Pairing Mechanism Research Articles

Little strokes fell big oaks: The use of weak magnetic fields and reactive oxygen species to fight cancer.

The increase in early-stage cancers, particularly gastrointestinal, breast and kidney cancers, has been linked to lifestyle changes such as consumption of processed foods and physical inactivity, which contribute to obesity and diabetes - major cancer risk factors. Conventional treatments such as chemotherapy and radiation often lead to severe long-term side effects, including secondary cancers and tissue damage, highlighting the need for new, safer and more effective therapies, especially for young patients. Weak electromagnetic fields (WEMF) offer a promising non-invasive approach to cancer treatment. While WEMF have been used therapeutically for musculoskeletal disorders for decades, their role in oncology is still emerging. WEMFs affect multiple cellular processes through mechanisms such as the radical pair mechanism (RPM), which alters reactive oxygen species (ROS) levels, mitochondrial function, and glycolysis, among others. This review explores the potential of WEMF in conjunction with reactive oxygen species as a cancer therapy, highlighting WEMFs selective targeting of cancer cells and its non-ionizing nature, which could reduce collateral damage compared to conventional treatments. In addition, synchronization of WEMF with circadian rhythms may further enhance its therapeutic efficacy, as has been demonstrated in other cancer therapies.

Intrinsic constraint on Tc for unconventional superconductivity

Can room temperature superconductivity be achieved in correlated materials under ambient pressure? Our answer to this billion-dollar question is probably no, at least for realistic models within the current theoretical framework. This is shown by our systematic simulations on the pairing instability of some effective models for two-dimensional superconductivity. For a square lattice model with nearest-neighbour pairing, we find a plaquette state formed of weakly-connected 2 × 2 blocks for sufficiently large pairing interaction. The superconductivity is suppressed on both sides away from its melting quantum critical point. Thus, the magnitude of Tc is constrained by the plaquette state for the d-wave superconductivity, in resemblance of other competing orders. We then extend our simulations to a variety of effective models covering nearest-neighbour or onsite pairings, single layer or two-layer structures, intralayer or interlayer pairings, and find an intrinsic maximum of the ratio Tc/J ≈ 0.04−0.07, where J is the pairing interaction, given by the onsite attractive interaction in the attractive Hubbard model or the exchange interaction in the repulsive Hubbard model. Our results agree well with previous quantum Monte Carlo simulations for the attractive Hubbard model. Comparison with existing experiments supports this constraint in cuprate, iron-based, nickelate, and heavy fermion superconductors, despite that these compounds are so complicated well beyond our simplified models. As a result, the known families of unconventional superconductivity, possibly except the infinite-layer nickelates, seem to almost exhaust their potentials in reaching the maximal Tc allowed by their respective J, while achieving room temperature superconductor would require a much larger J beyond 400–700 meV, which seems unrealistic in existing correlated materials and hence demands novel pairing mechanisms. The agreement also implies some deep underlying principles of the constraint that urge for a more rigorous theoretical understanding.

Dahuang chuanxiong decoction against contrast-induced nephropathy: Multi-omics, crosstalk between BNIP3-mediated mitophagy and IL-17 pathway.

