional superconductor, besides cuprates, with Tc above liquid nitrogen temperature. However, the phase diagram plotted in this report was mostly based on the transport measurement under low-temperature and high-pressure conditions, and the assumed corresponding X-ray diffraction (XRD) results were carried out at room temperature. This encouraged us to carry out in situ high-pressure and low-temperature synchrotron XRD experiments to determine which phase is responsible for the high Tc state. In addition to the phase transition from the orthorhombic Amam structure to the orthorhombic Fmmm structure, a tetragonal phase with the space group of I4/mmm was discovered when the sample was compressed to around 19 GPa at 40 K where the superconductivity takes place in La3Ni2O7. The calculations based on this tetragonal structure reveal that the electronic states that approached the Fermi energy were mainly dominated by the eg orbitals (3dz2 and 3dx2-y2) of Ni atoms, which are located in the oxygen octahedral crystal field. The correlation between Tc and this structural evolution, especially Ni-O octahedra regularity and the in-plane Ni-O-Ni bonding angles, is analyzed. This work sheds new light to identify what is the most likely phase responsible for superconductivity in double-layered nickelate.

Colossal Magnetoresistance in Layered Diluted Magnetic Semiconductor Rb(Zn,Li,Mn)4As3 Single Crystals.

Diluted magnetic semiconductors (DMSs) with tunable ferromagnetism are among the most promising materials for fabricating spintronic devices. Some DMS systems have sizeable magnetoresistances that can further extend their applications. Here, we report a new DMS Rb(Zn1-x-yLiyMnx)4As3 with a quasi-two-dimensional structure showing sizeable anisotropies in its ferromagnetism and transverse magnetoresistance (MR). With proper charge and spin doping, single crystals of the DMS display Curie temperatures up to 24 K. Analysis of the critical behavior via Arrott plots confirms the long-range ferromagnetic ordering in the Rb(Zn1-x-yLiyMnx)4As3 single crystals. We observed remarkable intrinsic MR effects in the single crystals (i.e., a positive MR of 85% at 0.4 T and a colossal negative MR of -93% at 7 T).

The Superconductivity in Bi-Doped BaFe2As2 Single Crystals.

We have successfully synthesized a series of Bi-doped BaFe2As2 high-quality single crystals for the first time. X-ray diffraction (XRD) patterns show an expansion of lattice parameter c with Bi doping, indicating a negative pressure effect. By investigating the resistivity, a Fermi liquid (FL) to non-Fermi liquid (NFL) crossover is observed from normal state to antiferromagnetic order state, accompanied by three superconducting transitions labeled as SC I, SC II and SC III, which are supposed to be induced by three superconducting realms with various Bi concentrations. Thus, we propose that the NFL behavior is closely related to the presence of superconductivity. The magnetic susceptibility measurements further speculate that the SC I and SC III phases should exhibit filamentary superconductivity while the SC II exhibits a possible bulk superconductivity of TC~7 K.

Antiferroelectricity-Induced Negative Thermal Expansion in Double Perovskite Pb2 CoMoO6.

Materials with negative thermal expansion (NTE) attract significant research attention owing to their unique physical properties and promising applications. Although ferroelectric phase transitions leading to NTE are widely investigated, information on antiferroelectricity-induced NTE remains limited. In this study, single-crystal and polycrystalline Pb2 CoMoO6 samples are prepared at high pressure and temperature conditions. The compound crystallizes into an antiferroelectric Pnma orthorhombic double perovskite structure at room temperature owing to the opposite displacements dominated by Pb2+ ions. With increasing temperature to 400 K, a structural phase transition to cubic Fm-3m paraelectric phase occurs, accompanied by a sharp volume contraction of 0.41%. This is the first report of an antiferroelectric-to-paraelectric transition-induced NTE in Pb2 CoMoO6 . Moreover, the compound also exhibits remarkable NTE with an average volumetric coefficient of thermal expansion αV = -1.33 × 10-5 K-1 in a wide temperature range of 30-420 K. The as-prepared Pb2 CoMoO6 thus serves as a prototype material system for studying antiferroelectricity-induced NTE.

