5 research outputs found
Probing optically silent superfluid stripes in cuprates
Unconventional superconductivity in the cuprates emerges from, or coexists
with, other types of electronic order. However, these orders are sometimes
invisible because of their symmetry. For example, the possible existence of
superfluid charge stripes in the normal state of single layer cuprates cannot
be validated with infrared optics, because interlayer tunneling fluctuations
vanish on average. Similarly, it is not easy to establish if charge orders are
responsible for dynamical decoupling of the superconducting layers over broad
ranges of doping and temperatures. Here, we show that TeraHertz pulses can
excite nonlinear tunneling currents between linearly de-coupled charge-ordered
planes. A giant TeraHertz third harmonic signal is observed in
La1.885Ba0.115CuO4 far above Tc=13 K and up to the charge ordering temperature
TCO = 55 K. We model these results by considering large order-parameter-phase
oscillations in a pair density wave condensate, and show how nonlinear mixing
of optically silent tunneling modes can drive large dipole-carrying
super-current oscillations. Our results provide compelling experimental support
for the presence of hidden superfluid order in the normal state of cuprates.
These experiments also underscore the power of nonlinear TeraHertz optics as a
sensitive probe of frustrated excitations in quantum solids.Comment: 9 pages main text, 5 figures, 12 page supplementar
A dynamical stability limit for the charge density wave in K0.3MoO3
We study the response of the one-dimensional charge density wave in K0.3MoO3
to different types of excitation with femtosecond optical pulses. We compare
the response to direct excitation of the lattice at mid-infrared frequencies
with that to the injection of quasi-particles across the low-energy charge
density wave gap and to charge transfer excitations in the near infrared. For
all three cases, we observe a fluence threshold above which the amplitude-mode
oscillation frequency is softened and the mode becomes increasingly damped. We
show that all the data can be collapsed onto a universal curve in which the
melting of the charge density wave occurs abruptly at a critical lattice
excursion. These data highlight the existence of a universal stability limit
for a charge density wave, reminiscent of the empirical Lindemann criterion for
the stability of a crystal lattice