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In most charge density wave (CDW) systems of different material classes, ranging from traditional correlated systems in low‐dimension to recent topological systems with Kagome lattice, superconductivity emerges when the system is driven toward the quantum critical point (QCP) of CDW via external parameters of doping and pressure. Despite this rather universal trend, the essential hinge between CDW and superconductivity has not been established yet. Here, the evidence of coupling between electron and CDW fluctuation is reported, based on a temperature‐ and intercalation‐dependent kink in the angle‐resolved photoemission spectra of 2H‐PdxTaSe2. Kinks are observed only when the system is in the CDW phase, regardless of whether a long‐ or short‐range order is established. Notably, the coupling strength is enhanced upon long‐range CDW suppression, albeit the coupling energy scale is reduced. Interestingly, the estimation of the superconducting critical temperature by incorporating the observed coupling characteristics into McMillan's equation yields results closely resembling the known values of the superconducting dome. The results thus highlight a compelling possibility that this new coupling mediates Cooper pairs, which provides new insights into the competing relationship not only for CDW but also for other competing orders. [ABSTRACT FROM AUTHOR]

[Display omitted] After several decades of studies of high-temperature superconductivity, there is no compelling theory for the mechanism yet; however, the spin fluctuations have been widely believed to play a crucial role in forming the superconducting Cooper pairs. The recent discovery of high-temperature superconductivity near 80 K in the bilayer nickelate La 3 Ni 2 O 7 under pressure provides a new platform to elucidate the origins of high-temperature superconductivity. We perform elastic and inelastic neutron scattering studies on a polycrystalline sample of La 3 Ni 2 O 7− δ at ambient pressure. No magnetic order can be identified down to 10 K. The absence of long-range magnetic order in neutron diffraction measurements may be ascribed to the smallness of the magnetic moment. However, we observe a weak flat spin-fluctuation signal in the inelastic scattering spectra at ∼ 45 meV. The observed spin excitations could be interpreted as a result of strong interlayer and weak intralayer magnetic couplings for stripe-type antiferromagnetic orders. Our results provide crucial information on the spin dynamics and are thus important for understanding the superconductivity in La 3 Ni 2 O 7. [ABSTRACT FROM AUTHOR]

The electron pairing mechanisms in topological superconductors are pivotal for understanding the emergent topology‐related quantum states and play key roles in condensed matter physics. Theoretically, the quantization of magnetic flux in nano‐hole arrays within topological superconductors can be studied for understanding the Bogoliubov quasiparticles via the Little–Parks oscillation. However, experimental evidence of the quasiparticle states in such structures of topological superconductors remains elusive. Here, the unconventional superconducting quantum oscillation phenomena of the proximity‐induced 2D topological superconductivity (TSC) is demonstrated in a nano‐hole array of WTe2/NbSe2 heterojunction. The unconventional oscillation period in WTe2 is substantially smaller than that in the s‐wave superconductor NbSe2 (corresponds to Cooper pairs), implying the probable presence of novel quasiparticle states associated with TSC. Interestingly, such phenomena of multi‐charge flux quanta might be related to the multi‐particle bound states of TSC. These observations provide a new approach for exploring the unconventional superconducting quantum states in topological superconductors. [ABSTRACT FROM AUTHOR]

Symmetry plays an important role in determining the physical properties in condensed matter physics, as the symmetry operations of any physical property must include the symmetry operations of the point group of the crystal. As a consequence, crystallographic polarity and chirality are expected to have an impact on the Cooper pairing in a superconductor. While superconductivity with crystallographic polarity and chirality have both been found in a few crystalline phases separately; however, their coexistence and material realizations have not been studied. Here, by utilizing transport, Raman scattering, and transmission electron microscopy, we unveil a unique realization of superconductivity in single-crystalline Mo3Al2C (superconducting Tc=8 K) with a polar charge-density-wave phase and well-defined crystallographic chirality. We show that the intriguing charge density wave order leads to a noncentrosymmetric-nonpolar to polar transition below T*=155K via breaking both the translational and rotational symmetries. Superconductivity emerges in this polar and chiral crystal structure below Tc=8 K. Our results establish that Mo3Al2C is a superconductor with crystallographic polarity and chirality simultaneously, and motivate future studies of unconventional superconductivity in this category. The coexistence of crystallographic polarity and chirality is rare in a superconductor. Here, the authors establish that Mo3Al2C is a superconductor with crystallographic polarity and chirality simultaneously. [ABSTRACT FROM AUTHOR]

Analogous to the condensation of Cooper pairs in superconductors, the Bose–Einstein condensation (BEC) of electron–hole pairs in semiconductors and semimetals leads to an emergence of an exotic ground state — the excitonic insulator state. In this paper, we study the electronic structure of 1T-TiSe2 utilizing angle-resolved photoemission spectroscopy and alkali-metal deposition. Alkali-metal adatoms are deposited in-situ on the sample surface, doping the system with electrons. The conduction bands of 1T-TiSe2 are thereby pushed down below the Fermi energy, which enables us to characterize its temperature dependence with precision. We found that the formation of the charge density wave (CDW) in 1T-TiSe2 at ~ 205 K is accompanied by a significant increase of the band gap, supporting the existence of excitonic pairing in the CDW state of 1T-TiSe2. More importantly, by analyzing the linewidth of the single-particle excitation spectrum, we unveiled an incoherence-to-coherence crossover at 165 K, which could be attributed to a possible exciton condensation that occurs beneath the CDW transition in 1T-TiSe2. Our results not only explain the exotic transport properties of 1T-TiSe2, but also highlight the possible existence of an excitonic condensate in this semiconducting material. Excitonic insulators remain a topic of great interest in condensed matter physics. Here, the authors provide spectroscopic evidence of increased electronic coherence in the charge-density-wave state of semiconducting 1T-TiSe2. [ABSTRACT FROM AUTHOR]

Vibrating probes when immersed in a fluid can provide powerful tools for characterising the surrounding medium. In superfluid 3 He-B, a condensate of Cooper pairs, the dissipation arising from the scattering of quasiparticle excitations from a mechanical oscillator provides the basis of extremely sensitive thermometry and bolometry at sub-millikelvin temperatures. The unique properties of the Andreev reflection process in this condensate also assist by providing a significantly enhanced dissipation. While existing models for such damping on an oscillating cylinder have been verified experimentally, they are valid only for flows with scales much greater than the coherence length of 3 He, which is of the order of a hundred nanometres. With our increasing proficiency in fabricating nanosized oscillators, which can be readily used in this superfluid, there is a pressing need for the development of new models that account for the modification of the flow around these smaller oscillators. Here we report preliminary results on measurements of the damping in superfluid 3 He-B of a range of cylindrical nanosized oscillators with radii comparable to the coherence length and outline a model for calculating the associated drag. [ABSTRACT FROM AUTHOR]

