[show abstract][hide abstract] ABSTRACT: Utilizing a multilayered composite approach, we have designed and constructed a new class of artificial materials for thermal conduction. We show that an engineered material can be utilized to control the diffusive heat flow in ways inconceivable with naturally occurring materials. By shielding, concentrating, and inverting heat current, we experimentally demonstrate the unique potential and the utility of guiding heat flux. Thermodynamics is a well-established discipline in sci-ence, and the concept of heat has been known for a long time. That often makes us forget how difficult it really is to manipulate heat flow in real life. Compared to the field of electric conduction armed with nonlinear solid-sate de-vices, heat conduction management is still in its infancy. The ability to precisely control heat current has significant implications beyond scientific curiosity, and can poten-tially lead to the development of thermal analogues of electronic transistors, rectifiers, and diodes. Here we show that an artificial material can be utilized to guide the heat flow in ways inconceivable with naturally occur-ring materials. We demonstrate this concept by engineer-ing a new class of artificial material for thermal conduction and experimentally shielding, concentrating, and inverting the applied heat flux. The results constitute a vivid dem-onstration of extreme heat flux control with artificial ma-terials and provide a conceptual insight that heat current, like electric and photonic current, should be viewed as a medium that can be manipulated, controlled, and processed. The ability to manipulate the path of energy propagation is a trait that distinguishes artificial materials from ordinary materials. In a solid material supporting heat current, the properties induced from artificially arranged thermal con-ductivities can be counterintuitive. Although some theo-retical work including the prediction of a thermal cloak has been carried out [1–3], such thermal ''meta''-materials have, so far, not been investigated experimentally. We first discuss the shielding operation and then proceed to con-centrating and inverting heat flux. See Fig. 1(a). When a block of material is placed between a heat source and a sink, a uniform temperature gradient is established across the material. Heat current flows from left to right as indicated by the arrows. Figure 1(b) depicts the same block with a hollow cylindrical shield inserted at the center. Here we require the exterior region to exhibit the same temperature profile as Fig. 1(a) without the shield, while the interior region now needs to have no temperature gradient. To gain control over the path of energy transport via thermal conduction, one needs to engineer an artificial material with prescribed anisotropy in its thermal conduc-tivity. One of the most practical ways to introduce such anisotropy is to build a stacked composite from macro-scopic layers of isotropic materials. Consider, for example, a composite made of alternating sheets of materials A and B. In a perpendicular direction, the two alternating con-ductances add in series, while they add in parallel in a transverse direction. Thus, the overall thermal conductivity of the effective medium becomes anisotropic, and the heat flux density vector changes direction as it propagates through the material. Building on this effect, one can design and assemble an artificial composite material that forces the heat flux to follow a particular path of interest. A concentric layered structure consisting of alternating layers of materials A and B of different homogeneous isotropic thermal conductivities A and B is depicted in Fig. 2(a). For the host background material, we use a 5% agar-water block with thermal conductivity h $ 0:56 W=ðmKÞ . For the device to blend into the back-ground thermally and not perturb the external field profile, the thermal resistance of the host material should be close to the reduced average of those of the two
[show abstract][hide abstract] ABSTRACT: Utilizing a non-resonant graded material consisting of an array of artificially patterned superconducting and soft ferromagnetic elements, we construct a dc magnetic cloak. When an external dc magnetic field is applied, we find that the interior of the cloak is completely shielded while the exterior field remains unperturbed, as if the cloak and the cloaked region are just an empty space.
[show abstract][hide abstract] ABSTRACT: We report the observation of superfluid quantum interference in a compact, large-area matter-wave interferometer consisting of a multiple-turn interfering path in reciprocal geometry. Utilizing the Sagnac effect from Earth's rotation in conjunction with a phase shifter made of superfluid heat current, we demonstrate that such a scheme can be extended for sensitive rotation sensing as well as for general interferometry.
[show abstract][hide abstract] ABSTRACT: We report a new kind of experiment in which we take an array of nanoscale apertures that form a superfluid (4)He Josephson junction and apply quantum phase gradients directly along the array. We observe collective coherent behaviors from aperture elements, leading to quantum interference. Connections to superconducting and Bose-Einstein condensate Josephson junctions as well as phase coherence among the superfluid aperture array are discussed.
[show abstract][hide abstract] ABSTRACT: We report a direct observation of dynamical bifurcation between two plasma oscillation states of a superfluid Josephson junction. We excite the superfluid plasma resonance into a nonlinear regime by driving below the natural plasma frequency and observe a clear transition between two dynamical states. We also demonstrate bifurcation by changing the potential well with temperature variations.