Ir-Sb Binary System: Unveiling Nodeless Unconventional Superconductivity Proximate to Honeycomb-Vacancy Ordering
arxiv(2024)
摘要
Vacancies play a crucial role in solid-state physics, but their impact on
materials with strong electron-electron correlations has been underexplored. A
recent study on the Ir-Sb binary system, Ir_16Sb_18 revealed a novel
extended buckled-honeycomb vacancy (BHV) order. Superconductivity is induced by
suppressing the BHV ordering through high-pressure growth with excess Ir atoms
or isovalent Rh substitution, although the nature of superconducting pairing
has remained unexplored. Here, we conduct muon spin rotation experiments
probing the temperature-dependence of the effective magnetic penetration depth
λ_eff(T) in Ir_1-δSb (synthesized at 5.5 GPa
with T_ c = 4.2 K) and ambient pressure synthesized optimally Rh-doped
Ir_1-xRh_xSb (x=0.3, T_ c = 2.7 K). The exponential
temperature dependence of the superfluid density n_ s/m^* at low
temperatures indicates a fully gapped superconducting state in both samples.
Notably, the ratio of T_ c to the superfluid density is comparable to
previously measured unconventional superconductors. A significant increase in
n_ s/m^* in the high-pressure synthesized sample correlates with
T_ c, a hallmark feature of unconventional superconductivity. We further
demonstrate a similar effect induced by chemical pressure (Rh substitution) and
hydrostatic pressure in Ir_1-xRh_xSb, highlighting that the dome-shaped
phase diagram is a fundamental feature of the material. These findings
underscore the unconventional nature of the observed superconductivity, and
classifies IrSb as the first unconventional superconducting parent phase with
ordered vacancies.
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