A history of superconductivity: milestones and evidence

Scope

The history of superconductivity includes discoveries, theories, material families and changing standards of evidence. These eighteen milestones connect major developments to their dates, measurement conditions and original evidence. A later author's recollection, an original discovery report and a modern reanalysis answer different historical questions. The cited review scope tells the reader which was checked. R1 R4 R7

Mathematical assumptions

There is no single mathematical curve that makes all reported transition temperatures directly comparable. A resistance onset, a midpoint, a noise-floor zero and a magnetic response can occur at different temperatures, even in one specimen. Pressure, composition, sample history and measurement field must remain attached to any point. The linked material articles preserve detailed records; this history does not create duplicate experimental Tc entries from narrative summaries. R12 R21 R22

L1 — 1911: mercury and the resistance transition

Onnes's 1911 mercury work opened the study of superconductivity. His 1913 Nobel lecture provides a firsthand account of the abrupt resistance decrease near 4.2 K and the limits of the electrical measurement. Resistance too small to resolve is an experimental statement; mathematical exactness is not read directly from an instrument. The lecture also discusses a current threshold above which a voltage appeared, anticipating the need to specify measuring current. R1

The checked scan contains later notes, including a 1914 addendum. Those observations must not all be assigned to the original 1911 discovery. Nor should the initial resistance experiment be described as already establishing the later Meissner effect or a complete microscopic theory. The original 1911 communication itself remains outside the directly reviewed material; the author lecture is identified as the historical source used here. R1

L2 — 1933: the Meissner–Ochsenfeld effect

Meissner and Ochsenfeld's 1933 work added magnetic behavior to the definition of the superconducting state. The selected original reproduction describes field redistribution around tin and lead as the samples became superconducting. This changed the question from whether a conductor can sustain current without detectable resistance to which magnetic state it reaches. An ideal conductor's history-dependent trapped field does not by itself supply the same equilibrium magnetic condition. R2

Geometry remains essential to reading the experiment. The original report also discusses retained field in a lead-tube cavity; a cavity is not the same region as the superconducting material. A simplified statement that every field everywhere becomes zero would erase this distinction. The historical paper's apparatus, uncertainty and complete translation have not been independently reconstructed here. The milestone records the new magnetic evidence while retaining the limits of the selected primary reproduction. R2

L3 — 1935: London electrodynamics

The London brothers' 1935 paper supplied an electromagnetic description of superconductors that accommodates magnetic screening. The selected original pages distinguish the consequence of perfect conductivity from an additional condition selecting the superconducting magnetic state. An integration constant associated with the initial field is therefore not a trivial detail: dropping it without stating the physical postulate would conceal what the theory adds. R3

The London description links current and electromagnetic fields under its stated local assumptions. It does not determine a material's microscopic pairing interaction or explain every spatially nonuniform state. Modern equations often use SI units and different notation from the original scan; a historical formula should not be copied into a modern calculation without checking those conventions. This milestone concerns a phenomenological advance in electrodynamics, not an experimental discovery of a new transition-temperature record. R3

L4 — 1950: Ginzburg–Landau theory

Ginzburg and Landau introduced a complex order parameter and a free-energy description of superconductivity in 1950. Ginzburg's later firsthand lecture explains the motivation to extend the London treatment, including spatial variation and interfaces. The resulting framework connects electromagnetic response to the amplitude and phase of an order parameter and provides a basis for studying boundaries and competing configurations near a transition. R4

The history is not identical to today's textbook presentation. Ginzburg recounts that the effective charge was not correctly settled at twice the electron charge in the original work; the later microscopic interpretation clarified that point. Their early analysis also focused on what are now called type-I superconductors. Avoid projecting every subsequent vortex result or the complete BCS interpretation back into 1950. The checked source is the 2004 retrospective, with its original-paper citation, rather than a full direct audit of the 1950 article. R4

L5 — 1957: the BCS microscopic theory

Bardeen, Cooper and Schrieffer's 1957 theory constructed a coherent paired many-electron state and related its excitation spectrum to superconducting observables. It moved beyond identifying macroscopic signatures by providing a microscopic explanation within a specified interaction model. The energy gap and thermodynamic behavior arise together in that framework, rather than being independent empirical labels attached to a zero-resistance state. R5

