Triplet Component Research Articles

Триплетные сверхпроводящие корреляции гибридной меза-структуры с двухслойной ферромагнитной прослойкой

We present results on electron transport in hybrid Josephson mesa-structure Sd/F1F2/S, consisting of epitaxial films of cuprate superconductor YBa2Cu3O7-δ (Sd), bi-layer ferromagnetic interlayer (F1F2), thin film of metallic Nb was deposited on the top of a thin protective Au film layer used as the upper superconducting electrode (S). The long-range triplet component of superconducting correlations arises when strontium ruthenate SrRuO3 F1 and manganiteLa0.7Sr0.3MnO3 with non-collinear magnetizations are used as ferromagnetic material F2. Superconducting current took place up to the thickness d = 52 nm of the F1F2 interlayer. Superconducting current disappeared in the case of a single ferromagnetic interlayer of manganite (La0.7Sr0.3MnO3 or La0.7Ca0.3MnO3) and SrRuO3 with minimized thicknesses, limited by the occurrence of pinholes. The magnetic field properties of mesa-structure are discussed as well, along with the impact of the second harmonic in the superconducting current-phase relation.

Analysis of the S1 triplet component in the DarkSide-50 experiment

The DarkSide-50 (DS-50) experiment aims at the direct detection of weakly interacting massive particles. It is a dual-phase liquid argon time projection chamber (LAr TPC) where Dark Matter (DM), which constitutes five sixths of all matter in the universe, is expected to interact with an argon nucleus resulting in a nuclear recoil. A scintillation signal (S1) is produced as a result of the ionising events from the DM-Ar interaction. The impurities in LAr, such as O,2, N2, H2O, etc., at the ppm level, quench the scintillation photons, leading to a reduction in the observed lifetime of the triplet state. In this contribution, the effect of impurities on the triplet lifetime is analyzed for individual events using DS-50 data, with a primary focus on nitrogen, one of the candidates for the impurities in LAr hypothesized to cause a suppression of triplet lifetime. This is done by determining the lifetime of the triplet component with a known purity, which can be used as a reference for the purity level of argon used in current and future dark matter searches.

Use of FOLFOXIRI Plus Bevacizumab and Subsequent Therapies in Metastatic Colorectal Cancer: An Age-Stratified Analysis

BackgroundTreatment recommendations for metastatic colorectal cancer (mCRC) do not differ by age group; nevertheless, aggressive multiagent chemotherapy comprising FOLFOXIRI+bevacizumab (triplet+bev) is routinely administered in younger patients. This study analyzed real-world data on index triplet+bev use and subsequent systemic therapies. Materials and MethodsThis retrospective, observational cohort study was conducted in patients aged ≥ 18 years with mCRC, who were initiated on triplet+bev. Data were derived from the Optum de-identified electronic health record dataset. ResultsOf 36,056 patients, 14%, 36%, and 50% were aged 18-49, 50-64, and ≥ 65 years, respectively. During the study period (2010-2021), triplet+bev use increased in patients aged 18-49 years (1%-4%) but remained at approximately 3% and 1% in patients aged 50-64 and ≥ 65 years, respectively. Patient demographics and clinical characteristics varied slightly; of patients receiving triplet+bev (n = 921) versus nontriplet+bev (n = 35,132) most were male (57% vs. 52%), resided in the Midwest (54% vs. 49%) and Northeast (18% vs. 14%) US regions, and had secondary malignancies (86% vs. 73%). Following triplet+bev, most patients received subsequent therapies (including continued triplet component therapies; 97%) or subsequent “new” therapies (therapies that did not include any agents comprising triplet+bev; 57%), most frequently EGFR inhibitors (28%) and regorafenib (21%), with a similar trend among all age groups. ConclusionsOverall, this study shows that younger patients with mCRC are more likely to receive first-line triplet+bev. These results also reveal that nonchemotherapy options are often used beyond first-line triplet chemotherapy for patients with mCRC.