We calculate the conductance of a junction between a disordered superconductor and a very strong half-metallic ferromagnet admitting electrons with only one spin projection. A usual mechanism of Andreev reflection is strongly suppressed in this case since Cooper pairs are composed of electrons with opposite spins. However, this obstacle can be overcome if we take into account spin-orbit scattering inside the superconductor. Spin-orbit scattering induces a fluctuational (zero on average) spin-triplet component of the superconducting condensate, which is enough to establish Andreev transport into a strong ferromagnet. This remarkably simple mechanism is quite versatile and can explain long-range triplet proximity effect in a number of experimental setups. One particular application of the suggested effect is to measure the spin-orbit scattering time τ SO in disordered superconducting materials. The value of Andreev conductance strongly depends on the parameter Δ τ SO and can be noticeable even in very disordered but relatively light metals like granular aluminum. [ABSTRACT FROM AUTHOR]

Bose metals are metals made of Cooper pairs, which form at very low temperatures in superconducting films and Josephson junction arrays as an intermediate phase between superconductivity and superinsulation. We predicted the existence of this 2D metallic phase of bosons in the mid 1990s, showing that they arise due to topological quantum effects. The observation of Bose metals in perfectly regular Josephson junction arrays fully confirms our prediction and rules out alternative models based on disorder. Here, we review the basic mechanism leading to Bose metals. The key points are that the relevant vortices in granular superconductors are core-less, mobile XY vortices which can tunnel through the system due to quantum phase slips, that there is no charge-phase commutation relation preventing such vortices from being simultaneously out of condensate with charges, and that out-of-condensate charges and vortices are subject to topological mutual statistics interactions, a quantum effect that dominates at low temperatures. These repulsive mutual statistics interactions are sufficient to increase the energy of the Cooper pairs and lift them out of condensate. The result is a topological ground state in which charge conduction along edges and vortex movement across them organize themselves so as to generate the observed metallic saturation at low temperatures. This state is known today as a bosonic topological insulator. [ABSTRACT FROM AUTHOR]

The high‐temperature layered superconductor (HTS) BSCCO is one of the key quantum material platforms in THz science and technology. Compact, stable, and reliable BSCCO THz photonic integrated circuit components can be developed to effectively and efficiently control and manipulate THz wave radiation, especially for future communication systems and network applications. Herein, the design, simulation, and modeling of ultrafast THz metamaterial photonic integrated circuits are reported on a few nanometer‐thick HTS BSCCO van der Waals (vdWs), capable of the active modulation of phase with constant transmission coefficient over a narrow‐frequency range. Meanwhile, the metamaterial circuit works as an amplitude modulator without significantly changing the phase in a different frequency band. Under the application of ultrashort optical pulses, the transient modulation dynamics of the THz metamaterial offer a fast‐switching timescale of 50 ps. The dynamics of picosecond light–matter interaction, Cooper pairs breaking, photoinduced quasiparticles generation and recombination, phonon bottleneck effect, and emission and relaxation of bosons in BSCCO vdW metamaterial arrays are discussed for the potential application of multifunctional superconducting photonic integrated circuits in communication and quantum technologies. [ABSTRACT FROM AUTHOR]

The precise measurement of minute displacements using light is a common practice in modern science and technology. The utilization of sound for precision displacement metrology remains scarce due to the diffraction limit of half-wavelength, while it holds crucial applications in some specific scenarios, such as underwater environments, biological tissues, and complex machinery components. Here, we propose an approach to super-resolution acoustic displacement metrology by introducing the concept of topological pairs in orbital meta-atoms, drawing inspiration from the analogy of Cooper pairs observed in spinful electrons. The topological pairs are conjugately formed to create two distinct pathways in mode space that enable robust generation of interference. This allows the realization of acoustic analogue of Malus's law and thereby enhances the resolution of displacement measurements. By incorporating a spiral twist configuration in orbital meta-atoms, we demonstrate the first acoustic prototype of a physical micrometer tailored for micron-scale displacement metrology. We observe experimentally a displacement resolving power of 1.2 μm at an audible frequency of 3.43 kHz, approximately 1/105 of the sound wavelength of 100 mm. Our work implies a new paradigm for precise displacement metrology within classical wave physics and lays the foundation for diverse acoustic applications. Precise displacement measurement via sound is crucial in science and engineering, yet limited by its low resolution. Here, the authors proposed the concept of topological pairs for achieving acoustic displacement metrology, and experimentally demonstrated an acoustic micrometer with resolving power of 1.2 μm at operating wavelength of 100 mm. [ABSTRACT FROM AUTHOR]

The quantum Josephson voltage standard is well established across the metrology community for many years. It relies on the synchronization of the flux tunneling in the S/I/S Josephson junctions (JJ) with the microwave radiation (MW) of frequency f such that V = Φ 0 f m , where m = 0, 1, 2, .... The phenomenon is called the Shapiro steps. Together with the quantum Hall resistance standard, the voltage standard forms the foundation of electrostatic metrology. The current is then defined as the ratio of the voltage and resistance. Realization of the quantum current standard would close the electrostatic metrological triangle of voltage–resistance–current. The current quantization I = 2 e f m , the inverse Shapiro steps, was recently shown using the superconducting nanowires and small JJ. The effect is a synchronization of the MW with the Cooper pair tunneling. This paves the way to combine the JJ voltage and current standards on the same chip and demonstrate feasibility of the multi-standard operation. We show the voltage and current quantization on the same chip up to frequency of 10 GHz, corresponding to the amplitudes ∼ 20.67 μV and ∼ 3.2 nA, respectively. The accuracy of the voltage and current quantization, however, is relatively low, 35 and 100 ppk, respectively. We discuss measures to optimize the JJs, circuit, and environment to boost the amplitude and accuracy of the standards. [ABSTRACT FROM AUTHOR]

