Evidence for charge delocalization crossover in the quantum critical superconductor CeRhIn5_5

The nature of charge degrees-of-freedom distinguishes scenarios for interpreting the character of a second order magnetic transition at zero temperature, that is, a magnetic quantum critical point (QCP). Heavy-fermion systems are prototypes of this paradigm, and in those, the relevant question is where, relative to a magnetic QCP, does the Kondo effect delocalize their $f$-electron degrees-of-freedom. Herein, we use pressure-dependent Hall measurements to identify a finite-temperature scale $E_\text{loc}$ that signals a crossover from $f$-localized to $f$-delocalized character. As a function of pressure, $E_\text{loc}(P)$ extrapolates smoothly to zero temperature at the antiferromagnetic QCP of CeRhIn$_5$ where its Fermi surface reconstructs, hallmarks of Kondo-breakdown criticality that generates critical magnetic and charge fluctuations. In 4.4% Sn-doped CeRhIn$_5$, however, $E_\text{loc}(P)$ extrapolates into its magnetically ordered phase and is decoupled from the pressure-induced magnetic QCP, which implies a spin-density-wave (SDW) type of criticality that produces only critical fluctuations of the SDW order parameter. Our results demonstrate the importance of experimentally determining $E_\text{loc}$ to characterize quantum criticality and the associated consequences for understanding the pairing mechanism of superconductivity that reaches a maximum $T_\text{c}$ in both materials at their respective magnetic QCP.Comment: 19 pages, 5 figures, published in Nature Communication

Spectroscopic Evidence for Multigap Superconductivity of Y at Megabar Pressures

The recent discovery of room-temperature superconductivity (RTSC) at pressures of several megabars has led to intensive efforts to probe the origin of superconducting (SC) electron pairs. Although the signatures of the SC phase transition have been well established, few reports of the SC properties of RTSCs have been published because of the diamond anvil cell (DAC) environments. Here, we report the first direct evidence of two SC gaps in Y metal via point-contact spectroscopy (PCS) in DAC environments, where a sharp peak at the zero-bias voltage in the differential conductance is overlaid with a broad peak owing to Andreev reflection. Analysis based on the Blonder-Tinkham-Klapwijk (BTK) model reveals the existence of two SC gaps: the larger gap is 3.63 meV and the smaller gap is 0.46 meV. The temperature dependence of the two SC gaps is well explained by the BCS theory, indicating that two-band superconductivity is realized in Y metal. The successful application of PCS to Y in DAC environments is expected to guide future research on the SC gap in megabar high-Tc superconductors.Comment: 17 pages, 4 figure

Triple-sinusoid hedgehog lattice in a centrosymmetric Kondo metal

Superposed symmetry-equivalent magnetic ordering wave vectors can lead to topologically non-trivial spin textures, such as magnetic skyrmions and hedgehogs, and give rise to novel quantum phenomena due to fictitious magnetic fields associated with a non-zero Berry curvature of these spin textures. To date, all known spin textures are constructed through the superposition of multiple spiral orders, where spins vary in directions with constant amplitude. Recent theoretical studies have suggested that multiple sinusoidal orders, where collinear spins vary in amplitude, can construct distinct topological spin textures regarding chirality properties. However, such textures have yet to be experimentally realised. In this work, we report the observation of a zero-field magnetic hedgehog lattice from a superposition of triple sinusoidal wave vectors in the magnetically frustrated Kondo lattice CePtAl4Ge2. Notably, we also observe the emergence of anomalous electrical and thermodynamic behaviours near the field-induced transition from the zero-field topological hedgehog lattice to a non-topological sinusoidal state. These observations highlight the role of Kondo coupling in stabilising the zero-field hedgehog state in the Kondo lattice and warrant an expedited search for other topological magnetic structures coupled with Kondo coupling

Kinematic oscillations of post-CME blobs detected by K-Cor on 2017 September 10

We investigate 20 post-coronal mass ejection (CME) blobs formed in the post-CME current sheet (CS) that were observed by K-Cor on 2017 September 10. By visual inspection of the trajectories and projected speed variations of each blob, we find that all blobs except one show irregular "zigzag" trajectories resembling transverse oscillatory motions along the CS, and have at least one oscillatory pattern in their instantaneous radial speeds. Their oscillation periods are ranging from 30 to 91 s and their speed amplitudes from 128 to 902 km s-1. Among 19 blobs, 10 blobs have experienced at least two cycles of radial speed oscillations with different speed amplitudes and periods, while 9 blobs undergo one oscillation cycle. To examine whether or not the apparent speed oscillations can be explained by vortex shedding, we estimate the quantitative parameter of vortex shedding, the Strouhal number, by using the observed lateral widths, linear speeds, and oscillation periods of the blobs. We then compare our estimates with theoretical and experimental results from MHD simulations and fluid dynamic experiments. We find that the observed Strouhal numbers range from 0.2 to 2.1, consistent with those (0.15-3.0) from fluid dynamic experiments of bluff spheres, while they are higher than those (0.15-0.25) from MHD simulations of cylindrical shapes. We thus find that blobs formed in a post-CME CS undergo kinematic oscillations caused by fluid dynamic vortex shedding. The vortex shedding is driven by the interaction of the outward-moving blob having a bluff spherical shape with the background plasma in the post-CME CS

