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The origin of the partial suppression of the electronic density states in the enigmatic pseudogap behavior, which is at the core of understanding high-$T_c$ superconductivity, has been hotly contested as either a hallmark of preformed Cooper pairs or an incipient order of competing interactions nearby. Here, we report the quasi-particle scattering spectroscopy of the quantum critical superconductor CeCoIn$_5$, where a pseudogap with energy $\Delta_g$ was manifested as a dip in the differential conductance ($dI/dV$) below the characteristic temperature of $T_g$. When subjected to external pressure, $T_g$ and $\Delta_g$ gradually increase, following the trend of increase in quantum entangled hybridization between Ce 4$f$ moment and conduction electrons. On the other hand, the superconducting (SC) energy gap and its phase transition temperature shows a maximum, revealing a dome shape under pressure. The disparate dependence on pressure between the two quantum states shows that the pseudogap is less likely involved in the formation of SC Cooper pairs, but rather is controlled by Kondo hybridization, indicating that a novel type of pseudogap is realized in CeCoIn$_5$., Comment: 4 figures

We investigated CeCoIn5 and LaCoIn5 single crystals, which have the same HoCoGa5-type tetragonal crystal structure, using infrared spectroscopy. However, while CeCoIn5 has 4f electrons, LaCoIn5 does not. By comparing these two material systems, we can extract the electronic properties of these f electrons. We observed that the differences caused by the f electrons are more obvious in low-energy optical spectra at low temperatures. We introduced a complex optical resistivity and found that the difference in optical resistivity between the two material systems is a clear indicator of the f electron response, which is intimately associated with the Kondo (f-electron) phenomena. From the temperature-related difference in optical resistivity, we also found that the onset temperature of the Kondo effect is much higher than what was previously reported. A large effective mass of 4f electrons for CeCoIn5 is obtained by applying the extended Drude model formalism. The effective masses of the two material systems are sharply contrasted. From this approach using optical resistivity, we demonstrate that the temperature-dependent optical properties of f electron can be extracted via a comparative study between CeCoIn5 and LaCoIn5.

Very high applied pressure induces superconductivity with the transition temperature (Tc) exceeding 19 K in elemental yttrium, but relatively little is known about the nature of that superconductivity. From point-contact spectroscopy (PCS) measurements in a diamond anvil cell (DAC), strong enhancement in the differential conductance is revealed near the zero-biased voltage owing to Andreev reflection, a hallmark of SC phase. Analysis of PCS spectra based on the extended Blonder-Tinkham-Klapwijk (BTK) model indicates two SC gaps at 48.6 GPa, where the large gap ΔL is 3.63 meV and the small gap ΔS is 0.46 meV. When scaled against the reduced temperature, both small and large SC gaps collapse on a single curve that follows the prediction from the BCS theory. The SC gap-to-Tc ratio is 8.2 for the larger gap and the initial slope of the upper critical field is -1.9 T/K, indicating that Y belongs to a family of the strongly coupled BCS superconductors. The successful application of PCS to Y in DAC environments demonstrates its utility for future research on other pressure-induced high-Tc superconductors.

We report the growth of CeIrIn

We investigated the influence of surface damage on the critical current density (Jc) of MgB2 thin films via 140-keV Co-ion irradiation. The Jc(H) of the surface-damaged MgB2 films was remarkably improved in comparison with that of pristine films. The strong enhancement of Jc(H) caused by a surface damage in MgB2 films can be ascribed to additional point defects along with an atomic lattice displacement introduced through low-energy Co-ion irradiation, which is consistent with the change in the pinning mechanism, from weak collective pinning to strong plastic pinning. The irreversible magnetic field (Hirr) at 5 K for surface-damaged MgB2 films with a thickness of 850 and 1300 nm was increased by a factor of approximately 2 compared with that of a pristine film. These results show that the surface damage produced by low energy ion irradiation can serve as an effective pinning source to improve Jc(H) in a MgB2 superconductor.

