Granular superconductivity and magnetic-field-driven recovery of macroscopic coherence in a cuprate/manganite multilayer

Abstract

We show that in Pr 0.5 La 0.2 Ca 0.3 MnO 3 /YBa 2 Cu 3 O 7 (PLCMO/YBCO) multilayers the low temperature state of YBCO is very resistive and resembles that of a granular superconductor or a frustrated Josephson-junction network. Notably, a coherent superconducting response can be restored with a large magnetic field which also suppresses the charge-orbital order in PLCMO. This coincidence suggests that the granular superconducting state of YBCO is induced by the charge-orbital order of PLCMO. The coupling mechanism and the nature of the induced inhomogeneous state in YBCO remain to be understood. [6,7] for which the magnetic field compensates a negative exchange field from magnetic ions, thereby reducing the pair breaking (Jacarino-Peter effect) [8], or suppresses detrimental magnetic fluctuations [9]. A reentrance of SC was also reported in Zn nanowires where the field seems to reduce quantum fluctuations by generating dissipative quasiparticles [10,11].In the following, we show that yet another kind of these rare cases can be found in cuprate/manganite multilayers. Here the magnetic field restores a coherent SC state in a thin YBa 2 Cu 3 O 7 (YBCO) layer, most likely since it suppresses an interaction with the neighboring Pr 0.5 La 0.2 Ca 0.3 MnO 3 (PLCMO) layers that is detrimental to a macroscopic SC coherence. PLCMO exhibits a combined charge-orbital order [12] and an antiferromagnetic (AF) order with a weak ferromagnetic (FM) component that arises either from a spin canting or phase segregation. A large magnetic field suppresses this charge-orbital ordered AF state towards an itinerant FM state [12]. Surprisingly, the latter state of PLCMO is less detrimental to the SC in YBCO than the former.PLCMO (20 nm)/YBCO (7, 9, and 20 nm)/PLCMO (20 nm) trilayers and PLCMO(20 nm)-YBCO(3.5 and 4.5 nm) bilayers were grown on La 0.3 Sr 0.7 Al 0.65 Ta 0.35 O 3 substrates by pulsed * benjamin

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

“…Instead, there exists evidence for a granular superconducting state with grains that are strongly superconducting and boundaries at which the macroscopic coherence of the superconducting wave function is broken. A terahertz spectroscopy study in zero magnetic field has indeed revealed a strong plasmonic mode at nonzero frequency that develops below 80 K and arises from a strongly confined superconducting condensate [36].…”

“…084801-3 Figure 1(a) recalls the R-T curves in zero magnetic field (blue line) and at 9 T (red line) of a PLCMO(20 nm)/YBCO(7 nm)/PLCMO(20 nm) (PYP) trilayer from Ref. [36]. These were interpreted in terms of a transition from a granular superconducting state with a Coulomb blockade at zero field to a macroscopically coherent superconducting one with T c ≈ 75 K at 9 T.…”

“…It is thus rather surprising that a severe suppression of the superconducting response was observed in YBCO/ Pr 0.5 La 0.2 Ca 0.3 MnO 3 (PLCMO) multilayers for which the YBCO layer consists of six monolayers (d YBCO ≈ 7 nm) [36]. Instead of a superconducting transition, they exhibit an insulator-like upturn of the dc resistivity toward low temperature.…”

“…1(a) (blue line). Here the manganite layer is not a ferromagnetic half-metal but an insulator with a CE-type antiferromagnetic order and a combined charge and orbital ordered (CO/OO) state with wave vectors Q OO = (1/4, 1/4, 0) and Q CO = (1/2, 0, 0) or (0, 1/2, 0) (expressed in reciprocal lattice units in pseudocubic notation) that develops below 220-240 K [6,7,36]. While there is evidence that the oxygen ions also play an important role in this CO/OO [37,38], for simplicity in the following we refer to it as Mn-CO/OO.…”

Large magnetoresistance of insulating silicon films with superconducting nanoprecipitates

“…20 Large MR has also been observed in several inhomogeneous or disordered materials that exhibit a superconductor-insulator transition 21,22 as e.g. thin amorphous or granular metallic films on insulators, [23][24][25][26] fractal Pb films on silicon, 27 Pb-Si hetorojunctions, 28 amorphous metal-metalloid films, [29][30][31][32][33] cuprate superconductors [34][35][36][37][38] and heavily doped semiconductors. [39][40][41][42][43] There has been an academic debate about the nature of this phase transition and the origin of the large negative MR. 12,[44][45][46] Some theories consider a global quantum phase transition 21,33,47,48 or quantum corrections to the classical magnetotransport.…”