Tuesday, December 23, 2014

New finding about pseudo gap in high temperature super-conductivity

There is an interesting news about high temperature superconductivity at Phys.org. The existence of so called pseudogap has been known for a couple of decades. At temperature Tc1 >Tc, where Tc is the critical temperature for high Tc superconductivity a phase transition to a new poorly understood phase occurs. Pseudo gap is assigned with this phase.

The new experimental result, led by researchers at Stanford University and the Department of Energy's SLAC National Accelerator Laboratory, is the culmination of 20 years of research aimed at finding out whether the pseudogap helps or hinders superconductivity. The researchers conclude that pseudogap competes with high Tc superconductivity. For more information see the article Makoto Hashimoto et al., Nature Materials, 2 November 2014.

In TGD based model for high Tc superconductivity this pseudo gap is predicted. Already at Tc1 rather short flux tube pairs carrying Cooper pairs are formed. The flux tubes have the form of flattened O looking like U:s at both ends and form two parallel flux tubes in the middle carrying opposite fluxes. Antiferromagnetism makes possible the emergence of these closed flux tubes. This gives rise to a superconductivity but in rather short scales only. The electrons of the Cooper pair are at flux tubes of U with opposite spins so that spin interaction energy is negative and gives rise to Cooper pairs.

At Tc <Tc1 these flux tubes combine by reconnection to form much longer flux tubes, and high Tc superconductivity appears as superconductivity in long length scales. The value of effective Planck constant heff=n×h increases in this process. This process is mathematically like percolation in which water starts to dribble through a layer of porous substance and it wets. The formation of a macroscopic supra current is analogous to wetting.

In TGD picture pseudogap is however a prerequisite for superconductivity: it competes but does not hinder. This is not in conflict with experimental findings. The competion has a simple interpretation: both reconnections and their reversals occur already above Tc, so that the two phases are present. The system is at criticality. Long scale superconductivity wins the competition at Tc!


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