Contrast-induced nephropathy (CIN), also known as contrast-induced acute kidney injury (CI-AKI), represents a prevalent form of hospital-acquired renal injury. However, the mechanisms underlying its pathogenesis remain unclear. Based on our previous research findings, the Dahuang Chuanxiong decoction (DCH), composed of Radix et Rhizoma Rhei (DH) and Rhizoma Chuanxiong (CX), has demonstrated efficacy for inhibiting CI-AKI by attenuating oxidative stress and apoptosis in renal tubular epithelial cells. Despite these findings, the detailed mechanisms underlying the renoprotective actions have not been thoroughly clarified. The objective of this study was to screen potential targets and signaling pathways involved in inhibition of CI-AKI by DCH using multi-omics analysis and to verify whether the renoprotective mechanism of DCH is related to these identified targets or pathways through in vivo and in vitro experiments. Initially, we identified the components of DCH using UPLC-Q-TOF-MS. Transcriptomics and proteomics, combined with experimental validation, were used to further elucidate the molecular mechanisms of the herbal pair in CI-AKI treatment. A CI-AKI rat model was established, and the expression levels of proteins related to mitophagy and the IL-17 signaling pathway were detected in renal tissues using immunofluorescence, immunohistochemistry, and western blotting analysis to elucidate the nephroprotective effects of DCH. Additionally, siRNA was used in the HK-2 cell model to investigate the crosstalk between the mitophagy and IL-17 signaling pathways and the impact on apoptosis when these pathways were inhibited. Multi-omics results revealed that the crucial signaling pathways involved were mitophagy, the MAPK signaling pathway, and the IL-17 signaling pathway. In vivo experiments indicated that contrast media (CM) led to an increase in AKI biomarkers, with upregulated expression of Parkin, BNIP3, IL-17, and p-NF-κB. Notably, pretreatment with DCH markedly reversed the expression of these proteins. Furthermore, we confirmed the importance of IL-17-mediated inflammation in the pathogenesis of CIN in vitro. We stimulated HK-2 cells with human IL-17 recombinant protein and observed an increase in the expression of p-NF-κB. Conversely, knockdown of IL-17 receptor A (IL-17RA) on the cell membrane reduced the expression of p-NF-κB and BNIP-3 under IL-17 stimulation. Additionally, the results revealed that BNIP3 knockdown reduced p-NF-κB production and alleviated the inflammation triggered by CM. The crosstalk between the two signaling pathways was initially explored. In conclusion, these findings suggested that DCH may exert ameliorative effects on CI-AKI through a multifaceted approach, including inhibition of BNIP3-mediated mitophagy and IL-17-mediated inflammation. This study elucidated the renoprotective mechanism of DCH through transcriptomics, proteomics, and experimental validation, providing evidence for the therapeutic potential of this agent in the clinical treatment of CI-AKI.

Magnetosensitivity of tightly bound radical pairs in cryptochrome is enabled by the quantum Zeno effect

AbstractThe radical pair mechanism accounts for the magnetic field sensitivity of a large class of chemical reactions and is hypothesised to underpin numerous magnetosensitive traits in biology, including the avian compass. Traditionally, magnetic field sensitivity in this mechanism is attributed to radical pairs with weakly interacting, well-separated electrons; closely bound pairs were considered unresponsive to weak fields due to arrested spin dynamics. In this study, we challenge this view by examining the FAD-superoxide radical pair within cryptochrome, a protein hypothesised to function as a biological magnetosensor. Contrary to expectations, we find that this tightly bound radical pair can respond to Earth-strength magnetic fields, provided that the recombination reaction is strongly asymmetric—a scenario invoking the quantum Zeno effect. These findings present a plausible mechanism for weak magnetic field effects in biology, suggesting that even closely associated radical pairs, like those involving superoxide, may play a role in magnetic sensing.

Prediction of p-block-based ternary superconductors XC2H8 at low pressure

Achieving room-temperature superconductivity under ambient conditions is one of the most important goals in solid-state physics and material science. Recent discoveries of high-Tc superconductivity in binary hydrides H3S and LaH10 at high pressures have focused the search for room-temperature superconductors on dense hydrides with conventional phonon-mediated pairing mechanisms. In this study, we predict a novel family of superconducting ternary hydrides under moderate compression, XC2H8 (X = Ga, In, Tl, Sn, Pb, Sb, Bi, Te, Po). Unlike H3S and LaH10, these new materials are stable at just around 20 GPa. Among the analyzed compounds, SbC2H8 exhibits the highest critical temperature of 73 K at a pressure of 100 GPa, which is attributed to its energetically favorable high-symmetry crystal structure (Fm3¯m), high density of states at the Fermi level (1.27 states/eV) and strong electron–phonon coupling constant (1.02). We expect that our findings provide crucial insights into achieving high-temperature superconductivity at moderate pressures and accelerate the progress of experimental research.

