Elsevier

Physica B: Condensed Matter

Volume 536, 1 May 2018, Pages 516-518
Physica B: Condensed Matter

Superconductivity in single crystalline ThBe13 and LuBe13

https://doi.org/10.1016/j.physb.2017.10.129Get rights and content

Abstract

Single crystals of ThBe13 and LuBe13 have been prepared using aluminum flux method. The crystals structure of both compounds was confirmed to be cubic of the NaZn13-type with the lattice parameters a = 10.183(6) Å and a = 10.395(3) Å for LuBe13 and ThBe13, respectively. The low temperature measurements of electrical resistance and ac susceptibility have revealed a BCS-type of superconductivity in ThBe13 below Tc = 125 mK. LuBe13 has been found to be superconducting below Tc = 630 mK.

Introduction

The compounds with general formula MBe13 crystallizing in the cubic NaZn13-type structure exist for a broad variety of M elements including alkaline earth metals [1], [2], rare earth metals, Zr [3] or U and Th [4]. The vast majority of studies concern a sole compound, the heavy fermion superconductor UBe13 [5]. Some of the compounds such as LuBe13 and YBe13 were even synthetizes for the first time in order to study impurity effects in UBe13 polycrystals [2]. Also ThBe13 has been almost exclusively discussed in the context of non-magnetic analog to UBe13 or Th-diluted UBe13 [6], [7].

In this manner, the low-temperature properties of most of the MBe13 compounds have remain almost omitted. Although superconductivity in some MBe13 such as HfBe13 (Tc = 0.35 K, fcc structure) ZrBe13 (Tc = 1.35), WBe13 (Tc = 4.13, bct structure) or LaBe13 with Tc = 0.45 K was mentioned in the mid-1980s [3], [8], to the best of our knowledge, no bulk data indicating superconductivity in these materials were presented. Recently, superconductivity in LaBe13 single crystals have been reported at Tc = 0.53 K by some of us [9].

In the present article, we focus on study of ThBe13 and LuBe13 in the low temperature range. These two compounds have been always considered to be paramagnetic down to lowest temperatures without any signs of superconductivity, however, the lowest temperatures of experiment reported were 0.45 K [3], [6], [8], [10]. Our current results have shown on the superconducting ground state of both compounds.

Section snippets

Sample preparation and experimental details

Single crystals of ThBe13 and LuBe13 were grown using aluminum flux [5]. The pure elements Th (99.5%, metal basis) or Lu (99.9%, metal basis), Be (99.95%, metal basis) and Al (99.999%, metal basis) were placed in ultra-pure Al2O3 (99.95%) crucibles with a cap in the respective molar ratio 1:13:45 and sealed in quartz glass under vacuum (p ~ 10−6 mbar at room temperature). The samples were heated up to 1050 °C where they were homogenized for 3 days and then slowly (2 °C/h) cooled down to 800 °C.

ThBe13

Single crystals of ThBe13 have been measured by means of electrical resistance and ac susceptibility down to 90 mK and 50 mK respectively as presented in Fig. 2. The temperature dependence of the electrical resistance shows metallic behavior. Because it was difficult to determine the geometrical factor, the electrical resistance data are scaled to resistance at 300 K (R/R300). The onset of the superconducting transition is observed below 180 mK on the resistivity data and shows zero resistance

Conclusion

We have reported on superconductivity of ThBe13 and LuBe13 compounds for the first time. Our results indicate that the materials are BCS type superconductors characterized by rapid suppression of superconductivity with application of magnetic fields. In both cases the superconducting transitions were confirmed by electrical transport measurement and by measurement of ac susceptibility and specific heat.

Acknowledgement

The present research was supported by SPS Grants-in-Aid for Scientific Research (KAKENHI), Grants nos. JP15H05882, JP15H05885, and JP15K21732 (J-Physics), and by the Strategic Young Researcher Overseas Visits Program for Accelerating Brain Circulation. via Grant no. R2501. The work of KU was supported by the Czech Science Foundation via Grant no. GP14-17102P. Experiments were performed in the Materials Growth and Measurement Laboratory MGML (see: http://mgml.eu).

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