CeCoIn5 (Co115) thin films have been grown on Al2O3 (000l) substrates through the pulsed laser deposition (PLD). The films are grown mainly along the c-axis, with CeIn3 and In-related alloys. The rock-salt type grains are nucleated, where Co115 grains mixed with excess indium are evenly distributed over the substrate. The electrical resistivity of the films shows a Kondo coherence peak near 47 K and the zero-resistance superconducting state at 1.8 K, which is the first observation in the PLD grown thin films of Co115. The Rietveld refinement of the thin films shows that the c/a ratio (tetragonality) is suppressed to 1.6312 from 1.6374 of single crystals, which is consistent with the linear relationship between the superconducting transition temperature and tetragonality. The good agreement indicates that the PLD could provide an alternative route to tune the 2D character of the critical spin fluctuations to understand the superconducting pairing mechanism of Co115., Comment: 15 pages, 4 figures, 1 table

The transition metal dichalcogenide $\mathrm{Ti}{\mathrm{Se}}_{2}$ is an ideal correlated system for studying the interplay between superconductivity (SC) and a charge density wave (CDW) because both symmetry-breaking phases can be easily controlled by either Cu intercalation or physical pressure. SC appears in proximity to a CDW quantum critical point (QCP) induced by both Cu intercalation and applied pressure, raising the possibility of CDW-driven SC. Here, we report tuning the CDW QCP by simultaneously controlling Cu intercalation and external pressure and the appearance of a SC dome centered on the tunable QCP. When subjected to pressure, CDW ordering of Cu-intercalated ${\mathrm{Cu}}_{0.025}\mathrm{Ti}{\mathrm{Se}}_{2}$ is completely suppressed at 2.3 GPa, where the residual resistivity and the resistivity-temperature exponent decrease sharply, indicating the presence of the CDW QCP. The upper critical field of ${\mathrm{Cu}}_{0.025}\mathrm{Ti}{\mathrm{Se}}_{2}$ is 3.51 kOe, 16 times larger than that of pristine $\mathrm{Ti}{\mathrm{Se}}_{2}$, and its temperature dependence is linear, indicating that SC of $\mathrm{Ti}{\mathrm{Se}}_{2}$ is switched from the two-dimensional- to anisotropic three-dimensional-like by Cu intercalation. These discoveries show that the simultaneous application of Cu intercalation and pressure move the CDW QCP and that the highest SC transition temperature is pinned to the QCP, suggesting that the SC in $\mathrm{Ti}{\mathrm{Se}}_{2}$ is strongly correlated with CDW quantum criticality.

The quantum breakdown of superconductivity (QBS) is the reverse, comprehensive approach to the appearance of superconductivity. A quantum phase transition from superconducting to insulating states tuned by using nonthermal parameters is of fundamental importance to understanding the superconducting (SC) phase but also to practical applications of SC materials. However, the mechanism of the transition to a nonzero resistive state deep in the SC state is still under debate. Here, we report a systematic study of MgB2 bilayers with different thickness ratios for undamaged and damaged layers fabricated by low-energy iron-ion irradiation. The field-induced QBS is discovered at a critical field of 3.2 Tesla (=Hc), where the quantum percolation model best explains the scaling of the magnetoresistance near Hc. As the thickness of the undamaged layer is increased, strikingly, superconductivity is recovered from the insulating state associated with the QBS, showing that destruction of quantum phase coherence among Cooper electron pairs is the origin of the QBS. Superconducting islands play a role in the breakdown of superconductivity in thin films according to researchers in South Korea and China. Superconductors offer no resistance to the flow of electricity below a critical temperature. Researchers try to create new superconducting materials by reducing temperature, but insulator properties can re-emerge even at low temperatures. Soon-Gil Jung and Tuson Park from Sungkyunkwan University in Suwon, South Korea, and co-workers have systematically investigated this so-called quantum breakdown of superconductivity in thin films of magnesium diboride. The researchers studied bilayers comprising a damaged film and an undamaged film. They found that the superconductivity suppressed by the damaged film was gradually restored as the thickness of the undamaged film was increased. This supports the hypothesis that quantum breakdown is caused by the loss of quantum-mechanical links between superconducting islands. The significance of our results is related to “the quantum breakdown of superconductivity (QBS) and the role of superconducting islands in disordered superconducting systems”. Study on the QBS uses a reverse, comprehensive approach to the appearance of superconductivity, which is of utmost importance not only to understanding the superconducting phase but also to practical applications of superconductors. However, the mechanism underlying the transition to the nonzero resistive state deep in the superconducting state is still under debate. In this work, we have successfully achieved the field-induced QBS in disordred MgB2 thin films via a unique technique of low-energy ion irradiation.

