Superconductivity

Superconductivity is a state in which paired electrons carry current with zero resistance below a critical temperature and field. The papers here cover how Tc and critical fields change with thinning, strain and pressure, signs of unconventional pairing, induced superconductivity in topological materials, and how the superconducting order recovers after a light pulse.

Students learn BCS theory as the rule, but several of these studies probe where it holds (thin aluminium) and where claims of unconventional behaviour rest on indirect evidence. Knowing the difference between measuring zero resistance and proving a pairing mechanism clears up much of the hype around new superconductors.

Claim ledger

What the evidence shows

Drawn from 9 studies in this library. Mix labels say which citation roles are present; they are not a strength score. Supports means evidence for a finding; Challenges means evidence against a stated position; Qualifies marks scope.

• ● Supporting studies only

  Structure at the nanometre scale can change Tc a lot.

  Thinning or straining a material can raise Tc sharply: aluminium films near four atomic layers reached Tc = 3.31 K versus 1.2 K in bulk, with a gap more than three times bulk, and strained regions near nanocomposite walls in La2CuO4 films gave an onset near 50 K versus about 35 K for conventional films.

  2 supporting · 2 qualifying

  Supports

  1. 1Does aluminum superconduct better when only a few atoms thick?
  2. 2Can stretching a cuprate vertically raise its superconducting temperature?

  Qualifies

  1. 1Can stretching a cuprate vertically raise its superconducting temperature?— Only about 5% of the film volume superconducts at the higher Tc; thick films did not reliably show it.
  2. 2Does aluminum superconduct better when only a few atoms thick?— Tc measured on only four films; mechanism unexplained.

  Study comparison

  Study	Role	Design	N	Population	Outcome
  Does aluminum superconduct better when only a few atoms thick?2023	Supports	OtherLab experiment: Al(111) films of different thicknesses grown in ultrahigh vacuum on Si(111) and probed in situ by scanning tunneling spectroscopy down to millikelvin temperatures, with magnetic fields and Usadel-equation simulations.	Many separately grown films; each data point in the gap-versus-coverage plot is one sample. Critical temperature was measured on only four films.	Epitaxial aluminum films roughly 4 to 35 monolayers thick on Si(111)-(7x7)	Superconducting gap and critical temperature versus film thickness; response to perpendicular and in-plane magnetic fields (vortices, spin-split gap, g-factor)
  Can stretching a cuprate vertically raise its superconducting temperature?2019	Supports	OtherPulsed-laser-deposited vertically aligned nanocomposite films on SrTiO3, characterised by resistance and magnetisation versus temperature, XPS, low-temperature STM/STS and atomic-resolution STEM lattice mapping.	No participant sample; more than 10 films were grown, and the reported analysis focuses on five ~25 nm films (S1 to S5), with different films used for different measurements.	Thin films of La2CuO4+δ (214) nanostructures embedded in a LaCuO3 (113) matrix on (001) SrTiO3 substrates	Superconducting transition temperature, superconducting volume fraction, tunnelling gap, and local lattice parameters c and a near the 214/113 interfaces

• ● Supporting studies only

  Some enhancements stay BCS-like; others reflect genuinely strong coupling.

  Enhanced Tc does not automatically mean exotic pairing: in thin aluminium the gap-to-Tc ratio stayed near the BCS value of 3.53, whereas bismuth's high-pressure Bi-III phase showed strong coupling (inferred λ about 2.75) and the highest upper critical field of any element, about 2.45 T.

  2 studies
  1. 1Does aluminum superconduct better when only a few atoms thick?
  2. 2Why does squeezed bismuth superconduct so strongly?

