Speaker
Cassandra Hunt
(University of Illinois at Urbana-Champaign;Max Planck Department for Structural Dynamics)
Description
C. R. Hunt (1,2), D. Nicoletti (1), S. Kaiser (1), W. Hu (1), I. Gierz (1), H. Liu (1),
M. Le Tacon (3), T. Loew (3), D. Haug (3), B. Keimer (3), A. Cavalleri (1,4)
(1) Max Planck Department for Structural Dynamics, University of Hamburg, Center for Free-Electron Laser Science, Hamburg, Germany
(2) Department of Physics and the Frederick Seitz Material Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois
(3) Max Planck Institute for Solid State Research, Stuttgart, Germany
(4) Department of Physics, Oxford University, Clarendon Laboratory, Oxford, United Kingdom
Using femtosecond mid-infrared pulses, we demonstrate that a photoinduced non-equilibrium superconducting state can be generated in underdoped YBa2Cu3Ox above Tc. Pumping nearly resonant to the Cu-O phonon mode at 15.8 micron along the c-axis (perpendicular to the Cu-O layers) establishes phase coherence throughout the pseudogap region of the phase diagram. The transient response at three doping levels (x = 6.5, 6.6, 7) was fully characterized using THz time-domain spectroscopy at temperatures ranging from below Tc to room temperature.
We measure the non-equilibrium superconducting state in two different ways: First, probing in-plane (along the a-axis) reveals a London-like inverse frequency dependence in the imaginary part of the conductivity which has a lifetime in the 20 ps range. Second, probing perpendicular to the Cu-O planes (along the c-axis) shows evidence of the so-called Josephson plasma resonance, which arises in the superconducting state of cuprates due to a tunneling current of Cooper pairs between the layers.
These results offer a new perspective on condensate formation in high temperature superconductors. The photoinduced non-equilibrium state will be discussed in the context of pre-formed pairs in the pseudogap phase.
Primary author
Cassandra Hunt
(University of Illinois at Urbana-Champaign;Max Planck Department for Structural Dynamics)