Knowledge Graph Embedding via Triplet Component Interactions

In knowledge graph embedding, multidimensional representations of entities and relations are learned in vector space. Although distance-based graph embedding methods have shown promise in link prediction, they neglect context information among the triplet components, i.e., the head_entity, relation, and tail_entity, limiting their ability to describe multivariate relation patterns and mapping properties. Such context information denotes the entity structural association inside the same triplet and implies the correlation between entities that are not directly connected. In this work, we propose a novel knowledge graph embedding model that explicitly considers context information in graph embedding via triplet component interactions (TCIE). To build connections between components and incorporate contextual information, entities and relations are represented as vectors comprised of two specialized parts, enabling comprehensive interaction. By simultaneously interacting with one-hop related head and tail entities, TCIE strengthens the connections between distant entities and enables contextual information to be transmitted across the knowledge graph. Mathematical proofs and experiments are performed to analyse the modelling ability of TCIE in knowledge graph embedding. TCIE shows a strong capacity for modelling four relation patterns (i.e., symmetry, antisymmetry, inverse, and composition) and four mapping properties (i.e., one-to-one, one-to-many, many-to-one, and many-to-many). The experimental evaluation of ogbl-wikikg2, ogbl-biokg, FB15k, and FB15k-237 shows that TCIE achieves state-of-the-art results in link prediction.

Triplet correlations in Cooper pair splitters realized in a two-dimensional electron gas

Cooper pairs occupy the ground state of superconductors and are typically composed of maximally entangled electrons with opposite spin. In order to study the spin and entanglement properties of these electrons, one must separate them spatially via a process known as Cooper pair splitting (CPS). Here we provide the first demonstration of CPS in a semiconductor two-dimensional electron gas (2DEG). By coupling two quantum dots to a superconductor-semiconductor hybrid region we achieve efficient Cooper pair splitting, and clearly distinguish it from other local and non-local processes. When the spin degeneracy of the dots is lifted, they can be operated as spin-filters to obtain information about the spin of the electrons forming the Cooper pair. Not only do we observe a near perfect splitting of Cooper pairs into opposite-spin electrons (i.e. conventional singlet pairing), but also into equal-spin electrons, thus achieving triplet correlations between the quantum dots. Importantly, the exceptionally large spin-orbit interaction in our 2DEGs results in a strong triplet component, comparable in amplitude to the singlet pairing. The demonstration of CPS in a scalable and flexible platform provides a credible route to study on-chip entanglement and topological superconductivity in the form of artificial Kitaev chains.

Superconductivity in Noncentrosymmetric LaNiZn Single Crystal

In this study, we observed bulk superconductivity in LaNiZn below Tc = 1.5 K, as confirmed by its electrical transport and specific heat capacity (ΔCel/γTc = 1.41). The upper critical fields along the hexagonal crystallographic c-axis and in the basal plane at 30 mK were found to be 0.36 and 0.24 T, respectively, suggesting mainly an orbital mechanism for field-induced depairing and a negligible spin triplet component in the superconducting order parameter. The angular dependence of Hc2 is explained by an effective mass model with an oblate-shaped effective Fermi surface. Our experimental and band calculation under local density approximation results suggested that LaNiZn is a Bardeen–Cooper–Schrieffer s-wave-type superconductor in the dirty limit, possibly involving multiple bands.

A Geminal Method Based on the Generalized Electron Pairing Applied to the Heisenberg Model of Hydrocarbons

In the approximate valence bond (VB) description of molecular electronic structures, the resonating VB effect might be incorporated in an efficient manner by mixing the triplet component into conventional singlet geminals. We developed a variational optimization scheme for this generalized pairing type wave function in the framework of the spin Hamiltonian model. With numerical verifications, we found the resonance stabilization is partially described through the contamination of higher spin states for molecules such as non-Kekulé hydrocarbons.

Topological superconductivity driven by correlations and linear defects in multiband superconductors

There have been several proposals for platforms sustaining topological superconductivity in high temperature superconductors, in order to make use of the larger superconducting gap and the expected robustness of Majorana zero modes towards perturbations. In particular, the iron-based materials offer relatively large $T_c$ and nodeless energy gaps. In addition, atomically flat surfaces enable the engineering of defect structures and the subsequent measurement of spectroscopic properties to reveal topological aspects. From a theory perspective, a materials-specific description is challenging due to the correlated nature of the materials and complications arising from the multiband nature of the electronic structure. Here we include both aspects in realistic interacting models, and find that the correlations themselves can lead to local magnetic order close to linear potential scattering defects at the surface of the superconductor. Using a self-consistent Bogoliubov-de Gennes framework in a real-space setup using a prototype electronic structure, we allow for arbitrary magnetic orders and show how a topological superconducting state emerges. The calculation of the topological invariant and the topological gap allows us to map out the phase diagram for the case of a linear chain of potential scatterers. While intrinsic spin-orbit coupling is not needed to enter the topological state in presence of spin-spiral states, it enlarges the topological phase. We discuss the interplay of a triplet component of the superconducting order parameter and the spin spiral leading effectively to extended spin orbit coupling terms, and connect our results to experimental efforts on the Fe(Se,Te) system.

