Nuclear Superfluidity is a monograph devoted exclusively to pair correlations in nuclei. It begins by exploring pair correlations in a variety of systems including superconductivity in metals at low ...temperatures and superfluidity in liquid 3He and in neutron stars. The book goes on to introduce basic theoretical methods, symmetry breaking and symmetry restoration in finite many-body systems. The last few chapters are devoted to introducing results on the role of induced interactions in the structure of both normal and exotic nuclei. The most important of these is the renormalization of the pairing interaction due to the coupling of pairs of nucleons to low energy nuclear collective excitations. This book will be essential reading for researchers and students in experimental and theoretical nuclear physics, and related research fields such as metal clusters, fullerenes and quantum dots.
Although the pairing mechanism of Fe-based superconductors (FeSCs) has not yet been settled with consensus with regard to the pairing symmetry and the superconducting (SC) gap function, the vast ...majority of experiments support the existence of spin-singlet sign-changing s-wave SC gaps on multi-bands (s±-wave state). This multi-band s±-wave state is a very unique gap state per se and displays numerous unexpected novel SC properties, such as a strong reduction of the coherence peak, non-trivial impurity effects, nodal-gap-like nuclear magnetic resonance signals, various Volovik effects in the specific heat (SH) and thermal conductivity, and anomalous scaling behaviors with a SH jump and condensation energy versus Tc, etc. In particular, many of these non-trivial SC properties can easily be mistaken as evidence for a nodal-gap state such as a d-wave gap. In this review, we provide detailed explanations of the theoretical principles for the various non-trivial SC properties of the s±-wave pairing state, and then critically compare the theoretical predictions with experiments on FeSCs. This will provide a pedagogical overview of to what extent we can coherently understand the wide range of different experiments on FeSCs within the s±-wave gap model.
We employ a functional renormalization group approach to ascertain the pairing mechanism and symmetry of the superconducting phase observed in rhombohedral trilayer graphene. Superconductivity in ...this system occurs in a regime of carrier density and displacement field with a weakly distorted annular Fermi sea. We find that repulsive Coulomb interactions can induce electron pairing on the Fermi surface by taking advantage of momentum-space structure associated with the finite width of the Fermi sea annulus. Furthermore, the degeneracy between spin-singlet and spin-triplet pairing is lifted by valley-exchange interactions that strengthen under the RG flow and develop nontrivial momentum-space structure. We find that the leading pairing instability is d-wave-like and spin-singlet, and that the theoretical phase diagram versus carrier density and displacement field agrees qualitatively with experiment.
We study the effects of a BCS-like pairing mechanism on the frustrated J1−J2 model on the square lattice. The model is expressed in a fermionic formulation, in which the fermions that represent the ...magnetic moments can also participate in the pair formation. A cluster mean-field approach allows to get an effective self-consistent problem in the grand canonical potential at half-filling. The competing antiferromagnetic (AF) interactions lead to a phase diagram with different AF orders separated by a discontinuous phase transition at the highly frustrated regime. As the strength of pairing increases, the criticality of the highly frustrated region is affected, with the arising of a triple point. Beyond a pairing strength threshold, the system exhibits absence of magnetic orders with a high density of double occupied sites near the highly frustrated point. Therefore, the frustration can assist the pairing by weakening the magnetic orders, giving possibility to a nonmagnetic ground-state.
miRNAs are small RNAs that guide Argonaute proteins to specific target mRNAs to repress their translation and stability. Canonically, miRNA targeting is reliant on base pairing of the seed region, ...nucleotides 2–7, of the miRNA to sites in mRNA 3′ untranslated regions. Recently, the 3′ half of the miRNA has gained attention for newly appreciated roles in regulating target specificity and regulation. In addition, the extent of pairing to the miRNA 3′ end can influence the stability of the miRNA itself. These findings highlight the importance of sequences beyond the seed in controlling the function and existence of miRNAs.
While canonical miRNA targeting involves pairing of the miRNA seed, nucleotides 2–7 of the miRNA, to target 3′ UTR sequences, recent studies have revealed roles for miRNA sequences beyond this region in specifying target recognition and regulation.
Auxiliary base pairing to sequences in the 3′ half of the miRNA can overcome seed imperfections and confer specificity for individual members of a miRNA family that share identical seed sequences.
Base pairing of 3′-end miRNA sequences enables targeting of protein-coding sequences that lack canonical seed-pairing interactions.
