Hole-Filling above Tc, at the Origin of the In-Plane Resistivity Anomaly in Bi-2212 Crystals

Abstract

We have observed a sharp peak (100%) in the in-plane resistivity r ab just above T c , in Bi-2212 crystals, in agreement with previous results from Han et al. who attributed this anomaly to the ªquasi-reentrant behaviourº already observed for polycrystalline samples. This explanation is very likely unadapted to these crystals and we propose another one related to a model we had used to fit r c T curves for Bi-2212 underdoped crystals, namely, an increase of the Fermi level (hole-filling) with decreasing temperature, above T c , probably due to a change in the Bi±O or Cu±O bonds. A previously reported c-axis lattice anomaly, occurring in the same temperature range, is most probably related to this bonding alteration.Nous avons observe Â, pour des cristaux de Bi-2212, un pic intense (100%) de re  sistivite  r ab (dans le plan des feuillets). Ceci est en accord avec des re  sultats ante  rieurs de Han et al. qui ont atttribue  l'anomalie en question au comportement ªquasi-re  entrantº caracte  ristique des e  chantillons polycristallins. Cette interpre  tation ne nous semble pas pertinente dans le cas de nos cristaux et nous proposons une autre origine (d'apre Á s un mode Á le que nous avions utilise  pour ajuster les courbes r c T de cristaux de Bi-2212 sous-dope  s) base  e sur une e  le  vation du niveau de Fermi lorsque la tempe  rature de  croõ Ãt (au-dessus de T c ). D'autres auteurs constatent par ailleurs une variation du parame Á tre de maille c, qui se produit dans la me à me gamme de tempe  rature. Ces deux phe  nome Á nes sont probablement lie  s a Á une modification des liaisons Bi±O ou Cu±O.

Temperature-induced frequency shift of the Raman-active CuO2planar oxygen vibrational modes of Bi-2212 related to a change of the Cu-O bonding

“…The increase of the coupling energy, with decreasing temperature, should be due to a hardening with decreasing temperature of the Cu-O bonding inside the CuO 2 planes. Such a hardening in the Cu-O bond with temperature can explain simultaneously (i) the anomalous dilatation and lattice parameter variations with temperature and (ii) the anomalous resistivity variation observed in the a-b plane as well as along c. In the latter case the increase of the Fermi level, previously suggested [6,11] to be at the origin of these resistivity anomalies, can be directly related to the change in the Cu-O bonding. For similar reasons a 'phase transition in the Cu-O ligands' was recently suggested to occur, by Owens [27], in cuprates with ladder-like structure.…”

“…On the basis of these measurements, and no structural change being observed in this temperature range, several authors have suggested a change either in the Cu-O or in the Bi-O bonds [1,2,6,11] to explain the existence of these anomalies, that can give rise to a 'hole filling' with decreasing temperature. Some other, very different, kinds of explanation have also been given.…”

“…(i) an anomalous variation of the lattice parameters with temperature and an anomalous thermal expansion [1][2][3]; (ii) an anomalous variation with temperature, in the normal state, of both the in-plane [4][5][6][7] and the out-of-plane resistivities [8][9][10][11].…”