Partnership for Reseach and Education in Materials

  • Image of nanoparticles
  • Image of nanoparticles.
  • Image of nanoparticles.
  • Image of nanoparticles.
  • Image of nanoparticles.

PREM Research

This PREM strives to solve fundamental problems in emergent materials that have vital scientific and technological importance as well as economical and societal impacts. A multidisciplinary team with coordinated and complementary skills in theory, computation and experiment is assembled into three interdisciplinary groups (IRGs):

IRG1: Interfacial Charge Transfer and Separation in Excitonic Photovoltaics
We will tackle a grand challenge in solar energy conversion – 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.

IRG2: Quantum Phenomena in Topological Materials
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.

IRG 3: Spintronics in Multifunctional Devices
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.

The news and photos from selected events, workshops and research.

Charge Separation and Exciton Dynamics at ZnO/Polymer Interface*
G. Wu, Z. Li, X. Zhang and G. Lu (California State University Northridge)

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.


Topological phase transition in the SmS Kondo insulator under pressure
Zhi Li,1 Jin Li,1 Peter Blaha,2 and Nicholas Kioussis1
1Dept. of Physics, California State University Northridge
2Institute for Materials Chemistry, Vienna University of Technology, Vienna, Austria

  • SmS undergoes a valence and semiconductor-to-metal transition (“black- gold” phase transition) at a relatively low pressure ∼ 0.65 GPa at room temperature
  • ØAt ambient pressure SmS is a nonmagnetic semiconductor (black phase) with a small band gap of ∼0.15 eV where the Sm ions have a divalent configuration (4f 6)
  • ØAt ∼ 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 

Supported by NSF-PREM grant DMR-1205734


Novel Family of Chiral-Based Topological Insulators: Elemental Tellurium under Strain*
Luis Agapito1, Nicholas Kioussis1, William A. Goddard III, 2 and N. P. Ong3
1Dept. of Physics, California State University Northridge
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.


Prediction of Carrier Mobility in Disordered Semiconductors for Organic Photovoltaics*
Zi Li, Xu Zhang and Gang Lu (California State University Northridge)

Phonon-assisted charge transfer model (below): Thermal fluctuations of geometry lead to overlap of localized electronic states  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.