Transparent conducting oxide (TCO) is a promising material system for transparent electrodes, which is one of the most essential elements in current electronic and energy devices. In particular, In...

Very high applied pressure induces superconductivity with the transition temperature ($T_c$) exceeding 19 K in elemental yttrium, but relatively little is known about the nature of that superconductivity. From point-contact spectroscopy (PCS) measurements in a diamond anvil cell (DAC), a strong enhancement in the differential conductance is revealed near the zero-biased voltage owing to Andreev reflection, a hallmark of the superconducting (SC) phase. Analysis of the PCS spectra based on the extended Blonder-Tinkham-Klapwijk (BTK) model indicates two SC gaps at 48.6 GPa, where the large gap $\Delta_L$ is 3.63 meV and the small gap $\Delta_S$ is 0.46 meV. When scaled against a reduced temperature, both small and large SC gaps collapse on a single curve that follows the prediction from BCS theory. The SC gap-to-$T_c$ ratio is 8.2 for the larger gap, and the initial slope of the upper critical field is -1.9 T/K, indicating that Y belongs to a family of strongly coupled BCS superconductors. The successful application of PCS to Y in DAC environments demonstrates its utility for future research on other pressure-induced high-$T_c$ superconductors., Comment: 4 figures

SrRuO3 (SRO) is an itinerant ferromagnet with strong coupling between the charge, spin, and lattice degrees of freedom. This strong coupling suggests that the electronic and magnetic behaviors of SRO are highly susceptible to changes in the lattice distortion. Here we show how the spin interaction and resultant magnon formation change with the modification in the crystallographic orientation. We fabricated SRO epitaxial thin films with (100), (110), and (111) surface orientations, to systematically modulate the spin interaction and spin dimensionality. The reduced spin dimensionality and enhanced exchange interaction in the (111)-oriented SRO thin film significantly suppresses magnon formation. Our study comprehensively demonstrates the facile tunability of magnon formation and spin interaction in correlated oxide thin films., 17 pages, 7 figures, 1 table, and 1 appendix

Two-dimensional (2D) molybdenum disulphide (MoS

The MgB2 films with the degraded MgB2 (SD) surface layer from the Cu ion bombardment show a large improvement in the field performance of critical current density (Jc) and a significant enhancement of the flux pinning force density (Fp). When the SD layer thickness is approximately 11% of the film thickness, the critical field corresponding to Jc = 105 A/cm2, a benchmark for large-scale practical applications, increases from 14.8 kOe at 5 K for the pristine film to 25 kOe. Being markedly different from the widely used chemical doping, the degradation of the small surface region does not lead to the suppression of the superconducting transition temperature (Tc) and low-field Jc. These results demonstrate that the formation of the small active area in MgB2 films is an effective way to improve their superconducting properties, thus paving the way for designing the geometry of flux pinning sites in MgB2.

CeIn

We report the dependence of antiferromagnetism on Zn-doping concentration in the newly synthesized $\mathrm{CeRh}{(\mathrm{I}{\mathrm{n}}_{1\text{\ensuremath{-}}x}\mathrm{Z}{\mathrm{n}}_{x})}_{5}$ single crystal with $x\ensuremath{\le}0.023$. X-ray-diffraction measurements showed a smooth decrease of lattice parameters with an increasing Zn concentration, indicating a positive chemical pressure effect. The electrical resistivity, specific heat, and magnetic susceptibility measurements revealed that the antiferromagnetic transition temperature ${T}_{\mathrm{N}}$ initially decreases from 3.8 K for pure $\mathrm{CeRhI}{\mathrm{n}}_{5}$ to 3.1 K at $x=0.012$; then, it becomes flat, remaining at approximately 3.1 K between Zn concentrations of 0.012 and 0.017, and finally, it increases to 3.3 K at 0.023 Zn concentration. These results suggest that the change in the electronic structure induced by Zn doping is more important than the chemical pressure effects with regard to tuning the magnetic order. A study on the electronic structure and pressure tuning of the newly synthesized heavy-fermion compound $\mathrm{CeRh}{(\mathrm{I}{\mathrm{n}}_{1\text{\ensuremath{-}}x}\mathrm{Z}{\mathrm{n}}_{x})}_{5}$, which does not include a toxic element, is expected to further enhance our understanding of the competing ground states emerging in heavy-fermion systems.

