By synthesizing the superlattice of perovskite oxides, I’ve observed unambiguous evidence of the coherent transport of phonons at short-period superlattices of SrTiO3-CaTiO3 and BaTiO3-SrTiO3. Several theoretical studies predicted the existence of these phenomena, but the experimental evidence of their existence remained largely absent or inconclusive. Thus, superlattice structures offer an ideal candidate to search for this novel phenomenon. The critical range being between 1-3 nanometers, the size of the system needs to reduce to this length scale in order to observe the effect of the wave nature of phonons on heat transport.

The key element for enabling the coherent transport of phonon in these superlattice systems is the range of phonon wavelengths, which carry most of the heat in the material. coherent phonon transport, phenomenon that is extremely rare to observe in bulk form. The measured thermal conductivity of these artificial superlattices exhibited a unique phonon transport, i.e. In this dissertation, artificial superlattices of complex oxides were synthesized in a thin-film geometry to enable the observation of fundamentally new physical phenomena, compared to their bulk counterparts, in few selected areas of investigation.įirst, I will present the experimental results on heat transport across superlattice structures composed of insulating perovskite oxides. These artificial superlattices and heterostructures continue to be the most promising candidate for exploring new phenomena and enhancing physical properties in complex oxide material systems. In literature, one can find plenty of examples from different areas of research such as superconductivity, magnetism, ferroelectricity and thermoelectricity, where artificial superlattices led to the observation of fundamentally different behavior, compared to bulk superlattice constituents. Complex oxides, in particular, are known to exhibit a strong interaction between various degrees of freedom available such as spin, charge, orbital and lattice degree, and thus offer a suitable choice of material system. One choice of such a system could be a strongly correlated material where the presence of strong electronic correlations has been known to enable unique electronic and magnetic properties. Given the capability of artificial heterostructures to enable new physical phenomena, with an appropriate choice of material system, these heterostructures hold the potential to uncover hidden physical phenomena and exotic phases, which are otherwise not observed in bulk systems. On the technological front, artificial heterostructures of conventional semiconductors were found to revolutionize optoelectronic and high-speed electronic industry. Several fundamental observations such as two-dimensional electron gas, quantum confinement effect, quantum Hall effect and fractional quantum Hall effect, were first realized in artificial heterostructures of conventional semiconductors.

One distinguishable example is superlattices and quantum-well heterostructures of conventional semiconductors (III-V). It is historically proven that artificial heterostructures are of paramount importance for both fundamental research and technological application.

Example of non physical phenomena