Quantum electron-doped cuprates link heat to 10% resistance

Quantum Electron‑Doped Cuprates: Heat, Scattering, and a 10% Resistance Link

Researchers have uncovered a striking correlation between normal‑state resistivity and the superconducting critical temperature (Tₙ) in the electron‑doped cuprate La₂₋ₓCeₓCuO₄. Unlike conventional superconductors, where resistivity follows a simple linear temperature dependence, these materials exhibit a highly anisotropic inelastic scattering component that diminishes as cerium doping increases. The result is a direct, roughly 10 % link between the magnitude of the scattering‑induced resistance and the temperature at which superconductivity sets in.

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1. Anisotropic Inelastic Scattering as the Key Parameter

High‑field magnetoresistance and low‑temperature resistivity measurements allowed the team to extract an anisotropic scattering rate, γ₁, that varies strongly with momentum (peaking at the antiferromagnetic zone‑boundary “hot spots”). As the electron concentration rises (higher x), γ₁ drops by an order of magnitude, mirroring the decline of Tₙ toward zero. This behavior points to a specific scattering channel—π, π spin‑fluctuation scattering—as the dominant mechanism governing both charge transport and Cooper‑pair formation.

2. Spin Fluctuations as the Pairing Glue

The data support a picture in which low‑energy spin fluctuations mediate the attractive interaction that binds electrons into Cooper pairs. The anisotropic scattering rate directly measures the strength of these fluctuations; its reduction with doping explains why superconductivity weakens. Crucially, the study shows that simply increasing the overall coupling strength cannot account for the higher Tₙ values observed in hole‑doped cuprates, indicating that electron‑ and hole‑doped systems rely on distinct pairing mechanisms.

3. Contrasting Electron‑ and Hole‑Doped Phase Diagrams

Electron‑doped cuprates retain antiferromagnetic correlations deep into the superconducting dome, leading to a coexistence of magnetic order and superconductivity over a narrow doping range. Hole‑doped counterparts, by contrast, suppress long‑range antiferromagnetism before superconductivity emerges and display a broader doping window with higher maximum Tₙ. This asymmetry underscores why the resistivity‑Tₙ link is unique to the electron‑doped side: the persistent spin fluctuations provide a measurable “glue” that fades as the system moves toward a more conventional metallic state.

4. Implications for Theory and Materials Design

The observed linear relationship between the anisotropic scattering strength and Tₙ challenges extensions of Bardeen‑Cooper‑Schrieffer (BCS) theory that rely solely on enhanced coupling to spin fluctuations. Instead, it suggests that any comprehensive theory of high‑temperature superconductivity must incorporate the momentum‑dependent nature of scattering and its evolution with carrier concentration. For materials engineering, the findings hint that tuning the electronic structure to control hotspot scattering—through precise doping or strain—could be a viable route to optimizing Tₙ in electron‑doped cuprates.

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Practical Takeaway

The study provides a clear experimental metric—γ₁, the anisotropic inelastic scattering rate—that tracks the superconducting transition temperature in electron‑doped cuprates. By focusing on how low‑energy spin fluctuations shape γ₁, researchers can better diagnose the pairing mechanism in these complex oxides and explore strategies to enhance superconductivity, whether through targeted doping, combinatorial film growth, or engineered heterostructures.