Control of iron acquisition by multiple small RNAs unravels a new role for transcriptional terminator loops in gene regulation.

Small RNAs (sRNAs) controlling gene expression by imperfect base-pairing with mRNA(s) are widespread in bacteria. They regulate multiple genes, including genes involved in iron homeostasis, through a wide variety of mechanisms. We previously showed that OmrA and OmrB sRNAs repress the synthesis of the Escherichia coli FepA receptor for iron-enterobactin complexes. We now report that five additional sRNAs, namely RprA, RybB, ArrS, RseX and SdsR, responding to different environmental cues, also repress fepA, independently of one another. While RprA follows the canonical mechanism of pairing with the translation initiation region, repression by ArrS or RseX requires a secondary structure far upstream within the long fepA 5' untranslated region. We also demonstrate a dual action of SdsR, whose 5'-part pairs with the fepA translation initiation region while its 3'-end behaves like ArrS or RseX. Strikingly, mutation analysis shows a key role for the loops of these sRNAs' intrinsic terminators in the regulation. Furthermore, regulation depends on both the Hfq chaperone and the RNase E endonuclease. Overall, our data strongly suggest that FepA levels must be tightly controlled under a variety of conditions and highlight the diversity of mechanisms that underly the regulation of gene expression by sRNAs in bacteria.

A mechanistic understanding of human magnetoreception validates the phenomenon of electromagnetic hypersensitivity (EHS)

Background Human electromagnetic hypersensitivity (EHS) or electrosensitivity (ES) symptoms in response to anthropogenic electromagnetic fields (EMFs) at levels below current international safety standards are generally considered to be nocebo effects by conventional medical science. In the wider field of magnetoreception in biology, our understanding of mechanisms and processes of magnetic field (MF) interactions is more advanced. Methods We consulted a range of publication databases to identify the key advances in understanding of magnetoreception across the wide animal kingdom of life. Results We examined primary MF/EMF sensing and subsequent coupling to the nervous system and the brain. Magnetite particles in our brains and other tissues can transduce MFs/EMFs, including at microwave frequencies. The radical pair mechanism (RPM) is accepted as the main basis of the magnetic compass in birds and other species, acting via cryptochrome protein molecules in the eye. In some cases, extraordinary sensitivity is observed, several thousand times below that of the geomagnetic field. Bird compass disorientation by radio frequency (RF) EMFs is known. Conclusions Interdisciplinary research has established that all forms of life can respond to MFs. Research shows that human cryptochromes exhibit magnetosensitivity. Most existing provocation studies have failed to confirm EHS as an environmental illness. We attribute this to a fundamental lack of understanding of the mechanisms and processes involved, which have resulted in the design of inappropriate and inadequate tests. We conclude that future research into EHS needs a quantum mechanistic approach on the basis of existing biological knowledge of the magnetosensitivity of living organisms.

Measuring kinetic inductance and superfluid stiffness of two-dimensional superconductors using high-quality transmission-line resonators

The discovery of van der Waals superconductors in recent years has generated a lot of excitement for their potentially novel pairing mechanisms. However, their typical atomic-scale thickness and micrometer-scale lateral dimensions impose severe challenges to investigations of pairing symmetry by conventional methods. We demonstrate an improved technique that employs high-quality-factor superconducting resonators to measure the kinetic inductance—up to one part per million—and loss of a van der Waals superconductor. We analyze the equivalent circuit model to extract the kinetic inductance, superfluid stiffness, penetration depth, and ratio of imaginary and real parts of the complex conductivity. We validate the technique by measuring aluminum and finding excellent agreement in both the zero-temperature superconducting gap as well as the complex conductivity data when compared with BCS theory. We then demonstrate the utility of the technique by measuring the kinetic inductance of multilayered niobium diselenide and discuss the limits to the accuracy of our technique when the transition temperature of the sample, NbSe2 at 7.06 K, approaches our Nb probe resonator at 8.59 K. Our method will be useful for practitioners in the growing fields of superconducting physics, materials science, and quantum sensing, as a means of characterizing superconducting circuit components and studying pairing mechanisms of the novel superconducting states which arise in layered two-dimensional materials and heterostructures. Published by the American Physical Society 2024

Pairing phase favored by magnetic frustration.

