[Paper Review] Thermodynamically stable room-temperature superconductors in Li-Na hydrides under high pressures

Decheng An, Defang Duan+4 more|arXiv (Cornell University)|Mar 17, 2023

Hydrogen Storage and Materials7 citations

TL;DR

This study identifies two thermodynamically stable, room-temperature superconductors—Fd-3m-Li₂NaH₁₇ and Pm-3n-LiNa₃H₂₃—in lithium-sodium hydrides under high pressure, achieving critical temperatures of 340 K at 300 GPa and 310 K at 350 GPa, respectively. The superconductivity arises from high hydrogen density of states at the Fermi level and strong Fermi surface nesting, offering a structural blueprint for future experimental and theoretical exploration of high-Tc superconductors.

ABSTRACT

Room-temperature superconductivity has been a long-standing goal for scientific progress and human development. Thermodynamic stability is a prerequisite for material synthesis and application. Here, we perform a combination of high-throughput screening and structural search and uncover two thermodynamically stable room-temperature superconductors, Fd-3m-Li2NaH17 and Pm-3n-LiNa3H23, exhibiting extraordinary critical temperature of 340 K at 300 GPa and 310 K at 350 GPa, respectively. Li2NaH17 possesses the highest Tc among all the thermodynamically stable ternary hydrides hitherto found. The dominated H density of states at the Fermi level and the strong Fermi surface nesting are favorable for the emergence of room-temperature superconductivity. Their excellent superconducting properties help us understand the mechanism of room-temperature superconductivity and find new room-temperature superconductors. Interestingly, the structures of LiNa3H23 and Li2NaH17 equal to the identified type-I and II clathrate geometry. Our results provide a structural reference and theoretical guidance for later experimental structure determination and theoretical search for high temperature superconductors.

Motivation & Objective

• To identify thermodynamically stable ternary hydrides that exhibit room-temperature superconductivity under high pressure.
• To overcome the challenge of metastability in high-Tc superconductors by focusing on thermodynamic stability as a prerequisite for synthesis and application.
• To explore the electronic and structural origins of high critical temperature (Tc) in complex hydrides through first-principles calculations.
• To provide a structural reference—specifically clathrate-type frameworks—for future experimental validation and theoretical screening of high-Tc superconductors.

Proposed method

• Employed high-throughput screening combined with evolutionary structural search algorithms to explore stable phases in the Li-Na-H system under high pressure.
• Used density functional theory (DFT) calculations to compute electronic structure, phonon dispersion, and electron-phonon coupling for candidate phases.
• Applied the McMillan formula and Allen-Dynes approach to estimate the critical temperature (Tc) from electron-phonon coupling and phonon spectra.
• Evaluated thermodynamic stability via formation energy calculations and phonon band structure analysis to ensure no soft modes or dynamic instabilities.
• Analyzed the Fermi surface nesting and hydrogen-dominated density of states at the Fermi level to explain the enhanced superconducting pairing mechanism.
• Identified two stable superconducting phases: Fd-3m-Li₂NaH₁₇ and Pm-3n-LiNa₃H₂₃, both exhibiting clathrate-type geometry.

Experimental results

Research questions

• RQ1 Can thermodynamically stable ternary hydrides in the Li-Na-H system support room-temperature superconductivity under high pressure?
• RQ2 What is the role of hydrogen-rich hydride frameworks with clathrate geometry in enabling high Tc superconductivity?
• RQ3 How do Fermi surface nesting and hydrogen-dominated density of states at the Fermi level contribute to enhanced electron-phonon coupling?
• RQ4 What is the maximum achievable Tc in stable, non-metastable hydride phases under high pressure?
• RQ5 Can the structural motifs of Li₂NaH₁₇ and LiNa₃H₂₃ serve as a design template for future high-Tc superconductors?

Key findings

• Fd-3m-Li₂NaH₁₇ exhibits a critical temperature of 340 K at 300 GPa, the highest among all known thermodynamically stable ternary hydrides.
• Pm-3n-LiNa₃H₂₃ achieves a critical temperature of 310 K at 350 GPa, demonstrating robust room-temperature superconductivity under extreme pressure.
• Both compounds are thermodynamically stable, as confirmed by negative formation energies and absence of soft phonon modes.
• The superconducting mechanism is driven by high hydrogen density of states at the Fermi level and strong Fermi surface nesting.
• The structures of Li₂NaH₁₇ and LiNa₃H₂₃ correspond to type-I and type-II clathrate geometries, respectively, offering a new structural motif for superconductor design.
• These findings provide a theoretical foundation and structural guidance for experimental synthesis and further discovery of high-Tc superconductors.