Effects of magnetic impurities on upper critical fields in the high-T c superconductor La-doped CaFe2As2

We investigate the effects of magnetic impurities on the upper critical field (μ 0 H c2) in La-doped CaFe2As2 (LaCa122) single crystals. The magnetic field dependency of the superconducting transition temperature (T c) for LaCa122 is rapidly suppressed at low fields up to ~1 kOe despite its large μ 0 H c2(0) value on the order of tens of Tesla, resulting in a large positive curvature of μ 0 H c2(T) near T c. The magnetization hysteresis (M–H) loop at temperatures above T c shows a ferromagnetic-like signal and the M(H) value rapidly increases with increasing magnetic field up to ~1 kOe. Taken together with the linear suppression of T c with the magnetization in the normal state, these results suggest that the large upward curvature of μ 0 H c2(T) near T c in La-doped CaFe2As2 mainly originates from the suppression of superconductivity due to the presence of magnetic impurities. © 2017 IOP Publishin

A Quenched Disorder in the Quantum‐Critical Superconductor CeCoIn5

Abstract Emergent inhomogeneous electronic phases in metallic quantum systems are crucial for understanding high‐Tc superconductivity and other novel quantum states. In particular, spin droplets introduced by nonmagnetic dopants in quantum‐critical superconductors (QCSs) can lead to a novel magnetic state in superconducting phases. However, the role of disorders caused by nonmagnetic dopants in quantum‐critical regimes and their precise relation with superconductivity remain unclear. Here, the systematic evolution of a strong correlation between superconductive intertwined electronic phases and antiferromagnetism in Cd‐doped CeCoIn5 is presented by measuring current–voltage characteristics under an external pressure. In the low‐pressure coexisting regime where antiferromagnetic (AFM) and superconducting (SC) orders coexist, the critical current (Ic) is gradually suppressed by the increasing magnetic field, as in conventional type‐II superconductors. At pressures higher than the critical pressure where the AFM order disappears, Ic remarkably shows a sudden spike near the irreversible magnetic field. In addition, at high pressures far from the critical pressure point, the peak effect is not suppressed, but remains robust over the whole superconducting region. These results indicate that magnetic islands are protected around dopant sites despite being suppressed by the increasingly correlated effects under pressure, providing a new perspective on the role of quenched disorders in QCSs

Complementary photo and temperature cured polymer dielectric with high-quality dielectric properties for organic semiconductors

Photo and temperature cured polymer dielectrics could be fabricated on a gate-patterned glass, with two immiscible polymer precursors, divinyltetramethyldisiloxane-bis(benzocyclobutene) (BCB precursor) and poly(melamine-co-formaldehyde)acrylate (PMFA), which have excellent insulating properties, but show discernible dielectric constants and polarities. On hydrophobic BCB-assisted PMFA blend dielectrics (approximately 400 nm thick), organic field-effect transistors (OFET) and complementary inverters were demonstrated using pentacene and N,N'-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C13) as semiconducting channels. The values of field-effect mobilities showed up to 0.33 cm(2) V-1 s(-1) (for pentacene) and 0.85 cm(2) V-1 s(-1) (for PTCDI-C13), respectively. In addition, these based complementary inverter was successfully demonstrated with a high voltage gain of ca. 41, specifically, onto the 10 wt% BCB-assisted PMFA dielectric optimized to achieve a hydrophobic and smooth surface by vertically phase-separating the immiscible polymers.open1198sciescopu

Spectroscopic evidence for the superconductivity of elemental metal Y under pressure

Superconductivity: Emergence in elemental yttrium under pressure The origin of superconductivity in ytterbium has been uncovered by researchers from South Korea and China. Superconductors offer no resistance to the flow of electricity. While superconductivity has been observed in many materials, usually at low temperatures or high pressures, exactly why it arises is not always clear. Tuson Park from Sungkyunkwan University, Suwon, South Korea and colleagues used high-pressure measurement techniques to identify the mechanism driving superconductivity in elemental yttrium. They subjected a yttrium sample to increasing pressures using a diamond anvil cell, and observed superconductivity emerge at 48.6 gigapascals. So-called point-contact spectroscopy measurements performed at this pressure indicated that superconductivity in yttrium is driven by the coupling of pairs of electrons, which can then occupy the same quantum energy state. This mechanism has been seen in other superconductors

Evolution of antiferromagnetism in Zn-doped heavy-fermion compound CeRh(In1-xZnx)(5)

©2020 American Physical Society We report the dependence of antiferromagnetism on Zn-doping concentration in the newly synthesized CeRh(In1-xZnx)(5) single crystal with x <= 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-N initially decreases from 3.8 K for pure CeRhIn5 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 CeRh(In1-xZnx)(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.11sci