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We report low-temperature specific heat measurements for high-quality single crystalline KFe2As2 (Tc ≈ 3.5 K). The investigated zero-field specific heat data yields an unusually large nominal Sommerfeld coefficient, γ3= 94(3) mJ/mol K2, which is, however, affected by extrinsic contributions as evidenced by a sizable residual linear specific heat and various theoretical considerations, including an analysis of Kadowaki-Woods relations. These results indicate that KFe2As2 should be classified as a weakly or intermediately coupled superconductor with a total electron-boson coupling constant λtot ∼ 1 (including a calculated weak electron-phonon coupling λph = 0.17). From specific heat and ac susceptibility studies in external magnetic fields the magnetic phase diagram is also constructed. We confirm the high anisotropy of the upper critical fields μHc2(r), ranging from a factor of 5 near Tc to a slightly reduced value around 4.5 approaching T = 0 for fields B || ab and || c and show that their ratio slightly exceeds the mean mass anisotropy of 4.4 derived from our full-relativistic local-density-approximation band structure calculations, also in accord with recent preliminary penetration depth data by Eskildsen et al. [Eskildsen, Forgan, and Kawano-Furukawa, Rep. Prog. Phys. 74, 124504 (2011)] near 4. Its slight reduction when approaching T = 0 is not a consequence of Pauli limiting as in less perfect samples but points likely to a multiband effect. We also report irreversibility field data obtained from ac susceptibility measurements. The double-maximum in the T dependence of its imaginary part for fields B || c indicates a peak effect in the T dependence of critical currents. [ABSTRACT FROM AUTHOR]

We report muon spin rotation and magnetization measurements under pressure on Fe1+δSe1-xSx with x ≈ 0.11. Above p ≈ 0.6 GPa we find a microscopic coexistence of superconductivity with an extended dome of long range magnetic order that spans a pressure range between previously reported separated magnetic phases. The magnetism initially competes on an atomic scale with the coexisting superconductivity leading to a local maximum and minimum of the superconducting Tc(p). The maximum of Tc corresponds to the onset of magnetism while the minimum coincides with the pressure of strongest competition. A shift of the maximum of Tc(p) for a series of single crystals with x up to 0.14 roughly extrapolates to a putative magnetic and superconducting state at ambient pressure for x ≥ 0.2. [ABSTRACT FROM AUTHOR]

Unconventional superconductivity is known for its intertwining with other correlated states, making exploration of the intertwined orders important for understanding its pairing mechanism. In particular, spin and nematic orders are widely observed in iron-based superconductors; however, the presence of charge order is uncommon. Using scanning tunnelling microscopy, and through expanding the phase diagram of iron-arsenide superconductor Ba 1-x K x Fe 2 As 2 to the hole-doping regime beyond KFe 2 As 2 by surface doping, we demonstrate the formation of a charge density wave (CDW) on the arsenide surface of heavily hole-doped Ba 1-x K x Fe 2 As 2 . Its emergence suppresses superconductivity completely, indicating their direct competition. Notably, the CDW emerges when the saddle points approach the Fermi level, where its wavevector matches with those linking the saddle points, suggesting saddle-point nesting as its most probable formation mechanism. Our findings offer insights into superconductivity and intertwined orders, and a platform for studying them in iron-based superconductors close to the half-filled configuration., Competing Interests: Competing interests: The authors declare no competing interests., (© 2025. The Author(s).)

We present the magnetic properties of the chiral, polar, and possibly magnetoelectric antiperovskite β-Fe 2 SeO as derived from magnetization and specific-heat measurements as well as from powder neutron diffraction and Mössbauer experiments. Our macroscopic data unambiguously reveal two magnetic phase transitions at T N1 ≈ 103 K and T N2 ≈ 78 K, while Rietveld analysis of neutron powder diffraction data reveals a noncollinear antiferromagnetic structure featuring magnetic moments in the a - b plane of the trigonal structure and a ferromagnetic moment along c . The latter is allowed by symmetry between T N1 and T N2 , weakly visible in the magnetization data yet unresolvable microscopically. While the intermediate phase can be expressed in the trigonal magnetic space group P 3 1 , the magnetic ground state is modulated by a propagation vector q = (1/2 1/2 0) resulting in triclinic symmetry and an even more complex low-temperature spin arrangement which is also reflected in the Mössbauer hyperfine patterns indicating additional splitting of Fe sites below T N2 . The complex noncollinear spin arrangements suggest interesting magnetoelectric properties of this polar magnet.

