Program Highlights

Wisconsin MRSEC researchers have developed a new way to see how molecules fit together with an electron microscope. They used the method to see how molecules rearrange when an organic semiconductor is heated. A modest change in temperature creates significantly improved molecular alignment. The improved alignment is reflected in both larger aligned regions and straighter lines of molecules inside each region.

The discovery of superconductivity in twisted graphene systems has generated tremendous interest, where low-energy flat bands with strong correlations play a key role. Flat bands may also be induced by moiré patterning in the transition metal dichalcogenides (TMDs), however experimental observation of superconductivity has remained absent. This raises the question as to whether superconductivity is a universal feature in flat-band, two-dimensional systems or there is some unique graphene-specific feature that makes superconductivity favorable.

Despite being a primary experimental probe of spin-charge coupled dynamics and transport, there have been virtually no calculations of THz radiation from such systems since the inception of this field in 1996. The MRSEC team at the University of Delaware this longstanding problem by introducing two new complementary frameworks, which combine time-dependent density functional theory (TDDFT) or time-dependent nonequilibrium Green’s functions (TDNEGF) with Jefimenko solutions of the Maxwell equations.

This study develops new design approaches for specifying the mutual interactions between many interacting subunit species such that they self-assemble into a user-specified two-dimensional tiling with high yield. By enumerating and assembling a wide variety of tilings with increasing unit-cell size and complexity, the authors identify economical design rules for targeting tilings with the largest unit-cell sizes using the minimum number of components.