Characterization of the current-induced resistive spots in superconducting YBa 2 Cu 3 O 7 strips K. Harrabi • A. F. Salem • K. Ziq • A. I. Mansour • S. Kunwar • J. P. Maneval • G. Berdiyorov Received: 27 January 2014 / Accepted: 10 July 2014 / Published online: 6 August 2014 Ó Springer-Verlag Berlin Heidelberg 2014 Abstract For over a decade, ultrathin superconducting films have been developed for the detection of single pho- tons at optical or near infrared frequencies, with competi- tive performances in terms of quantum efficiency, speed, and low dark count rate. In order to avoid the requirement of helium refrigeration, we consider here the use of high temperature materials, known to achieve very fast respon- siveness to laser irradiation. We excite thin filaments of the cuprate YBa 2 Cu 3 O 7 by rectangular pulses of supercritical current so as to produce either a phase-slip centre (PSC) or a normal hot spot (HS), according to the temperature and the current amplitude selected. That procedure provides infor- mation about the maximum bias current to be used in a particle detector, about the return current back to the qui- escent state after excitation, and about the rate of growth and decay of a HS. We also measure the time of PSC nucleation. A unique feature of that approach is to provide the rate of heat transfer between the film and its substrate at whatever temperature, in the superconducting state, in the practical conditions of operation. 1 Introduction Single-photon detectors based on Superconducting Nano- wires (SNSPDs) have been developed recently [1], with competitive performances in terms of quantum efficiency, speed, and dark count rates. The materials selected so far have been mainly the ultrathin (  5 nm) strips made of sputtered NbN [1, 2], Nb x Ti 1x N[3], or Nb [4], which have an adequate lasting time and a critical transition tempera- ture T c in a convenient range above the liquid helium temperature. In addition, since the first reports of single photon detection in NbN films, these devices have proved efficient in the detection of other single particles such as molecular ions or molecules [5], or keV electrons from a scanning electron microscope (SEM) microscope [6]. However, in order to avoid the requirement of helium refrigeration, and in view of the very high speed of response of the high-T c material YBa 2 Cu 3 O 7 (YBCO for brief) in the hot- electron mode [7, 8], we consider here YBCO thin films as possible substitutes for low-T c materials. Our experimental method, which involves the voltage response to nanosecond electrical pulses, provides data on the film thermal parameters not only in the bolometric sensitivity range around T c , but also far below T c , in the zero-resistance state prior to a detection event. The resistive states expected for quasi 1-D transport, namely phase-slip centres (PSC) [10] and localized hot spots (HS) [11], have also been observed in YBCO strips [9]. The current-controlled drive discriminates stable-in-time phase- slip centre structures near T c from expanding HS at lower temperatures. The voltage that appears after a delay time t d readily distinguishes a PSC signal from other types of resistive response, such as the presumably instantaneous vortex flow (VF) response [12, 13]. 2 Sample and experimental setup The YBCO thin films, purchased from Theva GmbH (Germany), were grown by thermal co-evaporation. The R- K. Harrabi (&)  A. F. Salem  K. Ziq  A. I. Mansour  S. Kunwar  G. Berdiyorov Physics Department, King Fahd University of Petroleum and Minerals, 31261 Dhahran, Saudi Arabia e-mail: harrabi@kfupm.edu.sa J. P. Maneval Laboratoire Pierre Aigrain, ENS 24 rue Lhomond, Paris 75231, France 123 Appl. Phys. A (2014) 117:2033–2036 DOI 10.1007/s00339-014-8613-y