Charge and spin ordered states are ubiquitous in the phase diagrams of high-Tc superconducting cuprates. A prototypical case is that of the so-called “stripes”. These consist of one-dimensional chains of doped holes separating regions of oppositely phased antiferromagnetism.
Recent experiments suggest that, while the individual Cu-O striped planes may be in a highly coherent state, in which superconductivity is spatially modulated, the stripes completely frustrate the interlayer tunnelling, thus inhibiting a 3D superconducting state.
In our group, using photo-excitation with femtosecond pulses in the mid infrared, we have discovered that stripe-ordered, non-superconducting La1.675Eu0.2Sr0.125CuO4 can be transiently switched into a state which exhibits the optical response of a 3D superconductor [1]. The emergence of coherent interlayer transport at temperatures as high as 20 K was demonstrated via time-domain THz spectroscopy, by detecting a Josephson Plasma Resonance in the transient optical reflectivity [1,2]. In addition, femtosecond resonant soft X-ray diffraction, performed under the same mid-infrared excitation at the Stanford Linac Coherent Light Source LCLS [3], allowed us to identify the optical melting of charge order as the driving mechanism for light-induced superconductivity in striped cuprates.
Figure 2: Side view of a layered cuprate like La1.675Eu0.2Sr0.125CuO4. By photo-exciting such non-superconducting striped compound with mid-infrared pulses, it can be transiently transformed into a superconductor within less than a picosecond.
More recently, photo-excitation at shorter wavelengths has turned out to be an alternative means to remove stripes and enhance superconductivity transiently. In La2-xBaxCuO4, we have discovered a response with induced Josephson coupling above Tc upon optical driving with near-infrared light pulses [4,5]. This was systematically investigated for different pump photon energies [6] and in presence of external dc magnetic fields as high as 7 Tesla [7], allowing us to gain key hints on the interplay between stripes and superconductivity out of equilibrium.
The most striking results of our research on high-Tc cuprates were obtained on the bi-layer compound YBa2Cu3O6+x, which has a maximum superconducting critical temperature at equilibrium, Tc, of about 90 K. Upon photo-stimulation with mid-infrared pulses, which triggered large-amplitude oscillations of the apical oxygen atomic positions, we induced a highly unconventional optical response, compatible with transiently enhanced inter-bilayer Josephson tunnelling [8,9,10]. Strikingly, this effect could be observed all the way up to room temperature, with light-induced superconducting properties emerging from a non-superconducting ground state throughout an extended region of the YBa2Cu3O6+x phase diagram [9,10].
While optical melting of charge order seemed not to play a fundamental role in the case of YBa2Cu3O6+x [11], femtosecond X-ray crystallography has revealed the emerge of a new, displaced crystal structure [12], which originates out of equilibrium as a result of a nonlinear coupling between different phonon modes [13]. This atomic rearrangement might be favouring superconductivity at higher temperature, although alternative scenarios which involve a direct modification of the electronic bands within the Cu-O planes shall also be considered to explain the observed dynamics.
Additional studies, that make also use of newly available pump devices [14], are being carried out, aiming at pinning down the mechanism behind optically-driven superconductivity in YBa2Cu3O6+x, with the perspective of optimising this phenomenon even further [15].