Inspired by recent remarkable sets of experiments on UTe 2 : discoveries of the fourth horizontal internal transition line running toward a tetra-critical point (TCP) at H = 15 T, the off-axis high-field phases, and abnormally large Knight shift (KS) drop below T c for H ‖ a -magnetic easy axis, we advance further our theoretical work on the field (H)-temperature (T) phase diagram for H ‖ b -magnetic hard axis which contains a positive sloped H c2 departing from TCP. A nonunitary spin-triplet pairing with three components explains these experimental facts simultaneously and consistently by assuming that the underlying normal electron system with a narrow bandwidth characteristic to the Kondo temperature ∼ 30 K unsurprisingly breaks the particle-hole symmetry. This causes a special invariant term in Ginzburg–Landau (GL) free energy functional which couples directly with the 5f magnetic system, giving rise to the T c splitting and ultimately to the positive sloped H c2 and the horizontal internal transition line connected to TCP. The large KS drop can be understood in terms of this GL invariance whose coefficient is negative and leads to a diamagnetic response where the Cooper pair spin is antiparallel to the applied field direction. The present scenario also accounts for the observed d-vector rotation phenomena and off-axis phase diagrams with extremely high H c2 ≳ 70 T found at angles in between the b- and c-axes and between the bc-plane and a-axis, making UTe 2 a fertile playground for a possible topological superconductor. [ABSTRACT FROM AUTHOR]

The conventional theory of superconductivity holds that Cooper pairs form due to electron–phonon coupling; however, this description may not be adequate to describe certain unconventional superconductors such as cuprates and iron chalcogenides. In these unconventional superconductors, it has been proposed that spin fluctuations may be responsible for the formation of Cooper pairs. In this study, we explore spin interactions in the transition metal, dichalcogenide niobium disulfide, induced through proximity effects by fabricating antiferromagnet/NbS2 heterostructures. We tested three different 2D antiferromagnetic materials, each with different spin textures: anganese phosphorus trisulfide, manganese phosphorus triselenide, and chromium trichloride. Our results showed a substantial reduction in the critical temperature in the case of NbS2/MnPSe3. We hypothesize that this could be due to spin fluctuations in MnPSe3 inducing proximity effects in NbS2. [ABSTRACT FROM AUTHOR]

The generation of Sz = 1 triplet Cooper pairs has been predicted theoretically in superconducting–ferromagnetic hybrid heterostructures in the presence of spin–orbit coupling [F. S. Bergeret and I. V. Tokatly, Phys. Rev. B 89, 134517 (2014) and Jacobsen et al., Sci. Rep. 6, 23926 (2016)]. In this study, we experimentally investigate vertical Josephson junctions where the weak link is formed from a ferromagnetic layer with perpendicular magnetic anisotropy sandwiched by two non-magnetic layers with weak or strong spin–orbit coupling. We find that the decay of the Josephson coupling is reduced in the latter case, possibly indicating the presence of Sz = 1 spin-triplet correlations. We speculate that the canted magnetization required for these correlations is provided by the interaction of magnetization with Meissner effect in the superconducting layers. [ABSTRACT FROM AUTHOR]

In the underdoped n-type cuprate Nd2-xCexCuO4, long-range antiferromagnetic order reconstructs the Fermi surface, resulting in a putative antiferromagnetic metal with small Fermi pockets. Using angle-resolved photoemission spectroscopy, we observe an anomalous energy gap, an order of magnitude smaller than the antiferromagnetic gap, in a wide portion of the underdoped regime and smoothly connecting to the superconducting gap at optimal doping. After considering all the known ordering tendencies in tandem with the phase diagram, we hypothesize that the normal-state gap in the underdoped n-type cuprates originates from Cooper pairing. The high temperature scale of the normal-state gap raises the prospect of engineering higher transition temperatures in the n-type cuprates comparable to those of the p-type cuprates. [ABSTRACT FROM AUTHOR]

FeTe monolayer islands situated on a topological insulator Bi2Te3 (0001) surface were recently reported to exhibit the opening of an energy gap below temperatures T ~ 6 K, which could be due to a superconducting phase transition. In this work, we present a magnetic field dependent transport study proving that this gap is indeed of superconducting origin. Upon cooling, several drops in resistance are observed in the temperature range between 6 K and 2 K, indicating multiple transitions. Using the Ginzburg-Landau theory, we show that the critical magnetic field of the dominant high-temperature transition at ~ 6 K is governed by orbital Cooper pair breaking in larger FeTe islands, large enough to exceed the superconductive coherence length ξ . At smaller island sizes, transitions at lower temperatures < 6 K become more prominent, showing significantly increased critical fields dominated by paramagnetic pair breaking. The multiphase superconducting behaviour is in line with an observed wide distribution of FeTe islands width 5–100 nm and seems to reflect disorder effects at the interface to Bi2Te3. The proof of local superconductivity makes the FeTe interface to the topological insulator Bi2Te3 substrate a potential host of topological superconductivity. [ABSTRACT FROM AUTHOR]

Proximity-coupled nanostructures of conventional superconductors (SCs) and half-metallic ferromagnets (hmFs) are promising candidates as materials with unconventional superconductivity. The interrelated superposition of spin singlet-triplet and frequency even-odd superconducting condensates characterizes the superconducting state in such heterostructures. In a multi-band SC, the collective modes associated with the excitations of the relative phase between superconducting bands without perturbation of the Cooper pairs symmetry (Leggett modes) are allowed. In this report, we present the results of experimental investigations via the point-contact transport measurements of the Leggett-like collective excitations in the superconducting state of the nanocomposite of s-wave two-band superconductor MgB2 and half-metallic ferromagnet (La,Sr)MnO3. Two types of point contacts (PCs) have been used: the nanocomposite-nonmagnetic metal PCs and the nanocomposite–hmF PCs. The conductance equidistant peaks against the background of the gap structure were observed in both types of high-quality point junctions. Their distinctive feature was their period: two times shorter for the nanocomposite–hmF contacts compared to the nonmagnetic metal PCs. We attribute these spin-selective conductance periodic peaks to the relative phase Leggett's excitations between "parents" MgB2 even-frequency singlet condensates and proximity-induced triplet superconducting condensates. The data obtained on the hmF PCs also demonstrate the features that may indicate a dynamic coupling between even-frequency condensates and odd-frequency gapless superconducting condensates. [ABSTRACT FROM AUTHOR]

On the occasion of the 50th anniversary of point-contact spectroscopy, we review and extend some of our recent studies on the effects of spin-orbit interactions located at an electric point contact connecting two bulk superconductors. In particular, we study the effects on the Josephson tunneling of Cooper pairs between the superconductors. We demonstrate that such tunneling forces the electronic spin to fluctuate quantum mechanically, transforming a BCS condensate into a quantum superposition of singlet and triplet pairs. The relative prevalence of those pairs can be controlled electrostatically and mechanically. The singlet pairs contribute to the Josephson charge current flowing through the point contact but not to the Josephson spin current injected into the superconductors. The spin-polarized pairs contribute to the injected Josephson spin current but not to the superconducting charge flow. These results allow for new functionalities of spin-active Josephson junctions. [ABSTRACT FROM AUTHOR]