High-Pressure Synthesis, Crystal Structure, and Physical Properties of a Spinel Compound Co0.7Al2S4.

In this paper, we report on the discovery of a spinel compound, Co0.7Al2S4, which was synthesized at high-pressure. The systematic characterizations were carried out by structural, magnetic, and heat capacity measurements. The compound crystallizes into a cubic structure with the space group Fd3̅m (no. 227) and the lattice constant a = 9.9580(1) Å. Magnetic susceptibility measurements suggest that Co0.7Al2S4 exhibits a spin glass ground state, freezing at Tf ∼ 7.2 K with a Weiss temperature Tθ ∼ -115.9 K, which is verified by ac magnetic susceptibility and heat capacity measurements. The frustration parameter f for Co0.7Al2S4 is calculated to be about 16.6, based on the formula f = | Tθ/Tf |, indicating that Co0.7Al2S4 is a high-frustration magnet. Specific heat data displays a T2 dependence below the freezing temperature, which is different from the linear dependence observed in a common spin glass system. Compared with the similar compound CoAl2O4, it is suggested that the vacancies in the Co sites should be responsible for the occurrence of the spin glass behavior of Co0.7Al2S4.

Superconducting State Properties of CuBa2Ca3Cu4O10+δ.

The superconducting state properties of the CuBa2Ca3Cu4O10+δ (Cu-1234) system, with a transition temperature as high as 117.5 K, were investigated. The ac magnetic susceptibility measurements confirmed a very sharp transition to the superconducting state. The upper critical field, Hc2, as high as 91 T, and the irreversibility field, Hirr, as high as 21 T at 77 K, were determined using dc SQUID magnetization measurements. The intragrain critical current density, jc, estimated from a magnetic hysteresis loop, is as high as 5 × 109 A/m2 in a self-generated magnetic field at 77 K. However, the intergrain critical current density in the studied material is smaller by four orders of magnitude due to very weak intergrain connections.

Phosphorus-Doped PdSn Nanocatalyst with Abundant Defective Atoms for Enhanced Methanol Oxidation.

The design of the nanostructure of palladium-based nanocatalysts is considered to be a very effective way to improve the performance of nanocatalysts. Recent studies have shown that multiphase nanostructures can increase the active sites of palladium catalysts, thus effectively improving the catalytic efficiency of palladium atoms. However, it is difficult to regulate the phase structure of Pd nanocatalysts to form a compound phase structure. In this work, PdSnP nanocatalysts with different compositions were synthesized by fine-regulating the doping amount of phosphorus atoms. The results show that the doping of phosphorus atoms not only changes the composition of PdSn nanocatalysts but also changes the microstructure, forming amorphous and crystalline multiphase structures. This multiphase nanostructure contains abundant interfacial defects, which effectively promotes the electrocatalytic oxidation efficiency of Pd atoms in small-molecule alcohols. Compared with the undoped PdSn nanocatalyst (480 mA mgPd-1 and 2.28 mA cm-2) and the commercial Pd/C catalyst (397 mA mgPd-1 and 1.15 mA cm-2), the mass (1746 mA mgPd-1) and specific activities (8.56 mA cm-2) of PdSn0.38P0.05 nanocatalysts in the methanol oxidation reaction were increased by 3.6 and 3.8 times and 4.4 and 7.4 times, respectively. This study provides a new synthesis strategy for the design and synthesis of efficient palladium-based nanocatalysts for the oxidation of small-molecule alcohols.

Nanoscale Manipulation of Wrinkle-Pinned Vortices in Iron-Based Superconductors.