Related Methods & Experiments
- Generation and Shaping of mid-infrared light pulses
- Broadband Time-resolved terahertz spectroscopy
- Femtosecond X-Ray diffraction techniques
- Pump-probe spectroscopy under extreme conditions
Related Publications
[1]
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)
[2]
Two distinct kinetic regimes for the relaxation of light-induced superconductivity in La1.675Eu0.2Sr0.125CuO4
C. R. Hunt, D. Nicoletti, S. Kaiser, T. Takayama, H. Takagi, and A. Cavalleri
Physical Review B 91, 020505(R) (2015)
[3]
Melting of Charge Stripes in Vibrationally Driven La1.875Ba0.125CuO4: Assessing the Respective Roles of Electronic and Lattice Order in Frustrated Superconductors
M. Först, R. I. Tobey, H. Bromberger, S. B. Wilkins, V. Khanna, A. D. Caviglia, Y.-D. Chuang, W. S. Lee, W. F. Schlotter, J. J. Turner, M. P. Minitti, O. Krupin, Z. J. Xu, J. S. Wen, G. D. Gu, S. S. Dhesi, A. Cavalleri, and J. P. Hill
Physical Review Letters, 112, 157002 (2014)
[4]
Optically-induced superconductivity in striped La2-xBaxCuO4 by polarization-selective excitation in the near infrared
D. Nicoletti , E. Casandruc, Y. Laplace, V. Khanna, C. R. Hunt, S. Kaiser, S. S. Dhesi, G. D. Gu, J. P. Hill, A. Cavalleri
Physical Review B, 90, 100503(R), (2014)
[5]
Restoring interlayer Josephson coupling in La1.885Ba0.115CuO4 by charge transfer melting of stripe order
V. Khanna, R. Mankowsky, M. Petrich, H. Bromberger, S. A. Cavill, E. Möhr-Vorobeva, D. Nicoletti, Y. Laplace, G. D. Gu, J. P. Hill, M. Först, A. Cavalleri and S. S. Dhesi
Physical Review B 93, 224522 (2016)
[6]
Wavelength-dependent optical enhancement of superconducting interlayer coupling in La1.885Ba0.115CuO4
E. Casandruc, D. Nicoletti, S. Rajasekaran, Y. Laplace, V. Khanna, G. D. Gu, J. P. Hill, and A. Cavalleri
Physical Review B, 91, 17 (2015)
[7]
Magnetic-Field Tuning of Light-Induced Superconductivity in Striped La2−xBaxCuO4
D. Nicoletti, D. Fu, O. Mehio, S. Moore, A. S. Disa, G. D. Gu, and A. Cavalleri
Physical Review Letters,121, 267003 (2018)
[8]
Optically enhanced coherent transport in YBa2Cu3O6.5 by ultrafast redistribution of interlayer coupling
W. Hu, S. Kaiser, D. Nicoletti, C. R. Hunt, I. Gierz, M. C. Hoffmann, M. Le Tacon, T. Loew, B. Keimer & A. Cavalleri
Nature Materials, 13, 705–711 (2014)
⇒ News & Views by N. Peter Armitage
⇒ Press release CFEL
⇒ Press release MPSD
[9]
Optically induced coherent transport far above Tc in underdoped YBa2Cu3O6+δ
S. Kaiser, C. R. Hunt, D. Nicoletti, W. Hu, I. Gierz, H. Y. Liu, M. Le Tacon, T. Loew, D. Haug, B. Keimer, and A. Cavalleri
Phys. Rev. B 89, 184516 (2014)
[10]
Dynamical decoherence of the light induced inter layer coupling in YBa2Cu3O6+δ
C. R. Hunt, D. Nicoletti, S. Kaiser, D. Pröpper, T. Loew, J. Porras, B. Keimer, A. Cavalleri
Physical Review B, 94, 224303 (2016)
[11]
Femtosecond x rays link melting of charge-density wave correlations and light-enhanced coherent transport in YBa2Cu3O6.6
M. Först, A. Frano, S. Kaiser, R. Mankowsky, C. R. Hunt, J. J. Turner, G. L. Dakovski, M. P. Minitti, J. Robinson, T. Loew, M. Le Tacon, B. Keimer, J. P. Hill, A. Cavalleri, and S. S. Dhesi
Physical Review B, 90, 90, 184514 (2014)
[12]
Nonlinear lattice dynamics as a basis for enhanced superconductivity in YBa2Cu3O6.5
R. Mankowsky, A. Subedi, M. Först, S.O. Mariager, M. Chollet, H. Lemke, J. Robinson, J. Glownia, M. Minitti, A. Frano, M. Fechner, N. A. Spaldin, T. Loew, B. Keimer, A. Georges, A. Cavalleri
Nature 516 , 71–73 (2014)
⇒ MPG Press release
⇒ SLAC Press release
[13]
Coherent modulation of the YBa2Cu3O6+x atomic structure by displacive stimulated ionic Raman scattering
R. Mankowsky, M. Först, T. Loew, J. Porras, B. Keimer, and A. Cavalleri
Physical Review B 91, 094308 (2015)
[14]
Generation of narrowband, high-intensity, carrier-envelope phase stable pulses tunable between 4 and 18 THz
B. Liu, H. Bromberger, A. Cartella, T. Gebert, M. Först, A. Cavalleri
Optics Letters, 42, 1, 129-131 (2017) [Editors‘ pick]
[15]
Pump Frequency Resonances for Light-Induced Incipient Superconductivity in YBa2Cu3O6.5
B. Liu, M. Först, M. Fechner, D. Nicoletti, J. Porras, B. Keimer, A. Cavalleri
Physical Review X 10, 011053 (2020)