The performance of superconducting qubits is degraded by a poorly characterized set of energy sources breaking the Cooper pairs responsible for superconductivity, creating a condition often called "quasiparticle poisoning". Both superconducting qubits and low threshold dark matter calorimeters have observed excess bursts of quasiparticles or phonons that decrease in rate with time. Here, we show that a silicon crystal glued to its holder exhibits a rate of low-energy phonon events that is more than two orders of magnitude larger than in a functionally identical crystal suspended from its holder in a low-stress state. The excess phonon event rate in the glued crystal decreases with time since cooldown, consistent with a source of phonon bursts which contributes to quasiparticle poisoning in quantum circuits and the low-energy events observed in cryogenic calorimeters. We argue that relaxation of thermally induced stress between the glue and crystal is the source of these events. Identifying sources of quasiparticle poisoning is an active problem in superconducting quantum circuits. Here the authors show that the rate of quasiparticle bursts in a cryogenic calorimeter decreases by two orders of magnitude in a low-stress suspended state, suggesting stress as a key mechanism. [ABSTRACT FROM AUTHOR]

Leggett mode is a collective excitation of the phase difference of superconducting condensates whose energy is determined by the strength of Josephson coupling between them. Since the Leggett mode does not perturb the symmetry of Cooper pairs, it should be sensitive to the spin symmetry of the condensate order parameters. Using the point-contact (Andreev) spectroscopy, we have revealed their presence in a three-gap superconducting state realized in MgB2/La0.67Sr0.33MnO3 nanocomposite. Two of them, Δπ and Δσ-enh, are directly connected to intrinsic gaps in MgB2, with a slight increase in the larger σ-gap probably due to a spin-triplet pairing contribution. The third spin-triplet gap Δtr is intrinsic to the La0.67Sr0.33MnO3 compound while manifests itself only when it is proximitized to a superconductor. In such nanocomposite, the appearance of periodic Leggett peaks of two symmetry types is expected to be associated with the spin state of superconducting condensates. The idea of our experiments was to use two types of counter-electrodes, an ordinary normal metal and a spin-polarized conductor. In the first case, the Leggett mode associated with two spin-singlet gaps would be dominant while, due to spin selectivity, excitations of the relative phase for two triplet-spin order parameters are expected to prevail in the second case. In the work, we confirmed this assumption by discovering that the period of Leggett peaks in contacts of the nanocomposite with an Ag tip turned out to be twice as large as those for contacts with La0.67Sr0.33MnO3 and La0.67Ca0.33MnO3 counter-electrodes. [ABSTRACT FROM AUTHOR]

We report on simulations of a novel design of optical design of optical titanium nitride (TiN)-based Kinetic Inductance Detectors (KIDs) in order to improve in order to improve their response to optical photons. We propose to separate the meander from the substrate to trap hot phonons generated by optical photons, preventing their rapid propagation through the substrate. These phonons would in turn contribute to the breaking of more Cooper pairs, thereby increasing the response of the detector. In our design, the meander is suspended a few hundred nanometers above the substrate. Furthermore, reflective gold (Au) or aluminum (Al)-based layers can be placed under the meander to improve photon coupling in the optical wavelengths. [ABSTRACT FROM AUTHOR]

The present investigation explores the spatial distribution of Cooper pair density in graph-shaped arrays of Josephson junctions using a Ginzburg–Landau approach. We specifically investigate double-comb structures and compare their properties with linear arrays as reference systems. Our findings reveal that the peculiar connectivity of the double-comb structure leads to spatial gradients in the order parameter, which can be readily detected through measurements of Josephson critical currents. We present experimental results which indicate the specific dependence of the order parameter on the branches of the graphs and are evidence of the theoretical predictions. [ABSTRACT FROM AUTHOR]

We review the main features of type-III superconductivity. This is a new type of superconductivity that exists in both 2 and 3 spatial dimensions. The main characteristics are emergent granularity and the superconducting gap being opened by a topological mechanism, with no Higgs field involved. Superconductivity is destroyed by the proliferation of vortices and not by the breaking of Cooper pairs, which survive above the critical temperature. The hallmark of this superconductivity mechanism, in 3 spatial dimensions (3D), is the Vogel–Fulcher–Taman scaling of the resistance with temperature. [ABSTRACT FROM AUTHOR]

Nb/Pt and Nb/Cu nanohybrids were sputtered on Si(100) substrate and systematically studied by transmission electron microscopy and magneto-transport measurements. Our experimental findings show that the colossal spin-valve effect measured in a hybrid formed by thick Pt layers deposited on Nb films is absent in equivalent Nb/Cu nanohybrids. In the latter, an ordinary spin-valve effect was experimentally measured and numerically quantified using the superconducting anisotropic phenomenon based on the Ginzburg–Landau model. The unusual enhancement of the spin-valve effect is explained considering the formation of odd-frequency triplet states of Cooper pairs at the Nb/Pt interface induced by the spin–orbit coupling of the Pt component. In a broad perspective, this study strongly evidences the role that the spin–orbit interaction can play for controlling the spin state of Cooper pairs at interfaces of superconductor-based hybrids in the absence of ferromagnetic materials. [ABSTRACT FROM AUTHOR]

In this paper, we study the key and challenging issues arising in the physics of doped cuprate superconductors, which depending on the doping level (or the Fermi energy ε F ) and the characteristic energy ε A of the attractive interaction between the charge carriers (holes or electrons) might be either in the limit of fermionic (weakly-bound) Cooper pairs just like in ordinary metals or in the limit of bosonic (tightly-bound) Cooper pairs. We argue that the underlying mechanism of superconductivity in doped cuprates depends on the fermionic or bosonic nature of Cooper pairs. We examine the validity criterion of the Bardeen–Cooper–Schrieffer (BCS)-like theory of Fermi-liquid superconductivity in these materials and determine the doping level at which this criterion is well satisfied. We find that the specific overdoped cuprates (with ε F ≫ ε A or ε F > 0. 3 eV) can become the BCS-type superconductors. Using a pertinent BCS-like pairing theory, we calculate the superconducting order parameter (defined as a BCS-like gap Δ BCS ) and the critical temperature T c of the superconducting transition and the doping dependences of Δ BCS and T c in various overdoped cuprates. Our results for Δ BCS and T c in specific overdoped cuprates are in fair agreement with the experimental findings reported for these systems. [ABSTRACT FROM AUTHOR]