Tuning interfacial two-component superconductivity in CoSi2/TiSi2 heterojunctions via TiSi2 diffusivity.

We report the observation of enhanced interfacial two-component superconductivity possessing a dominant triplet component in nonmagnetic CoSi2/TiSi2 superconductor/normal-metal planar heterojunctions. This is accomplished through the detection of odd-frequency spin-triplet even-parity Cooper pairs in the diffusive normal-metal component of T-shaped proximity junctions. We show that by modifying the diffusivity of the normal-metal part, the transition temperature enhancement can be tuned by a factor of up to 2.3 while the upper critical field increases by up to a factor of 20. Our data suggest that the C49 phase of TiSi2, which is stabilized in confined geometries, underlies this enhancement. These findings are addressed via a Ginzburg-Landau model and the quasi-classical theory. We also relate our findings to the enigmatic 3-K phase reported in Sr2 RuO4.

Magnetically textured superconductivity in elemental rhenium

Recent $\ensuremath{\mu}\mathrm{SR}$ measurements revealed remarkable signatures of spontaneous magnetism coexisting with superconductivity in elemental rhenium. Thus, pure rhenium could be the first elemental crystal where unconventional superconductivity is realized in nature. Here we provide a quantitative theory that uncovers the nature of the superconducting instability by incorporating every details of the electronic structure together with spin-orbit coupling and multiorbital physics. We show that conventional $s$-wave superconductivity combined with strong spin-orbit coupling is inducing even-parity odd-orbital spin triplet Cooper pairs, and in presence of a screw-axis Cooper pairs' migration between the induced equal-spin triplet component leads to an exotic magnetic state with atomic-scale texture. Our first-principles-based model contains two phenomenological parameters that characterizes the pairing interaction fixed by the experimental value of the superconducting transition temperature and the slope of the specific heat, and allows quantitative prediction of the magnetic structure.

Two-component doublet-triplet scalar dark matter stabilizing the electroweak vacuum

A two-component scalar dark matter scenario comprising an additional scalar doublet and a $Y=0$ scalar triplet is proposed. Key features of the ensuing dark matter phenomenology are highlighted with emphasis on interconversion between the two dark matter components. For suitable choices of the model parameters, we show that such interconversion can explain the observed relic abundance when the doublet dark matter component has mass in the desert region while the triplet component has sub-TeV mass. This finding is important in the context of such mass regions known to predict underabundant relic density for the stand-alone cases of the scalar doublet and triplet. In addition, we also show that the present scenario can stabilize the electroweak vacuum up to the Planck scale in the parameter space responsible for the requisite dark matter observables.

Quasiparticle density of states and triplet correlations in superconductor/ferromagnetic-insulator structures across a sharp domain wall

A ferromagnetic insulator (FI) in contact with a superconductor (S) is known to induce a spin splitting of the BCS density of states at the FI/S interface. This spin splitting causes the Cooper pairs to reduce their singlet-state correlations and acquire odd-in-frequency triplet correlations. We consider a diffusive FI/S bilayer with a sharp magnetic domain wall in the FI and study the local quasiparticle density of states and triplet superconducting correlations. In the case of collinear alignment of the domains, we obtain analytical results by solving the Usadel equation. For a small enough exchange field or weak superconductivity, we also find an analytical expression for arbitrary magnetic textures, which reveals how the triplet component vector depends on the local magnetization of the FI. For an arbitrary angle between the magnetizations and the strength of the exchange field, we numerically solve the problem of a sharp domain wall. We finally propose two different setups based on FI/S/F stacks, where F is a ferromagnetic layer, to filter out singlet pairs and detect the presence of triplet correlations via tunneling differential conductance measurements.

Dynamics of Two Ferromagnetic Insulators Coupled by Superconducting Spin Current.

A conventional superconductor sandwiched between two ferromagnets can maintain coherent equilibrium spin current. This spin supercurrent results from the rotation of odd-frequency spin correlations induced in the superconductor by the magnetic proximity effect. In the absence of intrinsic magnetization, the superconductor cannot maintain multiple rotations of the triplet component but instead provides a Josephson type weak link for the spin supercurrent. We determine the analog of the current-phase relation in various circumstances and show how it can be accessed in experiments on dynamic magnetization. In particular, concentrating on the magnetic hysteresis and the ferromagnetic resonance response, we show how the spin supercurrent affects the nonequilibrium dynamics of magnetization which depends on a competition between spin supercurrent mediated static exchange contribution and a dynamic spin pumping contribution. Depending on the outcome of this competition, a mode crossing in the system can either be an avoided crossing or mode locking.

