[Paper Review] High-temperature superconductivity with zero-resistance and strange metal behavior in La$_{3}$Ni$_{2}$O$_{7-δ}$

Yanan Zhang, Dajun Su+14 more|arXiv (Cornell University)|Jul 27, 2023

Magnetic and transport properties of perovskites and related materials42 citations

TL;DR

The study demonstrates zero-resistance superconductivity in La3Ni2O7 under high pressure (≈20–30 GPa) with a concurrent strange metal normal state, revealing a link between superconductivity and strange metal behavior.

ABSTRACT

Recently signatures of superconductivity were observed close to 80 K in \LN\ under pressure. This discovery positions \LN\ as the first bulk nickelate with high-temperature superconductivity, but the lack of zero resistance presents a significant drawback for validating the findings. Here we report pressure measurements up to over 30 GPa using a liquid pressure medium and show that single crystals of \LNO\ do exhibit zero resistance. We find that \LNO\ remains metallic under applied pressures, suggesting the absence of a metal-insulator transition proximate to the superconductivity. Analysis of the normal state $T$-linear resistance suggests an intricate link between this strange metal behaviour and superconductivity, whereby at high pressures both the linear resistance coefficient and superconducting transition are slowly suppressed by pressure, while at intermediate pressures both the superconductivity and strange metal behaviour appear disrupted, possibly due to a nearby structural instability. The association between strange metal behaviour and high-temperature superconductivity is very much in line with diverse classes of unconventional superconductors, including the cuprates and Fe-based superconductors. Understanding the superconductivity of \LNO\ evidently requires further revealing the interplay of strange metal behaviour, superconductivity, as well as possible competing electronic or structural phases.

Motivation & Objective

• Motivate the search for high-temperature superconductivity in layered nickelates under hydrostatic, high-pressure conditions.
• Determine whether La3Ni2O7 exhibits zero electrical resistance under pressure and map the superconducting transition temperature (Tc).
• Characterize the normal-state resistivity and its linear-in-T (strange metal) behavior and its relationship to Tc.
• Investigate how pressure influences superconductivity, strange metal behavior, and possible structural/electronic phase transitions.
• Compare findings to cuprates and Fe-based superconductors to understand unconventional pairing mechanisms.

Proposed method

• Apply hydrostatic pressure up to >30 GPa using liquid-pressure medium in piston-cylinder and diamond-anvil cells.
• Measure electrical resistance R(T) to identify Tc onset and zero-resistance state across pressures.
• Analyze normal-state R(T) with linear-in-T fits to quantify strange metal behavior (A′ coefficient).
• Perform magnetic-field dependent R(T) to extract upper critical fields Hc2 and their temperature dependence.
• Use thermally activated flux-flow (TAFF) analysis to extract activation energy U0(H) and its field dependence.
• Discuss structural considerations and potential phase transitions in relation to superconductivity.

Experimental results

Research questions

• RQ1 Does La3Ni2O7 under high pressure exhibit zero electrical resistance indicating bulk superconductivity?
• RQ2 What is the relationship between the observed strange metal behavior (linear-in-T resistivity) and superconductivity under pressure?
• RQ3 How do Tc and the strange metal parameters evolve with pressure, and what roles do structural phases play?
• RQ4 Is there evidence of competing electronic/structural orders (e.g., CDW, structural transitions) influencing superconductivity?

Key findings

• Zero resistance is observed in La3Ni2O7 around 40 K with Tc onset up to 66 K at 20.5 GPa.
• The material remains metallic under pressure with no metal-insulator transition proximate to superconductivity.
• Normal-state resistivity shows T-linear behavior over an extended range, strongest near the Tc maximum, with A′ decreasing under pressure.
• Upper critical fields extrapolate to about 97 T (20.5 GPa) and 83 T (26.6 GPa).
• Thermally activated flux-flow analysis yields U0(1 T) ≈ 702 K with weak field dependence U0(H) ∝ H^(-0.12).
• Tc and the T-linear resistivity region peak near 20–16 GPa and then decrease with further pressure, suggesting interplay with structural instability and competing phases.