arXiv:cond-mat/0410112v1 [cond-mat.supr-con] 5 Oct 2004 ANDREEV REFLECTION IN Bi 1.8 Pb 0.3 Sr 1.9 Ca 2 Cu 3 Ø x BREAK JUNCTION D.M. Gokhfeld 1 , D.A. Balaev 1 , K.A. Shaykhutdinov 1 , S.I. Popkov 1,2 , M.I. Petrov 1 1 L.V. Kirensky Institute of Physics, 660036, Krasnoyarsk, Russia. 2 M.F. Reshetnev Siberian State Aerospace University, 660014, Krasnoyarsk, Russia E-mail: smp@iph.krasn.ru The current-voltage characteristic (CVC) of break junction made from poly- crystalline Bi 1.8 Pb 0.3 Sr 1.9 Ca 2 Cu 3 Ø x is investigated. The experimental CVC has hysteretic feature that reflects a part of a curve with negative differential resistance. The CVC is discussed within the framework of the K¨ ummel- Gunsenheimer-Nicolsky theory considering multiple Andreev reflections in superconductor/normal-metal/superconductor junctions. PACS numbers: 75.70.Cn; 74.50.+r; 75.80.Dm 1. INTRODUCTION The transport properties of polycrystalline high temperature supercon- ductors (HTSC) are recognized to be determined by the intergrain bound- aries which are Josephson weak links. The investigation of CVCs should illuminate the mechanisms of current dissipation in the networks of weak links, formed in polycrystalline HTSC. Fundamental and applied aspects of this topic remains actual in present 1 . There are serious problems accom- panying a measurements of a CVCs of HTSC. The main is increasing of temperature due to the selfheating effect 2 at current higher than its critical value Ic and the heat emission on the contacts HTSC - current leads. These effects prevent a precise measure of a CVC in a wide range of currents, in- cluding the range I >> I c where the CVC becomes linear. Influence of the selfheating effects can be avoided by using the break junction technique. The formation of a microcrack in a bulk sample leads to a significant reduction of the effective cross-section area for charge transport. In the non-tunneling case two massive polycrystalline banks are connected by weak links consti-