Light-Induced Increase of the Transition Temperature in Superconductors

transition temperature
By irradiation of light, atoms are brought into superfluid order. (Photo: UHH / MIN / Mathey group)

Physicists from the University of Hamburg and from CUI have recently been able to show in a theoretical research that periodically shaking atoms of a cold quantum gas with the help of light can force a superfluid order that does not exist in the non-driven system. Now also the experimental confirmation took place. These findings clarify a controversial debate about experimental observations on the light-induced increase in transition temperature in electronic superconductors.

Superconductivity, the ability to conduct electricity without resistance, is a technically very useful feature of certain materials, which unfortunately requires extremely low temperatures below a characteristic critical temperature. In the superconducting state, the electrons form into pairs, which are subjected to a rigid order, which forces the pairs to move in exact step and thus without resistance. If the temperature is too high, this order is shaken by thermal fluctuations, so that a competitive state gains the upper hand, in which the pairs persist, but instead of moving in lockstep form a quasicrystalline structure, a so-called charge density wave. So how about

The idea: Shake and lockstep

At first glance, shaking and lockstep appear as opposites, and yet this is exactly the idea that has recently been tried on so-called high-temperature superconductors. The periodic shaking was realized by the irradiation of an intense light pulse, which resonantly excited a lattice vibration of the material. In fact, the cuprate superconductors used showed signs of an increased transition temperature. However, this finding was soon the subject of a controversial debate. Many scientists remained skeptical about the objection that shaking was supposed to cause additional disorder and heating rather than ordered lock-in of the electron pairs. A final clarification hardly seemed possible due to the extreme complexity of cuprate superconductors.

transition temperature
The atoms were positioned between two extremely reflective mirrors. (Photo: UHH / MIN / Hemmerich group)

In a joint research work, the theorists Dr. Jayson Cosme and Prof. Ludwig Mathey and the experimenters Christoph Georges and Prof. Andreas Hemmerich now show that periodic shaking can actually force an order of the same step. Instead of a complicated cuprate superconductor, the researchers considered a simpler model system, namely a Bose-Einstein condensate of atoms, which was positioned between two extremely reflective mirrors. This system, in addition to a supra-fluid phase, in which the atoms move in ordered stepwise motion, also has a competing state of density-wave character, and it has just the right degree of complexity, allowing a quantitative comparison between theory and experiment. The density wave-like state was indeed suppressed in the experiment by light-induced shaking, so that the supra-fluid state could be restored. The scientists first published their theoretical predictions in the prestigious Journal Physical Review Letters. In a second article approved for publication in Physical Review Letters, experimental confirmation has now been made. The insights gained here clarify the controversial debate on the observation of light-induced increase in the critical temperature in electronic superconductors. The scientists first published their theoretical predictions in the prestigious Journal Physical Review Letters. In a second article approved for publication in Physical Review Letters, experimental confirmation has now been made. The insights gained here clarify the controversial debate on the observation of light-induced increase in the critical temperature in electronic superconductors. The scientists first published their theoretical predictions in the prestigious Journal Physical Review Letters. In a second article approved for publication in Physical Review Letters, experimental confirmation has now been made. The insights gained here clarify the controversial debate on the observation of light-induced increase in the critical temperature in electronic superconductors.Text: UHH / MIN

Source : University of Hamburg