The achievement should not be turned into a claim that one elementary approximation describes every later material. The familiar isotropic weak-coupling results assume a particular pairing structure and energy-scale hierarchy. Strong coupling, multiple bands, unconventional symmetry and substantial fluctuations require further treatment. A historical timeline should distinguish the theory's established role from a material-specific mechanism assignment. Agreement with one BCS-like ratio is a consistency check, not proof that a newly observed superconductor has the same microscopic interaction. R5

L6 — 1962: tunnelling supercurrents and field compensation

Josephson's 1962 paper predicted new tunnelling effects between superconductors. His 1973 lecture distinguishes the theoretical prediction from the later experiments that convincingly attributed observed supercurrents to tunnelling. Earlier zero-voltage currents could instead have involved metallic shorts, and unsuccessful measurements were part of the development. Phase-dependent response, magnetic interference and microwave-induced voltage steps provided more specific tests than a zero-voltage branch alone. R6 R7

Another development in 1962 was Jaccarino and Peter's proposal of ultra-high-field superconductivity through compensation of an external field by an internal exchange effect. This is a separate idea, not part of Josephson tunnelling. Its original bibliographic identity is checked here; the full original derivation is not. Later field-induced experiments and their limits are discussed in the linked exchange-compensation article. Keeping the two contributions distinct prevents a shared calendar year from becoming a misleading shared mechanism. R8

L7 — 1973: Nb–Ge films above 22 K

Gavaler's 1973 report describes superconductivity in sputtered Nb–Ge films above 22 K. The checked original abstract reports 22.3 K. The often-quoted 23.2 K value is not the value reported in this specific discovery abstract. A later optimized result, if added, needs its own citation, sample description and date rather than being silently attached to the earlier report. R9

Processing is central to the historical interpretation: the source describes high-pressure sputtering, which is a deposition condition, not evidence that the superconducting transition was measured under high external pressure. Film composition, phase formation and preparation affect the result. Neither the reported temperature nor the A15 label defines a universal transition for all Nb–Ge samples or a strict ceiling for the entire structural family. Full methods and the exact operational transition criterion remain unreviewed at this abstract-level scope. R9

L8 — 1979: CeCu2Si2 and heavy fermions

The 1979 CeCu2Si2 report established a superconducting state in a system with strong Pauli paramagnetism and an unusually large electronic response. Its original abstract gives a transition scale around 0.5 K. The historical importance lies in opening a strongly correlated setting for superconductivity, not in raising the maximum known transition temperature. Different measures of progress therefore belong in a scientific timeline. R10

This original observation should be separated from later debates over gap structure, magnetic coexistence and sample classification. Modern CeCu2Si2 experiments distinguish crystals and transitions that cannot be reduced to a universal 0.5 K constant. The presence of a heavy-electron normal state also does not uniquely identify a pairing interaction from the discovery abstract alone. The original full measurements have not been reconstructed in this review; the linked heavy-fermion article follows the subsequent evidence and its competing interpretations. R10

L9 — 1986: the Ba–La–Cu–O discovery

Bednorz and Müller's 1986 paper deliberately used the title “Possible high Tc superconductivity” for its Ba–La–Cu–O result. The publisher's original abstract describes multiphase polycrystals and a current-dependent, percolative resistive onset in the 30 K range. That is the evidence actually checked here. This abstract does not establish a precise bulk magnetic transition at 35 K. R11

The milestone initiated a new materials direction, but the discovery report's sample and uncertainty deserve to remain visible. A connected superconducting path can strongly affect resistance without establishing that the whole sample occupies one superconducting phase. Later synthesis, phase identification and complementary measurements must retain their own citations. The original abstract and publication record were checked; the complete figures, apparatus and raw measurements remain outside this review scope. Historical significance does not remove the need to distinguish an initial report from later confirmation. R11

L10 — 1987: Y–Ba–Cu–O above liquid-nitrogen temperature

Wu and colleagues reported a transition above liquid-nitrogen temperature in mixed-phase Y–Ba–Cu–O material. The selected final paper distinguishes a resistance deviation at 93 K, a sharp drop beginning near 92 K, zero resistance at 80 K and a magnetic onset near 91 K. These values describe different criteria in the reported experiment; the 93 K headline is not a 93 K zero-resistance result. R12

