Source capture
Authors Zhehong Liu, Masamichi Nakajima, Markus Kriener, Shunsuke Kitou, Xiaowei Lyu, Chieko Terakura, Kosuke Karube, Ka Man Yip, Sorin Lazar, Nobuto Nakanishi, Keiko Shimada, Akiko Kikkawa, Yukako Fujishiro, Xiuzhen Yu, Taka-hisa Arima, Yoshinori Tokura, Yasujiro Taguchi
arXiv / Publisher https://arxiv.org/abs/2607.26990
PDF https://arxiv.org/pdf/2607.26990
Relevance score 5.957
Primary category cond-mat.supr-con
Published 2026-07-30
Research paradigm Experimental
Sample form Single Crystal

Summary

Using high-quality La3Ni2O7 single crystals, the researchers established a high-precision pressure–temperature phase diagram by accurately measuring in-plane and out-of-plane resistivity. They resolved two density-wave-related anomalies with distinct pressure dependences: the low-temperature anomaly T1 is initially suppressed and then sharply enhanced after a structural transition at about 10 GPa, while the high-temperature spin-density-wave anomaly T2 increases monotonically. The pressure-induced structural transition not only raises the resistivity in both directions but also significantly enhances the low-temperature resistivity anisotropy, indicating that the density-wave order profoundly affects charge dynamics. Once pressure completely suppresses the density-wave phase, zero-resistance superconductivity emerges at the phase boundary with an onset temperature up to 68 K, and the normal-state resistivity exhibits a linear temperature dependence over a wide range from just above the superconducting transition to 300 K, with the scattering rate falling within the Planckian limit. These results reveal that pressure reconstructs anisotropic charge transport by tuning the density-wave order, thereby generating a strongly scattering strange-metal state and superconductivity, and establish that density-wave correlations and Planckian dissipation are defining characteristics of La3Ni2O7.

Materials

Methods

  • high-pressure resistivity measurements
  • Montgomery method for anisotropic transport
  • synchrotron X-ray diffraction
  • transmission electron microscopy
  • scanning electron microscopy
  • energy-dispersive X-ray spectroscopy
  • Laue diffraction
  • single crystal X-ray diffraction
  • structural refinement

Keywords

Highlights

  • High-quality, oxygen-stoichiometric, stacking-fault-free La3Ni2O7 single crystals are synthesized for the first time.
  • The low-temperature density-wave anomalyT1 does not vanish below 10 GPa but is abruptly enhanced across the structural transition.
  • The transport anisotropy increases dramatically at low temperatures upon entering the tetragonal phase, driven by the density‑wave order.
  • The normal‑state T‑linear resistivity slope and Fermi velocity place La3Ni2O7 in the Planckian dissipation regime, similar to other strange metals.
  • The pressure–temperature phase diagram is highly reproducible across several single crystals, confirming the intrinsic nature of the electronic modifications.

Conclusions

  • Two distinct density-wave anomalies, T1 and T2, are resolved: T1 is initially suppressed and then sharply enhanced after the structural transition, while T2 (spin-density-wave) increases monotonically with pressure.
  • The orthorhombic-to-tetragonal structural transition enhances both in-plane and out-of-plane resistivities and strongly increases low-temperature resistivity anisotropy due to the density-wave order.
  • Superconductivity with zero resistance emerges near the boundary where the density-wave phases are fully suppressed, with an onset Tc up to 68 K.
  • Above Tc, the normal-state resistivity displays a T‑linear dependence over a wide temperature range, and the extracted scattering rate lies within the Planckian limit, revealing a strange‑metal state.
  • Robust density-wave correlations and Planckian dissipation are defining features of La3Ni2O7, and superconductivity develops from this strongly correlated normal state.

Main claims

  • Two distinct density-wave-related anomalies (T1 and T2) exhibit contrasting pressure dependences, with T1 enhanced after a structural transition.
    • Evidence: Temperature derivative of in-plane resistivity shows T1 and T2 anomalies,Phase diagram Fig. 2e shows T1 initially suppressed then sharply increased near 10 GPa, T2 monotonically increasing
  • The pressure-induced structural transition enhances low-temperature resistivity and its anisotropy.
    • Evidence: At ≈8-10 GPa, ρab and ρc increase at low T, and ρc/ρab rises sharply below 150 K (Figs. 3,4a),The change coincides with orthorhombic-to-tetragonal transition
  • Zero-resistance superconductivity emerges near the boundary where density-wave phases are fully suppressed.
    • Evidence: Tc onset and Tc zero appear at pressures >14 GPa where T1, T2 and resistivity upturn disappear (Fig. 2e),Tc onset up to 68 K, zero resistance up to 55 K at 20 GPa
  • The normal-state resistivity above Tc exhibits T-linear dependence and Planckian dissipation.
    • Evidence: ρab is T-linear from ≈80 K to 300 K at 18 and 20 GPa with small residual resistivity (Fig. 4f),Scattering rate α ≈ 1.6 ± 0.4, close to Planckian limit (Fig. 4c)

Workflow

  • sample_preparation — High-quality oxygen-stoichiometric bilayer La3Ni2O7 single crystals were obtained.
    • Materials: La2O3 (99.99%); NiO (99.99%); flux; oxygen agent
    • Methods: high-pressure growth in cubic-anvil press at 3 GPa; heating at 1373 K then slow cooling to 1073K; X-ray diffraction; Laue diffraction; STEM and EDS mapping
    • Observations: large single crystals up to 220 μm; orthorhombic Am2m structure; no oxygen vacancies; no stacking faults; homogeneous element distribution
  • measurement — Pressure-dependent resistivity and anisotropy reveal density-wave anomalies and superconductivity.
    • Materials: single crystal samples 2#-a, 2#-d, 2#-e; silver epoxy or nanoparticle silver paste electrodes; Daphne 7575/7676 pressure transmitting medium; cubic-anvil press; PPMS
    • Methods: four-contact resistivity measurements; Montgomery method for anisotropy; in-plane (ab) and out-of-plane (c) resistivity under pressure
    • Observations: ρab decreases with P at 300 K, then develops semiconducting upturn at intermediate P; two anomalies T1 and T2 in resistivity derivative; resistivity anisotropy ρc/ρab increases sharply at low T near 10 GPa; superconducting transition with Tc onset up to 68 K and zero resistance up to 55 K at 20 GPa
  • analysis — Density-wave orders are modified by pressure, and the normal state at high pressure exhibits Planckian dissipation.
    • Methods: temperature derivative of resistivity to identify characteristic temperatures; Drude model to extract scattering rate; comparison with Planckian limit α = (ħ/τ)/(k_B T); construction of P-T phase diagram
    • Observations: T1 initially suppressed then sharply increased around 10 GPa (structural transition); T2 increases monotonically with pressure; T-linear ρab from ≈80 K to 300 K at 18-20 GPa with slope ≈0.28 μΩ cm/K; scattering rate α ≈ 1.6 ± 0.4, close to Planckian limit
  • interpretation — Superconductivity in La3Ni2O7 develops from a strongly correlated state with Planckian dissipation when robust density-wave orders are fully suppressed.
    • Observations: superconductivity emerges only after full suppression of T1, T2, and resistivity upturn; strange-metal state with T-linear resistivity and strong scattering