Department of Physics, University of California, Berkeley
Materials Sciences Division, Lawrence Berkeley National Lab
Graphite is a convenient host for producing ordered systems where various physical properties can be tuned. By inserting foreign atoms or molecules called "intercalates" between the honeycomb 2D sheets of graphite, it is possible to form structurally ordered graphite intercalation compounds (GICs) with interesting properties such as superconductivity or low dimensional magnetism. In GICs, the dimensionality can be changed from 3D to 2D by changing the number of graphene sheets between the intercalate (i.e. changing the stage number n) or, equivalently, by varying the strength of interaction between intercalate layers. GICs are thus a tesing ground for studying 2D physics and dimensional crossover from 2D to 3D.
In donor GICs, electrons transferred from donor to graphite atoms occupy the anti-bonding p* band, while in acceptor GICs, the charge transfer from graphite to acceptor empties the top of the p bonding band. The charge transfer between graphite and the intercalate increases the number of electrons or holes around the Fermi energy EF and makes the GICs metallic. Interestingly, superconductivity exists in kC8, even though the ingredient elements (potassium and carbon) are not superconducting. Transition metal chlorides can also be intercalated into graphite to form magnetic GICs, where the effective interplanar exchange interaction can be tuned by the stage number n. The magnetic structures of GICs can provide important aspects of the physics of 2D magnetic systems.
We are interested in studying the dimensional crossover from 2D to 3D and the ARPES signature of weak 2D localization, as well as the mechanisms of superconductivity and magnetism in GICs. Also, we are interested in studying of the dimensional changes during intercalation processes which will used for applications ion transfer batteries.