Wanzheng Hu reported on some
recent developments in the Hamburg group’s continuing work on the light control
of correlated electron systems.
Wanzheng started by reviewing the
characteristic energy scales of solids and pointed out that conventionally
performed optical pump-probe experiments typically use pump energies that far
exceed many of the most interesting energy scales in solids. The Hamburg group has taken
advantage of recent technical developments to perform pump-probe experiments
where the pumping is done at energies that are resonant to important excitation
scales.
She briefly reviewed recent work
from this group on light enhanced superconductivity on LaEuSrCuO4 and YBCO and
the most recent work on K3C60.
In all these cases the claim is that by exciting the system one can
stabilize a transient superconducting state at temperatures well in excess of
the equilibrium Tc.
She then went on to discuss in
detail her work on light induced transient superconductivity up to room
temperature in YBCO. In this
work they resonantly pump the system at a frequency near an apical oxygen
phonon and observe a characteristic 1/omega dependence in the imaginary part of
the conductivity. They believe
that when they excite the system there are transient distortions which serve to
redistribute Jospheson coupling energies from between the YBCO bilayers to
between the unit cell couplings.
In this process they estimate that approximately 20% of the volume of
the sample undergoes this redistribution.
Time resolved XRD has been done and is consistent with a lattice
rearrangement in the transient state that is consistent with the inferred
changes in the Josephson energies.
Wanzheng then shifted topics to
discuss their groups work on whether or not one can excite a IR optical mode
and drive a metal-insulator transition in NdNiO3 films on LaAlO3. In this work they pump a
substrate phonon and trigger a metal-insulator transition. They observe that the THz
conductivity changes by 7 orders of magnitude. They have seen roughly similar physics in SmNiO3 films
on LaAlO3.
Blogged by Peter Armitage
No comments:
Post a Comment