The evolution of the temperature dependence of the pseudogap Δ*(T) in optimally doped (OD) YBa2Cu3O7–δ (YBCO) films with the superconducting critical temperature Tc = 88.7 K under the influence of a magnetic field B has been studied in detail. It has been established that the shape of Δ*(T) for various B over the entire range from the pseudogap opening temperature T* to T01, below which superconducting fluctuations occur, has a wide maximum at the BEC-BCS crossover temperature Tpair, which is typical for OD films and untwinned YBCO single crystals. T* was shown to be independent on B, whereas Tpair shifts to the low-temperature region along with the increase in B, while the maximum value of Δ*(Tpair) remains practically constant regardless of B. It was revealed that as the field increases, the low-temperature maximum near the 3D-2D transition temperature T0 is blurred and disappears at B > 5 T. Moreover, above the Ginzburg temperature TG, which limits superconducting fluctuations from below, for B > 0.5 T, a minimum appears on Δ*(T) at Tmin, which becomes very pronounced with a further increase in B. As a result, the overall value of Δ*(T) decreases noticeably most likely due to the pair-breaking effect. A comparison of Δ*(T) near Tc with the Peters–Bauer theory shows that the density of fluctuating Cooper pairs actually decreases from ⟨n↑n↓⟩ ≈ 0.31 at B = 0 to ⟨n↑n↓⟩ ≈ 0.28 in the field of 8 T. The observed behavior of Δ*(T) around Tmin is assumed to be due to the influence of a two-dimensional vortex lattice created by the magnetic field, which prevents the formation of fluctuating Cooper pairs near Tc. [ABSTRACT FROM AUTHOR]

The past two decades have seen an explosion of work on Josephson junctions containing ferromagnetic materials. Such junctions are under consideration for applications in digital superconducting logic and memory. In the presence of the exchange field, spin–singlet Cooper pairs from conventional superconductors undergo rapid phase oscillations as they propagate through a ferromagnetic material. As a result, the ground-state phase difference across a ferromagnetic Josephson junction oscillates between 0 and π as a function of the thickness of the ferromagnetic material. π-junctions have been proposed as circuit elements in superconducting digital logic and in certain qubit designs for quantum computing. If a junction contains two or more ferromagnetic layers whose relative magnetization directions can be controlled by a small applied magnetic field, then the junction can serve as the foundation for a memory cell. Success in all of those applications requires careful choices of ferromagnetic materials. Often, materials that optimize magnetic properties do not optimize supercurrent propagation, and vice versa. In this review, we discuss the significant progress that has been made in identifying and testing a wide range of ferromagnetic materials in Josephson junctions over the past two decades. The review concentrates on ferromagnetic metals, partly because eventual industrial applications of ferromagnetic Josephson junctions will most likely start with metallic ferromagnets (either in all metal junctions or junctions containing an insulating layer). We will briefly mention work on non-metallic barriers, including ferromagnetic insulators, and some of the exciting work on spin–triplet supercurrent in junctions containing non-collinear magnetic inhomogeneity. [ABSTRACT FROM AUTHOR]

Phonon-induced Cooper pair breaking, inciting nonequilibrium quasiparticle (QP) bursts, is known to deteriorate the performance of superconducting devices. However, a detailed understanding of QP-phonon dynamics is lacking due to the absence of a well-established theoretical framework. This paper presents a fully ab initio scheme of calculating nonequilibrium, polarization-dependent QP-phonon dynamics in superconductors. The authors find that with only an 8% deviation from the equilibrium phonon Bose–Einstein distribution, the resulting nonequilibrium QP population is 83 times larger than the equilibrium Fermi–Dirac distribution, and the longitudinal acoustic (LA) phonon polarization is most responsible for QP generation. The authors demonstrated that the qubit transition rate in Josephson junction-based transmon qubits is increased by orders of magnitude when taking these nonequilibrium distributions into account, compared to equilibrium distributions. This framework allows an in-depth exploration of nonequilibrium QP-phonon dynamics in various Josephson-junction-based superconducting devices. It paves the way for formulating advanced phonon shielding strategies to target the LA polarization, potentially leading to enhanced device performance, such as increased coherence time of transmon qubits or reduced thermal noise in cryogenics. [ABSTRACT FROM AUTHOR]

Finite-momentum Cooper pairing is an unconventional form of superconductivity that is widely believed to require finite magnetization. Altermagnetism is an emerging magnetic phase with highly anisotropic spin-splitting of specific symmetries, but zero net magnetization. Here, we study Cooper pairing in metallic altermagnets connected to conventional s-wave superconductors. Remarkably, we find that the Cooper pairs induced in the altermagnets acquire a finite center-of-mass momentum, despite the zero net magnetization in the system. This anomalous Cooper-pair momentum strongly depends on the propagation direction and exhibits unusual symmetric patterns. Furthermore, it yields several unique features: (i) highly orientation-dependent oscillations in the order parameter, (ii) controllable 0-π transitions in the Josephson supercurrent, (iii) large-oblique-angle Cooper-pair transfer trajectories in junctions parallel with the direction where spin splitting vanishes, and (iv) distinct Fraunhofer patterns in junctions oriented along different directions. Finally, we discuss the implementation of our predictions in candidate materials such as RuO2 and KRu4O8. An altermagnet has highly anisotropic spin splitting but zero net magnetization. Here, S.-B. Zhang et al. theoretically study the behavior of s-wave superconductor/altermagnet hybrid structures, finding that Cooper pairs in the proximitized altermagnet have an anisotropic non-zero momentum. [ABSTRACT FROM AUTHOR]

We discuss the two-step transitions in superconductors, where the intermediate state between the Cooper pair state and the normal metal is the 4-fermion condensate, which is called the intertwined vestigial order. We discuss different types of the vestigial order, which are possible in the spin-triplet superfluid 3He, and the topological objects in the vestigial phases. Since in 3He the order parameter represents the analog of gravitational tetrads, we suggest that the vestigial states are possible in quantum gravity. As in superconductors, the fermionic vacuum can experience two consequent phase transitions. At first transition the metric appears as the bilinear combination of tetrads , while the tetrad order parameter is still absent, . This corresponds to the bosonic Einstein general relativity, which emerges in the fermionic vacuum. The nonzero tetrads appear at the second transition, where a kind of the Einstein–Cartan–Sciama–Kibble tetrad gravity is formed. This suggests that on the levels of particles, gravity acts with different strength on fermions and bosons. [ABSTRACT FROM AUTHOR]

