Non-centrosymmetric superconductor Th$$_4$$Be$$_{{33}}$$Pt$$_{{16}}$$ and heavy-fermion U$$_4$$Be$$_{{33}}$$Pt$$_{{16}}$$ cage compounds

Abstract

Unconventional superconductivity in non-centrosymmetric superconductors has attracted a considerable amount of attention. While several lanthanide-based materials have been reported previously, the number of actinide-based systems remains small. In this work, we present the discovery of a novel cubic complex non-centrosymmetric superconductor $${\text {Th}}_4{\text {Be}}_{{33}}{\text {Pt}}_{{16}}$$ Th 4 Be 33 Pt 16 ($$I{\bar{4}}3d$$ I 4 ¯ 3 d space group). This intermetallic cage compound displays superconductivity below $$T_{\text {c}} = 0.90 \pm 0.04$$ T c = 0.90 ± 0.04 K, as evidenced by specific heat and resistivity data. $${\text {Th}}_4{\text {Be}}_{{33}}{\text {Pt}}_{{16}}$$ Th 4 Be 33 Pt 16 is a type-II superconductor, which has an upper critical field $${\text {H}}_{{\text {c}}2} = 0.27$$ H c 2 = 0.27 T and a moderate Sommerfeld coefficient $$\gamma _{\text {n}} = 16.3 \pm 0.8$$ γ n = 16.3 ± 0.8 mJ $${\text {mol}}^{-1}_{\text {Th}}$$ mol Th - 1 $${\text {K}}^{-2}$$ K - 2 . A non-zero density of states at the Fermi level is evident from metallic behavior in the normal state, as well as from electronic band structure calculations. The isostructural $${\text {U}}_4{\text {Be}}_{{33}}{\text {Pt}}_{{16}}$$ U 4 Be 33 Pt 16 compound is a paramagnet with a moderately enhanced electronic mass, as indicated by the electronic specific heat coefficient $$\gamma _{\text {n}} = 200$$ γ n = 200 mJ $${\text {mol}}^{-1}_{\text {U}}$$ mol U - 1 $${\text {K}}^{-2}$$ K - 2 and Kadowaki–Woods ratio $$A/\gamma ^2 = 1.1 \times 10^{-5}$$ A / γ 2 = 1.1 × 10 - 5 $$\upmu $$ μ $$\Omega $$ Ω cm $${\text {K}}^2$$ K 2 $${\text {mol}}_{\text {U}}^2$$ mol U 2 (mJ)$$^{-2}$$ - 2 . Both $${\text {Th}}_4{\text {Be}}_{{33}}{\text {Pt}}_{{16}}$$ Th 4 Be 33 Pt 16 and $${\text {U}}_4{\text {Be}}_{{33}}{\text {Pt}}_{{16}}$$ U 4 Be 33 Pt 16 are crystallographically complex, each hosting 212 atoms per unit cell.

Probing the superconducting pairing of the La4Be33Pt16 alloy via muon-spin spectroscopy

“…Our detailed µSR results suggest that La 4 Be 33 Pt 16 exhibits a nodeless SC with a preserved TRS, in hindsight compatible with its rather weak SOC. Upon replacing La with other nonmagnetic rare-earth metals (such as Y, Lu, or Th), the Y 4 Be 33 Pt 16 , Lu 4 Be 33 Pt 16 , and Th 4 Be 33 Pt 16 alloy compounds all undergo a superconducting transition at T c = 0.9, 0.7, and 1.0 K, respectively [50][51][52]. The T c of La 4 Be 33 Pt 16 increases upon substituting La with Th, with the highest T c = 3.2 K being reached in (La 1−x Th x ) 4 Be 22 Pt 16 for x = 0.33 [52].…”

“…Upon replacing La with other nonmagnetic rare-earth metals (such as Y, Lu, or Th), the Y 4 Be 33 Pt 16 , Lu 4 Be 33 Pt 16 , and Th 4 Be 33 Pt 16 alloy compounds all undergo a superconducting transition at T c = 0.9, 0.7, and 1.0 K, respectively [50][51][52]. The T c of La 4 Be 33 Pt 16 increases upon substituting La with Th, with the highest T c = 3.2 K being reached in (La 1−x Th x ) 4 Be 22 Pt 16 for x = 0.33 [52]. Considering that all these materials share similar electronic band structures with La 4 Be 33 Pt 16 , they too are expected to be conventional superconductors.…”

“…In this respect, La [50][51][52]. Their diverse physical properties encompass anti-and ferromagnets, paramagnets, and superconductors.…”

Investigation of the Influence of Pressure on the Physical Properties and Superconducting Transition Temperature of Chiral Noncentrosymmetric TaRh2B2 and NbRh2B2

“…The inversion symmetry is the general feature of most superconducting materials with the centrosymmetric structure, which maintains the conventional Cooper pairs. However, conventional Cooper pairs do not exist in the case of NCS superconductors due to the shortcoming of inversion symmetry. , The chiral structure is a crucial addition to the NCS superconductivity in which the superconducting gap function, Δ­( k ), the phase has to move either in a clockwise or in a counterclockwise way as k winds in direction to the Fermi surface. , There are a notable number of experimental investigations that have been accomplished on NCS superconductivity in recent years. − However, NCS superconductivity with the chiral structure is rare. ,, For the special feature of the chiral structure, both the Rh-based NCS TaRh 2 B 2 and NbRh 2 B 2 superconductors attract massive attention from researchers. − Mayoh and his coresearchers exhibited the multigap bulk type-II superconductivity in TaRh 2 B 2 with a higher upper critical field value of 15.2 T, crossing the Pauli limit . Mayoh et al also justified the bulk type-II superconductivity in NbRh 2 B 2 with a higher upper critical field along with a T c of ∼7.46 K .…”

Physical and Superconducting Properties of Chiral Noncentrosymmetric TaRh2B2 and NbRh2B2: A Comprehensive DFT Study

“…Parity is a prominent quantum number in the case of centrosymmetric superconductors, in which Cooper pair formation occurs in either spin-singlet or spin-triplet states. , However, the formation of a conventional Cooper pair does not occur in NCS superconductors due to the deficiency of inversion symmetry. In a chiral superconductor, the superconducting gap function phase, Δ­( k ), must have to turn either in the clockwise or counterclockwise direction as k travels toward the Fermi surface. , Several experimental research works have been carried out on NCS superconductors in the last few years. − Chiral NCS superconductors have been rarely reported. ,, Due to the special type of crystal structure of TaRh 2 B 2 and NbRh 2 B 2 superconductors, they exhibit unusual properties and have attracted tremendous attention of researchers in recent years. ,,, Both TaRh 2 B 2 and NbRh 2 B 2 exhibited exceptional upper critical field ( H c2 ) values exceeding the Pauli limit . Mayoh et al demonstrated the multigap nature of bulk type II superconductivity in TaRh 2 B 2 with a T c = 6.00(5) K .…”