Fermi surface, possible unconventional fermions, and unusually robust resistive critical fields in the chiral-structured superconductor AuBe

Abstract

The noncentrosymmetric superconductor (NCS) AuBe is investigated using a variety of thermodynamic and resistive probes in magnetic fields of up to 65 T and temperatures down to 0.3 K. Despite the polycrystalline nature of the samples, the observation of a complex series of de Haasvan Alphen (dHvA) oscillations has allowed the calculated bandstructure for AuBe to be validated. This permits a variety of BCS parameters describing the superconductivity to be estimated, despite the complexity of the measured Fermi surface. In addition, AuBe displays a nonstandard field dependence of the phase of dHvA oscillations associated with a band thought to host unconventional fermions in this chiral lattice. This result demonstrates the power of the dHvA effect to establish the properties of a single band despite the presence of other electronic bands with a larger density of states, even in polycrystalline samples. In common with several other NCSs, we find that the resistive upper critical field exceeds that measured by heat capacity and magnetization by a considerable factor. We suggest that our data exclude mechanisms for such an effect associated with disorder, implying that topologically protected superconducting surface states may be involved. arXiv:1812.02830v2 [cond-mat.supr-con]

Single-gap versus two-gap scenario: Specific heat and thermodynamic critical field of the noncentrosymmetric superconductor BeAu

“…the value of α = 1.686( 8) is only slightly smaller than the weakly coupled BCS value α BCS = 1.764. This agrees with the previous observations suggesting the presence of a single isotropic energy gap in BeAu [46][47][48][49].…”

“…[47,50], respectively. Note that currently, three sets of C e (T ) and B c (T ) data for BeAu are available in the literature [46][47][48][49][50][51]. Among them, the C e (T ) and B c (T ) dependences from Refs.…”

“…Our interest in interpreting the superfluid density, the specific heat, and the thermodynamic critical field within the single-gap and two-gap scenarios was initiated by recent publications pointing to contradictory results for the noncentrosymmetric BeAu superconducting compound [46][47][48][49][50]. Indeed, Refs.…”

“…[46][47][48][49] consider BeAu to host a single isotropic gap, which is a characteristic of predominantly s-wave spinsinglet pairing in the weak-coupling limit. Such evidence comes from the electronic specific heat measurements, suggesting that C e (T ) is well described within the single-gap * rustem.khasanov@psi.ch approach with the ratio α = (0)/k B T c ranging from the weakly coupled BCS value α BCS = 1.764 up to α 1.88 [46][47][48][49]. Here, (0), T c , and k B are the zero-temperature value of the gap, the superconducting transition temperature, and the Boltzmann constant, respectively.…”

Topological Engineering of Pt‐Group‐Metal‐Based Chiral Crystals toward High‐Efficiency Hydrogen Evolution Catalysts

“…Thanks to the development of topological materials, a new type of topological semimetals of multifold fermions were theoretically predicted and experimentally verified in a class of chiral crystals 25–31. Owing to the chiral crystal symmetry, the band structures of this type of materials present as multifold degenerated points with a large topological charge of Chern number 4 (Figure 1B,C).…”