The combination of strongly coupled Cooper pairs and weak superconducting fluctuations is an important prerequisite for achieving high-temperature superconductivity. The review is devoted to the implementation of this condition in multiband superconductors, in which strongly coupled pairs in the shallow conduction band (the Fermi level is close to the band edge) coexist with ordinary, weakly fluctuating Cooper pairs formed in the deep band. As a result of the Josephson coupling between condensates in different bands, such a system is characterized by a high critical coherence temperature due to the presence of strongly coupled pairs and the suppression of superconducting fluctuations. This suppression does not require any special preconditions, and is almost total even if the Josephson coupling between the bands is weak. [ABSTRACT FROM AUTHOR]

WDs and neutron stars are far-reaching and multi-faceted laboratories in the hunt for dark matter. We review detection prospects of wave-like, particulate, macroscopic and black hole dark matter that make use of several exceptional properties of compact stars, such as ultra-high densities, deep fermion degeneracies, low temperatures, nucleon superfluidity, strong magnetic fields, high rotational regularity, and significant gravitational wave emissivity. Foundational topics first made explicit in this document include the effect of the "propellor phase" on neutron star baryonic accretion, and the contribution of Auger and Cooper pair breaking effects to neutron star heating by dark matter capture. [ABSTRACT FROM AUTHOR]

In order to investigate the significance of electron–phonons interaction in the origin of high T c superconductivity, we synthesized Cd-doped Cu 0. 5 Tl 0. 5 (BaCa)(CaMg) 1. 5 Cu 4 − y CdyO 1 2 − δ (y = 0 , 1, 2, 3) samples and studied the superconducting properties. Onset temperature of the superconductivity Cu 0. 5 Tl 0. 5 (BaCa)(CaMg) 1. 5 Cu 4 − y CdyO 1 2 − δ (y = 0 , 1, 2, 3) samples suppress with the increased Cd doping ratio in the final. The phonon modes are associated to the vibrations of apical and planar oxygen whereas the CuO2 planar oxygen modes are observed to harden with increasing Cd ratio in sample doping. The phase relaxation time is suppressed for the superconducting charge carriers in Cd-doped samples. The energy amount required to break the Cooper pairs apart increases. Dielectric measurements of Cu 0. 5 Tl 0. 5 (BaCa)(CaMg) 1. 5 Cu 4 − y CdyO 1 2 − δ (y = 0 , 1, 2, 3) samples have been done. [ABSTRACT FROM AUTHOR]

Superfluid 3He is a paradigm for odd-parity Cooper pairing, ranging from neutron stars to uranium-based superconducting compounds. Recently it has been shown that 3He, imbibed in anisotropic silica aerogel with either positive or negative strain, preferentially selects either the chiral A-phase or the time-reversal-symmetric B-phase. This control over basic order parameter symmetry provides a useful model for understanding imperfect unconventional superconductors. For both phases, the orbital quantization axis is fixed by the direction of strain. Unexpectedly, at a specific temperature Tx, the orbital axis flops by 90∘, but in reverse order for A and B-phases. Aided by diffusion limited cluster aggregation simulations of anisotropic aerogel and small angle X-ray measurements, we are able to classify these aerogels as either "planar" and "nematic" concluding that the orbital-flop is caused by competition between short and long range structures in these aerogels. When imbibed in an anisotropic silica aerogel, superfluid 3He undergoes a temperature-driven "orbital flop" transition, where the orbital quantization axis rotates by 90 degrees. Here, by simulating planar and nematic aerogel, M. D. Nguyen et al. show that the orbital flop transition is driven by the distinct large- and small-scale structures of the aerogel. [ABSTRACT FROM AUTHOR]

Coherence and tunneling play central roles in quantum phenomena. In a tunneling event, the time that a particle spends inside the barrier has been fiercely debated. This problem becomes more complex when tunneling repeatedly occurs back and forth, and when involving many particles. Here we report the measurement of the coherence time of various charge states tunneling in a nanowire-based tunable Josephson junction; including single charges, multiple charges, and Cooper pairs. We studied all the charge tunneling processes using Landau-Zener-Stückelberg-Majorana (LZSM) interferometry, and observed high-quality interference patterns under a microwave drive. In particular, the coherence time of the charge states tunneling back and forth was extracted from the interference fringes in Fourier space. In addition, our measurements show the break-up of Cooper pairs, from a macroscopic quantum coherent state to individual particle states. Besides the fundamental research interest, our results also establish LZSM interferometry as a powerful technique to explore the coherence time of charges in hybrid devices. [ABSTRACT FROM AUTHOR]

The effects of hybridization and impurity (magnetic and nonmagnetic) potentials on the pairing symmetries and magnetic response of a two-band superconductor with an equal-time s -wave interband pairing order parameter in the framework of Green's function technique are investigated theoretically. First, the effects of spin-independent and spin-dependent hybridization on the generation of even- or odd-frequency Cooper pairs which determines the symmetry classification and the response of the superconductor are studied. Next, the impurity effect on creating different symmetry classes and the kernel response function of a two-band superconductor are discussed. By separating the contributions of even- and odd-frequency pairing to the Meissner kernel, it is shown that the competition between these two terms determines the total Meissner effect of the superconductor. For a two-band spin-singlet superconductor, nonmagnetic impurity scatterings do not change transition temperature according to Anderson's theorem, while both intra- and interband magnetic impurity scattering cause superconducting transition temperature suppression with the rate following the Abrikosov–Gor'kov theory. For spin-triplet pairing, interband magnetic scattering has no impact on pair breaking, whereas intraband magnetic scattering acts as a pair breaker and suppresses the transition temperature in the Born limit. In this case, the odd-frequency superconducting pairs can be induced in the simultaneous presence of both intra- and interband magnetic impurities. Thus, by controlling the concentration of magnetic impurities, it is possible to engineer triplet-pairing odd-frequency superconductors with a total diamagnetic Meissner response which stabilizes the superconducting state. This technique opens up an avenue for designing stable odd-frequency superconductors. [ABSTRACT FROM AUTHOR]

