title: Spin dynamics in Na(4-x)Ir₃O₈ (x  =  0.3 and 0.7) investigated by ²³Na NMR and μSR.
abstract: We report (23)Na nuclear magnetic resonance (NMR) and zero-field (ZF) and longitudinal-field (LF) muon spin relaxation (μSR) measurements of the depleted hyperkagome compounds Na(4-x)Ir3O8 (x  =  0.3 and 0.7), which undergo an insulator-semimetal transition as a function of x. The (23)Na spin-lattice relaxation rates, T1(-1), follow a T(2.5) power law behavior at accessible temperatures of T  =  120-350 K. A substantial temperature dependence of T1(-1) indicates the presence of gapped excitations at elevated temperatures through the transition to a semimetallic phase. ZF-μSR results reveal that hole-doping leads to a melting of quasi-static order to a dynamically fluctuating state. The very slow muon depolarization rate which varies hardly with temperature indicates that spins are close to an itinerant limit in the largest doping x  =  0.7. The dynamic relaxation rates extracted from the LF-μSR spectra show a three-dimensional diffusive transport. Our combined NMR and μSR results suggest the occurrence of intriguing spin and charge excitations across the insulator-semimetal transition.
authors.affiliation: Department of Physics, The Catholic University of Korea, Bucheon 420-743, Korea.
authors.forename: Sungwon
authors.initials: S
authors.lastname: Yoon
authors.forename: S-H
authors.initials: SH
authors.lastname: Baek
authors.forename: Ashiwini
authors.initials: A
authors.lastname: Balodhi
authors.forename: W-J
authors.initials: WJ
authors.lastname: Lee
authors.forename: K-Y
authors.initials: KY
authors.lastname: Choi
authors.forename: I
authors.initials: I
authors.lastname: Watanabe
authors.forename: J S
authors.initials: JS
authors.lastname: Lord
authors.forename: B
authors.initials: B
authors.lastname: Büchner
authors.forename: B J
authors.initials: BJ
authors.lastname: Suh
authors.forename: Yogesh
authors.initials: Y
authors.lastname: Singh