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Pseudogap of the high-temperature superconductorLa1.96−xSrxHo0.04Cu

“…Additionally, isotope effects on NMR/NQR parameters were observed in YBa 2 Cu 4 O 8 . 22,23 Similarly to isotope substitution, the application of pressure affects the lattice degrees of freedom, thus it could be used as an independent tool to confirm the experimental and theoretical findings concerning T * described above. Unfortunately, there are only a few pressure-dependent experiments on the pseudogap temperature T * in the literature, and the results are contradicting.…”

Synthesis, 89Y and 51V-NMR of Er-doped zircon-type YVO4 and LUVO4

“…Although 89 Y is a favorable spin- 1 2 nucleus, to date NMR studies are very scarce because of its low gyromagnetic ratio ($2.09 MHz/T), long relaxation times, and severe probe ringing which is generally observed at low frequencies (o30 MHz). While a number of wide-line and lowtemperature studies have been reported on Y-containing ceramic superconductors (see, e.g., [17]) and magnetic materials (see, e.g., [18]), only a few papers appeared about MAS studies of diamagnetic oxides. Grey et al [19] studied the effects of the incorporation of large amounts of paramagnetic lanthanides in diamagnetic pyrochlores Y 2 M 2 O 7 (M ¼ Sn, Ti), showing that the addition of the Ln ions caused the appearance of additional resonances.…”

Polaron effects on superexchange interaction: Isotope shifts of T N , T c , and T* in layered copper oxides

“…Substituting here (in electronvolts) ∆ Cu−O = 1.5 [13] and standard values hω a = 0.05, E a = 0.4 [10,14], and using the relationship ∆T N /T N ≈ ∆J/J characteristic for layered cuprates (see [1]), we find that the Neel temperature should decrease by 0.2% upon replacing 16 O with 18 O in YBa 2 Cu 3 O 6.383 . According to measurements in La 2 CuO 4 [15], the shift ≃ 0.6%.…”

“…It is known that the observation of an isotope shift of the superconducting transition temperature (T C ) was of crucial importance in ascertaining the phonon mechanism of pairing in conventional (low-temperature) superconductors. The fact that an isotope effect exists in hightemperature superconductors built up of copperoxygen planes has long been beyond question; however, the relative smallness of the coefficient (for example, α ∼ 0.056 for YBa 2 Cu 4 O 8 upon replacing 16 O with 18 O, instead of the standard value 0.5) and the specific features of its behavior in other compounds upon changing the number of holes in copper-oxygen planes do not fit the Bardeen-Cooper-Schrieffer (BCS) scenario. At the same time, the majority of authors of articles related to the isotope effect (see the recent review [1]) correctly point out that, nevertheless, phonon modes, in some mysterious way, affect the superconducting transition temperature.…”

“…In this context, we believe that the facts of observing an isotope effect for the characteristic temperature of the pseudogap state of underdoped cuprates (so-called pseudogap onset temperature T * ) gain great importance. Thus, according to [2], the isotope exponent upon replacing 16 O with 18 O corresponding to T * is = 0.061. It was natural that this fact suggested a common origin of α TC and α T * [2].…”