Due to the great differences in electron pairing characteristics between the hole-type (p-type) high-temperature superconductor (HTS) and the electron-type (n-type) HTS, when the Cooper pairs enter from a p-type to an n-type HTS or an n-type to a p-type HTS, pairing adjustment or even the recombination of them will inevitably occur at the interface, and the superconducting current dominated by them will be bound to change. Therefore, it is possible to better understand the electron pairing mechanism of the HTS and develop new HTS junction devices by studying these changes. In this paper, p-/n-type YBa2Cu3O7−δ/Nd1.85Ce0.15CuO4 (YBCO/NCCO) heterostructures were prepared via pulsed laser deposition on (00l)-oriented single-crystal SrTiO3 substrates. X-ray diffraction measurements indicate that the NCCO films prepared on YBCO do not exhibit good c-axis epitaxial growth, while excellent c-axis epitaxial growth is obtained for YBCO/NCCO heterostructures with NCCO at the bottom. Due to the high-temperature oxygen atmosphere and the deoxygenation process, the superconducting electrical properties of the bilayer structure are seriously degraded, and it is not possible to obtain good superconducting electrical properties for both the upper and lower layers using the traditional preparation process based on an oxygen atmosphere. Subsequently, the effects of different growth atmospheres on the electrical properties of the YBCO superconductors were studied, and high-quality YBCO superconducting films could be grown in oxygen, nitrous oxide, and nitrogen atmospheres. However, the oxygen and nitrous oxide atmospheres degrade the superconducting electrical properties of the underlying NCCO layer, while the nitrogen atmosphere does not seem to affect it significantly. YBCO/NCCO superconducting bilayers with critical transition temperatures of 85 and 8 K for YBCO and NCCO, respectively, were finally prepared by growing NCCO in an oxygen atmosphere and YBCO in a nitrogen atmosphere using a low-temperature oxygenation process. The successful preparation of the p-/n-type HTS heterostructure will help further study on the HTS. [ABSTRACT FROM AUTHOR]

In this study, the high temperature polycrystalline superconductor Y 3 B a 5 C u 8 O 18 ± δ (shortened-Y358) doped with 0.50 wt.% SnO2 (Tin-oxide) nanoparticles was produced through solid state reaction process. The excess conductivity of the sample as a function of magnetic field was systematically investigated by data of the resistivity. Two different procedures were used to determine the mean field temperature. The excess conductivity scaling, initiated through fluctuations, was obtained by two (2D) and three (3D) dimensional prototypes. In the region of close to the critical temperature, the Aslamazov and Larkin (AL) model was applied to achieve the mean field associated with the coherence length aimed at the sample. In various magnetic fields, while the temperature increased, a changeover from the 2D to the 3D area was detected at a crossover temperature ( T 3 D - 2 D ). The Maki-Thompson and Lawrence-Doniach (MT-LD) theory was examined to acquire the crossover temperatures. The results confirm that this temperature ( T 3 D - 2 D ) increases while the magnetic field rises. The crossover temperature was used for finding the phase-relaxation time correlated to the fluctuation pairs. The fluctuation pair lifetime, τ φ , accompany with the coherence length, ξ , were calculated by means of the transition temperature and the reduced temperature changeover data when the magnetic fields were applied to the sample. Increasing the magnetic field causes the reduction of phase-relaxation time. In all cases, because of the Cooper pairs, the excess conductivity dominates 2D dimensionality performance. [ABSTRACT FROM AUTHOR]

Superconducting materials exhibit unique physical properties and have great scientific value and vast industrial application prospects. However, due to limitations, such as the critical temperature (TC) and critical current density (JC), the large-scale application of superconducting materials remains challenging. Chemical doping has been a commonly used method to enhance the superconductivity of B(P)SCCO. However, satisfactory enhancement results have been difficult to achieve. In this study, we introduce green-light GaN p-n junction particles as inhomogeneous phases into B(P)SCCO polycrystalline particles to form a smart meta-superconductor (SMSC) structure. Based on the electroluminescence properties of the p-n junction, the Cooper pairs were stimulated and strengthened to enhance the superconductivity of B(P)SCCO. The experimental results demonstrate that the introduction of inhomogeneous phases can indeed enhance the critical temperature TC, critical current density JC, and complete diamagnetism (Meissner effect) of B(P)SCCO superconductors. Moreover, when the particle size of the raw material of B(P)SCCO is reduced from 30 to 5 μm, the grain size of the sintered samples also decreases, and the optimal doping concentration of the inhomogeneous phases increases from 0.15 wt.% to 0.2 wt.%, further improving the superconductivity. [ABSTRACT FROM AUTHOR]

The Josephson junction is a building block of quantum circuits. Its behavior, well understood when treated as an isolated entity, is strongly affected by coupling to an electromagnetic environment. In 1983, Schmid predicted that a Josephson junction shunted by a resistance exceeding the resistance quantum RQ = h/4e2 ≈ 6.45 kΩ for Cooper pairs would become insulating since the phase fluctuations would destroy the coherent Josephson coupling. However, recent microwave measurements have questioned this interpretation. Here, we insert a small Josephson junction in a Johnson-Nyquist-type setup where it is driven by weak current noise arising from thermal fluctuations. Our heat probe minimally perturbs the junction's equilibrium, shedding light on features not visible in charge transport. We find that the Josephson critical current completely vanishes in DC charge transport measurement, and the junction demonstrates Coulomb blockade in agreement with the theory. Surprisingly, thermal transport measurements show that the Josephson junction acts as an inductor at high frequencies, unambiguously demonstrating that a supercurrent survives despite the Coulomb blockade observed in DC measurements. The predicted dissipative quantum phase transition in a Josephson junction coupled to resistive environment has been examined in recent experiments. In a heat transport experiment, Subero et al. show that the junction acts as an inductor at high frequencies, while DC charge transport confirms insulating behaviour. [ABSTRACT FROM AUTHOR]

Using an operator scattering approach, we analyze the quantum dynamics of an ultrasensitive electrometer—a Cooper pair transistor embedded in a quarter-wave microwave cavity (cCPT). While the cCPT is inherently a tunable, strongly nonlinear system affording a diverse range of functionalities, we restrict our present analysis to a necessary first investigation of its linear charge sensing capabilities, limiting to low pump powers corresponding to an average cavity photon number of ≲ 1. Assuming realizable cCPT parameters [B. L. Brock et al., Phys. Rev. Applied 15, 044009 (2021)], and not including noise from the subsequent amplifier chain, we predict the fundamental, photon shot noise-limited charge sensitivity to be 0.12 μ e / Hz when the pumped cavity has an average of one photon and the cCPT is operated close to charge degeneracy. This is to be compared with a first reported charge sensitivity value of 14 μ e / Hz in the single-photon regime [B. L. Brock et al., arXiv:2102.05362 (2021)]. [ABSTRACT FROM AUTHOR]

