Signatures of a Lifshitz transition in pressurized electron-doped cuprate

It is well known that the electronic structure of hole-doped cuprate superconductors is tunable through both chemical doping and external pressure, which frequently offer us new insights of understanding on the high-Tc superconducting mechanism. While, for electron-doped cuprate superconductors, although the chemical doping effects have been systematically and thoroughly investigated, there is still a notable lack of experimental evidence regarding the pressure-driven coevolution of Tc and electronic structure. In this study, we report the first observation on the signatures of pressure-induced Lifshitz transition in Pr0.87LaCe0.13CuO4+delta (PLCCO) single crystal, a typical electron-doped cuprate superconductor, through the comprehensive high-pressure measurements of electrical resistance, Hall coefficient (RH) and synchrotron X-ray diffraction (XRD). Our results reveal that, at 40 K, the ambient-pressure RH with a significantly negative value decreases with increasing pressure until it reaches zero at a critical pressure (Pc ~ 10 GPa). Meanwhile, the corresponding Tc exhibits a slight variation within this pressure range. As pressure is further increased beyond Pc, RH changes its sign from negative to positive and then shows a slight increase, while Tc displays a continuous decrease. Our XRD measurements at 40 K demonstrate that no crystal structure phase transition occurs across the Pc. These results reveal that applying pressure to PLCCO can induce a Lifshitz transition at Pc, manifesting the reconstruction of the Fermi surface (FS), which turns the superconductivity toward fading out. Our calculation further reinforces the Fermi surface reconstruction from electron-dominated to hole-dominated ones at around Pc. These findings provide new evidence that highlights the strong correlation between the superconductivity and the Fermi surface topology in the electron-doped cuprates.

💡 Research Summary

This paper reports the first experimental observation of a pressure-induced Lifshitz transition in an electron-doped cuprate superconductor, Pr₀.₈₇LaCe₀.₁₃CuO₄±δ (PLCCO). The authors conducted comprehensive high-pressure, low-temperature measurements of electrical resistance, Hall coefficient, and synchrotron X-ray diffraction on single-crystal samples.

The key findings are as follows: At a temperature of 40 K, the Hall coefficient (R_H), which has a large negative value at ambient pressure, decreases continuously with increasing pressure until it reaches zero at a critical pressure P_c ≈ 10 GPa. Upon further compression beyond P_c, R_H changes sign from negative to positive and then increases slightly. Concurrently, the superconducting transition temperature (T_c) shows little variation below P_c but exhibits a monotonic decrease above P_c. High-pressure X-ray diffraction measurements at 40 K confirm that no structural phase transition occurs across this critical pressure; the crystal retains its tetragonal T’ phase (space group I4/mmm) up to at least 20.7 GPa, with continuous compression of the lattice parameters.

The combination of a carrier-type sign change (from electron-like to hole-like dominance) and the suppression of superconductivity in the absence of any structural transition provides strong evidence for a pressure-induced Lifshitz transition. This is a topological reconstruction of the Fermi surface where electron and hole pockets merge, fundamentally altering the electronic state. The anisotropic compression of the lattice, particularly a much larger compression along the c-axis compared to the a-axis, is identified as a likely driver for this electronic change.

To support the experimental interpretation, the authors performed theoretical calculations using an effective two-band model (considering upper and lower Hubbard bands). The model incorporates pressure-dependent parameters: the superconducting pairing strength J decreases relative to the hopping integral t, and the band splitting R between the Hubbard bands vanishes at P_c. The calculations successfully reproduce the experimental trends. Below P_c, the Fermi surface consists of coexisting electron and hole pockets, leading to a stabilized T_c due to competing effects. At P_c, a Lifshitz transition occurs as the band splitting vanishes. Above P_c, a single hole-dominated Fermi surface forms, and the continued reduction of J suppresses superconductivity, matching the observed decrease in T_c.

In conclusion, this work presents the first direct evidence of a pressure-driven Lifshitz transition in a bulk electron-doped cuprate superconductor. It highlights a distinct pressure response compared to hole-doped cuprates and provides crucial new evidence for the strong correlation between Fermi surface topology and superconductivity in cuprate materials. The findings offer valuable insights into the interplay among electronic correlations, Fermi surface reconstruction, and superconductivity.