Charge and spin supercurrents in magnetic Josephson junctions with spin filters and domain walls

We analyze theoretically the influence of domain walls (DWs) on the DC Josephson current in magnetic superconducting S$_{m}$/Fl/F/Fl/S$_{m}$ junctions. The Josephson junction consists of two "magnetic" superconductors S$_{m}$ (superconducting film covered by a thin ferromagnetic layer), spin filters Fl and a ferromagnetic layer F with or without DW (DWs). The spin filters Fl allow electrons to pass with one specific spin orientation, such that the Josephson coupling is governed by a fully polarized long-range triplet component. In the absence of DW(s), the Josephson and spin currents are nonzero when the right and left filters, Fl$_{r,l}$, pass electrons with equal spin orientation and differ only by a temperature-independent factor. They become zero when the \textbf{spins} of the triplet Cooper pairs passing through the Fl$_{r,l}$ have opposite directions. Furthermore, for the different chiralities of the injected triplet Cooper pairs the spontaneous currents arise in the junction yielding a diode effect. Once a DW is introduced, it reduces the critical Josephson current $I_{c}$ in the case of equal spin polarization and makes it finite in the case of opposite spin orientation. The critical current $I_{c}$ is maximal when the DW is in the center of the F film. A deviation of the DW from the center generates a force that pushes the DW to the center of the F film. In addition, we consider the case of an arbitrary number $N$ of DW's, with the case $N=2$ corresponding to a model system for a magnetic skyrmion.

Superconductivity near the saddle point in the two-dimensional Rashba system Si(111)−3×3−(Tl,Pb)

Two-dimensional Rashba superconductor Si(111)-$\sqrt{3}\times\sqrt{3}$-(Tl,Pb) is a candidate platform of mixed spin-singlet and -triplet superconductivity. A recent scanning tunneling microscope (STM) experiment revealed a pseudogap at the vortex core, suggesting the finite triplet component [T. Nakamura $\textit{et al.}$, Phys. Rev. B $\bf{ 98}$, 134505 (2018)]. Detailed spectroscopic information of the superconducting gap and the low-energy band structure is necessary to establish the putative triplet superconductivity. Here, we performed high-energy-resolution spectroscopic imaging experiments on Si(111)-$\sqrt{3}\times\sqrt{3}$-(Tl,Pb) using an ultra-low temperature STM. We found that various spectroscopic features, including the vortex-core spectrum, are consistent with spin-singlet $s$-wave superconductivity, having no sign of the triplet component. The apparent contradiction with the previous STM result suggests that the nature of superconductivity changes within the same system. From the analysis of the quasiparticle interference patterns, we found that the Fermi energy is in the close vicinity of the saddle point near the $\overline{\rm{M}}$ point. We speculate that the nature of superconductivity varies depending on the saddle-point energy with respect to the Fermi energy, which is sample-dependent due to different band filling.

Nonadiabatic dynamics with spin-flip vs linear-response time-dependent density functional theory: A case study for the protonated Schiffbase C5H6NH2.

Nonadiabatic trajectory surface hopping simulations are reported for trans-C5H6NH2 +, a model of the rhodopsinchromophore, using the augmented fewest-switches algorithm. Electronic structure calculations were performed using time-dependent density functional theory (TDDFT) in both its conventional linear-response (LR) and its spin-flip (SF) formulations. In the SF-TDDFT case, spin contamination in the low-lying singlet states is removed by projecting out the lowest triplet component during iterative solution of the TDDFT eigenvalue problem. The results show that SF-TDDFT qualitatively describes the photoisomerization of trans-C5H6NH2 +, with favorable comparison to previous studies using multireference electronic structure methods. In contrast, conventional LR-TDDFT affords qualitatively different photodynamics due to an incorrect excited-state potential surface near the Franck-Condon region. In addition, the photochemistry (involving pre-twisting of the central double bond) appears to be different for SF- and LR-TDDFT, which may be a consequence of different conical intersection topographies afforded by these two methods. The present results contrast with previous surface-hopping studies suggesting that the LR-TDDFT method's incorrect topology around S1/S0 conical intersections is immaterial to the photodynamics.

