The University of Tokyo · Engineering
Professor José Ordoñez-Miranda's research lab specializes in thermal transport phenomena at the nanoscale, with a focus on phase-change materials, thermal hysteresis, and the design of novel thermal devices inspired by electronic components. The lab investigates the fundamental mechanisms governing heat flow in complex systems, including nanocomposites, thin films, and quantum systems, using theoretical and computational approaches grounded in statistical mechanics and non-equilibrium thermodynamics. Key research directions include the development of thermal memristors, thermal diodes, and effective medium models for predicting thermal conductivity in heterogeneous materials.
Figures are computed from collected data and may differ slightly.
Based on Bruggeman's symmetric effective-medium formula and an explicit expression derived for the temperature evolution of the volume fractions of the metallic and isolating domains appearing during the heating and cooling of ${\mathrm{VO}}_{2}$, respectively, we develop a model to describe the hysteresis of its electrical and thermal conductivities as well as of its specific heat capacity. The model takes into account the average value and standard deviation of the transition temperatures of t
The surface phonon-polaritons contribution to the thermal conductivity of a nano thin film of silicon dioxide is investigated based on the Maxwell equations and the Boltzmann transport equation. It is shown that: (1) a small difference between the permittivities of the substrate and superstrate of the film can generate giant propagation lengths and therefore remarkably enhances its thermal conductivity with respect to values obtained for a freestanding one. (2) The propagation of surface phonon-
Based on the thermal hysteresis of a phase change material exchanging radiative heat with a phase invariable one, we propose a radiative thermal memristor characterized by a Lissajous curve between their exchanged heat flux and temperature difference periodically modulated in time. For a memristor with terminals of VO_{2} and a blackbody, it is shown that (i) the temperature variations of its memristance follow a closed loop determined by the thermal hysteresis width of VO_{2}, and (ii) the ther
The modified effective medium approximation model proposed by Minnich and Chen [Appl. Phys. Lett. 91, 073105 (2007)] for the thermal conductivity of nanocomposites is extended for spheroidal inclusions. It is shown that the dependence of the thermal conductivity of nanocomposites on the shape and size of particle inclusions can be described by: (1) the collision cross-section per unit volume of the particles and (2) the mean distance that the energy carriers (electrons or phonons) can travel ins
We demonstrate that two interacting spinlike systems characterized by different excitation frequencies and coupled to a thermal bath each, can be used as a quantum thermal diode capable of efficiently rectifying the heat current. This is done by deriving analytical expressions for both the heat current and rectification factor of the diode, based on the solution of a master equation for the density matrix. Higher rectification factors are obtained for lower heat currents, whose magnitude takes t
Manipulating the flow of heat, particularly in analogy to the flow of electrons (current), has become a major research theme. A $t\phantom{\rule{0}{0ex}}h\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}m\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}l$ $t\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}s\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}s\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}r$ made
The metal-nonmetal interface plays a critical role in modern electronic and energy conversion devices. For example, metal-nonmetal multilayered structures have recently been proposed as promising materials for solid-state thermionic devices, which could potentially achieve an efficiency that might not be feasible for metals or semiconductors alone. In this work, the effective thermal conductivity of a metal-nonmetal multilayered system (superlattices) is studied using the two-temperature model o
Hysteresis loops exhibited by the thermal properties of undoped and 0.8 at.% W-doped nanocrystalline powders of VO<sub>2</sub> synthesized by means of the solution combustion method and compacted in pellets, are experimentally measured by photothermal radiometry. It is shown that: (i) the W doping reduces both the hysteresis loops of VO<sub>2</sub> and its transition temperature up to 15 °C. (ii) The thermal diffusivity decreases (increases) until (after) the metallic domains become dominant in
The effective thermal conductivity of a layered system due to the propagation of surface phonon-polaritons is studied. We analytically demonstrate that the thermal conductivity of a set of nanolayers can be described as one of a single layer with an effective permittivity, which does not ordinarily appear in nature and depends on the permittivities and thicknesses of the individual components. For a two-layer system of SiO2 and BaF2 surrounded by air, it is shown that: (i) the propagation length
We analyze in detail the energy transport of surface phonon polaritons propagating in a chain of spheroidal polar nanoparticles with both longitudinal and transversal polarizations. Explicit and closed-form expressions for the dispersion relation and propagation length are derived and used to determine the values of the nanoparticle polarizability and the interparticle distance that maximize the polariton propagation length. The thermal conductance in the ballistic regime and the thermal conduct
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