The controlled manipulation of Abrikosov vortices is essential for both fundamental science and logical applications. However, achieving nanoscale manipulation of vortices while simultaneously measuring the local density of states within them remains challenging. Here, we demonstrate the manipulation of Abrikosov vortices by moving the pinning center, namely one-dimensional wrinkles, on the terminal layers of Fe(Te,Se) and LiFeAs, by utilizing low-temperature scanning tunneling microscopy/spectroscopy (STM/S). The wrinkles trap the Abrikosov vortices induced by the external magnetic field. In some of the wrinkle-pinned vortices, robust zero-bias conductance peaks are observed. We tailor the wrinkle into short pieces and manipulate the wrinkles by using an STM tip. Strikingly, we demonstrate that the pinned vortices move together with these wrinkles even at high magnetic field up to 6 T. Our results provide a universal and effective routine for manipulating wrinkle-pinned vortices and simultaneously measuring the local density of states on the iron-based superconductor surfaces.

Two superconducting states with broken time-reversal symmetry in FeSe1-xSx.

Iron-chalcogenide superconductors FeSe1-xSx possess unique electronic properties such as nonmagnetic nematic order and its quantum critical point. The nature of superconductivity with such nematicity is important for understanding the mechanism of unconventional superconductivity. A recent theory suggested the possible emergence of a fundamentally new class of superconductivity with the so-called Bogoliubov Fermi surfaces (BFSs) in this system. However, such an ultranodal pair state requires broken time-reversal symmetry (TRS) in the superconducting state, which has not been observed experimentally. Here, we report muon spin relaxation (µSR) measurements in FeSe1-xSx superconductors for 0 ≤ x ≤ 0.22 covering both orthorhombic (nematic) and tetragonal phases. We find that the zero-field muon relaxation rate is enhanced below the superconducting transition temperature Tc for all compositions, indicating that the superconducting state breaks TRS both in the nematic and tetragonal phases. Moreover, the transverse-field µSR measurements reveal that the superfluid density shows an unexpected and substantial reduction in the tetragonal phase (x > 0.17). This implies that a significant fraction of electrons remain unpaired in the zero-temperature limit, which cannot be explained by the known unconventional superconducting states with point or line nodes. The TRS breaking and the suppressed superfluid density in the tetragonal phase, together with the reported enhanced zero-energy excitations, are consistent with the ultranodal pair state with BFSs. The present results reveal two different superconducting states with broken TRS separated by the nematic critical point in FeSe1-xSx, which calls for the theory of microscopic origins that account for the relation between nematicity and superconductivity.

Synthesis of a one-dimensional carbon nanotube-decorated three-dimensional crucifix carbon architecture embedded with Co7Fe3/Co5.47N nanoparticles for high-performance microwave absorption.

Low-dimensional cell-decorated three-dimensional (3D) hierarchical structures are considered excellent candidates for achieving remarkable microwave absorption. In the present work, a one-dimensional (1D) carbon nanotube (CNT)-decorated 3D crucifix carbon framework embedded with Co7Fe3/Co5.47N nanoparticles (NPs) was fabricated by the in-situ pyrolysis of a trimetallic metal-organic framework (MOF) precursor (ZIF-ZnFeCo). Co7Fe3/Co5.47N NPs were uniformly dispersed on the carbon matrix. The 1D CNT nanostructure was well regulated on the 3D crucifix surface by changing the pyrolysis temperature. The synergistic effect of 1D CNT and the 3D crucifix carbon framework increased the conductive loss, and Co7Fe3/Co5.47N NPs induced interfacial polarization and magnetic loss; thus, the composite manifested superior microwave absorption performance. The optimum absorption intensity was -54.0 dB, and the effective absorption frequency bandwidth reached 5.4 GHz at a thickness of 1.65 mm. The findings of this work could provide significant guidance for the fabrication of MOF-derived hybrids for high-performance microwave absorption applications.

Giant Exchange-Bias-Like Effect at Low Cooling Fields Induced by Pinned Magnetic Domains in Y2 NiIrO6 Double Perovskite.

