Granular superconductivity and charge/orbital order in YBa2Cu3O7 /manganite trilayers

Abstract

We studied how the electronic, superconducting, and magnetic properties of YBa 2 Cu 3 O 7 / Nd 1−x (Ca 1−y Sr y ) x MnO 3 multilayers depend on the tolerance factor and the hole doping of the manganite. In particular, we investigated the granular superconducting state and the related magnetic-field-driven insulator-to-superconductor transition that was previously discovered in corresponding multilayers with Pr 0.5 La 0.2 Ca 0.3 MnO 3 [B. P. P. Mallett et al., Phys. Rev. B 94, 180503(R) ( 2016)]. We found that this granular superconducting state occurs only when the manganite layer is in a charge/orbital ordered and CE-type antiferromagnetic state (Mn-CO/OO). The coupling mechanism underlying this intriguing proximity effect seems to involve the domain boundaries of the Mn-CO/OO and/or the charge disordered regions of the manganite layer that become more numerous as the hole doping is reduced below x = 0.5.

Long-ranged Cu-based order with $$d_{z^2}$$ orbital character at a YBa2Cu3O7/ manganite interface

“…Notably, a coherent SC response below T c can be restored here by the application of a large magnetic field 25 , which is known to weaken and suppress the Mn-CO of the manganite. This unusual kind of magnetic-field-induced transition from an insulating to a superconducting state is absent in corresponding Nd 1-x (Ca 1-y Sr y ) x MnO 3 / YBa 2 Cu 3 O 7 / Nd 1-x (Ca 1-y Sr y ) x MnO 3 (NYN) multilayers for which the manganite has a larger tolerance factor (Sr content, y) and thus an itinerant ferromagnetic instead of the Mn-CO ground state 24 . These trends suggest that the granular superconducting state of the YBCO layers is induced by a proximity effect due to the coupling with the Mn-CO of the adjacent manganite layers.…”

“…The YBCO layers of the latter YBCO/NCSMO multilayers have anomalous superconducting properties. For multilayers for which the tolerance factor, t (or the Sr content, y) of the manganite is small enough to induce an insulating state with CE-type charge and orbital (Mn-CO) order, the YBCO layers exhibit a granular superconducting state which gives rise to an insulator-like upturn of the resistance below T c , instead of the expected drop to zero resistance [22][23][24] . This unusual behavior occurs only in multilayers for which the thickness of the YBCO layer is below a critical value of d YBCO ≤ 7−8 nm and where the manganite layers display the Mn-CO 23,25 .…”

“…In the following, we present a combined resonant inelastic and elastic X-ray spectroscopy (RIXS and REXS) and X-ray absorption spectroscopy (XAS) study at the Cu L 3 -edge of a NYN trilayer with x = 0.5 and y = 0.25. In this sample, the hole doping of the manganite has been adjusted to obtain a long-ranged Mn-CO order, unlike the previously studied multilayers with x = 0.3-0.35 for which the Mn-CO is strongly disordered 24,25 . To our surprise we find that a new kind of Cu-based order is induced in the YBCO layer that has an unusually short wave vector in the range of Q || ≈ 0.09-0.096 r.l.u., a large correlation length of about 40 nm, and a predominant d z 2 character, rather than the standard d x 2 Ày 2 one.…”

Backfolded acoustic phonons as ultrasonic probes in metal-oxide superlattices

“…However, for several reasons this is unlikely in our case, despite the significant Mn magnetic moments. First, longrange magnetic order is established only below T ≈ 140 K in our PLCMO and NCSMO samples [9,15,37], whereas these peaks are intense and sharp already at room temperature. Second, the new modes are only observed for superlattice samples, and not in films of the pure manganite material with a thickness comparable to that of the superlattices.…”

“…The multilayers studied here exhibit a range of electronic and magnetic phase transitions at temperatures below 300 K [9,15,37,51,52] and the materials are known for significant electron-phonon and spin-lattice coupling [4,5,7,13]. As such, we investigated the temperature dependence of the backfolded phonon modes.…”