The ability to efficiently control charge and spin in the cuprate high-temperature superconductors is crucial for fundamental research and underpins technological development. Here, we explore the tunability of magnetism, superconductivity, and crystal structure in the stripe phase of the cuprate La[Formula: see text]Ba[Formula: see text]CuO[Formula: see text], with [Formula: see text] = 0.115 and 0.135, by employing temperature-dependent (down to 400 mK) muon-spin rotation and AC susceptibility, as well as X-ray scattering experiments under compressive uniaxial stress in the CuO[Formula: see text] plane. A sixfold increase of the three-dimensional (3D) superconducting critical temperature [Formula: see text] and a full recovery of the 3D phase coherence is observed in both samples with the application of extremely low uniaxial stress of [Formula: see text]0.1 GPa. This finding demonstrates the removal of the well-known 1/8-anomaly of cuprates by uniaxial stress. On the other hand, the spin-stripe order temperature as well as the magnetic fraction at 400 mK show only a modest decrease under stress. Moreover, the onset temperatures of 3D superconductivity and spin-stripe order are very similar in the large stress regime. However, strain produces an inhomogeneous suppression of the spin-stripe order at elevated temperatures. Namely, a substantial decrease of the magnetic volume fraction and a full suppression of the low-temperature tetragonal structure is found under stress, which is a necessary condition for the development of the 3D superconducting phase with optimal [Formula: see text]. Our results evidence a remarkable cooperation between the long-range static spin-stripe order and the underlying crystalline order with the three-dimensional fully coherent superconductivity. Overall, these results suggest that the stripe- and the SC order may have a common physical mechanism., Competing Interests: Competing interests statement:The authors declare no competing interest.

We report on measurements of the in-plane magnetic penetration depth (λ_{ab}) in single crystals of Sr_{2}RuO_{4} down to ≃0.015  K by means of muon-spin rotation-relaxation. The linear temperature dependence of λ_{ab}^{-2} for T≲0.7  K suggests the presence of nodes in the superconducting gap. This statement is further substantiated by observation of the Volovik effect, i.e., the reduction of λ_{ab}^{-2} as a function of the applied magnetic field. The experimental zero-field and zero-temperature value of λ_{ab}=124(3)  nm agrees with λ_{ab}≃130  nm, calculated based on results of electronic structure measurements reported in A. Tamai et al. [High-resolution photoemission on Sr_{2}RuO_{4} reveals correlation-enhanced effective spin-orbit coupling and dominantly local self-energies, Phys. Rev. X 9, 021048 (2019)PRXHAE2160-330810.1103/PhysRevX.9.021048]. Our analysis reveals that a simple nodal superconducting energy gap, described by the lowest possible harmonic of a gap function, does not capture the dependence of λ_{ab}^{-2} on T, so the higher angular harmonics of the energy gap function need to be introduced.

Materials that break multiple symmetries allow the formation of four-fermion condensates above the superconducting critical temperature (T c ). Such states can be stabilized by phase fluctuations. Recently, a fermionic quadrupling condensate that breaks the Z 2 time-reversal symmetry was reported in Ba 1-x K x Fe 2 As 2 . A phase transition to the new state of matter should be accompanied by a specific heat anomaly at the critical temperature where Z 2 time-reversal symmetry is broken ([Formula: see text]). Here, we report on detecting two anomalies in the specific heat of Ba 1-x K x Fe 2 As 2 at zero magnetic field. The anomaly at the higher temperature is accompanied by the appearance of a spontaneous Nernst effect, indicating the breakdown of Z 2 symmetry. The second anomaly at the lower temperature coincides with the transition to a zero-resistance state, indicating the onset of superconductivity. Our data provide the first example of the appearance of a specific heat anomaly above the superconducting phase transition associated with the broken time-reversal symmetry due to the formation of the novel fermion order., (© 2023. Springer Nature Limited.)

Magnetic field penetrates type-II bulk superconductors by forming quantum vortices that enclose a magnetic flux equal to the magnetic flux quantum. The flux quantum is a universal quantity that depends only on fundamental constants. In this study, we investigated isolated vortices in the hole-overdoped Ba 1- x K x Fe 2 As 2 ( x = 0.77) by using scanning superconducting quantum interference device (SQUID) magnetometry. In many locations, we observed objects that carried only part of a flux quantum, with a magnitude that varied continuously with temperature. We demonstrated mobility and manipulability of these objects and interpreted them as quantum vortices with nonuniversally quantized (fractional) magnetic flux whose magnitude is determined by the temperature-dependent parameters of a multicomponent superconductor.

