Direct Observation of the Oxygen Isotope Effect on the In-Plane Magnetic Field Penetration Depth in Optimally DopedYBa2Cu3

Abstract

We report the first direct observation of the oxygen-isotope ((16)O/(18)O) effect on the in-plane penetration depth lambda(ab) in a nearly optimally doped YBa(2)Cu(3)O(7-delta) film using the novel low-energy muon-spin rotation technique. Spin-polarized low-energy muons are implanted in the film at a known depth z beneath the surface and process in the local magnetic field B(z). This feature allows us to measure directly the profile B(z) of the magnetic field inside the superconducting film in the Meissner state and to make a straightforward determination of lambda(ab). A substantial isotope shift Delta lambda(ab)/lambda(ab)=2.8(1.0)% at 4 K is observed, implying that the in-plane effective supercarrier mass m*(ab) is oxygen-isotope dependent with Delta m*(ab)/m*(ab)=5.5(2.0)%. These results are in good agreement with magnetization measurements on powder samples.

Multicomponent superconductivity: the complex interplay of spin charge and lattice

“…Further support for a break down of t-J type models stems from ARPES results which a reveal unique kink in the electronic dispersion, attributed to strong electron phonon coupling [30]. An even more obvious result supporting a lattice mediated pairing mechanism than the kink structure, is the observation of an isotope effect on the London penetration depth λ L [31]. Since this isotope effect is not present within conventional BCS theory, the role of the lattice to HTSC is different from the known phonon mediated scenario [32].…”

“…Chemical potential (doping) [31] of the oxygen-isotope effect on the zero-temperature in-plane magnetic penetration depth λ ab (0) and T c also included in Fig. 6.3 for direct comparison.…”

Path Integrals in the Physics of Lattice Polarons

“…In particular, anything that depends on the (bi)polaron mass should exhibit a large isotope exponent [86]. A large isotope effect was observed, for example, on the magnetic penetration depth in cuprates [97,98,99], which was interpreted as evidence for bipolaronic carriers in the superconducting state.…”

High Temperature Superconductivity Due to a Long-Range Electron–Phonon Interaction, Application to Isotope Effects, Thermomagnetic Transport and Nanoscale Heterogeneity in Cuprates

“…The most compelling evidence for (bi)polaronic carries in novel superconductors was provided by the discovery of a substantial isotope effect on the (super)carrier mass [13,14,15] [12]. In ordinary metals, where the Migdal adiabatic approximation [16] is believed to be valid, α m = 0 is expected.…”

“…Actually, such effects have been observed in ferromagnetic oxides at low temperatures [20], and in cuprates [13,14,15]. To address ARPES isotope exponents [19] one has to calculate the electron spectral function A(k, E) taking into account phonon side-bands (i.e.…”