6.11 Superconductivity and the Josephson Effect

Home ／ Chapter 6: Quantum Domain

I. Phenomena and Puzzles

When certain metals or ceramics are cooled sufficiently, their resistance plunges below measurable levels and a current can circulate for years without decay. External magnetic fields are expelled from the bulk, entering only as thin, quantized tubes. Place a thin insulating barrier between two superconductors and a steady current flows even with zero voltage; illuminate the junction with high-frequency radiation and the voltage develops discrete steps.

These are the hallmarks of superconductivity and the Josephson effect: zero resistance, perfect diamagnetism (with quantized flux penetration), zero-bias supercurrent, and radio-frequency “Shapiro-like” steps. The puzzles are clear: why does friction vanish upon cooling? Why can magnetic fields enter only as fixed quanta? How do we get a current across an insulator, and why do microwaves carve out neat voltage plateaus?

II. EFT Interpretation: Phase-Locked Electron Pairs, Closed Dissipation Channels, and Coherent Handoff Across a Barrier

1. Pair first, then stitch the phase.
2. In the Energy Filament Theory (EFT), an electron is a stable single-loop winding whose outer layer interacts with the Energy Sea and the lattice. Lowering the temperature reduces lattice jitter and, in some materials, opens a smoother “tension corridor” for electrons to follow one another. Two electrons pair with opposite loop orientations—these are the electron pairs. Pairing suppresses or cancels many dissipative channels. Cooling further aligns the outer-layer phases of many pairs, eventually laying down a sample-spanning, common-phase network—a “flowing carpet.”
3. Why zero resistance: close the loss channels collectively.
4. Ordinary resistance comes from countless tiny paths that leak energy into the environment—impurities, phonons, rough boundaries. Once the phase carpet spreads, local wrinkles that break coherence become hard to nucleate and the loss threshold rises sharply. As long as the drive does not tear the carpet, current does not shed energy, and we observe “zero resistance.”
5. Why expulsion and flux quantization: the phase resists twisting.
6. To remain smooth, the phase carpet cannot be twisted arbitrarily by a magnetic field. Screening currents appear at the surface and push the field out (Meissner expulsion). In some materials, the field is allowed to thread as thin tubes, each requiring the phase to wind by an integer number of turns—this is flux quantization. You can picture each tube as a hollow tension core around which the phase circulates; the tubes repel and can form geometric arrays.
7. Why Josephson current: coherent relay across a near-critical slit.
8. Separate two phase carpets with a very thin insulator or weak metal and the gap sits in a near-critical, sub-threshold state. Across this narrow gate, the pair phases can relay coherently—not by single particles “pushing through,” but by “stitching” a short phase bridge between the two sides.
   • If both sides keep the same beat, the bridge transmits phase steadily and a dc supercurrent flows with zero bias (dc Josephson).
   • If the beats differ—because of a dc voltage or an applied radio-frequency drive—the phase difference advances uniformly or locks to the external drive, and the bridge pumps supercurrent at set rhythms, producing an ac response and step-like voltages under rf irradiation.
9. Why imperfections matter: defects and tears reopen losses.
10. Large currents, strong fields, higher temperatures, or pinning defects can drag quantized vortices and tear holes in the carpet. Energy escapes through these holes, producing critical currents, loss peaks, and nonlinear response.

III. Canonical Settings

• Two superconductor classes.
• One almost fully expels magnetic field but fails abruptly beyond a threshold; the other admits flux as tubes, forms vortex lattices at high fields, and still carries current. These reflect different tolerances of the phase carpet to magnetic twisting.
• Superconducting rings and persistent currents.
• Around a closed loop, the phase must wind by an integer number of turns; without tearing, the current persists. Adjusting flux to a non-integer winding prompts a jump to the nearest integer, creating discrete, stable states.
• Tunnel junctions and weak links.
• In an ultra-thin slit, supercurrent flows at zero bias; under microwaves, the voltage locks into tidy steps, revealing phase locking to the external beat.
• Parallel loops: interferometers.
• Two “phase bridges” forming a small ring pick up different phase shifts from external flux. The net supercurrent oscillates periodically with flux, enabling ultrasensitive magnetometry.

IV. Observable Fingerprints

• Sudden drop to zero resistance at a critical temperature.
• Perfect diamagnetism or geometric arrays of flux tubes.
• Zero-bias supercurrent with a well-defined critical current.
• Radio-frequency voltage steps that reveal phase locking.
• Interference periodicity: ring currents oscillate with flux at a fixed period.
• Vortex pinning and slip: defects reduce dissipation but raise critical current; moving vortices produce loss peaks.

V. Alignment with Mainstream Theory

• Mainstream writes the pair condensate as a macroscopic order parameter (a complex amplitude with phase). Zero resistance arises from dissipationless phase flow; diamagnetism from the phase resisting twist; flux quantization and vortices from the requirement of integer windings.
• EFT rephrases the same physics in tangible geometry: electron pair = paired windings; phase carpet = sample-wide common-phase network; zero resistance = collective closure of loss channels; flux quantization = topological defects with hollow cores; Josephson effect = a short phase bridge across a near-critical slit. The narratives differ, but the phenomena and quantitative relations agree.

VI. Summary

Superconductivity is not “electrons suddenly becoming perfect.” It is pairing first and then phase-locking millions of pairs into a carpet:

• The carpet closes dissipation channels under gentle drive, yielding zero resistance.
• It refuses arbitrary twisting, expelling magnetic fields or admitting them only as quantized vortices.
• Between two carpets, a near-critical slit can stitch a phase bridge so supercurrent flows at zero bias and, under microwaves, locks into discrete steps.

In one line: pair up, lock phase, relay across the gap—the “magic” of superconductivity and the Josephson effect is the interplay of these three steps.