22 research outputs found
Nonlinear phononics: A new ultrafast route to lattice control
To date, two types of coupling between electromagnetic radiation and a
crystal lattice have been identified experimentally. One is direct, for
infrared (IR)-active vibrations that carry an electric dipole. The second is
indirect, it occurs through intermediate excitation of the electronic system
via electron-phonon coupling, as in stimulated Raman scattering. Nearly 40
years ago, proposals were made of a third path, referred to as ionic Raman
scattering (IRS). It was posited that excitation of an IR-active phonon could
serve as the intermediate state for a Raman scattering process relying on
lattice anharmonicity as opposed to electron phonon interaction. In this paper,
we report an experimental demonstration of ionic Raman scattering and show that
this mechanism is relevant to optical control in solids. The key insight is
that a rectified phonon field can exert a directional force onto the crystal,
inducing an abrupt displacement of the atoms from the equilibrium positions
that could not be achieved through excitation of an IR-active vibration alone,
for which the force is oscillatory. IRS opens up a new direction for the
coherent control of solids in their electronic ground state, different from
approaches that rely on electronic excitations.Comment: 10 manuscript pages, 3 figure
Free Baptist Church, Greenville, RI
https://digitalcommons.risd.edu/picturecollection_ripostcards/1095/thumbnail.jp
The Narrows Waterman\u27s Reservoir, Greenville, RI
https://digitalcommons.risd.edu/picturecollection_ripostcards/1092/thumbnail.jp
Light-induced superconductivity in a stripe-ordered cuprate.
One of the most intriguing features of some high-temperature cuprate superconductors is the interplay between one-dimensional "striped" spin order and charge order, and superconductivity. We used mid-infrared femtosecond pulses to transform one such stripe-ordered compound, nonsuperconducting La(1.675)Eu(0.2)Sr(0.125)CuO(4), into a transient three-dimensional superconductor. The emergence of coherent interlayer transport was evidenced by the prompt appearance of a Josephson plasma resonance in the c-axis optical properties. An upper limit for the time scale needed to form the superconducting phase is estimated to be 1 to 2 picoseconds, which is significantly faster than expected. This places stringent new constraints on our understanding of stripe order and its relation to superconductivity
Optical properties of a vibrationally modulated solid state Mott insulator
Optical pulses at THz and mid-infrared frequencies tuned to specific vibrational resonances modulate the lattice along chosen normal mode coordinates. In this way, solids can be switched between competing electronic phases and new states are created. Here, we use vibrational modulation to make electronic interactions (Hubbard-U) in Mott-insulator time dependent. Mid-infrared optical pulses excite localized molecular vibrations in ET-F2TCNQ, a prototypical one-dimensional Mott-insulator. A broadband ultrafast probe interrogates the resulting optical spectrum between THz and visible frequencies. A red-shifted charge-transfer resonance is observed, consistent with a time-averaged reduction of the electronic correlation strength U. Secondly, a sideband manifold inside of the Mott-gap appears, resulting from a periodically modulated U. The response is compared to computations based on a quantum-modulated dynamic Hubbard model. Heuristic fitting suggests asymmetric holon-doublon coupling to the molecules and that electron double-occupancies strongly squeeze the vibrational mode