Magnetism and superconductivity in CeRh_{1-x}Ir_xIn_5 heavy fermion materials

We report on zero-field muon spin relaxation studies of cerium based heavy-fermion materials CeRh_{1-x}Ir_xIn_5. In the superconducting x=0.75 and 1 compositions muon spin relaxation functions were found to be temperature independent across T_c; no evidence for the presence of electronic magnetic moments was observed. The x=0.5 material is antiferromagnetic below T_N=3.75 K and superconducting below T_c=0.8 K. Muon spin realxation spectra show the gradual onset of damped coherent oscillations characteristic of magnetic order below T_N. At 1.65 K the total oscillating amplitude accounts for at least 85% of the sample volume. No change in muon precession frequency or amplitude is detected on cooling below T_c, indicating the microscopic coexistence of magnetism and superconductivity in this material.Comment: 6 pages with 3 figures. Revision with corrected axis label (mK) in Fig.

Intrinsic ferromagnetic impurity phases in SmFeAsO1-xFx detected by muSR

We report about muSR measurements on SmFeAsO1-xFx which helped us to identify the signature of diluted ferromagnetic inclusions, ubiquitous in the iron pnictides. These impurities are characterized by a Curie temperature close to room temperature and they seem responsible for a non negligible magnetic relaxation of the implanted muons, that should not be confused with intrinsic pnictide properties.Comment: The International Conference on FeAs High Tc Superconducting Multilayers and Related Phenomena (Superstripes2008), Rome, Italy, December 9-13, 200

Effects of domain walls on hole motion in the two-dimensional t-J model at finite temperature

The t-J model on the square lattice, close to the t-J_z limit, is studied by quantum Monte Carlo techniques at finite temperature and in the underdoped regime. A variant of the Hoshen-Koppelman algorithm was implemented to identify the antiferromagnetic domains on each Trotter slice. The results show that the model presents at high enough temperature finite antiferromagnetic (AF) domains which collapse at lower temperatures into a single ordered AF state. While there are domains, holes would tend to preferentially move along the domain walls. In this case, there are indications of hole pairing starting at a relatively high temperature. At lower temperatures, when the whole system becomes essentially fully AF ordered, at least in finite clusters, holes would likely tend to move within phase separated regions. The crossover between both states moves down in temperature as doping increases and/or as the off-diagonal exchange increases. The possibility of hole motion along AF domain walls at zero temperature in the fully isotropic t-J is discussed.Comment: final version, to appear in Physical Review

Tomonaga–Luttinger liquid behavior and spinon confinement in YbAlO 3

Low dimensional quantum magnets are interesting because of the emerging collective behavior arising from strong quantum fluctuations. The one-dimensional (1D) S = 1/2 Heisenberg antiferromagnet is a paradigmatic example, whose low-energy excitations, known as spinons, carry fractional spin S = 1/2. These fractional modes can be reconfined by the application of a staggered magnetic field. Even though considerable progress has been made in the theoretical understanding of such magnets, experimental realizations of this low-dimensional physics are relatively rare. This is particularly true for rare-earth-based magnets because of the large effective spin anisotropy induced by the combination of strong spin–orbit coupling and crystal field splitting. Here, we demonstrate that the rare-earth perovskite YbAlO3 provides a realization of a quantum spin S = 1/2 chain material exhibiting both quantum critical Tomonaga–Luttinger liquid behavior and spinon confinement–deconfinement transitions in different regions of magnetic field–temperature phase diagram

Effect of a magnetic field on the spin- and charge-density wave order in La1.45Nd0.4Sr0.15CuO4

The spin-density wave (SDW) and charge-density wave (CDW) order in superconducting La1.45Nd0.4Sr0.15CuO4 were studied under an applied magnetic field using neutron and X-ray diffraction techniques. In zero field, incommensurate (IC) SDW order appears below ~ 40 K, which is characterized by neutron diffraction peaks at (1/2 +/- 0.134, 1/2 +/- 0.134, 0). The intensity of these IC peaks increases rapidly below T_Nd ~ 8 K due to an ordering of the Nd^3+ spins. The application of a 1 T magnetic field parallel to the c-axis markedly diminishes the intensity below T_Nd, while only a slight decrease in intensity is observed at higher temperatures for fields up to 7 T. Our interpretation is that the c-axis field suppresses the parasitic Nd^3+ spin order at the incommensurate wave vector without disturbing the stripe order of Cu^2+ spins. Consistent with this picture, the CDW order, which appears below 60 K, shows no change for magnetic fields up to 4 T. These results stand in contrast to the significant field-induced enhancement of the SDW order observed in superconducting La2-xSrxCuO4 with x ~ 0.12 and stage-4 La2CuO4+y. The differences can be understood in terms of the relative volume fraction exhibiting stripe order in zero field, and the collective results are consistent with the idea that suppression of superconductivity by vortices nucleates local patches of stripe order.Comment: 7 pages, 5 figure