Atomically thin binary 2-dimensional (2D) semiconductors exhibit diverse physical properties depending on their composition, structure and thickness. By adding another element in those materials, which will lead to formation of ternary 2D materials, the property and structure would greatly change and significantly expanded applications could be explored. In this work, we report structural and optical properties of atomically thin chromium thiophosphate (CrPS4), a ternary antiferromagnetic semiconductor. Its structural details were revealed by X-ray and electron diffractions. Transmission electron microscopy showed that preferentially-cleaved edges are parallel to diagonal Cr atom rows, which readily identified their crystallographic orientations. Strong in-plane optical anisotropy induced birefringence that also enabled efficient determination of crystallographic orientation using polarized microscopy. The lattice vibrations were probed by Raman spectroscopy for the first time and exhibited significant dependence on thickness of crystals exfoliated down to single layer. Optical absorption determined by reflectance contrast was dominated by d-d type transitions localized at Cr3+ ions, which was also responsible for the major photoluminescence peak at 1.31 eV. The spectral features in the absorption and emission spectra exhibited noticeable thickness-dependence and hinted a high photochemical activity for single layer CrPS4. The current structural and optical investigation will provide a firm basis for future study and application of this novel magnetic semiconductor., Comment: 32 pages, 5 figures

We report temperature ($T$)- and pressure ($P$)-dependent resistivity measurements on the isostructural compounds ${\mathrm{U}}_{2}\mathrm{R}{\mathrm{h}}_{1\ensuremath{-}x}\mathrm{P}{\mathrm{t}}_{x}{\mathrm{C}}_{2}$ ($x=0$, 0.5, and 0.9) from which we construct a $T\ensuremath{-}P\ensuremath{-}x$ phase diagram. Compounds with $x=0$ and $x=0.5$ are antiferromagnets below 22.1 and 9.4 K, respectively, and their N\'eel temperature $({T}_{N})$ decreases under applied pressure. For $x=0$, the critical pressure ${P}_{c}$ required to suppress ${T}_{N}$ to zero temperature is projected to be about 8.8 GPa, but ${P}_{c}$ for $x=0.5$ is between 1.6 and 2.1 GPa. At atmospheric pressure, increasing Pt concentration in ${\mathrm{U}}_{2}\mathrm{R}{\mathrm{h}}_{(1\ensuremath{-}x)}\mathrm{P}{\mathrm{t}}_{x}{\mathrm{C}}_{2}$ tunes magnetic transition temperatures to zero at a critical value of ${x}_{c}\ensuremath{\approx}0.7$, and, consequently, we surmise the existence of a quantum-phase boundary in the $P\ensuremath{-}x$ plane at $T=0$ K that extends from ($P=0, x={x}_{c}$) to (${P}_{c}\ensuremath{\approx}8.8\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}, x=0$). For $x=0.9$, superconductivity appears at ${T}_{\mathrm{c}}=1.09\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, which decreases at a rate of $\ensuremath{\approx}\ensuremath{-}1\phantom{\rule{0.16em}{0ex}}\mathrm{K}/\mathrm{GPa}$ that is nearly twice that found for ${\mathrm{U}}_{2}\mathrm{Pt}{\mathrm{C}}_{2}$ whose ${T}_{\mathrm{c}}$ is 1.47 K. Together, these results indicate that domes of magnetism and superconductivity formed with $T\ensuremath{-}P\ensuremath{-}x$ variations are detached and that the two broken symmetries are independent of each other. Fluctuations in average composition produce rare regions that play an important role in determining physical properties of materials with noninteger $x$.

