We presented the recent Hall effect data for a number of carriers in La(2-x)Sr(x)CuO4 as the sum of two components: the temperature independent term n0(x), which is due to external doping, and the thermally activated contribution. Their balance determines the crossover temperature T*(x) from the marginal Fermi liquid to pseudogap regime. The activation energy Delta(x) for thermally excited carriers equals the energy between the Fermi surface "arc" and the band bottom, as seen in angle-resolved photoemission spectroscopy experiments. Other implications for the (T, x)-phase diagram of cuprates are also discussed.

Using Cu nuclear quadrupole resonance (NQR) in Eu-doped La2-xSrxCuO4 we find the evidence of the pinned stripe phase at 1.3 K for 0. 080.18 correlating with the onset of bulk superconductivity corresponds to the depinning of the stripe phase.

No abstract

The heterogeneous coexistence of antiferromagnetism (SDW) and superconductivity on a mesoscopic scale was observed in iron-pnictides in many recent experiments. We suggest and discuss the scenario in which the heterogeneity is caused by formation of domain walls inherent to the SDW state of pnictides at a proper doping or under applied pressure. Superconductivity would emerge from the modulated SDW structure. The phenomenon is akin to the FFLO-phase in superconductors.

In La 1.48 Nd 0.4 Sr 0.12 CuO 4 the 139 La and 63 Cu nuclear quadrupole resonance relaxation rates and signal wipeout upon lowering temperature are shown to be due to purely magnetic fluctuations. They follow the same renormalized classical behavior as seen in neutron data, when the electronic spins order in stripes, with a small spread in spin stiffness ͑15% spread in activation energy͒. The La signal, which reappears at low temperatures, is magnetically broadened and experiences additional wipe out due to slowing down of the Nd fluctuations. DOI: 10.1103/PhysRevB.63.020507 PACS number͑s͒: 74.72.Dn, 76.60.Ϫk, 75.30.Ds, 75.40.Gb Strongly correlated electron systems such as layered cuprates exhibit very unusual properties. One of the most interesting among them is the coexistence of superconductivity with local antiferromagnetism ͑AF͒-a fingerprint of the topological effects of doping of AF insulators by holes. The charges segregate into a periodical array of stripes separating antiphase antiferromagnetic domains. Experimental evidence for stripe correlations has been provided by neutron studies in Nd-doped La 1.875 Sr 0.125 CuO 4 and in other cuprates and nickelates. 1,2 The spatial organization of the stripe structures is a subject of much debate. 3-8 Stripe formation is characterized by the temperatures of charge (T charge ) and spin T spin ordering with T charge ϾT spin . Since these different types of order coexist on the microscopic level, local methods of analysis, like NMR or nuclear quadrupole resonance ͑NQR͒, are well suited to see their interrelation. One striking feature in the NMR data is the wipe-out effect. In Cu-NQR experiments on a number of Sr doped La 2 CuO 4 samples, Hunt et al. 6 showed a correlation between the amount of the intensity loss and the development of charge order of the stripe phase. Curro et al. 7 found strong Cu wipe-out effect in their NMR experiments on La 2ϪyϪx Eu y Sr x CuO 4 and showed that this effect could be accounted for by a wide ͑100%͒ distribution in the energy of the thermally activated correlation times that determine the relaxation processes-so-called glassy behavior.In this communication the role of slow magnetic fluctuations is elucidated. We show that the variation of the line shape as well as wipe-out and relaxation effects probe the growing spin order in the stripe phase. Our investigation takes profit of the NQR frequency range of 139 La and 63 Cu, and especially of the low frequencies and relatively small line widths of La NQR in La 1.48 Nd 0.4 Sr 0.12 CuO 4 . In this compound both Cu and La exhibit strong wipe-out effects. Because La ͑contrary to Cu͒ nuclei are relatively weakly coupled to the electronic spins in the CuO 2 planes, La NQR signals can be followed down to the spin-ordering temperature, as seen by SR. Using the spin correlation times extracted from the activated La spin-lattice relaxation rates we are able to predict precisely these wipe-out features by introducing a spread of only 15% in the activation energy. Within experimental error t...

Gradual evolution of two phase coexistence between dynamical and static regimes in cuprates is first investigated in the real space by making use of available neutron scattering, NMR and μSR data. Analyses of the Hall effect and the ARPES spectra reveals the presence of two groups of charge carriers in LSCO. The T-dependent component is due to the thermal activation of bound electron-hole structures seen near antinodal points in the Brillouin zone, thus introducing the two component physics also for the momentum representation. Interpretation of so-called "van Hove bands" undergoes drastic changes. Importance of the findings for pseudo-gap physics is stressed. Relation to some recent STM and STS results is discussed.

We analyze anew experiments on the NMR in cuprates and find an important information on their phase separation and its stripe character hidden in the dependence of 1/ 63 T1 on degree of doping. In a broad class of materials 1/ 63 T1 is the sum of two terms: the temperature independent one attributed to "incommensurate" stripes that occur at external doping, and an "universal" temperature dependent term ascribed to moving metallic and AF sub-phases. We argue that the frustrated first order phase transition in a broad temperature interval bears a dynamical character.

The spin dynamics of copper pyrazine dinitrate (Cu(C4H4N2)(NO3)2), a model spin-1/2 Heisenberg antiferromagnetic (AF) chain system, was investigated by means of electron spin resonance (ESR). Using the high-field ESR we evidenced the inequivalence of Cu sites belonging to adjacent spin chains in the ac planes of this compound. It was revealed that the dominating interchain interaction is of zig-zag-type. This interaction gives rise to geometrical frustration strongly affecting the character of AF ordering. Combining our experimental findings with the results of a quasiclassical approach we predict that at low temperatures the system orders in an incommensurate spiral state.