Chapters:
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MuSR /
MuonDiamagnetiShift< From muon rates to London penetration | Index | Fitting Flux Lattices with a single Gaussian? > Let us consider a muon superconducting sample in the shape of a slab. In an infinite slab the external induction B0=μ0H must coincide with the average induction inside the slab.
The one well inside the slab, Pin, experiences a non uniform field, distributed along ˆz according to p(Bz), and ∫PinB⋅da=A¯B=A∫dBzp(Bz) therefore it must be B0=¯B. However experimentally it is not: the broadened precession line from muons implanted in the superconductor bulk is shifted diamagnetically, well beyond experimental error, to and average Bd≪B0.
Of course magnetic Gauss law is still valid (easy to see on Gaussian surface P), but one cannot neglect the transverse components of the induction and the measured Bd is related, but not equal to the average Bz value. A slightly more complex case arises for powders where the average N over the grain shapes and orientations may need to be considered. To estimate this effect, a typical TF experiment will observe a shift of order μ0χNeffH, proportional to the SQUID magnetization detected in the same magnetic field. < From muon rates to London penetration | Index | Fitting Flux Lattices with a single Gaussian? > |