DQMP Seminar - Recently reported superconductivity in the full-Heusler and boride compounds - Tomasz Klimczuk

20.06.2023 13:00 – 14:30

Tomasz Klimczuk
Faculty of Applied Physics and Mathematics and Advanced Materials Centre Gdansk University of Technology, Poland

Recently reported superconductivity in the full-Heusler and boride compounds

There are more than 1000 reported compounds in the full Heusler family and only about 40 reveal superconductivity [1,2]. Here we present details of the synthesis and physical properties (resistivity, magnetization, and heat capacity) of MgPd2Sb [2] and the recently reported Li-based ternary intermetallic superconductors LiGa2Ir [3] and LiPd2Ge [4]. The first compound, together with isoelectronic LiGa2Rh [5], is one of the only two superconductors known in this system with valence electron count (VEC) = 16. The experiments confirm bulk superconductivity with Tc = 2.95 K and suggest that LiGa2Ir is a weak-coupling type-II superconductor. The second compound was synthesized together with LiPd2Si and LiPd2Sn. Superconductivity above 1.7 K was found only in LiPd2Ge (Tc = 1.96 K) but theoretical studies suggest that LiPd2Si and LiPd2Sn should also reveal superconducting behavior. We propose that the enhanced electron-phonon coupling in LiPd2Ge is due to presence of the soft phonon modes. Surprisingly, LiPd2Ge is a type-I superconductor, which is very rare among ternary intermetallic compounds.
In the second part of the lecture, we will present a new class of non-centrosymmetric superconductors (NCS). The boride compounds with MRh2B2 and MIr2B2 (M = Nb, Ta) stoichiometry were first reported by Carnicom, et al. [6] and Górnicka, et al. [7], respectively. They form in the brand-new crystal structure types, both noncentrosymmetric, presented in the figure below. MRh2B2 is found in the chiral space group P31 whereas isoelectronic MIr2B2 crystallizes in the monoclinic Cc space group. Common features of these subfamilies are boron dimers and repeating units marked as X, Y, Z shown in the figure.

The highest superconducting critical temperature is observed in NbRh2B2 and NbIr2B2 with Tc = 7.6 K and 7.2 K, respectively. Slightly lower Tc is observed for TaRh2B2 (5.8 K) and TaIr2B2 (5.2 K).
The derived superconducting parameters show that MRh2B2 and MIr2B2 (M = Nb, Ta) are type II BCS moderately coupled superconductors with the upper critical field 0Hc2(0) exceeding the Pauli limit 0Hc2 for the all studies superconductors.
This project is supported by a National Science Centre (PL) project: 2017/27/B/ST5/03044.

[1]T. Klimczuk, et al., Phys. Rev. B, 85, 174505 (2012).
[2]M.J. Winiarski, et al., Phys. Rev. B, 103, 214501 (2021).
[3]K. Górnicka, et al., Scientific Reports, 11, 16517 (2021).
[4]K. Górnicka, et al., Phys. Rev. B, 102, 024507 (2020).
[5]E. Carnicom, et al., Chem. Mater. 31, 2164−2173 (2019).
[6]E. Carnicom, et al., Sci. Adv. 4, eaar7969 (2018).
[7]K. Górnicka, et al., Adv. Funct. Mater. 31, 2007960 (2021).

Organisé par: Prof. Fabian von Rohr

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Bâtiment: Ecole de Physique

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entrée libre

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Tomasz Klimczuk_Abstract_.pdf

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