The recent discovery of magnetic van der Waals (vdW) materials provides a platform to answer fundamental questions on the two-dimensional (2D) limit of magnetic phenomena and applications. An important question in magnetism is the ultimate limit of the antiferromagnetic layer thickness in ferromagnetic (FM)/antiferromagnetic (AFM) heterostructures to observe the exchange bias (EB) effect, of which origin has been subject to a long-standing debate. Here, we report that the EB effect is maintained down to the atomic bilayer of AFM in the FM (Fe3GeTe2)/AFM (CrPS4) vdW heterostructure, but it vanishes at the single-layer limit. Given that CrPS4 is of A-type AFM and, thus, the bilayer is the smallest unit to form an AFM, this result clearly demonstrates the 2D limit of EB; only one unit of AFM ordering is sufficient for a finite EB effect. Moreover, the semiconducting property of AFM CrPS4 allows us to electrically control the exchange bias, providing an energy-efficient knob for spintronic devices.

The quasi-one-dimensional spin ladder compounds, ${\mathrm{BaFe}}_{2}{\mathrm{S}}_{3}$ and ${\mathrm{BaFe}}_{2}{\mathrm{Se}}_{3}$, are investigated by infrared spectroscopy and density functional theory (DFT) calculations. We observe strong anisotropic electronic properties and an optical gap in the leg direction that is gradually filled above the antiferromagnetic (AFM) ordering temperature, turning the systems into a metallic phase. Combining the optical data with the DFT calculations we associate the optical gap feature with the $p\ensuremath{-}d$ transition that appears only in the AFM ordered state. Hence, the insulating ground state along the leg direction is attributed to Slater physics rather than Mott-type correlations.

Although nanoscale deformation, such as nanostrain in iron-chalcogenide (FeSexTe1−x, FST) thin films, has attracted attention owing to its enhancement of general superconducting properties, including critical current density (Jc) and critical transition temperature, the development of this technique has proven to be an extremely challenging and complex process thus far. Herein, we successfully fabricated an epitaxial FST thin film with uniformly distributed nanostrain by injection of a trace amount of CeO2 inside an FST matrix using sequential pulsed laser deposition. By means of transmission electron microscopy and geometric phase analysis, we verified that the injection of a trace amount of CeO2 forms nanoscale defects, with a nanostrained region of tensile strain (ezz ≅ 0.02) along the c-axis of the FST matrix. This nanostrained FST thin film achieves a remarkable Jc of 3.5 MA/cm2 under a self-field at 6 K and a highly enhanced Jc under the entire magnetic field with respect to those of a pristine FST thin film. The maximum amount of current that can be carried by iron-based superconductors can be improved by introducing deliberate defects during fabrication. Iron–selenium–tellurium thin films have recently been identified as high-temperature superconductors that may pass large quantities of current. Sanghan Lee from the Gwangju Institute of Science and Technology in South Korea and co-workers have now used lasers to deposit small amounts of cerium oxide atoms between layers of an iron–selenium–tellurium thin film. The cerium oxide particles create defects, such as selenium-deficient sites, that slightly strain the crystal lattice and let more current move through the film. Mapping these nanostrain effects with electron microscopy enabled the team to find conditions needed to enhance superconductivity while minimizing cerium oxide by-products. To enhance supercurrent of iron-chalcogenide (FST) superconductor thin films, we induced nanostrain in FST thin films. The nanostrain was generated around nanoscale defects which were formed by the inserted a trace amount of oxide artificially inside FST matrix during the growth of FST thin film using sequential pulsed laser deposition. In particular, the critical current density (Jc) of the nanostrained FST thin films was significantly improved without dominant degradation of critical transition temperature.

