Orateur
Description
Governed by the fundamental Heisenberg uncertainty principle, two ground states are expected in two-dimensional (2D) Cooper pair systems: the zero-resistance superconducting state with phase-coherent Cooper pairs and the insulating state with localized Cooper pairs. Whether an intermediate metallic ground state exists in 2D superconducting system has been a long debate.
In the thin films of three high-Tc superconducting families, we observe the ubiquitous emergence of anomalous metal state (i.e., quantum metal or Bose metal), which is characterized by resistance saturations approaching the zero-temperature limit. In high-Tc superconducting YBCO films patterned with triangular array of nanoholes, we detected a robust intervening anomalous metal state [1]. The suppressed Hall coefficient and the charge-2e quantum oscillations reveal the bosonic nature of this metallic ground state. Then, in the ultrathin crystalline FeSe films grown on SrTiO3, we observed a high-temperature anomalous metal state, which persists up to an exceptionally high temperature of 20 K [2]. Furthermore, a linear-in-temperature resistance is observed below onset superconducting critical temperature, uncovering a bosonic strange metallic behaviour. We also develop a microscopic model for the anomalous metal state based on the ohmic dissipation-influenced quantum tunnelling of vortices, which gives a quantitative explanation for the temperature dependence of resistance. Recently, in the nanoholes patterned infinite-layer nickelate Nd0.8Sr0.2NiO2 films, we uncover the direct correlation between the ground-state resistance saturation and the saturation of phase coherence length among Cooper pairs [3]. The modulation on the macroscopic superconducting phase further drives an anomalous reversal of superconducting anisotropy, where the in-plane critical fields become even below the out-of-plane values ("B" "c∥" <"B" ("c" ⟂)).
Our findings uncover the ubiquitous existence of anomalous quantum metallic ground states in 2D high-Tc superconducting systems [4]. More broadly, our works highlight the critical role of phase coherence in determining the macroscopic superconducting states in two dimensions, and establish a general methodology by nano-fabrication.
[1] C. Yang et al., Science 366, 1505-1509 (2019)
[2] Y. Li et al., Phys. Rev. Lett. 132, 226003 (2024)
[3] H. Ji et al., arXiv: 2603.00670 (2026)
[4] Z. Wang et al., Rep. Prog. Phys. 87, 014502 (2024)