The original nominal sample composition was not a phase-pure YBa2Cu3O7 crystal. A subsequent structural, transport and magnetic study identified the principal YBa2Cu3Ox phase. Combining those papers is useful only when their roles remain distinct. Likewise, a low-temperature diamagnetic signal compared with lead is not automatically an independently corrected volume fraction. This milestone records both the striking temperature advance and the continuing work needed to establish the responsible phase and quantitative superconducting properties. R12 R13

L11 — 1993: mercury-based cuprates above 130 K

Schilling and colleagues' 1993 report describes superconductivity above 130 K in the Hg–Ba–Ca–Cu–O system, with magnetic and resistive evidence summarized near 133 K. The commonly cited 135 K value should not replace the approximately 133 K result in this specific original report. Oxygen content, phase composition and the experimental criterion matter when later samples yield somewhat different quoted temperatures. R14

Gao and colleagues' 1994 pressure study is a separate milestone in the development of this material family. Its abstract reports resistive superconductivity up to 164 K under quasihydrostatic pressure. That high-pressure result is neither an ambient-pressure value nor evidence that the state survives unloading. The exact pressure of the maximum and its onset-versus-zero criterion have not been re-extracted here. A plot that joins these numbers without marking conditions would confuse distinct experiments; the linked cuprate and pressure-quench pages preserve those boundaries. R14 R15

L12 — 2001: MgB2 at 39 K

Nagamatsu and colleagues' 2001 MgB2 paper showed that a chemically simple binary compound could superconduct at a surprisingly high temperature for that class of material. In the selected final report, resistance begins to fall at 39 K and reaches its endpoint near 38 K; a separate low-field magnetization measurement supports the interpretation. The two criteria should not be merged into one exact temperature independent of the measurement. R16

The synthesis pressure quoted in the methods is a preparation condition, not the pressure at which the reported transition was measured. The discovery also precedes the detailed body of isotope, spectroscopy and anisotropic electron–phonon work that established MgB2 as a multigap benchmark. Those later results do not all belong to the original discovery paper. Its role in the timeline is the 2001 observation with the sample and probes actually described, while the linked material article develops the subsequent microscopic evidence. R16

L13 — 2008: the iron-arsenide expansion

The 2008 fluorine-substituted LaOFeAs report brought a transition near 26 K to the iron-pnictide field. The publisher record distinguishes its February online publication from the later journal issue. The selected original abstract supports the composition range and reported temperature, but the detailed operational transition criterion remains unassigned at this review scope. Do not infer that criterion from the title alone. R17

This was not the first superconducting iron-containing compound or even the first reported layered iron pnictide: the same research group's LaOFeP paper appeared in 2006. That earlier source is retained to avoid compressing the family history into an incorrect first-discovery claim. The 2008 advance instead marks the higher-temperature arsenide platform and the beginning of rapid diversification into related systems. Iron-based materials subsequently require separate structural, magnetic and pairing analyses; the presence of iron does not fix a universal gap symmetry. R17 R18

L14 — 2015: sulfur hydride near 203 K

The 2015 sulfur-hydride report extended superconducting temperatures into a much higher range under extreme pressure. The selected author passages and published captions distinguish resistance measurements from the magnetic response, including a reported onset near 203 K at 155 GPa for the magnetic specimen. The pressure and measurement definition belong with the number; the result is not an ambient-pressure material property. R19

The superconducting phase assignment also developed through further structural work. A sulfur-hydride starting composition is not by itself proof of the final high-pressure stoichiometry, and the later diffraction study must remain separately cited when discussing H3S. The selected scientific review did not independently reconstruct magnetization background subtraction or all raw transport data. This milestone records the reported evidence and the pressure-enabled material setting without treating the historical headline as a complete audit of every experimental inference. R19 R20

L15 — 2019: lanthanum hydride and infinite-layer nickelates

Two distinct materials developments occurred in 2019. The lanthanum-hydride experiment reported a resistive transition around 250 K near 170 GPa. The selected final paper includes resistance, isotope comparison and field suppression, but no SQUID measurement. Applied magnetic fields and extrapolated upper-critical-field estimates are different quantities. This high-pressure result should not be plotted as an ambient-pressure room-temperature superconductor. R21

