Unlike ordinary metals, superconductors have the unique capability of transporting electrical currents without any loss. Nowadays, their technological application is hindered by their low operating temperature, which in the best case can reach -70 degrees Celsius. Researchers of the group of Prof. A. Cavalleri at the Max Planck Institute of the Structure and Dynamics of Matter (MPSD) in Hamburg have routinely used intense laser pulses to stimulate different classes of superconducting materials. Under specific conditions, they have detected evidences of superconductivity at unprecedented high temperatures, although this state persisted very shortly, just for a small fraction of a second.
An important example is that of K3C60, an organic molecular solidformed by weakly-interacting C60 “buckyball” molecules (60 carbon atoms bond in the shape of a football),which is superconducting at equilibrium below a critical temperature of -250 degrees Celsius. In 2016, Mitrano and coworkers at the MPSD discovered that tailored laserpulses, tuned to induce vibrations of the C60 molecules,can induce a short-lived, highly conducting state with properties identical to those of a superconductor, up to a temperature of at least -170 degrees Celsius, far higher than the equilibrium critical temperature (Mitrano et al., Nature, 530, 461–464 (2016)).
In their most recent investigation, A. Cantaluppi, M. Buzzi and colleagues at MPSD in Hamburg went a decisive step further by monitoring the evolution of the light-induced state in K3C60 once external pressure was applied by a diamond anvil cell (Figure 1). At equilibrium, when pressure is applied, the C60 molecules in the potassium-doped fulleride are held closer to each other. This weakens the equilibrium superconducting state and significantly reduces the critical temperature. The steady state optical response of K3C60 at different pressures and temperatures was determined via Fourier-transform infrared spectroscopy, by exploiting the high brightness of the synchrotron radiation available at the infrared beamline SISSI at Elettra.
Image: Light-induced superconductivity in K3C60 was investigated at high pressure in a Diamond Anvil Cell.
Credit: Jörg Harms / MPSD