Seminars

Dr. Mikael Kuisma seeks quantitative and qualitative understanding of nanoscale quantum dynamics, such as collective excitations in functionalized noble metal nanoparticles and hot carrier generation with potential applications from microscopy to photovoltaics. He is also a developer of GPAW electronic structure program, which he further utilized to run large scale parallel models of electron dynamics in nanosystems.

Experimental research at the nanoscale continues to challenge our ability to predict the behavior of quantum systems. Advances with lithographically patterned solid-state electronic devices have enabled multiple platforms for the simulation of quantum matter. In particular, semiconductor quantum dots and superconducting qubits provide tools for studying the wealth of physics induced by nonlinearities at the single electron and single microwave-photon level, respectively, and have been separately pursued as enabling technologies for qubits. In recent years, hybrid devices that combine such historically distinct lines of research have received greater attention, whether to enable novel sensing or measurement applications, or to couple small systems of qubits together at long range (e.g. quantum transduction). I will showcase the rich behaviors and phases of quantum matter that coupled quantum dots can exhibit, including a surprising transport mechanism called cotunneling drag, signatures of Kondo physics with emergent symmetry , and non-Fermi liquid states. I will also discuss my work towards fabricating superconducting qubits on silicon-on-insulator substrates for hybrid device applications. The integration of quantum dots and superconducting resonators promises to yield new probes for studying quantum matter, and superconducting qubits are coming of age in their own right for the implementation of many-body spin models.

When atomically thin two-dimensional (2D) materials are layered, they often form incommensurable noncrystalline structures that exhibit long-period moiré patterns when examined by scanning probes. In this presentation we will use graphene and hexagonal boron nitride as examples of gapless and gapped Dirac materials to illustrate how the moire superlattices due to interlayer coupling can alter the materials' intrinsic electronic properties. The derivation of the effective models for these van der Waals materials heterojunctions for arbitrary twist angles can benefit from input obtained from ab initio calculations carried out for commensurate short period crystalline structures. We will discuss how the moire pattern modified electronic structures give rise to a variety of experimentally measurable features including enhanced density of states through van Hove singularities, and flat bands, or to their suppression due to formation of band gaps.

Advances in atomic force microscopy (AFM) have made it possible to achieve unprecedented images of covalent bonds, in some cases even to resolve the bond order in polycyclic aromatics.   However, fundamental questions remain about interpreting the images and modeling the AFM tip.  For example, the bright spots in non-contact AFM images can have a close correspondence to the atomic structure of a given specimen, but there can be contrast changes with tip height that cannot be interpreted directly by atomic positions.  While the nature of the tip can be crucial in...