Thermodynamic properties of excess-oxygen-doped La2CuO4.11 near a simultaneous transition to superconductivity and long-range magnetic order

We have measured the specific heat and magnetization {\it versus} temperature in a single crystal sample of superconducting La$_{2}$CuO$_{4.11}$ and in a sample of the same material after removing the excess oxygen, in magnetic fields up to 15 T. Using the deoxygenated sample to subtract the phonon contribution, we find a broad peak in the specific heat, centered at 50 K. This excess specific heat is attributed to fluctuations of the Cu spins possibly enhanced by an interplay with the charge degrees of freedom, and appears to be independent of magnetic field, up to 15 T. Near the superconducting transition $T_{c}$($H$=0)= 43 K, we find a sharp feature that is strongly suppressed when the magnetic field is applied parallel to the crystallographic c-axis. A model for 3D vortex fluctuations is used to scale magnetization measured at several magnetic fields. When the magnetic field is applied perpendicular to the c-axis, the only observed effect is a slight shift in the superconducting transition temperature.Comment: 8 pages, 8 figure

Muon spin relaxation studies of incommensurate magnetism and superconductivity in stage-4 La2_{2}CuO4.11_{4.11} and La1.88_{1.88}Sr0.12_{0.12}CuO4_{4}

This paper reports muon spin relaxation (MuSR) measurements of two single crystals of the title high-Tc cuprate systems where static incommensurate magnetism and superconductivity coexist. By zero-field MuSR measurements and subsequent analyses with simulations, we show that (1) the maximum ordered Cu moment size (0.36 Bohr magneton) and local spin structure are identical to those in prototypical stripe spin systems with the 1/8 hole concentration; (2) the static magnetism is confined to less than a half of the volume of the sample, and (3) regions with static magnetism form nano-scale islands with the size comparable to the in-plane superconducting coherence length. By transverse-field MuSR measurements, we show that Tc of these systems is related to the superfluid density, in the same way as observed in cuprate systems without static magnetism. We discuss a heuristic model involving percolation of these nanoscale islands with static magnetism as a possible picture to reconcile heterogeneity found by the present MuSR study and long-range spin correlations found by neutron scattering.Comment: 19 pages, 15 figures, submitted to Phys. Rev. B. E-mail: [email protected]

Muon spin relaxation and susceptibility measurements of an itinerant-electron system Sr 1-xCa xRuO 3: Quantum evolution from ferromagnet to paramagnet

Muon spin relaxation (\u3bcSR) and magnetic susceptibility measurements have been performed in the itinerant-electron magnet Sr 1-xCa xRuO 3, with x= 0.0, 0.3, 0.5, 0.65, 0.7, 0.75, 0.8, 0.9, and 1.0. SrRuO 3 is a ferromagnet with the critical temperature T c 3c160 K. Upon (Sr, Ca) substitution, T c decreases monotonically with increasing Ca concentration x and the ferromagnetic order disappears around x= 0.7. Very weak static magnetism is observed in the x= 0.75 and 0.8 systems, while the x= 0.9 and 1.0 systems remain paramagnetic in their full volume. Phase separation between volumes with and without static magnetism was observed in the x= 0.65, 0.7, 0.75, and 0.8 systems, near the magnetic crossover around x= 0.7. In this concentration region, \u3bcSR measurements revealed discontinuous evolution of magnetic properties in contrast to magnetization measurements, which exhibit seemingly continuous evolution. Unlike the volume-integrated magnetization measurements, \u3bcSR can separate the effects of the ordered moment size and the volume fraction of magnetically ordered regions. The muon spin relaxation rate 1/T 1 exhibits critical slowing down of spin fluctuations near T c in the ferromagnetic systems with x= 0.0-0.65, consistent with the behavior expected in the self-consistent renormalization theory of itinerant electron ferromagnets. The lack of maximum of 1/T 1 in the x= 0.7 system indicates the disappearance of critical slowing down. These results demonstrate a first-order quantum evolution in the ferromagnet to paramagnet crossover near x= 0.7. \ua9 2011 American Physical Society.Peer reviewed: YesNRC publication: Ye