The hexadecafluorophthalocyanine-iron complex FePcF 16 was recently shown to convert olefins into ketones in the presence of stoichiometric amounts of triethylsilane in ethanol at room temperature under an oxygen atmosphere. Herein, we describe an extensive mechanistic investigation for the conversion of 2-vinylnaphthalene into 2-acetylnaphthalene as model reaction. A variety of studies including deuterium- and 18 O 2 -labeling experiments, ESI-MS, and 57 Fe Mössbauer spectroscopy were performed to identify the intermediates involved in the catalytic cycle of the oxidation process. Finally, a detailed and well-supported reaction mechanism for the FePcF 16 -catalyzed Wacker-type oxidation is proposed., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

There is considerable evidence that the superconducting state of Sr 2 RuO 4 breaks time reversal symmetry. In the experiments showing time reversal symmetry breaking, its onset temperature, T TRSB , is generally found to match the critical temperature, T c , within resolution. In combination with evidence for even parity, this result has led to consideration of a d xz  ± id yz order parameter. The degeneracy of the two components of this order parameter is protected by symmetry, yielding T TRSB  = T c , but it has a hard-to-explain horizontal line node at k z  = 0. Therefore, s ± id and d ± ig order parameters are also under consideration. These avoid the horizontal line node, but require tuning to obtain T TRSB  ≈ T c . To obtain evidence distinguishing these two possible scenarios (of symmetry-protected versus accidental degeneracy), we employ zero-field muon spin rotation/relaxation to study pure Sr 2 RuO 4 under hydrostatic pressure, and Sr 1.98 La 0.02 RuO 4 at zero pressure. Both hydrostatic pressure and La substitution alter T c without lifting the tetragonal lattice symmetry, so if the degeneracy is symmetry-protected, T TRSB should track changes in T c , while if it is accidental, these transition temperatures should generally separate. We observe T TRSB to track T c , supporting the hypothesis of d xz  ± id yz order.

We present a piezoelectric-driven uniaxial pressure cell that is optimized for muon spin relaxation and neutron scattering experiments and that is operable over a wide temperature range including cryogenic temperatures. To accommodate the large samples required for these measurement techniques, the cell is designed to generate forces up to ∼1000 N. To minimize the background signal, the space around the sample is kept as open as possible. We demonstrate here that by mounting plate-like samples with epoxy, a uniaxial stress exceeding 1 GPa can be achieved in an active volume of at least 5 mm 3 . We show that for practical operation, it is important to monitor both the force and displacement applied to the sample. In addition, because time is critical during facility experiments, samples are mounted in detachable holders that can be rapidly exchanged. The piezoelectric actuators are likewise contained in an exchangeable cartridge.

Employing optical spectroscopy we have performed a comparative study of the dielectric response of extracellular matrix and filaments of electrogenic bacteria Shewanella oneidensis MR-1, cytochrome c, and bovine serum albumin. Combining infrared transmission measurements on thin layers with data of the terahertz spectra, we obtain the dielectric permittivity and AC conductivity spectra of the materials in a broad frequency band from a few cm -1 up to 7000 cm -1 in the temperature range from 5 to 300 K. Strong absorption bands are observed in the three materials that cover the range from 10 to 300 cm -1 and mainly determine the terahertz absorption. When cooled down to liquid helium temperatures, the bands in Shewanella oneidensis MR-1 and cytochrome c reveal a distinct fine structure. In all three materials, we identify the presence of liquid bound water in the form of librational and translational absorption bands at ≈ 200 and ≈ 600 cm -1 , respectively. The sharp excitations seen above 1000 cm -1 are assigned to intramolecular vibrations.

The compound Sr 0.5 Ce 0.5 FBiS 2 belongs to the intensively studied family of layered BiS 2 superconductors. It attracts special attention because superconductivity at T sc  = 2.8 K was found to coexist with local-moment ferromagnetic order with a Curie temperature T C  = 7.5 K. Recently it was reported that upon replacing S by Se T C drops and ferromagnetism becomes of an itinerant nature. At the same time T sc increases and it was argued superconductivity coexists with itinerant ferromagnetism. Here we report a muon spin rotation and relaxation study (μSR) conducted to investigate the coexistence of superconductivity and ferromagnetic order in Sr 0.5 Ce 0.5 FBiS 2-x Se x with x = 0.5 and 1.0. By inspecting the muon asymmetry function we find that both phases do not coexist on the microscopic scale, but occupy different sample volumes. For x = 0.5 and x = 1.0 we find a ferromagnetic volume fraction of ~8 % and ~30 % at T = 0.25 K, well below T C  = 3.4 K and T C  = 3.3 K, respectively. For x = 1.0 (T sc  = 2.9 K) the superconducting phase occupies most (~64 %) of the remaining sample volume, as shown by transverse field experiments that probe the Gaussian damping due to the vortex lattice. We conclude ferromagnetism and superconductivity are macroscopically phase separated.

