Type 1 and Type 2 Superconductors: Differences, Examples and Uses

Type 1 superconductors expel a magnetic field completely and lose superconductivity suddenly at a single critical field H_c, which is small (a few hundredths of a tesla). Type 2 superconductors have two critical fields, H_c1 and H_c2; between them the field enters as tiny flux vortices while the material still carries current with zero resistance, and H_c2 can reach tens of tesla. That second behaviour is why every practical superconducting magnet, from hospital MRI scanners to particle accelerators, uses Type 2 materials.

Types of superconductors in one line each

• Type 1 (soft) superconductor: a perfect diamagnet up to one critical field H_c, then normal. Mostly pure elements such as mercury, lead, tin and aluminium.
• Type 2 (hard) superconductor: a perfect diamagnet only up to H_c1, then a mixed (vortex) state up to H_c2, then normal. Alloys, compounds and all high-temperature cuprate superconductors, plus the elements niobium, vanadium and technetium.

Superconductors are also grouped by critical temperature: low-temperature (LTS, usually cooled by liquid helium at 4.2 K) and high-temperature (HTS, T_c above about 30 K, many above the 77 K boiling point of liquid nitrogen). All HTS materials are Type 2.

Difference between Type 1 and Type 2 superconductors

Why the Ginzburg-Landau parameter decides the type

Two length scales control a superconductor. The penetration depth λ is how far a magnetic field leaks in from the surface. The coherence length ξ is the shortest distance over which the superconducting electron pairs can change in density. Their ratio is κ = λ/ξ.

When ξ is long compared with λ (κ < 1/√2), creating a boundary between normal and superconducting regions costs energy, so the material avoids letting any field in: Type 1. When λ is longer (κ > 1/√2), the boundary energy is negative and it becomes cheaper to let the field thread through in many thin tubes: Type 2. Pure, clean metals tend to have long coherence lengths; alloying and disorder shorten ξ, which is why alloys and compounds are almost always Type 2. Alexei Abrikosov worked out this vortex picture in 1957 and shared the 2003 Nobel Prize in Physics for it with Vitaly Ginzburg and Anthony Leggett.

Magnetisation curves of Type 1 and Type 2 superconductors

The standard way to show the difference is a plot of magnetisation (usually drawn as -M) against applied field H.

• Type 1: -M rises in a straight line with slope 1 (M = -H, perfect diamagnetism) all the way to H_c, then drops vertically to zero. The whole sample turns normal at once.
• Type 2: -M rises along the same straight line only up to H_c1. It then peaks and falls gradually as more and more vortices enter, reaching zero at H_c2. The region between H_c1 and H_c2 is the mixed state, and the resistance stays zero there as long as the vortices are held in place.

Exam tip: if a question shows a curve with a sharp vertical drop, it is Type 1; a peak followed by a slow tail to zero is Type 2.

Vortices and the flux quantum

In the mixed state the field does not spread evenly. It passes through the material in thin tubes called vortices (or fluxoids). Each vortex has a normal core about the size of ξ, circled by a whirl of supercurrent, and each carries exactly one magnetic flux quantum:

Φ₀ = h / 2e = 2.07 × 10^-15 Wb

The factor 2e appears because the current carriers are Cooper pairs, each with charge 2e. The vortices repel each other and settle into a triangular pattern called the Abrikosov lattice. As the field rises they crowd closer until their cores overlap at H_c2 and superconductivity is lost.

For a real wire carrying current, vortices feel a sideways force and would drift, which dissipates energy. Magnet conductors are therefore made with deliberate defects (precipitates in NbTi, grain boundaries in Nb₃Sn) that “pin” the vortices in place.

Worked example: flux quanta in an MRI field

Problem: A Type 2 superconductor sits in a uniform field of 1.5 T, the field of a common MRI scanner. How many flux quanta pass through an area of 1 mm², and roughly how far apart are the vortices?

1. Total flux: Φ = B × A = 1.5 T × 1 × 10^-6 m² = 1.5 × 10^-6 Wb.
2. Number of vortices: N = Φ / Φ₀ = 1.5 × 10^-6 / 2.068 × 10^-15 ≈ 7.25 × 10⁸, about 725 million vortices in one square millimetre.
3. Area per vortex: Φ₀ / B = 2.068 × 10^-15 / 1.5 = 1.38 × 10^-15 m². Treating each vortex as occupying a square, the spacing is √(1.38 × 10^-15) ≈ 3.7 × 10^-8 m, or about 37 nm. (The true triangular lattice gives a slightly larger value, about 40 nm.)

Doubling the field to 3 T doubles N to about 1.45 × 10⁹ and shrinks the spacing by a factor of √2.

Examples of Type 1 and Type 2 superconductors

Mercury is historic: it was the first superconductor ever found, by Heike Kamerlingh Onnes in 1911. Niobium is the common trap in exam questions. It is a pure element, yet it is Type 2 (just barely, with κ close to 1), and it has the highest T_c of any element at normal pressure.

Why Type 2 superconductors are the practical ones

A Type 1 wire loses superconductivity at well under 0.1 T, and even the magnetic field made by its own current can push it normal. Type 2 materials keep zero resistance up to many tesla, so they can make strong magnets.

• NbTi is ductile and easy to draw into multifilament wire in a copper matrix. It is the workhorse for MRI magnets (1.5 T and 3 T scanners, cooled with liquid helium) and for the 1,232 main dipole magnets of CERN’s Large Hadron Collider, which are designed for 8.33 T at 1.9 K. India’s SST-1 tokamak at the Institute for Plasma Research, Gandhinagar, also uses NbTi coils.
• Nb₃Sn handles higher fields but is brittle, so coils are usually wound first and then heat-treated to form the compound. It is used in the toroidal field coils and central solenoid of ITER (fields up to about 12-13 T) and in the new focusing quadrupoles of the High-Luminosity LHC upgrade.
• REBCO / YBCO coated-conductor tapes work at far higher fields, or at 20-77 K instead of 4.2 K. They are used in very high-field research magnets, compact fusion magnet designs and superconducting power cables and fault-current limiters.
• MgB₂ is cheap and light, and has been used in some cryogen-free MRI systems and in cable projects.

Type 1 materials still matter in research: lead and aluminium are used in some sensitive detectors and superconducting circuits, and they are the cleanest way to teach the Meissner effect. For magnetic resonance imaging background, see MRI.

FAQs

What are the two types of superconductors?

Type 1 and Type 2. Type 1 shows a complete Meissner effect up to one critical field and then turns normal suddenly. Type 2 has two critical fields, H_c1 and H_c2, with a mixed vortex state in between.

What is the main difference between Type 1 and Type 2 superconductors?

How they respond to a magnetic field. Type 1 expels all field and fails at a low H_c. Type 2 lets field in as quantised vortices above H_c1 and stays superconducting up to a much higher H_c2. The dividing line is κ = λ/ξ = 1/√2.

Is niobium a Type 1 or Type 2 superconductor?

Niobium is Type 2, even though it is a pure element. Its T_c is about 9.3 K. Vanadium and technetium are the other elemental Type 2 superconductors.

Why are Type 2 superconductors used in MRI machines?

MRI needs a steady field of 1.5-3 T. Type 1 materials go normal below 0.1 T, while NbTi, a Type 2 alloy, stays superconducting up to about 15 T near 0 K and can be made into long, flexible wire.

Are high-temperature superconductors Type 1 or Type 2?

All known high-temperature superconductors, including YBCO and BSCCO, are Type 2, with very short coherence lengths and very high upper critical fields.

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