Exchange bias (EB) is highly desirable for widespread technologies. Generally, conventional exchange-bias heterojunctions require excessively large cooling fields for sufficient bias fields, which are generated by pinned spins at the interface of ferromagnetic and antiferromagnetic layers. It is crucial for applicability to obtain considerable exchange-bias fields with minimum cooling fields. Here, an exchange-bias-like effect is reported in a double perovskite, Y2 NiIrO6 , which shows long-range ferrimagnetic ordering below 192 K. It displays a giant bias-like field of 1.1 T with a cooling field of only 15 Oe at 5 K. This robust phenomenon appears below 170 K. This fascinating bias-like effect is the secondary effect of the vertical shifts of the magnetic loops, which is attributed to the pinned magnetic domains due to the combination of strong spin-orbit coupling on Ir, and antiferromagnetically coupled Ni- and Ir-sublattices. The pinned moments in Y2 NiIrO6 are present throughout the full volume, not just at the interface as in conventional bilayer systems.

High ambient temperature increases the number of emergency visits for upper urolithiasis in Hefei City, China.

Background: Few studies have examined the effect of ambient temperature on upper urolithiasis in developing countries, with even fewer considering individual factors. Methods: The present study analyzed data on emergency department visits for upper urolithiasis from three hospital sites of a large hospital in Hefei, China, during 2016-2020. Data on environmental factors during the same period were also analyzed. A time series analysis employing a generalized Poisson regression model (GPRM) combined with a distributed lag non-linear model (DLNM) was conducted to evaluate the effect of ambient temperature on the number of emergency department visits for upper urolithiasis. Results: We found that ambient temperatures above 9 °C were positively associated with the frequency of upper urolithiasis visits, with the relationship being most significant on the current day and with a one-day lag. In the single-day lag effect, the most significant relative risk (RR) for mild heat (75th percentile) and high heat (95th percentile) was 1.229 (95% CI: 1.100-1.373) and 1.337 (95% CI: 1.134-1.577), respectively. The cumulative lag effect was significantly higher than the single-day lag effect, with maximum relative risks (RRs) of 1.779 (95% CI: 1.356-2.335) and 2.498 (95% CI: 1.688-3.697), respectively. The maximum lag time was 7 days. RRs were also higher among women and individuals aged 30-44 years. Conclusions: Increased ambient temperature is a risk factor for upper urolithiasis, and there is a hysteresis effect. Women and individuals aged 30-44 years are the most susceptible.

Record high Tc element superconductivity achieved in titanium.

It is challenging to search for high Tc superconductivity (SC) in transition metal elements wherein d electrons are usually not favored by conventional BCS theory. Here we report experimental discovery of surprising SC up to 310 GPa with Tc above 20 K in wide pressure range from 108 GPa to 240 GPa in titanium. The maximum Tconset above 26.2 K and zero resistance Tczero of 21 K are record high values hitherto achieved among element superconductors. The Hc2(0) is estimated to be ∼32 Tesla with coherence length 32 Å. The results show strong s-d transfer and d band dominance, indicating correlation driven contributions to high Tc SC in dense titanium. This finding is in sharp contrast to the theoretical predications based on pristine electron-phonon coupling scenario. The study opens a fresh promising avenue for rational design and discovery of high Tc superconductors among simple materials via pressure tuned unconventional mechanism.

High-Pressure Synthesis and Physical Properties of a Spinel Compound FeAl2S4.

A spinel compound FeAl2S4 was successfully synthesized under high-pressure and high-temperature conditions and was systematically characterized via the structural, magnetic, and specific heat measurements. It crystallizes into a cubic structure with the space group Fd3̅m (no. 227) and the lattice constant a = 10.0207(2) Å. A Fe/Al site inversion is found; that is, the molecular formula can be rewritten as (Fe1-xAlx)(Al2-xFex)S4, and the inversion parameter x is about 0.22. Magnetic susceptibility measurements indicate that FeAl2S4 undergoes a spin glass behavior, which is confirmed by ac susceptibility and specific heat measurements. The freezing temperature Tf ∼ 10.5 K and Weiss temperature Tθ ∼ -107.4 K lead to a high frustration parameter f = |Tθ/Tf| of about 10, which suggests that FeAl2S4 is a high-frustration magnet. Our results indicate that high pressure can help stabilize the spinel structure with small R̅σ and the cation inversion plays an important role in the formation of the spin glass state.