Extensive pairing interactions between a miRNA and its target can lead to target-directed miRNA degradation.
We show that the symmetry-restored paired mean-field states (quasiparticle vacua) properly account for isoscalar versus isovector nuclear pairing properties. Full particle-number, spin, and isospin ...symmetries are restored in a simple SO(8) proton-neutron pairing model, and prospects to implement a similar approach in a realistic setting are delineated. Our results show that, provided all symmetries are restored, the pictures based on pair-condensate and quartet-condensate wave functions represent equivalent ways of looking at the physics of nuclear proton-neutron pairing.
Computing Heights via Limits of Hodge Structures Bloch, Spencer; de Jong, Robin; Sertöz, Emre Can
Experimental mathematics,
04/2023, Letnik:
ahead-of-print, Številka:
ahead-of-print
Journal Article
Recenzirano
Odprti dostop
We consider the problem of explicitly computing Beilinson-Bloch heights of homologically trivial cycles on varieties defined over number fields. Recent results have established a congruence, up to ...the rational span of logarithms of primes, between the height of certain limit mixed Hodge structures and certain Beilinson-Bloch heights obtained from odd-dimensional hypersurfaces with a node. This congruence suggests a new method to compute Beilinson-Bloch heights. Here we explain how to compute the relevant limit mixed Hodge structures in practice, then apply our computational method to a nodal quartic curve and a nodal cubic threefold. In both cases we explain the nature of the primes occurring in the congruence.
Recently synthesized Kagome compounds AV3Sb5 attract great attention due to the unusual coexistence of the topology, charge density wave, and superconductivity. In this work, based on the band ...structures for CsV3Sb5 in the pristine phase, we construct an effective six-band model for the low-energy processes; utilizing the random phase approximation on the effective six-band model, we show that the E1u (p wave) pairing dominates in the region of 0<U<0.32 eV, the A2g (I wave) in the region of 0.32<U<0.75 eV and the E2g (d wave) in the region of 0.75<U<1 eV. Considering that the correlation in AV3Sb5 is weak or intermediate, these results suggest that pairing symmetry is A2g (I-wave) in the CsV3Sb5, which can explain some recent experiments about pairing symmetry.
Spin-triplet superconductors are of extensive current interest because they can host topological state and Majorana fermions important for quantum computation. The uranium-based heavy-fermion ...superconductor UTe2 has been argued as a spin-triplet superconductor similar to UGe2, URhGe, and UCoGe, where the superconducting phase is near (or coexists with) a ferromagnetic (FM) instability and spin-triplet electron pairing is driven by FM spin fluctuations. Here we use neutron scattering to show that, although UTe2 exhibits no static magnetic order down to 0.3 K, its magnetism in the 0, K, L plane is dominated by incommensurate spin fluctuations near an antiferromagnetic ordering wave vector and extends to at least 2.6 meV. We are able to understand the dominant incommensurate spin fluctuations of UTe2 in terms of its electronic structure calculated using a combined density-functional and dynamic mean-field theory.
Homologous pairing establishes the foundation for accurate reductional segregation during meiosis I in sexual organisms. This Commentary summarizes recent progress in our understanding of homologous ...pairing in meiosis, and will focus on the characteristics and mechanisms of specialized chromosome sites, called pairing centers (PCs), in Caenorhabditis elegans and Drosophila melanogaster. In C. elegans, each chromosome contains a single PC that stabilizes chromosome pairing and initiates synapsis of homologous chromosomes. Specific zinc-finger proteins recruited to PCs link chromosomes to nuclear envelope proteins--and through them to the microtubule cytoskeleton--thereby stimulating chromosome movements in early prophase, which are thought to be important for homolog sorting. This mechanism appears to be a variant of the 'telomere bouquet' process, in which telomeres cluster on the nuclear envelope, connect chromosomes through nuclear envelope proteins to the cytoskeleton and lead chromosome movements that promote homologous synapsis. In Drosophila males, which undergo meiosis without recombination, pairing of the largely non-homologous X and Y chromosomes occurs at specific repetitive sequences in the ribosomal DNA. Although no other clear examples of PC-based pairing mechanisms have been described, there is evidence for special roles of telomeres and centromeres in aspects of chromosome pairing, synapsis and segregation; these roles are in some cases similar to those of PCs.
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