The interplay between magnetic frustration and pairing is investigated by adopting a BCS-like pairing mechanism on the frustrated $J_1-J_2$ Ising model on the square lattice. The ground-state and thermal phase transitions of the model are analyzed using a fermionic formulation within a cluster mean-field method. In this approach, the lattice system is divided into identical clusters, where the intracluster dynamic is exactly solved, and the intercluster interactions are replaced by self-consistent mean fields. We introduce a framework with two pairing couplings: an intracluster local coupling, $g$, which controls the electron pairing and its mobility within the clusters, and an intercluster coupling, $g'$, which adjusts the pairing mechanism between clusters. Tuning $g'/g$ allows evaluating how the pairing phase evolves from a weak pairing coupling between clusters (clustered system) to a strong one ($g' \rightarrow g$, homogeneous system). In the range $0 \le g'/g \le 1$, we find that a gradual increase in $g'/g$ favors the pairing phase and induces a change in criticality. In particular, our results reveal the presence of tricriticality for a certain range of $g'/g$. In addition, an increase in competing magnetic interactions weakens the magnetic orders, causing the pairing phase to occur at lower strengths of pairing interactions, especially when $g' = g$. Therefore, our findings support that magnetic frustration favors the pairing phase, contributing to the onset of a superconducting state.

Tunable Mirror-Symmetric Type-III Ising Superconductivity in Atomically-Thin Natural Van der Waals Heterostructures.

Van der Waals (vdW) crystals with strong spin-orbit coupling (SOC) provide great opportunities for exploring unconventional 2D superconductors, wherein new pairing states emerge due to the interplay of SOC with crystalline symmetries, electronic correlations, quenched disorders and external modulation forces, etc. Here, a distinct mirror-symmetry protected Ising pairing state with unprecedented Γ- and M-valley symmetries in natural vdW heterostructures (vdWH) of interweaving tetragonal SnSe and trigonal 1H-TaSe2 monolayers is reported, in which the unidirectional lattice interlocking effectively suppresses the K-valley Ising pairing mechanism by incommensurate charge-density-wave (CDW) transitions. In the 2D limit of an TaSe2/SnSe bilayer with intact basal mirror symmetry (Mz), the mirror-symmetric vdWH Ising superconductors show anomalous in-plane magnetic field B‖-controlled enhancements in the critical temperature Tc, which is completely absent for multilayer vdWHs with broken Mz induced by orthorhombic stacking between nearest-neighbour TaSe2 monolayers. The experimental observations consistently reveal a mirror symmetry-protected type-III Ising state in the inversion asymmetric lattice of 1H-TaSe2, which is predicted to be a mixture of spin-singlet and spin-tripletstates.

Quantum theory of a potential biological magnetic field sensor: Radical pair mechanism in flavin adenine dinucleotide biradicals

Recent studies in vitro and in vivo suggest that flavin adenine dinucleotide (FAD) on its own might be able to act as a biological magnetic field sensor. Motivated by these observations, in this study, we develop a detailed quantum theoretical model for the radical pair mechanism (RPM) for the flavin adenine biradical within the FAD molecule. We use the results of existing molecular dynamics simulations to determine the time-varying distance between the radicals on FAD, which we then feed into a quantum master equation treatment of the RPM. In contrast to previous semi-classical models, which are limited to the low-field and high-field cases, our quantum model can predict the full magnetic field dependence of the transient absorption signal. Our model's predictions are consistent with experiments at physiological pH values.

