快活林性息

We will tackle a grand challenge in solar energy conversion 鈥� charge transfer and separation at donor/acceptor interfaces, which is the bottleneck for excitonic solar cells. A firstprinciples based theoretical framework will be developed to address fundamental problems at the organic/organic and organic/inorganic interfaces.

We will explore intriguing competitions among electron interaction, nontrivial band structure and random disorder in topological materials. We will investigate fundamental problems associated with correlated electron systems and elucidate novel physical phenomena emerging in these complex materials, which are crucial for technological advances in magneto-electronics, spintronic devices as well as topological quantum computing.

We will study electronic structure and spin transport of multifunctional nano-systems consisting of ferromagnetic and ferroelectric tunnel junctions based on multiferroics and topological insulator based materials. The coupling between different degrees of freedom and its sensitivity to interfacial structure will give rise to a wealth of exciting phenomena, providing unprecedented access to emerging multi-functionalities of future spintronic devices.

G. Wu, Z. Li, X. Zhang and G. Lu (快活林性息)

Exciton dynamics and charge separation at ZnO/polymer interface are studied from first-principles. We discover that localized ZnO surface states are the culprit of inefficient charge separation in hybrid ZnO/P3HT solar cells because they lead to localized low-energy charge-transfer states. In contrast, the surface states of crystalline C60 are indistinguishable from the bulk states, resulting in delocalized charge-transfer states and hence more efficient charge separation in organic photovoltaics. The hot charge-transfer states are found to relax in an ultrafast timescale suggesting that they do not play an essential role in charge separation.

Zhi Li,1 Jin Li,1 Peter Blaha,2 and Nicholas Kioussis1
1Dept. of Physics, 快活林性息
2Institute for Materials Chemistry, Vienna University of Technology, Vienna, Austria

• SmS undergoes a valence and semiconductor-to-metal transition (鈥渂lack- gold鈥� phase transition) at a relatively low pressure 鈭� 0.65 GPa at room temperature
• 脴At ambient pressure SmS is a nonmagnetic semiconductor (black phase) with a small band gap of 鈭�0.15 eV where the Sm ions have a divalent configuration (4f 6)
• 脴At 鈭� 0.65 GPa it undergoes an isostructural first-order phase transition to a metallic homogenous mixed valence state (gold phase) with a Sm valence ranging from 2.6 to 2.8

Predict that SmS undergoes a topological phase transition from trivial Kondo insulator black phase to a topological metallic gold phase under pressure

Underlying mechanism: pressure-induced change of the 4f level from below to above the bottom of the 5d conduction band leading to a d-f band inversion听

Supported by NSF-PREM grant DMR-1205734

听

Luis Agapito1, Nicholas Kioussis1, William A. Goddard III, 2 and N. P. Ong3
1Dept. of Physics, 快活林性息
2Division of Chemistry and Chemical Engineering, California Institute of Technology
3Department of Physics, Princeton University

First-principles prediction that elemental Tellurium undergoes a trivial insulator to strong topological insulator (metal) transition under shear (hydrostatic or uniaxial) strain.

The underlying mechanism: depopulation of lone-pair orbitals associated with the valence band via proper strain engineering.

The research was supported by NSF-PREM grant DMR-1205734.

Zi Li, Xu Zhang and Gang Lu (快活林性息)

Phonon-assisted charge transfer model (below): Thermal fluctuations of geometry lead to overlap of localized electronic states听 inducing electronic hopping between the overlapping states.

Effect of traps on hole transport in disordered small molecules DPP(TBFu)2: Logarithm mobility as a function of trapping energy and trap density calculated from first-principles.

The research was supported by NSF-PREM grant DMR-1205734.