Widely tunable terahertz laser enhances photo induced superconductivity in K3C60

Researchers at the Max Planck Institute for Material Structure and Dynamics (MPSD) in Hamburg, Germany, have long been exploring the effect of using custom laser drivers to manipulate the properties of quantum materials to deviate from equilibrium states.

One of the most eye-catching demonstrations of these physics is unconventional superconductors, where enhanced electron coherence and super transport characteristics have been recorded in the resulting non equilibrium states. However, mainly due to the complexity of the experiment, these phenomena have not been systematically studied or optimized. Therefore, the application of technology is still far from reality.

In a recent experiment, the same group of researchers discovered a more effective method of using lasers to create previously observed metastable, superconducting like states in K 3C 60. The research results of the Cavalieri group are published in the journal Nature Physics.

Researchers have shown that when the laser is tuned to a specific low-frequency resonance, much lower intensity light pulses can produce the same effect at higher temperatures. The laser technology developed by the research institute is the key to this work. By adjusting the light source to 10 THz (a frequency lower than previously possible), the team successfully reproduced a long-lived superconducting state in fullerene based materials, while reducing the pulse intensity by 100 times. This light induced state can be directly observed to last for 100 picoseconds at room temperature, but its lifespan is expected to be at least 0.5 nanoseconds (nanoseconds are billionths of a second, picoseconds are trillions of a second).

Edward Rowe, a doctoral student and lead author of the Cavalieri group, said that their findings provide new clues to the potential microscopic mechanism of photo induced superconductivity: "Identification of resonance frequencies will enable theorists to understand which excitations are actually important, as there is currently no widely accepted theoretical explanation for this effect in K3C60

Rowe envisions that a light source with a higher repetition rate at a frequency of 10 THz can help maintain metastable states for a longer time: "If we can transmit each new pulse before the sample returns to its non superconducting equilibrium state, then it is possible to maintain a quasi superconducting state continuously.

Andrea Cavalleri, Director of MPSD, said: "These experiments demonstrate well how appropriate technological advancements can make many so far unrealistic phenomena feasible." He believes that two years of effort in exploring these effects will converge into future technologies. It is equally evident that a key bottleneck that needs to be addressed is the type and availability of laser sources, which should go hand in hand with these studies to promote the development of this field.

The study was conducted at the MPSD Free Electron Laser Science Center (CFEL) in Hamburg. It is supported by DFG (German Research Foundation) through the Excellence Cluster CUI: Advanced Material Imaging. The K 3 C 60 sample was prepared at the University of Parma in Italy.

Source: Laser Network