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Light control of superconductivity:
Inducing superconductivity with light

One of the most intriguing features of some high-temperature cuprate superconductors is the interplay between one-dimensional, “striped”, spin- and charge-order and superconductivity. This fits in the quest to understand competing order in doped Mott Insulator and to understand how high temperature superconductivity emerges in two dimensions.

In this study, we have used mid-infrared femtosecond pulses to manipulate the lattice directly, to transform non-superconducting La1.675Eu0.2Sr0.125CuO4 into a transient three-dimensional superconductor. The emergence of coherent interlayer transport was evidenced by the c-axis optical properties, which were measured with THz radiation ad revealed the emergence of a Josephson tunnelling resonance. The timescale needed to form the superconducting phase was estimated to be 1-2 ps, significantly faster than expected.

This places stringent new constraints on our understanding of unconventional superconductivity in the cuprates and its relationship to charge order. To understand this process we will be performing experiments at the Stanford Linac Coherent Light Source LCLS, where we will interrogate the electronic and magnetic order with soft x-ray scattering. The key question to be addressed relates to the “friend or foe” dichotomy between stripes and superconductivity. By clocking the relative time for superconductivity to emerge and that for stripe order to disappear, we wish to establish if the two phenomena can coexist or if they are mutually exclusive.

 

Structure of a LaEuSrCuO4 crystal (positions of La, Eu, Sr are not distinguishable).
CuO4 builds connected tilted octahedral structures. Their base, the CuO4 squares  are used as a simplified representation of a crystal plane in the image below.


Side view of a layered copper-oxide insulator, exhibiting one-dimensional “stripes” of aligned spins and trapped charges within a buckled lattice. By irradiating one such striped compound with light it has transformed from an insulator to a superconductor within one millionth of a millionth of a second, freeing electrons from their traps and making it possible for them to tunnel in pairs between second neighbouring planes (the same stripe direction).


Related publication:

Light induced Superconductivity in a Stripe-ordered Cuprate

D. Fausti, R.I. Tobey, N. Dean, S. Kaiser, A. Dienst, M.C. Hoffmann, S. Pyon, T. Takayama, H. Takagi and A. Cavalleri

Science, 331, 6014 189-191 (2011)
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