Nickel Age of High‐Temperature Superconductivity

AbstractUnconventional high‐temperature superconductivity has long been a captivating puzzle in condensed matter physics. The 1987 Nobel Prize in Physics celebrated the discovery of high‐temperature superconductivity in copper oxide ceramics. Nearly four decades later, a broad class of high‐temperature superconducting oxides has yet to be demonstrated, and the fundamental understanding of the pairing mechanism remains inconclusive. Recently, nickel oxides have emerged as a new class of high‐temperature superconductors, beyond copper, where correlated phases can be controlled by doping, pressure, strain, and dimensionality. In this article, we provide our perspective on the recent developments and prospects of the nickel age of high‐temperature superconductivity.

Bulk and surface Dirac states accompanied by two superconducting domes in FeSe-based superconductors

Recent investigations of FeSe-based superconductors have revealed the presence of two superconducting domes and suggest possible distinct pairing mechanisms. Two superconducting domes are commonly found in unconventional superconductors and exhibit unique normal states and electronic structures. In this study, we conducted electromagnetic transport measurements to establish a complete phase diagram, successfully observing the two superconducting domes in FeSe1-xSx (0 ≤ x ≤ 0.25) and FeSe1-xTex (0 ≤ x ≤ 1) superconductors. The normal state resistivity on SC1 shows the strange metal state, with a power exponent approximately equal to 1 (ρ(T) ∝ Tn with n ~ 1), whereas the exponent on SC2 is less than 1. A bulk Dirac state observed on SC1, completely synchronized with the strange metal behavior, indicating a close relationship between them. While a topological surface Dirac state is witnessed on SC2 and undergoes a sign change near the pure nematic quantum critical point. The evolution of the Dirac states indicates that the appearance of the two superconducting domes may originate from the Fermi surface reconstruction. Our findings highlight distinct Dirac states and normal state resistivity across the two superconducting domes, providing convincing evidence for the existence of the two different pairing mechanisms in FeSe-based superconductors.

Verification of radical pair mechanism predictions for weak magnetic field effects on superoxide in planarians.

Superoxide concentration and tissue regeneration in planarians exhibit a complex non-monotonic dependence on the strength of an applied weak magnetic field. While this is difficult to understand based on classical physics, a recently proposed quantum model based on a flavin-superoxide radical pair mechanism could replicate the previously observed superoxide concentrations. However, this model also predicts increased superoxide concentrations for both lower and higher fields. This seemed to conflict with earlier experimental observations on blastema sizes, which were correlated with superoxide in the previously observed regime but were known not to follow the predicted trends for lower and higher fields. Motivated by this apparent contradiction, we here directly experimentally tested the predictions of the quantum model for superoxide for lower and higher fields. To our own surprise, our experiments confirmed the predictions of the radical pair model for superoxide, and incorporating interactions with multiple nuclei further improved the model's agreement with the experimental data. While open questions remain regarding the exact relationship between blastema sizes and superoxide, which is revealed to be more complex than previously observed, and the detailed properties of the underlying radical pair, our results significantly support a quantum biological explanation for the observed magnetic field effects.

Linear spectroscopy of collective modes and the gap structure in two-dimensional superconductors

We consider optical response in multiband, multilayer two-dimensional superconductors. Within a simple model, we show that linear response to AC gating can detect collective modes of the condensate, such as Leggett and clapping modes. We show how trigonal warping of the superconducting order parameter can help facilitate detection of clapping modes. Taking rhombohedral trilayer graphene as an example, we consider several possible pairing mechanisms and show that all-electronic mechanisms may produce in-gap clapping modes. These modes, if present, should be detectable in the absorption of microwaves applied via the gate electrodes, which are necessary to enable superconductivity in this and many other settings; their detection would constitute strong evidence for unconventional pairing. Last, we show that absorption at frequencies above the superconducting gap 2|Δ| also contains a wealth of information about the gap structure. Our results suggest that linear spectroscopy can be a powerful tool for the characterization of unconventional two-dimensional superconductors. Published by the American Physical Society 2024