Self-assembled nanocomposite films containing ferroelectric and ferromagnetic phases have attracted enormous research interest because they are the most promising candidates for practical multiferroic applications. However, obtaining a genuine magnetoelectric (ME) coupling effect is still challenging in this research area. To substantially improve the ME effect, new heterostructure designs with efficient strain control between two phases are urgently needed. Herein, a novel three-dimensional (3D) nanocup architecture of a heterostructure film is developed. To establish the unique architecture, a heavily Co, Fe-doped ferroelectric Bi3.25La0.75Ti3O12 (BLT) target was used during the growth of BLT thin films via pulsed laser deposition. Consequently, 3D nanocup-structured CoFe2O4 (CFO) particles formed inside the BLT via spontaneous nucleation and agglomeration. The 3D nanocup BLT-CFO film exhibited magnetically controlled reversible dielectric switching, which is direct evidence of strong ME coupling caused by the efficient interfacial strain coupling and low leakage of the novel nanocup architecture. The obtained results strongly suggest that the 3D nanocup heterostructure film significantly improves the ME coupling effect. In addition, we propose a new paradigm in the architecture design of self-assembled nanocomposite films for diverse multifunctional devices. A technique for controlling the growth of nanostructures on thin films can improve switches that manipulate both electrical and magnetic signals. Hyunji An from the Gwangju Institute of Science and Technology in South Korea and colleagues mixed cobalt and iron atoms into a bismuth–lanthanum–titanium ceramic that responds to external electric fields. By using pulsed laser on the ceramics, the team identified that the cobalt and iron components were spontaneously assembled into teacup-shaped nanostructures on the film’s surface. Characterization of the composite revealed that this new morphology provided a large area for coupling magnetic and electrical properties, while avoiding the signal losses associated with similar switches, such as thin films infused with vertically oriented magnetic pillars. Three-dimensional nanocup Bi3.25La0.75Ti3O12–CoFe2O4 heterostructure film is obtained via a heavily Co, Fe co-doped ferroelectric Bi3.25La0.75Ti3O12 target during pulsed laser deposition. The unique 3D nanocup architecture beyond usual architectures enables reversible magnetoelectric switching of the multiferroic heterostructure film through overcoming leakage issues, as well as efficient interfacial strain coupling based on their structural benefits.

Deoxyribonucleic acid (DNA) doped with transition metal ions shows great versatility for molecular-based biosensors and bioelectronics. Methodologies for developing DNA lattices (formed by synthetic double-crossover tiles) and DNA layers (used by natural salmon) doped with vanadium ions (V3+), as well as an understanding of the physical characteristics of V3+-doped DNA nanostructures, are essential in practical applications in interdisciplinary research fields. Here, DNA lattices and layers doped with V3+ are constructed through substrate-assisted growth and drop-casting methods. In addition, enhanced physical characteristics such as the band gap energy, work function, dielectric constant, and susceptibility of V3+-doped DNA nanostructures with varying V3+ concentration ([V 3+ ]) are investigated. The critical concentration ([V 3+ ]C ) at a given amount of DNA was predicted based on an analysis of the phase transition of DNA lattices from crystalline to amorphous with specific [V 3+ ]. Generally, the [V 3+ ]C provided crucial information on the structural stability and extremum physical characteristics of V3+-doped DNA nanostructures due to the optimum incorporation of V3+ into DNA. We obtained the optical absorption spectra for energy band gap estimation; Raman spectra for identifying the preferential coordination sites of V3+ in DNA; x-ray photoelectron spectra to examine the chemical state, chemical composition, and functional groups; and ultraviolet photoelectron spectra to estimate the work function. In addition, we addressed the electrical properties (i.e. current, capacitance, dielectric constant, and storage energy) and magnetic properties (magnetic field-dependent and temperature-dependent magnetizations and susceptibility) of DNA layers in the presence of V3+. The development of biocompatible materials with specific optical, electrical, and magnetic properties is required for future applications because they must have designated functionality, high efficiency, and affordability.