In a different materials setting, Li and colleagues reported superconductivity in reduced, Sr-substituted infinite-layer nickelate films. A representative Nd0.8Sr0.2NiO2 sample has separately defined onset, midpoint and noise-floor zero values of 14.9, 13.6 and 9.1 K. The result must not be relabelled as superconductivity in undoped bulk NdNiO2. Epitaxy, reduction, capping and sample preparation are part of the observation. The common year links these discoveries chronologically, not through an established common mechanism. R22

L16 — 2018: magic-angle twisted bilayer graphene

Cao and colleagues' superconductivity report appeared in 2018, not 2022. The discovery year should remain separate from the dates of later studies. In the selected final paper, two devices with different nominal twist angles have different transition scales: approximately 0.5 K and 1.7 K under the stated half-normal-resistance criterion. A device label, carrier density and transport definition belong with each number. R23

The paper's tentative BKT analysis supplies another temperature scale, while a 70 mK measurement floor is not a transition temperature. These distinctions prevent one figure from becoming several apparently interchangeable records. The broader advance is geometric control of electronic bands and interactions through a moiré structure; it does not establish that every magic-angle device has the same phase diagram or that a flat band alone guarantees superconductivity. The chronological guide places this discovery before the 2019 hydride and nickelate results. R23

L17 — 2023: bilayer nickelate signatures near 80 K

The 2023 La3Ni2O7 paper reported signatures near 80 K under pressure. For the selected run, the resistance onset occurs near 18.5 GPa, with nonzero residual resistance. A separate magnetic measurement is part of the broader paper, but its sample and pressure must not be silently attached to that particular resistance record. The wording “signatures” and the operational criterion are scientifically meaningful. R24

The checked passages also distinguish applied fields from an upper-critical-field extrapolation and retain pressure calibration and measurement-current conditions. A later zero-resistance result, thin-film experiment or structurally modified nickelate would be a separate entry with its own evidence. The historical milestone therefore establishes the reported pressure-induced phenomenon and the questions it raised, rather than declaring an independently reproduced 80 K bulk transition for every bilayer nickelate. Full raw-data and replication review remains open. R24

L18 — 2026: recovered cuprates, re-entrance and transport

Three recent papers illustrate different research directions; their dates and observables must remain separate. Deng and colleagues' pressure-quench article appeared online on 9 March 2026. Its highest retained ambient-pressure value, 151 K, is a resistive onset after a specific pressure-and-temperature preparation. A magnetic result on a different retrieved sample and cold-storage tests cannot be reassigned to that highest-onset specimen. R25

The Eu-substituted infinite-layer nickelate paper and the iron-chalcogenide Planckian-scattering paper were published on 23 April 2026. The first concerns field-dependent re-entrance under specified conditions; the second analyzes normal-state transport with parallel conduction channels. A model-dependent scattering rate is not a new Tc record or proof of a universal pairing mechanism. These studies are recent research directions with scoped checks, not one combined discovery or a completed independent replication programme. R26 R27

Chronological guide

Follow the links to the evidence for each milestone. The graphene discovery appears in 2018, before the 2019 hydride and nickelate results. Temperatures in the detailed sections are conditional reported values, not a uniform record-ranking dataset.

Experimental criteria

A reported milestone is not a standardized material benchmark. Preserve the experimental criterion and distinguish the year of observation, first public report, journal publication and later author account. An accurate timeline can include a theory, a measurement or a material platform without assigning each one a transition-temperature point. Links to primary evidence make the interpretation inspectable. R1 R7 R12 R22

Limits and disputes

Some early sources remain checked only at abstract or bibliographic level; other entries reuse selected original-paper reviews from the linked core articles. Those limitations remain attached rather than being upgraded by appearing in a history handbook. Later recollections help explain reasoning but are not the original laboratory record. Complete scientific acceptance, full final-version comparisons, supplementary data and independent replication remain open where stated. R4 R6 R9 R18

Discovery implications

Progress has come from new materials, better preparation, more discriminating probes and theories that make testable predictions. A higher reported onset is only one kind of advance. The historical examples encourage a workflow that separates initial observations from phase identification, reproducibility and mechanism tests, preserving negative results and corrections instead of rewriting them out of the story. R7 R12 R16 R24

Related topics

Continue with experimental methods, theoretical tools, applications, cuprates, iron-based materials, nickelates, hydrides, pressure quenching, and exchange compensation.

Material cases

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