Synthesis, Characterization, and Measurement of New 1144‐Type Iron‐Based Superconductors: A Systematic Review

ABSTRACTThe newly discovered 1144‐type iron‐based superconductors (FeBSCs) are hybrids of the same two 122‐type structures. The novel 1144‐type FeBSCs were synthesized with a superconducting transition temperature ranging from 31 to 37 K. This study systematically investigates the current findings and future possibilities of EuRbFe4As4, EuCsFe4As4, CaRbFe4As4, and CaKFe4As4 FeBSCs since they have high upper critical magnetic field, high critical current density and low anisotropy, strong vortex pinning properties. The current review article gives a brief explanation on the crystal structure, electronic structure, band gap, magnetic properties, superconductivity, pairing mechanism, synthesis methods, characterization, and measuring mechanisms of the selected novel 1144‐type FeBSCs.

Numerical and analytical inspection of magnetic field effects in the radical pair mechanism by a simplified rate equation model.

The radical pair mechanism is by now the most prominent candidate for a biologically relevant quantum effect of magnetic fields. Recently, N. Ikeya and J. R. Woodward demonstrated a magnetic field effect for sub-extremely low frequency (ELF) fields in the mT range by investigating the autofluorescence spectrum of flavin adenine dinucleotide in living HeLa cells. We apply a simple rate equation model to show numerically and analytically that magnetic field effects can be expected to exist in the whole ELF range.

Charge stripe manipulation of superconducting pairing symmetry transition

Charge stripes have been widely observed in many different types of unconventional superconductors, holding varying periods (P) and intensities. However, a general understanding on the interplay between charge stripes and superconducting properties is still incomplete. Here, using large-scale unbiased numerical simulations on a general inhomogeneous Hubbard model, we discover that the charge-stripe period P, which is variable in different real material systems, could dictate the pairing symmetries—d wave for P≥4,s and d waves for P≤3. In the latter, tuning hole doping and charge-stripe amplitude can trigger a d-s wave transition and magnetic-correlation shift, where the d-wave state converts to a pairing-density wave state, competing with the s wave. These interesting phenomena arise from an unusual stripe-induced selection rule of pairing symmetries around on-stripe region and within inter-stripe region, giving rise to a critical point of P=3 for the phase transition. In general, our findings offer important insights into the differences in the superconducting pairing mechanisms across many P-dependent superconducting systems, highlighting the decisive role of charge stripe.

Superconductivity in Ternary Mg4Pd7As6

AbstractThe synthesis and characterization of a new compound Mg4Pd7As6, which is found to be a superconductor with Tc = 5.45 K is reported. Powder X‐ray diffraction confirms the U4Re7Si6 structure (space group Im‐3m, no. 229) with the lattice parameter a = 8.2572(1) Å. Magnetization, specific heat, and electrical resistivity measurements indicate that it is a moderate‐coupling (λ = 0.72) type‐II superconductor. The electronic and phonon structures are calculated, highlighting the importance of antibonding Pd–As interactions in determining the properties of this material. The calculated electron–phonon coupling parameter λ = 0.76 agrees very well with the experimental finding, which confirms the conventional pairing mechanism in Mg4Pd7As6.

Quantum phenomena in biological systems

Quantum biology is a modern field of research that aims to understand how quantum effects can affect the chemistry underlying various biological processes. This paper reviews several examples of biological processes where quantum effects might play a notable role. Initially, the photon capture mechanism present in vision is discussed, where the energy of the photon is used to cause conformational changes to chromophoric proteins. The second example elaborates the highly efficient energy transfer process present in photosynthesis and discusses, in particular, how the random quantum walk process may enhance the performance drastically. Subsequently, the vertebrate magnetoreception, and the possible associated role of the radical pair mechanism in the process is considered. The review concludes with the discussion of some speculative ideas of putative quantum effects arising in neural processes.