The article discusses the exploration of quantum magnetic materials and their importance in developing modern information technology. The researchers investigate a specific quantum magnetic system called the Shastry-Sutherland model (SSM) and its realization in SrCu2(BO3)2. They study the behavior of the system under high magnetic fields and observe the appearance of field-induced magnetization plateaux. Through neutron scattering experiments and model calculations, they provide evidence for the condensation of bound states of triplets, forming a spin nematic phase. The researchers suggest that high-field inelastic neutron scattering is a valuable tool for studying spin dynamics in various systems. [Extracted from the article]

UTe2 is one triplet superconductor that defies conventional relation between ferromagnetism and superconductivity. Our search for a theoretical explanation starts with one spin-triplet state of two electrons and construct a two-particle exchange interaction that favors the formation of Cooper pairs under the configuration. A modified application of the Bardeen–Cooper–Schrieffer (BCS) theory using parameters derived from ab-initio density functional calculations for electrons and phonons enables us to derive the critical temperature of 1.64 K and an average superconducting gap of 0.25 meV at 0 K. We extend the investigation further into the superconductivity under pressure, showing how Tc and the gap of UTe2 change under compression in ways that are consistent with the results of experiment. [ABSTRACT FROM AUTHOR]

UTe2 is one triplet superconductor that defies conventional relation between ferromagnetism and superconductivity. Our search for a theoretical explanation starts with one spin-triplet state of two electrons and construct a two-particle exchange interaction that favors the formation of Cooper pairs under the configuration. A modified application of the Bardeen–Cooper–Schrieffer (BCS) theory using parameters derived from ab-initio density functional calculations for electrons and phonons enables us to derive the critical temperature of 1.64 K and an average superconducting gap of 0.25 meV at 0 K. We extend the investigation further into the superconductivity under pressure, showing how Tc and the gap of UTe2 change under compression in ways that are consistent with the results of experiment. [ABSTRACT FROM AUTHOR]

The superconducting state and mechanism are among the least understood phenomena in twisted graphene systems. Recent tunneling experiments indicate a transition between nodal and gapped pairing with electron filling, which is not naturally understood within current theory. We demonstrate that the coexistence of superconductivity and flavor polarization leads to pairing channels that are guaranteed by symmetry to be entirely band-off-diagonal, with a variety of consequences: most notably, the pairing invariant under all symmetries can have Bogoliubov Fermi surfaces in the superconducting state with protected nodal lines, or may be fully gapped, depending on parameters, and the band-off-diagonal chiral p-wave state exhibits transitions between gapped and nodal regions upon varying the doping. We demonstrate that band-off-diagonal pairing can be the leading state when only phonons are considered, and is also uniquely favored by fluctuations of a time-reversal-symmetric intervalley coherent order motivated by recent experiments. Consequently, band-off-diagonal superconductivity allows for the reconciliation of several key experimental observations in graphene moiré systems. The authors theoretically study superconductivity in twisted-bilayer and twisted-trilayer graphene, finding that flavor polarization allows for Cooper pairing in which the pairs consist of electrons in different bands. Both intervalley phonons and fluctuations of a time-reversal-symmetric intervalley coherent order can favor such pairing. [ABSTRACT FROM AUTHOR]

The unconventional superconductor Sr2RuO4 has long served as a benchmark for theories of correlated-electron materials. The determination of the superconducting pairing mechanism requires detailed experimental information on collective bosonic excitations as potential mediators of Cooper pairing. We have used Ru L3-edge resonant inelastic x-ray scattering to obtain comprehensive maps of the electronic excitations of Sr2RuO4 over the entire Brillouin zone. We observe multiple branches of dispersive spin and orbital excitations associated with distinctly different energy scales. The spin and orbital dynamical response functions calculated within the dynamical mean-field theory are in excellent agreement with the experimental data. Our results highlight the Hund metal nature of Sr2RuO4 and provide key information for the understanding of its unconventional superconductivity. The authors present resonant inelastic x-ray scattering measurements of Sr2RuO4 in the normal Fermi-liquid state. They find that spin excitations are confined below 200 meV, while orbital fluctuations appear only at higher energies. This separation of energy scales is a hallmark of Hund's-rule-induced electron correlations. [ABSTRACT FROM AUTHOR]

On the recent report of a field-induced first order transition in the superconducting state of CeRh2As2, which is a possible indication of a parity-switching transition of the superconductor, the microscopic physics is still under investigation. However, if two competing paring channels of opposite parities do exist, a particle-particle collective mode referred to as the Bardasis-Schrieffer (BS) mode should generically exist below the pair-breaking continuum. The BS mode of the CeRh2As2 superconductor can couple to the light, as it arises from a pairing channel with the parity opposite to that of the superconducting condensate. Here, by using a generic model Hamiltonian we carry out a qualitative investigation on the excitation energy of the BS mode with respect to the out-of-plane magnetic fields and its contribution to the optical conductivity. Our findings indicate that the distinct coupling between the BS mode and the light can serve as evidence for the competing odd-parity channels of CeRh2As2 and other locally non-centrosymmetric superconductors. Superconductors with odd-parity Cooper pairs are rare and their experimental confirmation is significantly challenging. In the CeRh2As2 superconductor, the authors' investigation reveals that the presence of competing pairings with opposite parities gives rise to a unique collective mode, which can be observed through the optical response. [ABSTRACT FROM AUTHOR]

Proximity-induced long-range spin-triplet supercurrents, important for the field of superconducting spintronics, are generated in superconducting/ferromagnetic heterostructures when interfacial magnetic inhomogeneities responsible for spin mixing and spin flip scattering are present. The multilayer stack Nb/Cr/Fe/Cr/Nb has been shown to support such currents when fabricated into Josephson junction devices. However, creating pure spin currents controllably in superconductors outside of the Josephson junction architecture is a bottleneck to progress. Recently, ferromagnetic resonance was proposed as a possible direction, the signature of pure supercurrent creation being an enhancement of the Gilbert damping below the superconducting critical temperature, but the necessary conditions are still poorly established. Here, we demonstrate that pumping pure spin currents into a superconductor in the presence of an external magnetic field is only possible when conditions supporting proximity-induced spin-triplet effects are satisfied. Our study is an important step forward for pure spin supercurrent creation, considerably advancing the field of superconducting spintronics. Superconducting spintronics has the potential to enhance device functionality by realising spin polarised supercurrents with greater coherence and reduced dissipation. Here, using ferromagnetic resonance, the authors investigate the temperature dependence of the Gilbert damping for the Fe layer of Nb/Fe/Nb and Nb/Cr/Fe/Cr/Nb stacks and the impact superconducting spin triplets have on the spin pumping behaviour. [ABSTRACT FROM AUTHOR]