Biomass-derived ultralight superior microwave absorber Towards X and Ku bands.

Biomass-derived microwave absorbers have attracted extensive attention due to their natural abundance, low cost and eco-friendliness. However, it is still a challenge to achieve superior absorptivity under the extremely low filler content in such absorbers. Herein, we engineer a hybrid of Co3Fe7 alloy nanoparticles (NPs) anchoring on the biomass shaddock peel derived porous carbon nanosheets (CNs) for superlight and efficient microwave absorption. The CNs exhibit attractive graphene-like morphology with Co3Fe7 alloy NPs uniformly dispersing throughout the CNs. It is revealed that the EM parameters could be well controlled by tailoring the deposition ratio of Co3Fe7 NPs to optimize impedance matching. Specifically, the sample with relatively sparse Co3Fe7 NPs exhibit a reflection loss (RL) of -22.3 dB and broad absorption bandwidth of 5.3 GHz in Ku band under the ultralow filler content of only 8.0 wt%. As the deposition ratio of magnetic Co3Fe7 NPs increases, the optimized absorption peak moves to X band with -50.6 dB of RL value and 4.5 GHz of effective absorption, completely covering the whole X band. The elaborative studies demonstrate the significant influence of impedance matching on the ultimate absorption performance. This work paves a new way for the development of biomass-derived composites as superlight and tunable microwave absorber.

Novel Valence Transition in Elemental Metal Europium around 80 GPa.

Valence transition could induce structural, insulator-metal, nonmagnetic-magnetic and superconducting transitions in rare-earth metals and compounds, while the underlying physics remains unclear due to the complex interaction of localized 4f electrons as well as their coupling with itinerant electrons. The valence transition in the elemental metal europium (Eu) still has remained as a matter of debate. Using resonant x-ray emission scattering and x-ray diffraction, we pressurize the states of 4f electrons in Eu and study its valence and structure transitions up to 160 GPa. We provide compelling evidence for a valence transition around 80 GPa, which coincides with a structural transition from a monoclinic (C2/c) to an orthorhombic phase (Pnma). We show that the valence transition occurs when the pressure-dependent energy gap between 4f and 5d electrons approaches the Coulomb interaction. Our discovery is critical for understanding the electrodynamics of Eu, including magnetism and high-pressure superconductivity.

Ordered and tunable Majorana-zero-mode lattice in naturally strained LiFeAs.

Majorana zero modes (MZMs) obey non-Abelian statistics and are considered building blocks for constructing topological qubits1,2. Iron-based superconductors with topological bandstructures have emerged as promising hosting materials, because isolated candidate MZMs in the quantum limit have been observed inside the topological vortex cores3-9. However, these materials suffer from issues related to alloying induced disorder, uncontrolled vortex lattices10-13 and a low yield of topological vortices5-8. Here we report the formation of an ordered and tunable MZM lattice in naturally strained stoichiometric LiFeAs by scanning tunnelling microscopy/spectroscopy. We observe biaxial charge density wave (CDW) stripes along the Fe-Fe and As-As directions in the strained regions. The vortices are pinned on the CDW stripes in the As-As direction and form an ordered lattice. We detect that more than 90 per cent of the vortices are topological and possess the characteristics of isolated MZMs at the vortex centre, forming an ordered MZM lattice with the density and the geometry tunable by an external magnetic field. Notably, with decreasing the spacing of neighbouring vortices, the MZMs start to couple with each other. Our findings provide a pathway towards tunable and ordered MZM lattices as a platform for future topological quantum computation.