Mission

Emergent Behavior in Low-Dimensional Systems

One of the most critical questions in condensed matter physics concerns the mechanisms that govern emergent physical phenomena in correlated systems. In emergent phenomena the correlated behavior of many components leads to an unexpected collective outcome. Colossal electro- and magneto- resistance, high Tc superconductivity and metal-insulator transitions are some of the fascinating emergent behaviors caused by the delicate interplay between spin, charge, orbital and lattice interactions. The motivation for the experiments that we conduct is based on a critical need to gain fundamental insight into emergent phenomena in materials at low dimensions. The overarching goal of this work is to understand and control such emergent phenomena.

Currently, it is unclear how the many types of interactions within these materials balance to form the seeding points for electronic phase domain nucleation. Exploring the balance in these interactions in both complex oxide materials and atomic scale surface systems, we are working to selectively tune the underlying energetics through doping, interfacial magnetic pinning and strain in order to disentangle the specific contributions originating in spin, charge, orbital and lattice interactions.

Phase transition and separation are prime examples of the complex behavior of emergent phenomena. In order to fundamentally understand this behavior, two critical questions need to be resolved. What properties are due to intrinsic energy scales and static driving forces in the phase transitions? What characteristics are governed by dynamical fluctuations in time and space? To address these issues, we are following a two-pronged approach. Firstly, in wires etched from materials that exhibit electronic phase separation, time-resolved electronic transport measurements can be employed to address system dynamics while separately tuning the phase transition energetics. Secondly, atomic scale surface charge-density wave systems can be self-assembled. Their energetics controlled using subsurface doping and strain engineering while the dynamic fluctuations are addressed using time-resolved tunneling current and photoemission, as well as atom scattering experiments.

Each type of correlation in complex materials carries with it a separate length scale to be explored. By systematically confining complex materials across a wide range of length scales, it is possible to address each separate correlation length. The resultant properties of these materials will thus depend on the degree of confinement. This method opens complex materials to better fundamental scrutiny while introducing us to never before seen functionalities.

Science is now entering a new age based on the control of matter and energy at the electronic, atomic and molecular levels. We can now build materials atom by atom, opening new horizons for understanding and creating materials that do not occur in the natural world. Since advanced low-dimensional systems lie at the heart of technological innovation, we primarily focus on systems with reduced dimensionality, often under nanoscale confinement. In this spirit of the Grand Challenges identified by DOE BES, this allows for the observation of complex behavior in low-dimensional materials systems at the electronic and atomic levels and the fine-tuning of their structures to optimize their properties.