Evidence for strong lattice effects as revealed from huge unconventional oxygen isotope effects on the pseudogap temperature in La${}_{2-x}$Sr${}_x$CuO${}_4$

Abstract

The oxygen isotope (${}^{16}$O/${}^{18}$O) effect (OIE) on the pseudogap (charge-stripe ordering) temperature $T^{\ast }$ is investigated for the cuprate superconductor La${}_{2-x}$Sr${}_x$CuO${}_4$ as a function of doping $x$ by means of x-ray absorption near edge structure (XANES) studies. A strong $x$ dependent and sign reversed OIE on $T^{\ast }$ is observed. The OIE exponent ${\alpha }_{T^{\ast }}$ systematically decreases from ${\alpha }_{T^{\ast }}=-0.6(1.3)$ for $x=0.15$ to ${\alpha }_{T^{\ast }}=-4.4(1.1)$ for $x=0.06$, corresponding to increasing $T^{\ast }$ and decreasing superconducting transition temperature $T_c$. Both $T^{\ast }{(}^{16}\mathrm{O})$ and $T^{\ast }{(}^{18}\mathrm{O})$ exhibit a linear doping dependence with different slopes and critical end points (where $T^{\ast }{(}^{16}\mathrm{O})$ and $T^{\ast }{(}^{18}\mathrm{O})$ fall to zero) at $x_c{(}^{16}\mathrm{O})=0.201(4)$ and $x_c{(}^{18}\mathrm{O})=0.182(3)$, indicating a large positive OIE of $x_c$ with an exponent of ${\alpha }_{x_c}=0.84(22)$. The remarkably large and strongly doping dependent OIE on $T^{\ast }$ signals a substantial involvement of the lattice in the formation of the pseudogap, consistent with a polaronic approach to cuprate superconductivity and the vibronic character of its ground state.

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• Cooperative enhancement of superconducting correlations by electron-electron and electron-phonon interactions in the quarter-filled band
• Multiple electronic components and Lifshitz transitions by oxygen wires formation in layered cuprates and nickelates
• A framework for the description of charge order, pseudo and superconducting gap, critical temperature and pairing interaction in cuprate superconductors
• Universal phonon softening in the pseudogap state of Tl${}_2$Ba${}_2$Ca${}_{n-1}$Cu${}_n$O${}_{2n+4+\delta }$
• Pseudogap isotope effect as a probe of bipolaron mechanism in high temperature superconductors
• Phonon-assisted insulator-metal transitions in correlated systems driven by doping
• Oxygen Isotope Effect Resulting from Polaron-induced Superconductivity in Cuprates