  Study comparison

  Study	Role	Design	N	Population	Outcome
  Does aluminum superconduct better when only a few atoms thick?2023	Supports	OtherLab experiment: Al(111) films of different thicknesses grown in ultrahigh vacuum on Si(111) and probed in situ by scanning tunneling spectroscopy down to millikelvin temperatures, with magnetic fields and Usadel-equation simulations.	Many separately grown films; each data point in the gap-versus-coverage plot is one sample. Critical temperature was measured on only four films.	Epitaxial aluminum films roughly 4 to 35 monolayers thick on Si(111)-(7x7)	Superconducting gap and critical temperature versus film thickness; response to perpendicular and in-plane magnetic fields (vortices, spin-split gap, g-factor)
  Why does squeezed bismuth superconduct so strongly?2018	Supports	OtherLab measurements of resistivity and magnetization of bismuth under pressure, combined with ab initio electronic-structure and phonon calculations.	No participant count; samples cut from a single commercial bismuth crystal measured in pressure cells.	Elemental bismuth in its high-pressure incommensurate host-guest phase (Bi-III)	Superconducting transition temperature, upper and lower critical fields, normal-state resistivity slope, and inferred electron-phonon coupling constant

• ● Supporting studies only

  Broken symmetry and thinness produce behaviour ordinary superconductors lack.

  Two-dimensional superconductors can exceed the usual Pauli paramagnetic limit for in-plane fields: printed 1T'-WS2 monolayer films had an extrapolated in-plane critical field of about 30 T against a 13.1 T Pauli limit, and twisted MoTe2 junctions showed critical currents with a V-shaped minimum at zero field that vanished in untwisted controls.

  2 supporting · 1 qualifying

  Supports

  1. 1Can a water-based ink of 2D sheets superconduct?
  2. 2Does a twisted MoTe2 bilayer superconduct in an unusual way?

  Qualifies

  1. 1Can a water-based ink of 2D sheets superconduct?— In-plane field is extrapolated from a fit beyond the 9 T measured.

  Study comparison

  Study	Role	Design	N	Population	Outcome
  Can a water-based ink of 2D sheets superconduct?2023	Supports	OtherChemical exfoliation of K0.5WS2 into 1T'-WS2 monolayer ink, structural characterization (AFM, TEM, EELS, XRD, Raman, XPS), then low-temperature transport and magnetization on drop-cast films.	No single N; over 200 nanosheets sized by AFM, over 50 checked by local diffraction/STEM, two printed transport devices.	Films and pellets of chemically exfoliated 1T'-WS2 monolayer nanosheets	Superconducting transition temperature, in-plane and out-of-plane upper critical fields, critical current, and stability after air exposure
  Does a twisted MoTe2 bilayer superconduct in an unusual way?2025	Supports	OtherLow-temperature transport and electron-microscopy experiment on Pd7MoTe2/twisted-MoTe2/Pd7MoTe2 junctions, with a natural-bilayer junction as a control	A handful of devices: twisted-bilayer transport devices D2 and D3, natural-bilayer device D4, a monolayer comparison device, and separate TEM samples	Twisted (about 3.7°) and natural bilayer MoTe2 junctions about 100 nm long between superconducting Pd7MoTe2 pads	Resistance versus temperature, critical current versus magnetic field, critical field, and normal-state resistance

• ○ Limited citations

  Unconventional pairing is inferred from signatures, not seen directly.

  Evidence for time-reversal-symmetry breaking or mixed pairing comes from indirect probes: muon-spin relaxation in NbRuSi and TaRuSi polycrystals detected tiny spontaneous fields below Tc and a fully gapped superfluid density consistent with s + ip pairing.

  1 study
  1. 1Do topological semimetals NbRuSi and TaRuSi superconduct unusually?

• ● Supporting studies only

  Hybrid devices can carry pair correlations into topological films.

  Superconductivity can be induced into topological materials: niobium fingers on a quantum anomalous Hall film produced crossed Andreev reflection with a decay length of about 100 nm, and a Nb-contacted BiSbTeSe2 nanowire showed a gate- and field-tunable superconducting diode effect with efficiency up to about 0.3.

  2 studies
  1. 1Can a superconductor induce pairing in a magnetic topological edge?
  2. 2Can a tiny topological wire act as a switchable superconducting diode?

