Random singlet physics in the S = 1 2 pyrochlore antiferromagnet NaCdCu 2 F 7

We report a random singlet ground state in the S = 1 2 Heisenberg pyrochlore antiferromagnet NaCdCu 2 F 7 . Cationic Na + / Cd 2 + disorder on the pyrochlore A site generates a broad distribution of Cu 2 + – F − – Cu 2 + exchange couplings, introducing intrinsic magnetic bond disorder. Despite strong antiferromagnetic interactions ( θ CW = − 72 K ) , no magnetic order or global spin freezing is observed in dc and ac susceptibility, specific heat, or Na 23 nuclear magnetic resonance to 120 mK, with muon spin relaxation experiments confirming persistent spin dynamics to 58 mK. T -linear specific heat, a Curie-like susceptibility tail, and power-law scaling with data collapse in χ ( T ) , M ( H ) , C mag / T , Na 23 ( 1 / T 1 T ) , and the muon spin polarization P ( t ) reveal a disorder-driven network of random singlets and orphan spins. Scaling across multiple bulk and local probes is consistent with a broad distribution of exchange energies, P [ J ] ∼ J − α . This behavior contrasts with previously studied Na A ″ B 2 F 7 pyrochlore fluorides, where magnetic bond disorder precipitates spin-glass freezing, underscoring the crucial role of strong S = 1 2 quantum fluctuations in NaCdCu 2 F 7