Nuanced superconductivity in endohedral gallide Mo₈Ga₄₁

Abstract

We report on synthesis and characterization of gallide cluster based Mo 8 Ga 41 superconductor. Transport and magnetization measurements confirm the superconducting transition temperature to be 9.8 K. The upper critical field (H c2 ), lower critical field (H c1 ), Ginzburg-Landau coherence length (ξ GL ) and penetration depth(λ) are estimated to be 11.8T, 150G, 5.2nm, 148nm respectively. The electronic band structure, density of states and phonon dispersion curve calculations are obtained by using Density Functional Theory. The core level X-ray Photoelectron Spectroscopy (XPS) reveals the binding energy information of the constituting elements Mo and Ga in Mo 8 Ga 41 .The valence band spectra from XPS is in good agreement with calculated density of states (DOS). The zero field critical current density (J c ) at T = 2 K is ~ 3×10 5 A/cm 2 which is indicative of efficient flux pinning in the as grown compound. About two fold enhancement in critical current density with application of external pressure (1.1 GPa) is observed with marginal decrease in transition temperature. The fitting of current density to double exponential model confirms possibility of two gap superconductivity in Mo 8 Ga 41 .

Three-dimensional Fermi surface and small effective masses in Mo8Ga41

“…Interestingly, band structure of Mo 8 Ga 41 features narrow band dispersion whereas the density of states at the Fermi level is dominated by Mo 4d and Ga4p orbital hybridization. 12 The 3D character of dHvA oscillations is consistent with first principle calculations 13 where four different bands cross the Fermi level. Based on the effective masses obtained in our experiment, it is reasonable to α and β frequencies with electron pocket near the Brillouen zone corner and large anisotropic part of the Fermi surface, respectively whereas other frequencies probably arise due to band associated with two hole pockets near the Γ point that exhibit weak coupling with phonons and where superconducting gap is smaller.…”

“…Its superconducting T c = 9.7 K and upper critical field µ 0 H c2 = 8.36 T. 7 It has been pointed out that, like MgB 2 , Mo 8 Ga 41 is also on the verge of a structural instability, 8,9 exhibits strong-coupling two-gap BCS superconductivity and good flux pinning potential. [10][11][12][13][14][15] In light of the relatively high critical temperature and upper critical field, further studies of this material are highly desirable.…”

Single-gap superconductivity in Mo8Ga41

“…Recently, it was suggested that Mo 8 Ga 41 features two-gap superconductivity [10][11][12] that vanishes upon the V for Mo substitution [10]. The material is a member of endohedral gallium cluster compounds.…”

“…In the subsequent study by means of muon spin rotation/relaxation spectroscopy, it was suggested [10] that two superconducting energy gaps exist in Mo 8 Ga 41 . Later on, the reports on possible existence of two energy gaps in Mo 8 Ga 41 followed from the critical current [11] and STS measurements [12].…”

New Tetragonal ReGa5(M) (M = Sn, Pb, Bi) Single Crystals Grown from Delicate Electrons Changing

“…Currently, the only known T m Ga n superconductors are low-temperature superconductors, making them potential materials for producing high magnetic fields at low temperatures. This can be observed in the superconductors Mo 8 Ga 41 and Mo 6 Ga 31 -as the electron counts decrease, the T c increases and the clusters form vertex-sharing interactions rather than edge-sharing [9]. MnGa 4.96 is another Ga-rich cluster which crystallizes into a tetragonal unit cell with capped face sharing Mn@Ga 8 clusters and correspondingly exhibits no superconductivity [10].…”