  Study comparison

  Study	Role	Design	N	Population	Outcome
  Can a superconductor induce pairing in a magnetic topological edge?2024	Supports	OtherLow-temperature three-terminal transport on V-doped (Bi,Sb)2Te3 Hall bars with Nb finger electrodes of different widths, plus tight-binding transport simulations	Several devices (A to F) with Nb finger widths from 160 to 520 nm; no single sample count	Thin-film quantum anomalous Hall insulator devices contacted by superconducting niobium fingers	Downstream (nonlocal) resistance versus magnetic field, temperature and finger width
  Can a tiny topological wire act as a switchable superconducting diode?2025	Supports	OtherLow-temperature transport on Nb-contacted BiSbTeSe2 nanowire junctions versus parallel field and gate voltage, with tight-binding simulations and a phenomenological SQUID model	No sample N; main data from device A, rectification from device B, and three further devices in supplementary material	Bulk-insulating BiSbTeSe2 topological-insulator nanowires side-contacted by niobium electrodes, measured near 30 mK	Critical currents in each direction and diode efficiency versus parallel magnetic field and back-gate voltage

• ○ Limited citations

  An 'anomalous metal' can be a superconductor with moving vortices.

  Disorder and vortices control low-temperature resistance in atom-thin films: in monolayer Pb on Si, resistance saturated at a finite value between about 25 and 100 mT, the same range in which STM imaged stable vortex lattices, and added step disorder lowered Tc from 1.53 K to 1.21 K.

  1 study
  1. 1Why does a 2D superconductor keep a little resistance near zero kelvin?

Debates

Tensions and limits

Some items are genuine disagreements on the same question. Others mark different assays, populations, or outcomes.

Timeline

How understanding moved

Study years are when the paper was published. Evidence edits are dated changes to this page's claims. Explanations are when PaperFren added a Discovery — not a claim that the science happened that day.

Papers

9 studies in this library bear on Superconductivity, ordered by citations.

• Can a water-based ink of 2D sheets superconduct?

  A water-based ink of single-layer tungsten disulfide sheets can be printed into films that superconduct below about 7 kelvin, resist in-plane magnetic fields unusually well, and survive a month in air.

  Science advances · 2023 · 17 citations

• Can stretching a cuprate vertically raise its superconducting temperature?

  Embedding a cuprate superconductor inside a stiffer partner material stretched its crystal layers vertically near their shared walls and raised the superconducting transition to about 50 K, above what ordinary films of this compound reach.

  Science advances · 2019 · 11 citations

• Does aluminum superconduct better when only a few atoms thick?

  Ultrathin, clean aluminum films superconduct at roughly three times the temperature of bulk aluminum, and the enhancement grows steadily as the film gets thinner.

  Science advances · 2023 · 9 citations

• Why does squeezed bismuth superconduct so strongly?

  When pressure turns bismuth into a structure with mismatched, interpenetrating atomic chains, it becomes an unusually strong superconductor, likely because the chains can slide and create very soft vibrations.

  Science advances · 2018 · 9 citations

• Does a twisted MoTe2 bilayer superconduct in an unusual way?

  Short junctions of twisted bilayer MoTe2 carried supercurrent that survived higher fields and temperatures than the superconducting contacts and was weakest at zero magnetic field, unlike an untwisted control.

  Science advances · 2025 · 9 citations

• Do topological semimetals NbRuSi and TaRuSi superconduct unusually?

  Ruthenium silicides NbRuSi and TaRuSi, which are topological semimetals, become superconductors that spontaneously generate tiny internal magnetic fields, a hallmark of unconventional pairing.

  Science advances · 2022 · 8 citations

• Can a superconductor induce pairing in a magnetic topological edge?

  A narrow superconducting strip on the edge of a quantum anomalous Hall insulator turns incoming electrons into outgoing holes, showing superconducting correlations have leaked into the edge state.

  Nature physics · 2024 · 8 citations

• Can a tiny topological wire act as a switchable superconducting diode?

  A topological-insulator nanowire between two superconductors carries more supercurrent one way than the other, and both the size and direction of this diode effect can be flipped with a magnetic field or a gate voltage.

  Science advances · 2025 · 1 citations

Questions

What is still open

1. Topological or not? Both hybrid-device studies see signatures compatible with topological superconductivity, but simulations in the QAH study show trivial pairing produces the same crossed Andreev signal, and the nano-SQUID link to Majorana modes is theoretical; neither detects Majoranas.

   Monitor this question

2. Thin-film enhancement looks different in different systems: aluminium's Tc rose on thinning, but monolayer Pb's Tc fell when step disorder was added, so 'thinner is better' depends on disorder and material.

   Monitor this question

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