Is room-temperature superconductivity at ambient pressure possible?

Scope

Room-temperature superconductivity at ambient pressure remains an open materials question in the evidence reviewed here. The cited theoretical models do not establish a universal prohibition at 300 K, but they also do not supply an experimentally verified ambient-pressure material at that temperature. Mathematical permission, a candidate calculation and a reproducible specimen are different levels of evidence. A negative experiment or a retracted claim does not prove that every possible material must fail. R1 R2 R7 R10

For a precise target, this page uses 300 K, approximately 27 °C, and near-atmospheric operating pressure. This is an explicit convention rather than a universal definition of room temperature. Preparation at high pressure and measurement after decompression must be reported separately. A recovered specimen may operate at ambient pressure while remaining metastable, cold-stored or difficult to manufacture; those are different practical questions. R3 R6

Mathematical assumptions

A temperature target first sets a thermal energy, not a pairing mechanism. At 300 K,

$$k_BT=25.852\ {\rm meV}.$$

In the isotropic weak-coupling BCS limit, the zero-temperature gap obeys

$$\frac{\Delta(0)}{k_BT_c}=\frac{\pi}{e^\gamma}\simeq1.764.$$

A hypothetical BCS transition at 300 K would therefore correspond to a zero-temperature gap of about 45.60 meV. This is a conditional conversion: observing a gap of that size does not determine its origin, phase coherence or transition temperature. Strong coupling, anisotropy and competing orders can invalidate the weak-coupling ratio. Independent quadrature of the finite-cutoff BCS equations approaches the stated limiting ratio; it does not identify a viable compound. R1 R2

For a strictly two-dimensional system with a BKT transition, define phase stiffness by $F=(D_s/2)\int d^2r\,|\nabla\theta|^2$. The renormalized stiffness just below the transition satisfies $D_s(T_c^-)=2k_BT_c/\pi$. At 300 K this would require about 16.46 meV in that convention. A zero-temperature mean-field stiffness is not automatically this finite-temperature response. The flat-band bounds question explains why model-specific upper bounds are necessary constraints rather than sufficient evidence of superconductivity. The BKT relation is not a universal three-dimensional temperature limit. R7

Pairing, coherence and stability

For phonon-mediated candidates, raising a characteristic frequency or electron–phonon coupling cannot be assessed in isolation. The Allen–Dynes analysis depends on coupling, screened Coulomb repulsion and spectral moments; it does not justify an arbitrary extrapolation of one fitted parameter. Ashcroft's hydrogen-dominant-alloy proposal motivates chemical precompression, but its proposal is not a demonstration of ambient-pressure superconductivity. The existence, stability and synthesis of the required structure remain separate problems. R2 R3

A useful candidate must sustain pair formation and a coherent current response in the same accessible state. In two dimensions, phase fluctuations can constrain a transition even when pairing is strong. For a metastable recovered state, the pressure–temperature–time path and the lifetime at the intended operating temperature also matter. Neither a large calculated pairing scale nor a specimen recovered briefly at ambient pressure establishes all of these conditions. R6 R7

What experiments establish

High-pressure hydrides show why temperature and pressure must remain paired. The 2015 sulfur-hydride work reports a magnetic onset of 203(1) K at 155 GPa in the checked author figure; its transport comparison uses a different pressure. Drozdov and colleagues' final 2019 lanthanum-hydride paper reports a resistive onset near 250–252 K around 170 GPa, zero resistance and field/isotope observations, while explicitly noting the sample was below their available SQUID sensitivity. These are substantial high-pressure results, not ambient-pressure demonstrations or interchangeable magnetic criteria. The hydrides article preserves the measurement-specific qualifications. R4 R5

Deng and colleagues' 2026 Hg-1223 report separates preparation from observation: S4 was quenched from 18.9 GPa at 4.2 K, then showed derivative-defined resistive onsets of 151 K on warming and 150 K on cooling at ambient pressure. Those are not 300 K transitions or a 151 K zero-resistance threshold. The retrieved-sample magnetic estimate belongs to S2, while cold-storage tests used S3; neither can be silently assigned to the highest-onset S4 specimen. An unreproduced anomaly extending to 172 K remains unassigned. R6

These examples establish different experimental constraints and motivate follow-up; this selection is not an exhaustive world-record survey. The 2026 final main text and selected author figures were checked, but the final supplementary file and raw data remain outside the completed review. Independent laboratory replication of that pressure-quench result has not been verified here; this does not establish that no replication exists. R6

Experimental criteria

A persuasive room-temperature claim needs mutually consistent evidence tied to identified samples: composition and structure, calibrated temperature and pressure, resistance with a stated noise floor and contact geometry, field/current dependence, and an appropriately calibrated magnetic or thermodynamic response. Their evidential weight depends on geometry and scale; a thin film cannot simply be judged by an uncorrected bulk shielding fraction. Preserve unsuccessful preparations and differences among specimens instead of combining each specimen's strongest result into an imaginary single sample. This is a synthesis of the measurement limitations in the cited primary studies. R4 R5 R6

Independent replication should reproduce the synthesis and relevant observations, with raw traces, calibration, backgrounds and transition criteria available for examination. An onset, midpoint, instrumental zero and magnetic onset answer different questions. Near-atmospheric operation should also survive the specified temperature cycle and useful measurement duration; a claim of practical applicability requires additional current, field, mechanical and manufacturing evidence beyond this scientific existence question. R4 R5 R6

Limits and disputes

The carbonaceous-sulfur-hydride and nitrogen-doped lutetium-hydride reports were retracted in 2022 and 2023, respectively. Their claimed transition temperatures cannot be treated as established benchmarks. In particular, a near-ambient label must not replace the numerical pressure: 10 kbar equals 1 GPa, about ten thousand times atmospheric pressure. Publication status, sample identity and the actual operating conditions must accompany any historical mention. R8 R9

The independent LuH₂±xNᵧ study found no superconductivity above 2 K in its tested samples across 0.4–40.1 GPa. That negative result constrains the tested preparation and composition, not every possible member of a chemical system. Likewise, the absence of a demonstrated 300 K material in the sources reviewed here is not a mathematical impossibility proof. It is a reason to demand better, reproducible evidence for a new claim. R10

Discovery implications

The productive question is which concrete composition, structure and preparation route could supply pairing, phase coherence and sufficient stability under the same stated conditions. Predictions should identify their approximation, uncertainty and falsifying observations; experiments should test the same conditions and distinguish reproduction within one laboratory from independent confirmation. This page offers a framework for evaluating that question, not a prediction that a room-temperature material will or will not be discovered. R1 R3 R6 R7

Related topics

Continue with BCS theory, hydrides, experimental methods, research methods, and flat-band temperature bounds.

Material cases

No sample-specific material records are included in this article. Model results are not experimental transition temperatures.