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Utilizing the QCD sum rule approach to the behavior of the ω meson in nuclear matter we derive evidence for in-medium changes of particular four-quark condensates from the recent CB-TAPS experiment for the reaction γ + A → A ′ + ω(→ π 0 γ) with A = Nb and LH2. The chiral condensate qq is an order parameter for the spontaneous breaking of chiral symmetry in the theory of strong interaction (cf. e.g. [1] for introducing this topic). The role of qq is highlighted, e.g., by the GellMann-Oakes-Renner relation m 2 π f 2 π ∝ − qq (cf. [2]; the explicit chiral symmetry breaking is essential for a finite pion mass m π , while the relation of the pion decay constant f π to qq qualifies the latter as an order parameter) or by Ioffe's formula M N ∝ − qq for the nucleon mass (cf. [3] and in particular the discussion in [4]). There is growing evidence that the quark-gluon condensate is another order parameter [5]. The QCD trace anomaly related to scale invariance breaking gives rise to the gluon condensate. There are many other condensates characterizing the complicated structure of the QCD vacuum. In a medium, described by temperature and baryon density n, these condensates change, i.e., the ground state is rearranged. Since hadrons are considered as excitations above the vacuum, a vacuum change should manifest itself as a change of the hadronic excitation spectrum. This idea triggered widespread activities to search for in-medium modifications of hadrons. Such in-medium modifications of hadronic observables are found (cf. the lists in [6,7]), and it is timely to relate them to corresponding order parameters.We deduce here evidence for a noticeable drop of inmedium four-quark condensates in cold nuclear matter from results of the recent CB-TAPS experiment [6] for the reaction γ + A → A ′ + ω(→ π 0 γ). The CB-TAPS collaboration observed the occurrence of additional lowenergy ω decay strength for a Nb (A = 93) target compared to a LH 2 (A = 1) target. The link of observables to quark and gluon condensates is established by QCD sum rules [8], which are expected to be sensitive to four-quark condensates in the vector channels [9]. Four-quark condensate combinations which contain only left-right helicity flipping terms (as the chiral condensate does) represent other order parameters of chiral symmetry.Concentrating on the iso-scalar part of the causal current-current correlator [3]here for the ω meson with the current j ω µ = ūγ µ u +dγ µ d /2 and nuclear matter states |Ω (the symbol T means time ordering, and u, d denote quark field operators), an operator product expansion and a Borel transformation (cf. [3,10] for arguments in favor of Borel sum rules) of the twice-subtracted dispersion relation result inwhere Π ω (0, n) = 9n/(4M N ) with the nucleon mass M N is a subtraction constant having the meaning of Landau damping or ω N forward scattering amplitude, and the coefficients c j contain condensates and Wilson coefficients; M is the Borel mass. The first coefficients c j have been spelled out in many papers (cf.[11] for our ...

The field of magnon spintronics is experiencing an increasing interest in the development of solutions for spin-wave-based data transport and processing technologies that are complementary or alternative to modern CMOS architectures. Nanometer-thin yttrium iron garnet (YIG) films have been the gold standard for insulator-based spintronics to date, but a potential process technology that can deliver perfect, homogeneous large-diameter films is still lacking. We report that liquid phase epitaxy (LPE) enables the deposition of nanometer-thin YIG films with low ferromagnetic resonance losses and consistently high magnetic quality down to a thickness of 20 nm. The obtained epitaxial films are characterized by an ideal stoichiometry and perfect film lattices, which show neither significant compositional strain nor geometric mosaicity, but sharp interfaces. Their magneto-static and dynamic behavior is similar to that of single crystalline bulk YIG. We found, that the Gilbert damping coefficient α is independent of the film thickness and close to 1 × 10 -4 , and that together with an inhomogeneous peak-to-peak linewidth broadening of ∆H 0|| = 0.4 G, these values are among the lowest ever reported for YIG films with a thickness smaller than 40 nm. These results suggest, that nanometer-thin LPE films can be used to fabricate nano-and micro-scaled circuits with the required quality for magnonic devices. The LPE technique is easily scalable to YIG sample diameters of several inches.