Scientific Calendar Event

Starts 3 Jun 2024 11:00
Ends 3 Jun 2024 12:00
Central European Time
Leonardo Building, Luigi Stasi Seminar Room (and via Zoom)

Carlo Di Castro
 (Accademia dei Lincei; Department of Physics, University of Roma “Sapienza”)
The recent high-resolution RIXS (resonant inelastic X-ray scattering) experiments have given a new impulse to the physics of cuprates [1]. In particular, I will show that the newly discovered dynamical charge density fluctuations with short correlation length [2], precursors of the three-dimensional long range charge density waves, mediate quasi-isotropic scattering between the fermionic quasiparticles and account for the long-standing problem of the strange metal behaviour of the cuprates, with linear-in-T resistivity [3]. Within a time-dependent Landau-Ginzburg approach with parameters derived by fitting the RIXS experiments, the fluctuation bubbles whose sizes are of the order of the correlation length, relax with a characteristic frequency given by the ratio between the inverse correlation length squared and the Landau damping parameter. Around optimal doping and above the superconductive critical temperature, sets up the lowest temperature limit for obtaining the strange metal behaviour [3]. However, the linearity in T of the resistivity and a divergent specific heath [4], are observed down to the lowest measured temperatures (the so called Planckian behavior) by experiments in the presence of high pulsed magnetic field to suppress superconductivity. To extend our approach to low temperature we must then reduce possibly to zero as T goes to zero and reach a quantum criticality. Usually, the diverging correlation length is invoked to this purpose, but in our case the experiments suggest that the correlation length stays finite.
We are then proposing a new paradigm [5] and [6] in contrast with the standard approach. Both the linearity in T of the resistivity and a diverging specific heat are accounted for by a logarithmic increase of the damping parameter only. When the damping increases by lowering the temperature, the charge density fluctuations relax at longer and longer times giving rise to an anomalous criticality for a glass of small islands of charge density fluctuations correlated in time not in space.
[1] R. Arpaia & G. Ghiringhelli. Charge order at high temperature in cuprate superconductors.
 J. Phys. Soc. Jpn. 90, 111005 (2021). 
 [2] R. Arpaia, S. Caprara, R. Fumagalli, G. De Vecchi, Y.Y. Peng, E. Andersson, D. Betto, G. M. De Luca, N. B. Brookes, F. Lombardi, M. Salluzzo, L. Braicovich, C. Di Castro, M. Grilli, G. Ghiringhelli, Dynamical charge density fluctuations pervading the phase diagram of a copper-based high-Tc superconductor, Science 365, 906 (2019)
[3] G. Seibold, R. Arpaia, Y. Y. Peng, R. Fumagalli, L. Braicovich, C. Di Castro, M. Grilli, G. