Room-Temperature Superconductor

• Room-Temperature Superconductors are materials that demonstrate zero electrical resistance and complete magnetic expulsion near 300 K, crucial for efficient energy transport and electronics.
• Advances in high-pressure synthesis and computational modeling have led to hydrogen-rich clathrate hydrides, such as LaH10, showing superconductivity near room temperature under extreme pressures.
• Controversies surrounding ambient-pressure candidates like LK-99 underscore the need for rigorous verification protocols to confirm true superconducting behavior.

A room-temperature superconductor is a material that exhibits superconductivity—zero electrical resistance and the expulsion of magnetic fields (the Meissner effect)—at or above ambient temperature (≈300 K) and, in some reports, under ambient atmospheric pressure. The pursuit of such materials is motivated by their potential to enable lossless energy transmission, advanced electronic applications, and transformative impacts on many sectors of modern technology. This entry provides a comprehensive review of the theoretical models, historical progress, practical realizations, mechanisms, controversies, and future research directions relating to room-temperature superconductors, strictly referencing published research and technical claims from the scientific literature.

1. Theoretical Foundations and Criteria for Superconductivity

Superconductivity is rigorously characterized by three primary features: exactly zero DC resistance, near-complete diamagnetism (the Meissner effect), and a signature thermodynamic anomaly—typically a jump in electronic heat capacity—at the superconducting transition temperature $T_c$ (Luo, 4 Mar 2025). In conventional BCS (Bardeen–Cooper–Schrieffer) theory, superconductivity arises from the condensation of electron pairs (Cooper pairs) into a coherent quantum state protected by an energy gap at the Fermi level. The BCS gap equation yields:

$T_{\mathrm{c}} \propto \exp(-1/\lambda),$

where $\lambda$ is the electron–phonon coupling constant (Luo, 4 Mar 2025). The Eliashberg and Migdal–Eliashberg extensions account for strong coupling and energy-dependent phenomena, using the electron–phonon spectral function $\alpha^2F(\omega)$ and computing $T_c$ through equations such as the Allen–Dynes formula:

$$T_c = \frac{\omega_{\mathrm{log}}}{1.2} \exp{\left[-\frac{1.04(1+\lambda)}{\lambda-\mu^*(1+0.62\lambda)}\right]},$$

where $\omega_{\mathrm{log}}$ is the logarithmic-averaged phonon frequency and $\mu^*$ is the Coulomb pseudopotential (Pickett, 2017, Zheng et al., 2019, Pickett, 2022).

A reliable identification of superconductivity, especially claims at room temperature, mandates the demonstration of zero resistance, strong diamagnetic shielding, and a clear calorimetric signature associated with energetically distinct phase transitions (Luo, 4 Mar 2025). Claims based solely on incomplete or ambiguous data sets are frequently categorized as unidentified superconducting objects (USOs) (Luo, 4 Mar 2025).

2. Historical Perspective and Timeline of Room-Temperature Superconductivity Research

The quest for room-temperature superconductors spans over a century, originating with the 1911 discovery of superconductivity in Hg at 4 K (Pickett, 2017). The mid-20th-century search was guided by empirical “Matthias rules” emphasizing transition-metal binaries with cubic symmetry (Pickett, 2017). While transition temperatures slowly increased through the 1970s (e.g., 23 K in Nb₃Ge), projections—such as Bruce Friday’s 1973 extrapolation—pushed room-temperature superconductivity to centuries in the future.

Breakthroughs accelerated with the discovery of high-$T_c$ cuprates in the 1980s and progressed into hydrogen-rich materials and hydrides (Pickett, 2017, Pickett, 2022). The first experimental evidence of $T_c$ above 200 K was observed in H₃S at 200 K under 160–200 GPa (Pickett, 2017, Pickett, 2022). Computational methods, notably DFT and high-throughput crystal structure prediction algorithms, facilitated rapid prediction and discovery, culminating in reports of hydride superconductors—such as LaH₁₀, YH₉, and C–S–H—approaching or reportedly exceeding room temperature under megabar pressures (Pickett, 2022, Lamichhane et al., 2021, An et al., 2023).

Historically, verified increases in $T_c$ have relied on advances in both experimental high-pressure synthesis and computational prediction, with the current frontiers lying in complex hydride systems and materials engineering (Pickett, 2017, Pickett, 2022).

3. Materials Realizing Room-Temperature Superconductivity

3.1 High-Pressure Hydrides

Most confirmed room-temperature superconductors are hydrogen-rich clathrate hydrides, synthesized and maintained at multipart (100–350 GPa) pressures:

• LaSc₂H₂₄ (hexagonal, P6/mmm symmetry): $T_c$ = 271–298 K at 195–266 GPa; four-probe electrical measurements, Meissner effect, and suppression of $T_c$ under magnetic field conclusively confirm superconductivity (Song et al., 29 Sep 2025). The structure consists of distinct La-centered H₃₀ cages and Sc-centered H₂₄ cages, providing high hydrogen-derived DOS and enhanced electron–phonon coupling.
• Li₂NaH₁₇ and LiNa₃H₂₃ (type-II and type-I clathrate hydrides): $T_c$ = 340 K at 300 GPa and 310 K at 350 GPa, respectively; the high critical temperatures are attributed to high H DOS at $E_F$ and strong Fermi surface nesting (An et al., 2023). Both compounds offer thermodynamic stability at high pressure and serve as structural archetypes for further design.
• LaH₁₀, YH₉, C–S–H: $T_c$ values in the 250–288 K range at pressures of 160–260 GPa; the sodalite-like clathrate cages stabilize high symmetric hydrogen frameworks (Yi et al., 2020, Pickett, 2022, Lamichhane et al., 2021).
• Heavy rare-earth hexahydrides (e.g., YLu₃H₂₄): $T_c$ = 288 K at 110 GPa, stabilized via chemical precompression with heavy lanthanide cations (Du et al., 2022).

3.2 Low-Pressure and Ambient-Pressure Candidates

Reports of room-temperature superconductivity at ambient or moderately elevated (≤1 atm) pressures remain controversial:

• LK-99 (Pb₁₀₋ₓCuₓ(PO₄)₆O, $0.9: Initial experiments claimed zero resistivity above 400 K, Meissner effect, and levitation at ambient pressure (Lee et al., 2023, Lee et al., 2023). However, independent replications failed to observe robust bulk superconductivity; some anomalies were traced to Cu₂S impurities with structural transitions at ~400 K (Habamahoro et al., 2023).
• Bi/Pb-based ceramic cuprates: A new family synthesized via melt processing in concentrated solar furnaces exhibits 3D bulk $T_c$ ≈ 100–140 K and pronounced 2D superconductivity at grain boundaries/interfaces with onset as high as 395 K, substantiated by sharp resistance drops and partial Meissner effect at ambient pressure (Dzhumanov et al., 5 Jan 2024).
• Ultrathin carbon nanotube (CNT) composites: Single-walled (2,1) and (3,0) CNT zeolite composites report zero resistance above 230 K (ambient to slightly pressurized), with scale factor analysis attributing high $T_c$ to phonon softening, electronic DOS enhancement via chirality and doping, and lattice regularity (Wong et al., 25 Sep 2025).

4. Mechanisms Underpinning Elevated Superconducting Transition Temperatures

4.1 Enhanced Electron–Phonon Coupling in Light-Element Frameworks

The record-high $T_c$ values in hydride superconductors are rationalized by strong electron–phonon coupling ($\lambda > 2$) and high-frequency phonon modes due to light atom (H) frameworks, as described by the McMillan and Allen–Dynes formulae (Pickett, 2022, Zheng et al., 2019). For room-temperature $T_c$ in standard electron–phonon systems, a Debye temperature $T_D \approx 1800$ K or higher and a phonon exchange factor $\lambda \lesssim 2.67$ are considered necessary (Zheng et al., 2019). The stabilization of cubic or clathrate hydrogen cages is critical for maintaining high phonon frequencies and robust coupling (An et al., 2023).

4.2 Hole Doping and Multinary Structural Optimization

Incorporation of light or multivalent cations (e.g., C doping in C–S–H, Sc in LaSc₂H₂₄) modifies the carrier density and can introduce hole doping, further boosting $T_c$ (Lamichhane et al., 2021, Song et al., 29 Sep 2025). The sharing of electrons between electride-like metal frameworks (as in LaH₁₀) and the hydrogen lattice, as well as ionic–covalent hybridization at the metal–hydrogen interface, are essential for stabilizing these high-symmetry cages (Yi et al., 2020).

4.3 Interface and Dimensionality Effects

The emergence of 2D superconducting domains in Bi/Pb-based ceramic cuprates provides evidence for enhanced $T_c$ at interfaces, grain boundaries, and multilayer blocks, with theoretical models based on Bose–liquid superconductivity for tightly bound Cooper pairs (Dzhumanov et al., 5 Jan 2024). The 2D critical temperature $T_c^{(2D)}$ is theoretically given by

$$T_c^{(2D)} = -\frac{T_0^*}{\ln\left[1 - \exp\left(-2\gamma_B/(\gamma_B + 2)\right)\right]},$$

where $T_0^*$ and $\gamma_B$ denote characteristic boson energy and coupling, respectively.

4.4 Non-BCS Mechanisms and Unconventional Superconductivity

In ultra-thin carbon nanotubes, the standard McMillan formula underestimates $T_c$ by two orders of magnitude; however, ab initio and scale-factor-based approaches indicate that enhanced electron–phonon effects, not exotic order or unconventional mechanisms, are responsible (Wong et al., 25 Sep 2025). There is as yet no robust evidence for non-phonon-mediated pairing mechanisms achieving bulk room-temperature superconductivity, though alternative “pairing glues” (magnetic fluctuation mediated, polaronic, plasmonic, or interfacial) remain active research frontiers (Luo, 4 Mar 2025).

5. Experimental and Design Methodologies

Advances in first-principles computational materials design—especially density functional theory (DFT), density functional perturbation theory (DFPT), and structure prediction algorithms (USPEX, CALYPSO, AIRSS)—have underpinned much of the modern discovery pipeline for high-$T_c$ hydrides (Pickett, 2022, Du et al., 2022, An et al., 2023). High-pressure synthesis is realized with diamond anvil cells (DACs) and laser heating, enabling stabilization and in-situ characterization via synchrotron X-ray diffraction and transport measurements (Song et al., 29 Sep 2025). Synthesis at ambient pressure, when claimed, commonly uses solid-state or melt processing; interface engineering, chemical substitution, and defect or doping strategies are essential tools in pushing the limits of $T_c$ (Dzhumanov et al., 5 Jan 2024, Wong et al., 25 Sep 2025).

AI and data-driven approaches are increasingly used for high-throughput screening and rational design, leveraging structure–property databases and machine learning models (Luo, 4 Mar 2025).

6. Verification, Controversies, and Criteria for Robust Claims

Stringent verification protocols demand that zero resistivity, the Meissner effect with nearly 100% shielding fraction, and a thermodynamic heat capacity anomaly must all be observed and be robust against magnetic field, cycling, and sample reproducibility (Luo, 4 Mar 2025). Many claims—particularly those for LK-99 and related ambient-pressure candidates—have failed these criteria upon replication. Anomalous behaviors (e.g., partial levitation, minor diamagnetism, incomplete resistance drop) are often traced to experimental artifacts, impurity phases, or structural transitions of non-superconducting inclusions (e.g., Cu₂S in LK-99) rather than intrinsic superconductivity (Habamahoro et al., 2023).

The field continues to be marked by both rapid advances and scientific debate, underscoring the necessity of cross-validated, multimodal characterization for establishing true room-temperature superconductivity.

7. Outlook and Future Research Directions

Current consensus holds that further progress toward ambient-pressure room-temperature superconductors will likely depend on breakthroughs in:

• Lowering stabilization pressures for hydride or hydrogen-rich frameworks via "chemical precompression" (selection of optimal cationic and anionic species, e.g. heavy rare earths, multinary alloys) (Du et al., 2022, Song et al., 29 Sep 2025).
• Engineering of interface-driven or low-dimensional systems, where interface superconductivity may offer practical pathways to high-$T_c$ states without extreme pressure (Dzhumanov et al., 5 Jan 2024, Luo, 4 Mar 2025).
• The discovery of new material systems through high-throughput experimental and AI-guided computational screening (Luo, 4 Mar 2025).
• Fundamental studies of pairing mechanisms beyond traditional phonon mediation, including explorations into strongly correlated and disordered systems, organic–inorganic hybrids, and exotic pairing glues (Luo, 4 Mar 2025).
• Clarifying and, where feasible, synthesizing single-phase, bulk superconductors that satisfy all physical criteria for a genuine superconducting state above room temperature and under practical conditions (Habamahoro et al., 2023).

Realization of robust, practically applicable room-temperature superconductors continues to represent a major open challenge in condensed matter physics, demanding both sustained experimental innovation and rigorous theoretical scrutiny.