--- title: "Giaever’s junction: current revealed the superconducting gap" description: "How could a thin insulating layer turn electrical current into spectroscopy?" canonical_url: "https://sandboxphysics.com/stories/condensed-matter/giaever-gap-spectroscopy/" language: "en" page_type: "story" alternate_languages: zh-CN: "https://sandboxphysics.com/zh/stories/condensed-matter/giaever-gap-spectroscopy/" last_modified: "2026-10-23" --- [Cold liquids and superconducting order](https://sandboxphysics.com/stories/condensed-matter/#collective) Materials · Measurements · Explanation # Giaever’s junction: current revealed the superconducting gap How could a thin insulating layer turn electrical current into spectroscopy? Sandbox Physics · 2026-10-23 Nobel contribution: 1973-1 1. Form a metal–insulator–superconductor junction 2. Cool one electrode 3. Sweep a small voltage 4. Read the onset and shape of tunneling The threshold depends on which electrodes are superconducting; a normal–superconducting junction and two superconductors probe different gap combinations. ## The insulating film became a probe Giaever’s 1960 experiments used tunneling through a thin insulating layer to probe superconducting electrodes. A sufficiently transparent barrier permitted measurable current while retaining sensitivity to the states on either side. Suppressed low-voltage current and its recovery at higher bias made the superconducting excitation gap electrically accessible. This was different from Esaki’s semiconductor occupation-overlap effect. Sources: [1] [2] ## Voltage selects accessible final states For a normal metal coupled to a superconductor at low temperature, the onset is associated with the superconducting gap. With two superconducting electrodes, their densities of states are convolved and the prominent threshold involves both gaps. Thermal occupation rounds either result. Sources: [1] ## Junction defects can imitate extra states Pinholes provide ordinary conduction that bypasses the intended tunnel process. Heating and finite temperature also create subgap current. A quantitative density-of-states inference therefore needs junction checks and temperature dependence, not a threshold voltage alone. Sources: [1] ## The related barrier model supplies the tunneling step Barrier transmission explains why the insulating film need not stop every electron. It omits electrode occupations and superconducting coherence factors. The historical gap evidence belongs to the complete electrical junction experiment, recognized with Esaki’s work in the experimental half of the 1973 prize. Sources: [1] [2] [3] Continue with the physics ## Try the related models ### [Barrier transmission](https://sandboxphysics.com/labs/quantum-tunneling/) Compare transmission as barrier width and incident energy change. A single-particle barrier has no semiconductor occupations or superconducting density of states. ### [Pairing across the crossover](https://sandboxphysics.com/labs/bec-bcs-crossover/) Compare weak pairs with tightly bound pairs. The teaching crossover does not predict a cuprate mechanism or helium-three order parameter. ## Sources and reading notes 1. [Giaever: Electron tunneling and superconductivity (1973)](https://www.nobelprize.org/uploads/2018/06/giaever-lecture.pdf) Metal–insulator–superconductor junctions probe an excitation gap, with temperature and junction quality important. 2. [Giaever: Energy gap in superconductors measured by electron tunneling (1960)](https://doi.org/10.1103/PhysRevLett.5.147) Original experimental report; the publisher page exposes bibliographic metadata, with full text subject to access. 3. [Nobel Prize in Physics 1973: official award](https://www.nobelprize.org/prizes/physics/1973/summary/) Official attribution and award year. The observation or theoretical paper may be much earlier. [Condensed matter: from a material to its evidence](https://sandboxphysics.com/stories/condensed-matter/) [Liquid helium: building access to a new temperature range](https://sandboxphysics.com/stories/condensed-matter/liquid-helium-onnes/) [Landau’s helium: describe the liquid’s excitations](https://sandboxphysics.com/stories/condensed-matter/landau-superfluid-helium/) [Kapitsa’s helium flow: viscosity depended on how it was tested](https://sandboxphysics.com/stories/condensed-matter/kapitsa-helium-flow/) [BCS theory: one paired state had to explain several experiments](https://sandboxphysics.com/stories/condensed-matter/bcs-pairing-evidence/) [Josephson’s prediction: phase could drive a zero-voltage current](https://sandboxphysics.com/stories/condensed-matter/josephson-phase-current/) [Cuprate superconductivity: a ceramic changed the temperature scale](https://sandboxphysics.com/stories/condensed-matter/cuprate-superconductivity/) [Helium-three: a pressure anomaly changed its interpretation](https://sandboxphysics.com/stories/condensed-matter/helium-three-superfluid/) [Ginzburg–Landau theory: describe how superconducting order varies](https://sandboxphysics.com/stories/condensed-matter/ginzburg-landau-order/) [Abrikosov vortices: magnetic flux entered without ending superconductivity](https://sandboxphysics.com/stories/condensed-matter/abrikosov-vortex-lattice/) [Leggett’s helium-three: resonance identified the pairing order](https://sandboxphysics.com/stories/condensed-matter/leggett-helium-three/)