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We show that water-induced decomposition reduces magnon thermal conductivity in a spin-ladder polycrystal, while the absence of grain boundaries or a metal coating prevents degradation, ensuring stability for thermal management applications. 

Budget constraints are ubiquitous in online advertisement auctions. To manage these constraints and smooth out the expenditure across auctions, the bidders (or the platform on behalf of them) often employ pacing: each bidder is assigned a pacing multiplier between zero and one, and her bid on each item is multiplicatively scaled down by the pacing multiplier. This naturally gives rise to a game in which each bidder strategically selects a multiplier. The appropriate notion of equilibrium in this game is known as a pacing equilibrium. In this work, we show that the problem of finding an approximate pacing equilibrium is PPAD-complete for second-price auctions. This resolves an open question of Conitzer et al. [Conitzer V, Kroer C, Sodomka E, Stier-Moses NE (2022a) Multiplicative pacing equilibria in auction markets. Oper. Res. 70(2):963–989]. As a consequence of our hardness result, we show that the tâtonnement-style budget-management dynamics introduced by Borgs et al. [Borgs C, Chayes J, Immorlica N, Jain K, Etesami O, Mahdian M (2007) Dynamics of bid optimization in online advertisement auctions. Proc. 16th Internat. Conf. World Wide Web (ACM, New York), 531–540] are unlikely to converge efficiently for repeated second-price auctions. This disproves a conjecture by Borgs et al. [Borgs C, Chayes J, Immorlica N, Jain K, Etesami O, Mahdian M (2007) Dynamics of bid optimization in online advertisement auctions. Proc. 16th Internat. Conf. World Wide Web (ACM, New York), 531–540], under the assumption that the complexity class PPAD is not equal to P. Our hardness result also implies the existence of a refinement of supply-aware market equilibria which is hard to compute with simple linear utilities. Funding: This work was supported by National Science Foundation (CCF-1703925, IIS-1838154). 

Abstract Spin excitations, including magnons and spinons, can carry thermal energy and spin information. Studying spin‐mediated thermal transport is crucial for spin caloritronics, enabling efficient heat dissipation in microelectronics and advanced thermoelectric applications. However, designing quantum materials with controllable spin transport is challenging. Here, highly textured spin‐chain compound Ca₂CuO₃is synthesized using a solvent‐cast cold pressing technique, aligning 2D nanostructures with spin chains perpendicular to the pressing direction. The sample exhibits high thermal conductivity anisotropy and an excellent room‐temperature thermal conductivity of 12 ± 0.7 W m⁻¹K⁻¹, surpassing all polycrystalline quantum magnets. Such a high value is attributed to the significant spin‐mediated thermal conductivity of 10 ± 1 W m⁻¹K⁻¹, the highest reported among all polycrystalline quantum materials. Analysis through a 1D kinetic model suggests that near room‐temperature, spinon thermal transport is dominated by coupling with high‐frequency phonons, while extrinsic spinon‐defect scattering is negligible. Additionally, this method is used to prepare textured La₂CuO₄, exhibiting highly anisotropic magnon thermal transport and demonstrating its broad applicability. A distinct role of defect scattering in spin‐mediated thermal transport is observed in two spin systems. These findings open new avenues for designing quantum materials with controlled spin transport for thermal management and energy conversion.