Two dimensional (2D) van der Waals (vdW) materials have demonstrated fascinating optical, electrical and thickness-dependent characteristics. These have been explored by numerous authors but reports on magnetic properties and spintronic applications of 2D vdW materials are scarce by comparison. By performing anomalous Hall effect transport measurements, we have characterised the thickness dependent magnetic properties of single crystalline vdW Fe3GeTe2. The nanoflakes of this vdW metallic material exhibit a single hard magnetic phase with a near square-shaped magnetic loop, large coercivity (up to 550 mT at 2 K), a Curie temperature near 200 K and strong perpendicular magnetic anisotropy. Using criticality analysis, we confirmed the existence of magnetic coupling between vdW atomic layers and obtained an estimated coupling length of ~ 5 vdW layers in Fe3GeTe2. Furthermore, the hard magnetic behaviour of Fe3GeTe2 can be well described by a proposed model. The magnetic properties of Fe3GeTe2 highlight its potential for integration into vdW magnetic heterostructures, paving the way for spintronic research and applications based on these devices., Accepted by Nature Communications

Inhomogeneous superconductivity in rare-earth (RE)-doped CaFe2As2 (Ca122) compounds leads to a novel state of matter in which the superconducting and magnetic states can be simultaneously controlled by using an electric current (I). Both La- and Ce-doped Ca122 single crystals show a very broad superconducting transition width (ΔTc) due to their non-bulk nature. Surprisingly, ΔTc becomes sharper or broader after an electric current larger than a threshold value (It) is applied, with a concomitant change in the normal-state magnetism. The sharpened (broadened) ΔTc is accompanied by a decrease (an increase) in the amplitude of the ferromagnetic signals. The sensitive changes in the superconductivity and magnetism that occur when an external current is applied are related to the inhomogeneous electronic states that originate from the Fe magnetic state and/or self-organized superconducting/magnetic composites in Ca122 compounds. These discoveries shed new light on the role of Fe in Fe-based superconductors and will provide new ideas for the design of novel superconducting devices. Clues to the superconducting behavior of a complex, iron-based substance can be revealed with a technique based on electric current. When rare-earth atoms are incorporated into calcium–iron–arsenic (CaFe2As2) crystals, simultaneous magnetic and superconductive properties emerge after cooling below 50 K. Soon-Gil Jung and Tuson Park from South Korea’s Sungkyunkwan University, Suwon, and colleagues report that passing milliamp-level electric currents through rare-earth-doped CaFe2As2 causes unexpected shifts in superconducting transition temperatures and magnetic field responses. In some samples, a sharpening of the superconductivity onset point was accompanied by a loss of magnetic signals, while in others magnetism improved at the expense of well-defined superconducting temperatures. The researchers conclude that these changes arise from inhomogeneities within doped CaFe2As2, possibly from iron magnetic states or tiny self-assembled nanocomposites that become unstable past a current threshold. Large inhomogeneous electronic states in rare-earth-doped CaFe2As2 produce striking results of manipulating the superconducting phases via current-driven magnetic state. Magnetization hysteresis loops at superconducting state (2 K) and normal state (50 K) for La-doped CaFe2As2 are largely changed by the electric current because their high-Tc regions are localized. Current path between high-Tc regions is considered as a long wire, thus current-induced large magnetic field around the path can modulate the magnetic state in normal/weak superconducting regions. These observations provide new insights into the role of Fe in the Fe-based superconductors and ideas for the design of new superconducting devices.

We report the synthesis of the Ce-based quaternary compound CePtAl4Ge2 that crystallizes in the trigonal structure (space group R 3 ¯ m, 166) with unit cell parameters, a = 4.1995(5) A, c = 31.851(7) A, and γ = 120°. Powder X-ray diffraction and energy dispersive X-ray spectroscopy show that CePtAl4Ge2 (LaPtAl4Ge2) is in a single, homogeneous phase. Magnetic susceptibility, electrical resistivity, and heat capacity measurements of CePtAl4Ge2 show that it exhibits antiferromagnetic behavior below 2.3 K. The magnetic susceptibility for the magnetic field applied perpendicular (χab) and parallel (χc) to the crystalline c-axis is very anisotropic, and the susceptibility ratio (χab/χc) reaches a maximum value of 10, indicating that the spin easy axis is within the Ce plane. The entropy recovered at TN is consistent with the doublet ground state of the crystal field split J = 5/2 multiplet of Ce3+ ions.