A quantum critical point (QCP) is currently being conjectured for the BaFe 2 (As 1-x P x ) 2 system at the critical value x c  ≈ 0.3. In the proximity of a QCP, all thermodynamic and transport properties are expected to scale with a single characteristic energy, given by the quantum fluctuations. Such a universal behavior has not, however, been found in the superconducting upper critical field H c2 . Here we report H c2  data for epitaxial thin films extracted from the electrical resistance measured in very high magnetic fields up to 67 Tesla. Using a multi-band analysis we find that H c2 is sensitive to the QCP, implying a significant charge carrier effective mass enhancement at the doping-induced QCP that is essentially band-dependent. Our results point to two qualitatively different groups of electrons in BaFe 2 (As 1-x P x ) 2 . The first one (possibly associated to hot spots or whole Fermi sheets) has a strong mass enhancement at the QCP, and the second one is insensitive to the QCP. The observed duality could also be present in many other quantum critical systems.

The Hall effect is a powerful tool for investigating carrier type and density. For single-band materials, the Hall coefficient is traditionally expressed simply by , where e is the charge of the carrier, and n is the concentration. However, it is well known that in the critical region near a quantum phase transition, as it was demonstrated for cuprates and heavy fermions, the Hall coefficient exhibits strong temperature and doping dependencies, which can not be described by such a simple expression, and the interpretation of the Hall coefficient for Fe-based superconductors is also problematic. Here, we investigate thin films of Ba(Fe1-xCox)2As2 with compressive and tensile in-plane strain in a wide range of Co doping. Such in-plane strain changes the band structure of the compounds, resulting in various shifts of the whole phase diagram as a function of Co doping. We show that the resultant phase diagrams for different strain states can be mapped onto a single phase diagram with the Hall number. This universal plot is attributed to the critical fluctuations in multiband systems near the antiferromagnetic transition, which may suggest a direct link between magnetic and superconducting properties in the BaFe2As2 system.

A new iron-catalyzed reaction for the coupling of perfluoroalkyl iodides (RFI) with aromatic substrates is described. The perfluoroalkylated arene products are obtained in good to excellent yields in the presence of a [(bpy)Fe(ii)] catalyst (10%) electrochemically regenerated or generated from [(bpy)Fe(iii)] at room temperature. The development, scope, and preliminary mechanistic studies of these transformations are reported.

In general, the critical current density, Jc, of type II superconductors and its anisotropy with respect to magnetic field orientation is determined by intrinsic and extrinsic properties. The Fe-based superconductors of the '122' family with their moderate electronic anisotropies and high yet accessible critical fields (Hc2 and Hirr) are a good model system to study this interplay. In this paper, we explore the vortex matter of optimally Co-doped BaFe2As2 thin films with extended planar and c-axis correlated defects. The temperature and angular dependence of the upper critical field is well explained by a two-band model in the clean limit. The dirty band scenario, however, cannot be ruled out completely. Above the irreversibility field, the flux motion is thermally activated, where the activation energy U0 is going to zero at the extrapolated zero-kelvin Hirr value. The anisotropy of the critical current density Jc is both influenced by the Hc2 anisotropy (and therefore by multi-band effects) as well as the extended planar and columnar defects present in the sample.

The recently discovered oxypnictide superconductor SmFeAs(O,F) is the most attractive material among the Fe-based superconductors due to its highest transition temperature of 56 K and potential for high-field performance. In order to exploit this new material for superconducting applications, the knowledge and understanding of its electro-magnetic properties are needed. Recent success in fabricating epitaxial SmFeAs(O,F) thin films opens a great opportunity to explore their transport properties. Here we report on a high critical current density of over 10(5) A/cm(2) at 45 T and 4.2 K for both main field orientations, feature favourable for high-field magnet applications. Additionally, by investigating the pinning properties, we observed a dimensional crossover between the superconducting coherence length and the FeAs interlayer distance at 30-40 K, indicative of a possible intrinsic Josephson junction in SmFeAs(O,F) at low temperatures that can be employed in electronics applications such as a terahertz radiation source and a superconducting Qubit.

The vast material concerned with the surgical treatment of patients with external abdominal hernias collected for 10 years includes 913 planned operations and 608 emergency operations for incarcerated hernias. The overall lethality was 3.4%, lethality after planned operations being 0.1%, after emergency operations--8.4%. It was noted that the amount of elderly and senile patients among patients with incarcerated hernias had increased up to 79%. The traditional methods of autoplasty were used in 95% of the patients. In 5% of the patients the autoabdominal plasty modified by the authors was used for badly amenable to treatment inguinal hernias and postoperative ventral hernias. Better results of treatment of patients with incarcerated external hernias of the abdomen were due to early diagnosis of such hernias, timely hospitalization with special reference to the patient's age, correctly performed surgery and prophylactic measures to avoid cardiovascular and pulmonary complications at the postoperative period.

Based on an analysis of results of treatment of 2828 patients with acute appendicitis the authors discuss the causes and give recommendations for prophylactics of incompetence of the vermiform process stump.