Superconducting Graphene Beckons
The International Technology Roadmap for Semiconductors believes that the post-silicon era will begin in about 2028 and Graphene is considered to be the revolutionary, replacement material.
The electron mobility of Graphene at room temperature is already more than 10 times that of silicon (15.000 cm2/Vs compared to 1,400 cm2/Vs). Researchers at the University of British Columbia (UBC) have now achieved infinity—superconductivity by doping Graphene with lithium and then cooling it to 5.9 degrees Kelvin.
UBC professor Andrea Damascelli, however, has hopes to push doped graphene into higher temperatures of criticality by augmenting the methods of his predecessors.
“Increasing the ultimate value of Tc achievable on monolayer graphene is at present our key goal,” Damascelli said. “We are exploring specific combinations of new substrates and dopants in order to further enhance and stabilize superconductivity, in much the same way that enhanced transition temperatures have been achieved in other two-dimensional quantum materials, such as single-layer FeSe.”
He has already begun experimenting with dopants in single atomic layers (monolayers) of graphene and has been measuring whether or not the adsorbed atoms diffuse over the surface and get stuck within the graphene lattice.
“The key advantages of one dopant versus the other are the easiness in donating the right amount of electrons to monolayer graphene, the stability of the adatoms on the graphene surface (some diffuse or intercalate more easily than others, which may be detrimental to stabilizing superconductivity), as well as the modification they induce in the interaction between electrons and atomic vibration of the graphene layer which in the end directly controls the strength of superconductivity and the value of the critical temperature. Finding the ideal dopants — the most stable and the ones leading to the highest Tc — is crucial for possible future applications.”
“Our monolayer graphene was epitaxially grown [under an argon atmosphere on hydrogen-etched silicon carbide substrates] by our collaborators at the Max Planck Institute in Stuttgart, in researcher Ulrich Starke’s group. These samples were reconditioned [annealed at 500 degrees Celsius] immediately before the angle resolved photo emission spectroscopy (ARPES) measurements in our chamber at UBC in the Quantum Materials Lab, to obtain atomically-clean pristine graphene,” Damascelli said. “Lithium adatoms were then deposited in ultra-high-vacuum conditions from a commercial alkali metal source, with the graphene samples held at a temperature of 8 degrees Kelvin. The low temperature turned out to be key in being able to decorate graphene with a well ordered Li-superstructure, which in turn is essential for observing superconductivity.”
Along with associates worldwide, the Damascelli group at UBC will tune the parameters of his doped graphene material in the hope of achieving superconductivity at room temperature and normal atmospheric pressures.