Hall effect sign change

Hall-effect studies of cuprate superconductors 3.1. Anomalous sign change in the vicinity ofT ... 

It also becomes clear that in TmSe a change of the lattice constant in either direction, which can be achieved by pressure, stoichiometry variation or alloying, will move more or less electrons in or out of the 4f band. One can also say that the 4f band gets moved through the Fermi level. Thus it is no surprise that the Hall effect and the thermopower change sign when the Fermi level crosses the middle of the 4f band. The same effect occurs in SniS, where, however, it has been observed with various amounts of alloying (Jayaraman 1979). 

As was discussed above, the absence of a kink in the nodal band below Ev [11] in NCCO, supports the possibility that it is also a real n-type cuprate. It is possible that the change in the sign of the TEP slope in NCCO with doping is an anomalous band-structure effect, probably associated with the peculiar evolution of its FS with doping, detected in ARPES [34], The position of the kink (below or above /q.) is determined by the inequality (11) between dq+ and d L, which is less susceptible to band-structure effects than the inequality (11) between bq+ and bq, determining the sign of the TEP slope. Anomalous behavior is observed also in the Hall constant of NCCO [32], which changes... 

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