Strong vortex pinning intrinsic in high-Tc oxide superconductors

The case is made that the spin-liquid state of a Mott insulator, hypothesized to exist by Anderson and identified by him as the correct context for discussing high-temperature superconductors, occurs in these materials and exhibits the principles of fractional quantization identified in the fractional quantum Hall effect. The most important of these is that particles carrying a fraction of an elementary quantum number, in this case spin, attract one another by a powerful gauge force, which can lead to a new kind of superconductivity. The temperature scale for the superconductivity is set by an energy gap in the spin-wave spectrum, which is also the fundamental measure of how "liquid" the spins are.

https://science.sciencemag.org/content/sci/242/4878/525.full.pdf

The Relationship Between High-Temperature Superconductivity and the Fractional Quantum Hall Effect

Classical BCS superconductive couplings leading to small Tc‘s rely on phonon mediated weak coupling of delocalized electrons in three dimensional structures. Attempts to produce or explain higher Tc have considered the breakdown of one or several of these hypotheses. The possible role of quasilowdimensionality for delocalized electrons will be stressed, and the potential superiority of fine mesh three dimensional networks of chain conductors argued from that point of view.

https://iopscience.iop.org/article/10.1088/0953-8984/1/42/001/pdf

The high-Tc superconductors: a conservative view

The superconductivity of the noncentrosymmetric compound La(7)Ir(3) is investigated using muon spin rotation and relaxation. Zero-field measurements reveal the presence of spontaneous static or quasistatic magnetic fields below the superconducting transition temperature T(c)=2.25  K-a clear indication that the superconducting state breaks time-reversal symmetry. Furthermore, transverse-field rotation measurements suggest that the superconducting gap is isotropic and that the pairing symmetry of the superconducting electrons is predominantly s wave with an enhanced binding strength. The results indicate that the superconductivity in La(7)Ir(3) may be unconventional and paves the way for further studies of this family of materials.

/pdf/unconventional-superconductivity-in-la-7-ir-3-revealed-by-596h03ku8u.pdf

Unconventional Superconductivity in La(7)Ir(3) Revealed by Muon Spin Relaxation: Introducing a New Family of Noncentrosymmetric Superconductor That Breaks Time-Reversal Symmetry.

The high-Tcsuperconductors: a conservative view

The muon relaxation rate (sigma) was measured in the high critical temperature superconductors YBa2Cu3O(x) for x = 6.66, 6.95, 7.0, and La1.85 SrO.15 CuO4 in transverse external magnetic fields 1 is approximately 4 kG. A simple relation is found which connects the transition temperature T(c), the magnetic field penetration depth lambda(L), the carrier concentration n(s) and the effective mass m* as T(c) varies as sigma which varies as 1/lambda(L) squared which varies as n(s)/m*. The linear dependence T(c) varies as n(s)/m* suggests a high energy scale for the coupling between superconducting carriers.

Systematic variation of magnetic-field penetration depth in high- T c superconductors studied by muon-spin relaxation

Muon spin rotation and neutron scattering studies on powder and single-crystal specimens of La2CuO(4-y) are compared. The apparent difference between the muon and neutron results for the ordered moment in the antiferromagnetic state is interpreted as the signature of increasingly short-ranged spatial spin correlations with increasing oxygen content.

Comparison between muon spin rotation and neutron scattering ttudies on the 3-dimensional magnetic ordering of La2CuO4-y

The AGS proton synchrotron at Brookhaven National Laboratory facilitates a medium-intensity polarized muon channel. Muon spin relaxation (μSR) experiments on single-phase specimens of (La1.85Sr0.15)CuO4 and YBa2Cu3O7 have been carried out at this facility field (500 – 1000 G) applied perpendicular to the initial muon spin direction, the magnetic-field penetration depth λ in the superconducting state has been determined.

D. Opie

Papers

Systematic variation of magnetic-field penetration depth in high- T c superconductors studied by muon-spin relaxation

Comparison between muon spin rotation and neutron scattering ttudies on the 3-dimensional magnetic ordering of La2CuO4-y

Muon Spin Relaxation Studies on High-Tc Superconductors