Dynamic control of heat flow using a spin-chain ladder cuprate film and an ionic liquid

Abstract

Dynamic control of heat flow for applications in thermal management has attracted much interest in fields such as electronics and thermal engineering. Spin-chain ladder cuprates are promising materials to realize dynamic control of heat flow, since their magnon thermal conductivity is sensitive to the hole density in the spin ladders, which can be dynamically controlled by an external field. Here, we demonstrate the electric control of heat flow using a polycrystalline cuprate film and an ionic liquid. The results showed that a voltage application to the interface causes imperfectly recoverable decreases in both the thermal conductance of the film and the peak due to magnons in the Raman spectra. This result may be attributed to an increase in the hole density in the spin ladders. This report highlights that magnon thermal conduction has potential for the development of advanced thermal management applications. Recently, dynamic control of heat flow, such as via thermal conductivity control using field-effect changes in material properties 1-4 and the spin Seebeck effect 5,6 , has attracted much interest and has been demonstrated. These control methods have great potential for advanced thermal management, including active heat dissipation, storage, and switching, as they provide stability in highly integrated electronic devices and enable effective reuse of waste heat; moreover, these methods allow temporal-spatial and precise control of temperature in devices and materials whose performance may decrease due to temperature perturbation 3. Spin-chain ladder cuprates such as La 5 Ca 9 Cu 24 O 41 could be promising materials to achieve dynamic control of heat flow, since they possess unique thermal conduction due to magnons 7-10 (for the structural property details, see the reviews by Hess 7 and Vuletić et al. 11). Briefly, La 5 Ca 9 Cu 24 O 41 , which possesses the highest magnon thermal conductivity at room temperature of these types of cuprates, consists of CuO 2 , La/Ca, and Cu 2 O 3 layers stacked towards the b-axis (Fig. 1a); among them, the remarkable structure is the Cu 2 O 3 layer composed of corner-and edge-sharing CuO 4 squares (Fig. 1a), in which the S = 1/2 spins of Cu 2+ form spin ladders 11. In the ladders, magnons, corresponding to excitations of the singlet state of the paired electron spins to the triplet state, act as heat carriers similar to phonons and conduction electrons along the ladders, i.e., towards the c-axis in Fig. 1a, yielding high anisotropic thermal conductivity 7. Notably, the magnon thermal conductivity is known to be sensitive to the hole density in the spin ladders 7. For example, Sr 14 Cu 24 O 41 and La 5 Ca 9 Cu 24 O 41 have the same spin ladder structure (Fig. 1a), but their magnon thermal conductivity at room temperature, with values of ~ 10 and ~ 90 W/(m K) 7 , respectively, differ by nearly an order of magnitude. This difference is attributable to the difference in the hole density in the spin ladders; that is, while La 5 Ca 9 Cu 24 O 41 has no holes in the spin ladders, Sr...

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