J. Phys. IV France 131 (2005) 343–345 C  EDP Sciences, Les Ulis DOI: 10.1051/ jp4:2005131087 Charge density wave and pressure-induced reentrant superconductivity in ZrTe 3 K. Yamaya 1 , R. Yomo 1 , K. Inagaki 1 , S. Tanda 1 , M. Abliz 2 , M. Hedo 2 and Y. Uwatoko 2 1 Department of Applied Physics, Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan 2 Insitute of Solid State of Physics, University of Tokyo, Kashiwa 277-8581, Chiba, Japan Abstract. We have investigated the pressure effects near the phase boundary between the CDW and the pressure-induced reentrant-superconductivity (r-SC) in ZrTe 3 , where, simultaneously with the collapse of the CDW state, appears again the SC. Fluctuations of the CDW and the SC have become stronger as both transitions approach to the phase boundary. We discuss the possible exsitence of a novel state between the CDW and the r-SC phases. 1. INTRODUCTION Competition between superconductivity (SC) and charge-density-wave (CDW) is basically understood by the Fermi surface (FS) nesting [1]. On the one hand, quantum mechanical nature of a collapse of CDW has been extensively studied [2, 3]. We have recently discovered an appearance of pressure-induced reentrant-SC (r-SC) simultaneously with the collapse of CDW at the critical pressure P C = 5.2 GPa in ZrTe 3 , as shown in Fig. 1 [4]. This result leads us to an interest whether the CDW to r-SC transition is explained by the FS nesting or by quantum nature. The pressure effects near the phase boundary between the CDW and the r-SC have been investigated and the results are discussed. 0 5 10 10 0 10 1 10 2 T [K] P [GPa] T C T C T CDW CDW Metal r–SC SC ZrTe 3 Figure 1. Pressure dependences of T CDW and T C . 2. EXPERIMENTAL RESULTSAND DISCUSSION Figure 2 shows the pressure dependences of  parameter which is defined as  = (R 1 - R 2 )/R 1 , where R 1 is the peak resistance in the resistance anomaly due to the CDW transition and R 2 is the resistance that is expected in the absence of CDW formation. At a temperature where the CDW gap is sufficiently developed,  can be represented as  = N/N 0 , where N 0 is the density of states at Fermi energy in the absence of CDW formation and N denotes a reduction of N 0 due to the CDW gap formed on the FS [5]. Article published by EDP Sciences and available at http://www.edpsciences.org/jp4 or http://dx.doi.org/10.1051/jp4:2005131087