Muon spin relaxation studies of incommensurate magnetism and superconductivity in stage-4La2CuO4.11and

A. T. Savici

¹

,

Y. Fudamoto

²

,

I. M. Gat

³

et al.

Abstract

We report muon spin relaxation (SR) measurements using single crystals of oxygen-intercalated stage-4 La 2 CuO 4.11 ͑LCO:4.11͒ and La 1.88 Sr 0.12 CuO 4 ͑LSCO:0.12͒, in which neutron scattering studies have found incommensurate magnetic Bragg reflections. In both systems, zero-field SR measurements show muon spin precession below the Néel temperature T N with frequency 3.6 MHz at T→0, having a Bessel function line shape, characteristic of spin-density-wave systems. The amplitude of the oscillating and relaxing signals of these systems is less than half the value expected for systems with static magnetic order in 100% of the volume. Our results are consistent with a simulation of local fields for a heuristic model with ͑a͒ incommensurate spin amplitude modulation with the maximum ordered Cu moment size of ϳ0.36 B , ͑b͒ static Cu moments on the CuO 2 planes forming ''islands'' having typical radius 15-30 Å, comparable to the in-plane superconducting coherence length, and ͑c͒ the measured volume fraction of magnetic muon sites V increasing progressively with decreasing temperature below T N towards V ϳ40% for LCO:4.11 and 18% for LSCO:0.12 at T→0. These results may be compared with correlation lengths in excess of 600 Å and a long range ordered moment of 0.15Ϯ0.05 B measured with neutron scattering techniques. In this paper we discuss a model that reconciles these apparently contradictory results. In transverse magnetic field SR measurements, sensitive to the in-plane magnetic field penetration depth ab , the results for LCO:4.11 and LSCO:0.12 follow correlations found for underdoped, overdoped and Zn-doped high-T c cuprate systems in a plot of T c versus the superconducting relaxation rate (T→0). This indicates that the volume-integrated value of n s /m* ͑superconducting carrier density / effective mass͒ is a determining factor for T c , not only in high-T c cuprate systems without static magnetism, but also in the present systems where superconductivity coexists with static spin-densitywave spin order.

Cu nuclear magnetic resonance study of charge and spin stripe order inLa1.875Ba0.125CuO4

“…A fit of relation (2) to the data in Fig. 4 gives ∆ ≈ 80 K and T V F T ≈ 20 K (a pure activational dependence would have T V F T = 0); while the value of T V F T should be taken with caution due to the limited range of the fit, it is consistent with the temperatures where Cu spin freezing is observed 41,42 in LSCO and LESCO using µSR, with the temperature range where 139 La spin-lattice relaxation rates start to decrease 13 , and with the temperature where 2D superconductivity is formed through a Berezinski-Kosterlitz-Thouless transition 2 . We note that diverging relaxation times were also observed in early work on Cu NQR in LBCO powders 46 in a broadly similar temperature range.…”

Condensation, excitation, pairing, and superfluid density in high-Tc superconductors: the magnetic resonance mode as a roton analogue and a possible spin-mediated pairing

“…Thus the situation looks again like the "swiss cheese", with "nonsuperconducting magnetic islands" replacing the "normal area around Zn". In zero-field µSR measurements of oxygen overdoped La 2 CuO 4.11 [25], we found the average size of such magnetic islands to be comparable to the in-plane coherence length ξ ∼ 15-30Å in radius. The Zndoped and magnetic-island systems follow the same trend as other less perturbed underdoped cuprates in Fig.…”

“…So, the incommensurate/stripe state could also be viewed as a competing ground state connected to the resonance mode. Indeed, in La 2 CuO 4.11 , the magnetic islands with stabilized incommensurate spin correlations coexist with surrounding superconducting and non-magnetic regions [25]. So, the superconducting and stripe states should have very close ground state energies and be competing with each other.…”

Coexistence of superconductivity and magnetism in FeSe1−xunder pressure

“…In this intermediate pressure region between 0.8 ≥ p ≥ 1.2 GPa the magnetic signal is described best by a Bessel function which indicates the presence of incommensurate magnetic order in the samples. 17 As shown in Fig. 4 for p 1.2 GPa (above the local minimum of T c ) superconductivity and magnetic order coexist in the full sample volume.…”