SRC Users' Meeting - Synchrotron Radiation Center - University of ...

TEMPERATURE DEPENDENCE OF N=1 BISMUTH-BASED
HTSC AS SEEN IN ARPES
L. Dudy 1 , B. Müller 1 , A. Krapf 1 , H. Dwelk 1 , H. Höchst 2 and R. Manzke 1
1 Humboldt Universität zu Berlin 2 Synchrotron Radiation Center (SRC)
High temperature superconductivity in the cuprates mainly results from the twodimensional
electronic structure of the hole-doped CuO-planes. The maximum transition
temperature of this kind of material is dependent of the number of CuO-planes per unit-cell
and of the layers between the CuO-layers. These layers basically isolate the CuO-planes from
each other and dope holes in them. The current status of our investigations focuses on the
single-layer material Bi 2 Sr 2-x La x CuO 6+ (Bi-2201), which is available in high quality single
crystals. Substituting divalent Sr by trivalent La varies the hole concentration of our samples
almost continuously. Because of the low transition temperature this material provides in
addition the advantage of investigating the normal state with extremely small temperature
broadening. For photoemission measurements Bi-2201 also benefits of the absence of bilayer
splitting. This effect occurs by the interaction of electrons between narrow CuO-planes
as e.g. observed in Bi 2 Sr 2 CaCu 2 O 8+ (Bi-2212).
In the past we presented high-resolution photoemission results performed at SRC
which below a certain temperature show along the direction of the CuO-bonds a
characteristic two-peak structure [1]. It has been shown that the low energy sharp peak is
strongly dependent of the applied polarization of the incident light (Fig.1a) [2]. To going
further it seems like the structure isn’t visible in each M-direction (Fig. 1b). Another
remarkable observation is that this structure is not only seen in the superconducting regime
but also persists above the transition temperature and vanishes at higher temperatures
(Fig.1c). The comparison of temperature dependence with a pseudo-1d-system [3] points to a
pseudo-1d effect. In our interpretation these features are associated with one-dimensionality
of the electronic structure leading to spin-charge separation [4]. The necessary condition for
this state is the formation of an asymmetric electronic density, a phenomenon called stripes
[5]. The present contribution follows this interpretation but profits from the raise of data
collected at the SRC in order to explain the phase diagram more precisely and identifies the
vanishing of the one-dimensionality with the closing of the pseudogap [6]. Recent results [7]
of the universality of the pseudogap temperature T* for every CuO-plane in every cuprate
will also be tried to be discussed.