We address the fundamental question: how are pair correlations and structure factors of hard-sphere fluids affected by confinement between hard planar walls at close distance? For this purpose, we combine x-ray scattering from colloid-filled nanofluidic channel arrays and first-principles inhomogeneous liquidstate theory within the anisotropic Percus-Yevick approximation. The experimental and theoretical data are in remarkable agreement at the pair-correlation level, providing the first quantitative experimental verification of the theoretically predicted confinement-induced anisotropy of the pair-correlation functions for the fluid. The description of confined fluids at this level provides, in the general case, important insights into the mechanisms of particle-particle interactions in dense fluids under confinement.

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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

We have developed a unique approach for studying the ensemble-averaged nearestneighbor coordination of confined fluids by combining small-angle X-ray scattering and phaseretrieval-based X-ray diffraction from fluid-filled nanofluidic channel arrays. We apply the method to a charge-stabilized quasi-two-dimensional colloidal fluid (particle diameter 48 nm), focusing on the structural transition from a monolayer to a bilayer with increasing fluid film thickness. In contrast to theoretical work on the paradigmatic hard-sphere fluid, we find unambiguous experimental evidence for orientational alignment of fluids in extreme confinement.

The observation of a charge density wave in the underdoped cuprate high T c superconductors (Cu-CDW) raised a debate about its relationship with superconductivity. In bulk YBa 2 Cu 3 O 7−δ the Cu-CDW is incipient and mainly pinned by defects. Nevertheless, a large magnetic field can induce a true long-range Cu-CDW order as it suppresses superconductivity. An enhanced Cu-CDW order was also observed in YBa 2 Cu 3 O 7 /La 2/3 Ca 1/3 MnO 3 multilayers. Here, we show that the magnitude of the Cu-CDW in YBa 2 Cu 3 O 7−δ / Nd 0.65 (Ca 1y Sr y) 0.35 MnO 3 multilayers can be varied by adjusting the strength of the manganite charge and orbital order via the Sr content (tolerance factor). Furthermore, we resolve the reconstruction of the crystal field levels of the interfacial Cu ions that are also affected by the manganite charge and orbital order. This tuneable interfacial coupling and Cu-CDW in YBa 2 Cu 3 O 7−δ can be used for studying the relationship between the Cu-CDW and superconductivity and, possibly, for inducing new intertwined quantum states.