arXiv subjects

Yao-hui Zhu

Publications and source records attributed to Yao-hui Zhu.

5 recordsLinked to original sources

arXiv2026

Superconducting $T_\mathrm{c}$ up to 20.6 K in bulk YSi$_2$ and YSi$_2$/Si superlattices due to chemical flattening

Currently, the fundamental building blocks of leading quantum computers are Josephson junctions, whose core is usually the superconducting Al on Si wafers. However, the transition temperature $T_\mathrm{c}$ of bulk Al ($\sim1.1$ K) is below the boiling point of liquid helium ($\sim4.2$ K), which is one of the challenges to its widespread application. Here, we propose a Si-matched AlB$_2$-type superconductor YSi$_2$ as a promising alternative to Al. The solution of anisotropic (isotropic) Migdal-Eliashberg equation without (with) anharmonicity gives $T_\mathrm{c}\sim20.6$ K ($17.2$ K), which is at the highest level in silicides. Its excellent superconductivity can be attributed mainly to the Si honeycombs, which become plane here due to the 'chemical flattening' effects of the Y atoms instead of being buckled in most silicides. We tested its thermodynamical, kinetic, dynamical, and mechanical stability by first-principles calculations. Particularly, the negative elastic stiffness constant $C_{66}$ calculated by usual methods turns positive even without the zero-point energy once the Si honeycombs are compressed below a threshold. This strain can also make its calculated lattice constants agree with the experimental ones. We propose structures to realize this strain, i.e., YSi$_2$(0001)/Si(111) superlattices, which can also strengthen the overall stability of YSi$_2$ while maintaining its $T_\mathrm{c}$ above $7.0$ K.

cond-mat.supr-con↗

arXiv2026

Double-Bridge Mechanism for Enhancing Tc in Oxide Superconductors

We propose a new double-bridge mechanism to significantly enhance $T_c$ in ionic oxide superconductors. Based on our recently proposed ionic-bond-driven O/Cu-bridged (bridge-I) pairing e$^-$-O-e$^-$/h$^+$-Cu-h$^+$ formed in the pseudogap phase ($T_c<T<T^*$), we reveal a key bridge-II Cu/O-mediated inter-pair attraction that overcomes direct Coulomb repulsion and drives coherent Bose-Einstein condensation (BEC) of preformed Cooper pairs. Within the BEC framework (Eq.(3)), $T_c$ follows the Uemura scaling $(n_{\rm pair}^{\rm 3D})^{2/3}/m_{\rm pair}^*$ or $n_{\rm pair}^{\rm 2D}/m_{\rm pair}^*$ and increases linearly with the attractive scattering length $a<0$. Strengthening bridge-II attraction, minimizing $m_{\rm pair}^*$, and optimizing $n_{\rm pair}^{\rm 3D}$ are the key to maximizing $T_c$. This double-bridge mechanism unifies the \textbf{eV-scale} strong pairing at room temperature and BEC, provides a universal route toward higher $T_c$, and guides the design of next-generation superconductors.

cond-mat.supr-con↗

arXiv2026

Ionic-Bond-Driven Atom-Bridged Room-Temperature Cooper Pairing in Cuprates and Nickelates: a Theoretical Framework Supported by 32 Experimental Evidences

Unlike ordinary conductors and semiconductors, which conduct electricity through individual electrons, superconductors usually conduct electricity through electron pairs, known as Cooper pairs. Even after 4 decades of intense study, no one knows what holds electrons together in high-$T_c$ cuprates. Here, targeting the critical challenge of pairing mechanism behind high-$T_c$ superconductivity in oxides and considering the dominance of eV-scale ionic bonding, affinity of O$^-$ (1.46 eV) and O$^{2-}$ (-8.08 eV) and large two-electron ionization energy ($\sim$15-28 eV) of metal atoms, we propose an innovative idea of electron e$^-$ (hole h$^+$) pairing bridged by oxygen O (metal M) atoms, i.e., the ionic-bond-driven $\mathbf{e^--O-e^-}$ ($\mathbf{h^+-M-h^+}$) itinerant Cooper pairing formed at pseudogap temperature $T^*>T_c$, by following the principle of "tracing electron footprints to explore pairing mechanisms" and by standing on the solid foundation of chemical-bond$\rightarrow$structure$\rightarrow$property relationship. It is applicable to cuprates, nickelates, iron-based and other new ionic superconductors. Its correctness and universality are confirmed by 32 diverse experimental evidences, especially, the STM image in the CuO$_2$ plane combining with the small pair size. Any other sub-eV and covalent-binding pairing mechanisms would be doubtful. Our findings, which provide the missing link between ionic bonding and superconductivity, resolve a 40-year puzzle and validate the feasibility of room-temperature carrier-pairing in ionic superconductors. We further create a new theoretical framework rooted in our universal $\mathbf{e^--O-e^-}$ ($\mathbf{h^+-M-h^+}$) picture with the strongest pairing strength and Bose-Einstein condensation, which opens a new avenue for understanding high-$T_c$ mechanism and brings the dream of room-temperature superconductivity one step closer.

cond-mat.supr-con↗

arXiv2024

O-bridged electron pairing: the microscopic mechanism for high-temperature superconductivity in cuprates and nickelates

Based on the energy level structure of neutral oxygen atom O and its anions, through in-depth analysis of the bonding process and formation mechanism of anion O$^{x-}$ ($1<x\leq{2}$) in oxide superconductors dominated by ionic bonds, we propose an emerging and important novel idea of electron pairing with oxygen atoms as a bridge, different from the previously proposed electronic pairing schemes. This microscopic electronic pairing image is very intuitive and vivid, which can naturally explain the d-wave symmetry of Cooper pairs, large superconducting energy gaps, and small electron-pair sizes in copper oxide high-temperature superconductors. It is the electron-electron pairing mechanism mediated by oxygen atoms that directly determines the unconventional high-temperature superconductivity of cuprates and nickelates.

cond-mat.supr-con↗

arXiv2023

Metal-bonded perovskite lead hydride with phonon-mediated superconductivity up to 46 K under atmospheric pressure

In the search for high-temperature superconductivity in hydrides, a plethora of multi-hydrogen superconductors have been theoretically predicted, and some have been synthesized experimentally under ultrahigh pressures of several hundred GPa. However, the impracticality of these high-pressure methods has been a persistent issue. In response, we propose a new approach to achieve high-temperature superconductivity under atmospheric pressure by implanting hydrogen into lead to create a stable few-hydrogen metal-bonded perovskite, Pb$_4$H. This approach diverges from the popular design methodology of multi-hydrogen covalent high critical temperature ($T_c$) superconductors under ultrahigh pressure. By solving the anisotropic Migdal-Eliashberg (ME) equations, we demonstrate that perovskite Pb$_4$H is a typical phonon-mediated superconductor with a $T_c$ of 46 K, which is six times higher than that of bulk Pb (7.22 K) and higher than that of MgB$_2$ (39 K). The high $T_c$ can be attributed to the strong electron-phonon coupling (EPC) strength of 2.45, which arises from hydrogen implantation in lead that induces several high-frequency optical phonon modes with a relatively large phonon linewidth resulting from H atom vibration. The metallic-bonding in perovskite Pb$_4$H not only improves the structural stability but also guarantees better ductility than the widely investigated multi-hydrogen, iron-based, and cuprate superconductors. These results suggest that there is potential for the exploration of new high-temperature superconductors under atmospheric pressure and may reignite interest in their experimental synthesis soon.

cond-mat.supr-con↗