Differentiated roles of Lifshitz transition on thermodynamics and superconductivity in La2-xSrxCuO4

The effect of Lifshitz transition on thermodynamics and superconductivity in hole-doped cuprates has been heavily debated but remains an open question. In particular, an observed peak of electronic specific heat is proposed to originate from fluctuations of a putative quantum critical point p* (e.g., the termination of pseudogap at zero temperature), which is close to but distinguishable from the Lifshitz transition in over-doped La-based cuprates where the Fermi surface transforms from hole-like to electron-like. Here we report an in situ angle-resolved photoemission spectroscopy study of three-dimensional Fermi surfaces in La2-xSrxCuO4 thin films (x = 0.06 to 0.35). With accurate k(z) dispersion quantification, the said Lifshitz transition is determined to happen within a finite range around x = 0.21. Normal state electronic specific heat, calculated from spectroscopy-derived band parameters, reveals a doping-dependent profile with a maximum at x = 0.21 that agrees with previous thermodynamic microcalorimetry measurements. The account of the specific heat maximum by underlying band structures excludes the need for additionally dominant contribution from the quantum fluctuations at p*. A d-wave superconducting gap smoothly across the Lifshitz transition demonstrates the insensitivity of superconductivity to the dramatic density of states enhancement.

Automated summary

The effect of Lifshitz transition on thermodynamics and superconductivity in hole-doped cuprates has been debated, but this study provides new insights. By using angle-resolved photoemission spectroscopy, the Lifshitz transition in La2-xSrxCuO4 thin films is found to occur around x=0.21. The calculated electronic specific heat agrees with previous measurements and suggests that the specific heat maximum is explained by underlying band structures rather than additional contributions from quantum fluctuations at p*. Additionally, the d-wave superconducting gap remains smooth across the Lifshitz transition, indicating insensitivity of superconductivity to changes in the density of states.