Doped high-Tc Superconductors Research Articles

High‐performance diffusion model for inverse design of high Tc superconductors with effective doping and accurate stoichiometry

AbstractThe pursuit of designing superconductors with high Tc has been a long‐standing endeavor. However, the widespread incorporation of doping in high Tc superconductors significantly impacts electronic structure, intricately influencing Tc. The complex interplay between the structural composition and material performance presents a formidable challenge in superconductor design. Based on a novel generative model, diffusion model, and doping adaptive representation: three‐channel matrix, we have designed a high Tc superconductors inverse design model called Supercon‐Diffusion. It has achieved remarkable success in accurately generating chemical formulas for doped high Tc superconductors. Supercon‐Diffusion is capable of generating superconductors that exhibit high Tc and excels at identifying the optimal doping ratios that yield the peak Tc. The doping effectiveness (55%) and electrical neutrality (55%) of the generated doped superconductors exceed those of traditional GAN models by more than tenfold. Density of state calculations on the structures further confirm the validity of the generated superconductors. Additionally, we have proposed 200 potential high Tc superconductors that have not been documented yet. This groundbreaking contribution effectively reduces the search space for high Tc superconductors. Moreover, it successfully establishes a bridge between the interrelated aspects of composition, structure, and property in superconductors, providing a novel solution for designing other doped materials.image

Electron–hole asymmetry in magnetic properties of lightly doped high-TC superconductors: A quantum Monte Carlo study

Using a recently developed variational quantum Monte Carlo method, magnetic properties of high-TC superconductors are studied at zero temperature (T), by numerical simulations on the 2D t–J model. Our focus here is to explore the difference in the properties of p- and n-type cuprates as a function of the carrier concentrations close to half filling. As observed experimentally, it is found that the antiferromagnetically ordered phase persists even for a small, yet finite amount of carrier doping, and that this phase is more robust in the electron-doped case.

Insulator-Conductor Transition in Doped HTS as a Consequence of -U-Centers Generation

It is supposed that the transition from insulator to metal state under doping in high-T c superconductors (HTS) passes through the stage of -U-centers formation, which arise on the neighbor Cu ions when the definite spatial arrangement of the doping atoms is realized. In this doping region the free hole carriers (just as in hole-, so in electron-doped HTS) are generated when electron pairs transfer from the oxygen band into -U-centers.

Inelastic neutron scattering in cuprate superconductors: Evidence for inhomogeneous materials properties

There is increasing experimental evidence for the coexistence of different types of local regions in doped high-Tc superconductors of “123” and “214” type. They may be classified into local regions of undoped, intermediately doped, and highly doped character. The doping mechanism makes the system inhomogeneous, and the superconducting state is reached by a percolation process. Very detailed information about the volume fractions and the spatial extent of the local regions can be obtained by neutron spectroscopic investigations of the crystal-field interaction at the rare-earth site which is an ideal local probe of the charge distribution in the superconducting copper oxide planes. The inhomogeneous materials properties have to be taken into account in any interpretation of the physical properties of doped high-Tc superconductors. This is exemplified for the static and dynamic copper spin correlations of YBa2Cu3Ox (6≤x≤7). We show that the spin fluctuations observed in the superconducting state can be associated with the undoped and intermediately doped regions of the system, whereas no magnetic scattering occurs for the highly doped regions.

The nature of insulator-metal transition and the mechanism of carrier generation in doped high-Tc superconductors

It is proposed that the local atomic complexes consisting of two adjacent cations (Cu or Bi) with intermediate O-ion and having-U-center properties are formed in high-Tc superconductors (HTSC) at the certain concentration of localized doped carriers. The pair level of arising-U-centers lies at the top of the fulfilled oxygen valence band. Such type of electronic structure is supposed to be responsible for unusual properties of HTSC. The broad outline of HTSC doping process is sketched. It is supposed that doped carriers are well localized at least for small doping concentration while the mobile hole carriers result from the transfer of a part of electrons from the oxygen band to-U-centers. In the framework of proposed model the dielectric-metal transition and the evolution of HTSC properties with doping can be understood.

Vibronic pairwise charge transfer in copper-oxide sheets: A possible approach to high temperature superconductivity theory

To accommodate the number of holes and fractional number of atoms in doped highTc superconductors, and to produce a periodic structure with given symmetry, we postulate a quadruple cell with four copper atoms on the CuO2 layer. The quadruple cell structure hasD2h symmetry which can be distorted toC2h geometry underB1g vibration. Such a structure allows the interconversion of different spin angular momenta into paired spins similar to Cooper pairs. It also provides vibronic interactions that lower the energy of the ground state. For electron (hole) pairing, we construct the running wave Bloch sums consisting of linear combination of bonding/antibonding geminals (instead of one-electron atomic orbitals) in these quadruple cells. For “bond” movement we construct the Bloch sums consisting of linear combination of “Covalon” waves in quadruple cells related to the movement of conjugate (alternating) bonds. In both cases the pair-wise charge (hole/electron) transfer is coupled with antisymmetric vibrations under a double-well potential related to Peierls distortion. The vibronic mixing of different running bonds with different antisymmetric vibrations at various distances, accounts for the different long-range order of charge transfer. Our formulations represent an alternative view of BCS theory, Bisoliton theory and Resonanting Valence Bond theory by using a quantum chemical, position-space approach to a more tight binding situation.

EFFECT AND MECHANISM OF SLOW NEUTRON IRRADIATION WITH LOW FLUENCE IN NORMAL RESISTIVITY OF SUPERCONDUCTORS

This work studies the effect and mechanism of slow neutron irradiation of low fluence (～108n/cm2) in normal resistivity of Y and Bi system and the doped high Tc superconductors. The experimental results indicate that the normal resistivity R not only follows the law that R is increasing exponentially with the enhancement of fluence φn, but also decreases greatly after irradiation of slow neutron with low fluence.