We performed zero and transverse field µSR experiments on a large number of YBa2Cu3O6+x samples. We detect coexistence of antiferro-type (AF) short range magnetism with superconductivity below T f 10 K in compositions 0.37 x 0.39. Most muons experience local AF fields, even when SQUID detects a full superconducting volume fraction, which points to a local minimal interference organization of short AF stripes embedded in the superconductor. A detailed phase diagram is produced and the consequences of the minimal interference are discussed. Neutron scattering also detects magnetic correlations, notably [10] in YBa 2 Cu 3 O 6.35 , exclusively dynamic in nature, although their static counterpart could be elusive due to a very short correlation length. The doubled magnetic unit cell indicates an antiferromagnetic (AF) structure, with a suggested stripe-like character.In all the samples explored so far by µSR [5,6,7,8,9] it has been hinted that the cluster spin glass nature of magnetism (low spin freezing temperature, T f , large distributions of B i and absence of long range order as from neutron diffraction [11,12]) might be favored by the disorder inherent in cation substituted perovskites, which directly influences the CuO 2 layers. Conversely in YBa 2 Cu 3 O 6+x (123, hereafter) the source of disorder, namely the basal CuO x layers, are farther removed from the CuO 2 layers, but systematic µSR data were lacking, prior to the present work. Our aim is to clarify whether the appearance of coexisting superconducting and magnetic properties is indeed intrinsic to the unperturbed underdoped CuO 2 layers and whether the two properties cooperate or interfere.We performed µSR measurements on twenty-four polycrystalline 123 samples (Y 1−24 ) prepared by the topotactic technique, which consists of oxygen equilibration of stoichiometric quantities of the two end member specimens, tightly packed in sealed vessels [13]. Low temperature annealing yields high quality homogeneous samples with an absolute error of δx=±0.02 in oxygen content per formula unit and a much smaller relative error between samples of the same batch. The width of the interval were the resistance drops from 90% to 10% of the onset value is 0.5 K at optimal doping and 6-7K at x 0.4 (vs. e.g. 10K in Ref.10). The hole content h was determined from the resistive T c for the superconducting samples [14], and from the Seebeck coefficient S at 290 K for the non-superconducting ones, using the exponential dependence [14] of S on h, with fit parameters determined from our series of samples [15]. Samples Y 1−8 , with oxygen content 0.20≤x≤0.32 and hole content per planar Cu atom 0.033≤h≤0.055, never superconduct, and their AF properties were reported previously [16]. Samples Y 9−24 , with 0.32≤x≤0.42 and 0.055≤h≤0.08, are superconductors and are the subject of the present work.The µSR experiment were performed on the MUSR spectrometer of the ISIS pulsed muon facility, where the external magnetic field H may be applied either parallel to the initial muon spin S µ , in...

We demonstrate that the [Yb(trensal)] molecule is a prototypical coupled electronic qubit-nuclear qudit system. The combination of noise-resilient nuclear degrees of freedom and large reduction of nutation time induced by electron-nuclear mixing enables coherent manipulation of this qudit by radio frequency pulses. Moreover, the multilevel structure of the qudit is exploited to encode and operate a qubit with embedded basic quantum error correction.

55 Mn NMR experiments were carried out at 1.3-4.2 K on six samples of lanthanum manganites, with a hole doping concentration ranging from the antiferromagnetic-insulator to the ferromagnetic-conductor region of the phase diagram. The dependence of the resonance frequencies on external fields is either as expected for ferromagnets ͑FM͒ or for antiferromagnets ͑AF͒. No indication of a canted phase could be detected. FM and AF resonances were found to coexist in all samples and are grouped in three broad bands, whose frequencies do not depend in first order on hole concentration. Strong evidence of interaction between AF and FM regions was provided by longitudinal relaxation experiments in several samples. An explanation of this behavior is offered in terms of intrinsic phase separation of the holes into FM microdomains. We determine the 55 Mn hyperfine coupling to be isotropic in all cases, with Aϭ6.2 T/ B for the on-site term in the AF domains.

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We report on the recovery of the short-range static magnetic order and on the concomitant degradation of the superconducting state in optimally F-doped SmFe1−xRuxAsO0.85F0.15 for 0.1 ≤ x 0.5. The two reduced order parameters coexist within nanometer-size domains in the FeAs layers and finally disappear around a common critical threshold xc ∼ 0.6. Superconductivity and magnetism are shown to be closely related to two distinct well-defined local electronic environments of the FeAs layers. The two transition temperatures, controlled by the isoelectronic and diamagnetic Ru substitution, scale with the volume fraction of the corresponding environments. This fact indicates that superconductivity is assisted by magnetic fluctuations, which are frozen whenever a short-range static order appears, and totally vanish above the magnetic dilution threshold xc.The appearance of high-T c superconductivity (SC) close to the disruption of static magnetic (M) order is a general feature of the Fe-based superconductors either as a function of doping or external pressure. In the REFeAsO family (RE1111) it is found that SC and M strongly compete and hardly coexist simultaneously [1, 2], apart for RE=Sm and Ce [3,4] within a small doping range where both order parameters are depressed. Coexistence implies short range magnetic order, that is detected only by local probes such as muon-spin rotation (µSR) [4] or nuclear quadrupole resonance (NQR) [5], since it eludes long coherence probes such as powder diffraction [6]. The competition between the superconducting and magnetic ground-states must be reconciled with the prevailing models of pairing mediated by spin fluctuations [7]. These models are seemingly in contradiction with the evidence that the two mutually excluding orders coexist only when phase separation occurs.Here we show, by means of µSR and 75 As NQR, that magnetism is surprisingly still at play in optimally F-doped SmFe 1−x Ru x AsO 0.85 F 0.15 . The isoelectronic Fe:Ru substitution is found to deteriorate the superconducting state in optimally electron-doped SmFeAsO 0.85 -F 0.15 samples and simultaneously to recover static magnetism within the FeAs layers, for 0.1 ≤ x 0.5. This is accompanied by a local electronic rearrangement within the FeAs layers. When Ru doping approaches the critical threshold x c = 0.6, corresponding to percolation of a magnetic square lattice with nearest neighbor (n.n.) and next-nearest neighbor hopping, both magnetism and SC vanish.The investigated polycrystalline SmFe 1−x Ru x AsO 0.85 -F 0.15 samples are the same of Ref. 8. From 19 F nuclear magnetic resonance the relative fluorine content was found to be constant within ∆ 0.01 in the whole set of samples investigated. To investigate the bulk character of the superconducting state we carried out transverse field (TF)-µSR measurements, where a sample is fieldcooled (FC) in a magnetic field larger than the lower superconducting critical field H c1 , applied perpendicular to the initial muon-spin orientation (H ⊥ S µ ). A flux-line lattice (FLL) i...