The ability to control electromagnetic fields, heat currents, electric currents, and other physical phenomena by coordinate transformation methods has resulted in novel functionalities, such as cloaking, field rotations, and concentration effects. Transformation optics, as the underlying mathematical tool, has proven to be a versatile approach to achieve such unusual outcomes relying on materials with highly anisotropic and inhomogeneous properties. Most applications and designs thus far have been limited to functionalities within a single physical domain. Here we present transformation optics applied to thermoelectric phenomena, where thermal and electric flows are coupled via the Seebeck coefficient. Using laminates, we describe a thermoelectric cloak capable of hiding objects from thermoelectric flow. Our calculations show that such a cloak does not depend on the particular boundary conditions and can also operate in different single domain regimes. These proof-of-principle results constitute a significant step forward towards finding unexplored ways to control and manipulate coupled transport.

The thermoelectric properties of PEDOT:PSS/Bi0.5Sb1.5Te3 polymer/inorganic bulk composites with different Bi0.5Sb1.5Te3 content were investigated. The composites were prepared at various concentrations of Bi0.5Sb1.5Te3 by a solution-phase process before grinding to fine powders in liquid N2 for hot pressing into bulk polymer composite materials. The measured transport properties are well described within a theoretical model for effective media involving a tunneling mechanism induced by thermal voltage fluctuations. Our results present a strategy for the preparation of bulk polymer composites and demonstrate an avenue for optimization of the thermoelectric properties of PEDOT:PSS/Bi0.5Sb1.5Te3 bulk composites.

Low temperature resistivity measurements on dense polycrystalline quaternary chalcogenides Ag 2þx Zn 1-x SnSe 4 , with x ¼ 0, 0.1, and 0.3, indicate polaronic type transport which we analyze employing a two-component Holstein model based on itinerant and localized polaron contributions. Electronic structure property calculations via density functional theory simulations on Ag 2 ZnSnSe 4 for both energetically similar kesterite and stannite structure types were also performed in order to compare our results to those of the compositionally similar but well known Cu 2 ZnSnSe 4. This theoretical comparison is crucial in understanding the bonding that results in polaronic type transport for Ag 2 ZnSnSe 4 , as well as the structural and electronic properties of both crystal structure types. In addition to possessing this unique electronic transport, the thermal conductivity of Ag 2 ZnSnSe 4 is low and decreases with increasing silver content. This work reveals unique structure-property relationships in materials that continue to be of interest for thermoelectric and photovoltaic applications.

Transformation optics (TO) is a powerful technique for manipulating diffusive transport, such as heat and electricity. While most studies have focused on individual heat and electrical flows, in many situations thermoelectric effects captured via the Seebeck coefficient may need to be considered. Here we apply a unified description of TO to thermoelectricity within the framework of thermodynamics and demonstrate that thermoelectric flow can be cloaked, diffused, rotated, or concentrated. Metamaterial composites using bilayer components with specified transport properties are presented as a means of realizing these effects in practice. The proposed thermoelectric cloak, diffuser, rotator, and concentrator are independent of the particular boundary conditions and can also operate in decoupled electric or heat modes.

The equations of motion (EOM) for the position and gauge invariant crystal momentum are considered for multiband wave packets of Bloch electrons. For a localized packet in a subset of bands well-separated from the rest of the band structure of the crystal, one can construct an effective electromagnetic Hamiltonian with respect to the center of the packet. We show that the EOM can be obtained via a projected operator procedure, which is derived from the adiabatic approximation within perturbation theory. These relations explicitly contain information from each band captured in the expansion coefficients and energy band structure of the Bloch states as well as non-Abelian features originating from interband Berry phase properties. This general and transparent Hamiltonian-based approach is applied to a wave packet spread over a single band, a set of degenerate bands, and two linear crossing bands. The generalized EOM hold promise for novel effects in transport currents and Hall effect phenomena.