Spin texture in a bilayer high-temperature cuprate superconductor

We investigate the possibility of spin texture in the bilayer cuprate superconductor $\rm Bi_2Sr_2CaCu_2O_{8+\delta}$ using cluster dynamical mean field theory (CDMFT). The one-band Hubbard model with a small interlayer hopping and a Rashba spin-orbit coupling is used to describe the material. The $d$-wave order parameter is not much affected by the presence of the Rashba coupling, but a small triplet component appears. We find a spin texture circulating in the same direction around $\mathbf{k}=(0,0)$ and $\mathbf{k}=(\pi,\pi)$ and stable against the superconducting phase. The amplitude of the spin structure, however, is strongly affected by the pseudogap phenomenon, more so than the spectral function itself.

Proximity Effect in Heterostructures Based on a Superconductor/Half-Metal System

We demonstrated that with increasing the exchange splitting of the conduction band of a ferromagnet and, respectively, of the degree of the spin polarization, the probability of transmission of the superconducting Cooper pairs through the S/F interface decreases. We concluded that the spin imbalance plays a key role in the processes taking place at the interface between a superconductor and a ferromagnet with spin-polarized conduction electrons. We have studied the superconducting spin-valve effect in F1/F2/S heterostructures containing the Heusler alloy Co2Cr1−xFexAly as one of two ferromagnetic (F1 or F2) layers. We used the Heusler alloy layer in two roles: as a weak ferromagnet on the place of the F2 layer and as a half-metal on the place of the F1 layer. In the first case, we obtained the full switching between the normal and superconducting states is realized with the dominant aid of the long-range triplet component of the superconducting pair condensate which occurs at the perpendicular mutual orientation of magnetizations. In the second case, we observed separation between the superconducting transitions for perpendicular and parallel configurations of magnetizations reaching 0.5 K. We also find a good agreement between our experimental data and theoretical results.

Cyclometalated Ir(III) complexes as potential electron acceptors for organic solar cells.

Cyclometalated iridium(iii) complexes have been investigated as promising electron donor (D) materials in organic solar cells (OSCs) due to their unique octahedral configuration for optimized morphology and their significantly long lifetimes potentially for enhanced exciton dissociation. However, the application as electron acceptor (A) materials has never been reported. In order to fill this blank, herein, two cyclometalated heteroleptic Ir complexes, TRIr and 2TRIr, based on electron donating-accepting type organic ligands with different π-conjugation lengths are reported as electron acceptor materials in comparison with their corresponding main organic ligands. The two Ir complexes exhibit suitable HOMO/LUMO energy levels of -5.55/-3.47 eV and -5.44/-3.48 eV, which are ∼0.1 eV higher in the HOMO and ∼0.15 eV deeper in the LUMO than the TR and 2TR ligands, respectively. 2TRIr with extended ligand π-conjugation displays a poor triplet feature, while TRIr demonstrates obvious metal-to-ligand charge transfer (MLCT) transition absorption, with a triplet component photoluminescence (PL) lifetime of 85 ns in neat films. When blended with PBDB-T in bulk heterojunction (BHJ) OSCs, the power conversion efficiencies (PCEs) are 2-3 times higher than their relevant ligands, with values of 1.20% and 1.62% for TRIr and 2TRIr, and 0.58% and 0.47% for the TR and 2TR ligand-based devices, respectively. TRIr and 2TRIr based active layer blends exhibit poorer hole and electron mobilities, whereas compared with their relatively linear planar ligands, both of the two octahedral Ir complexes exhibit an optimized surface morphology for less bimolecular recombination and more efficient exciton dissociation, thus contributing to improved photovoltaic performance.

Superconductivity in crystals with spin-orbit coupling

The electron Bloch states in crystals with spin-orbit coupling do not always transform under symmetry operations in the same way as the pure spin-1/2 states. This has profound consequences for the gap symmetry and nodal structure of superconductors. Based on the generalization of the Ueda–Rice prescription for the Bloch bases in twofold degenerate bands, we develop the general symmetry classification of multi-band superconducting pairing in non-magnetic centrosymmetric crystals. For the intraband pairing, we identify four exceptional cases in which the triplet gap function does not transform under the point group operations as a pseudovector, with a significant impact on the nodal structure. For the interband pairing, we show that the conventional ([Formula: see text]-wave) gap functions can have such unconventional features as triplet components and odd parity. The [Formula: see text]-wave interband pairing can also be odd in momentum and have a triplet component.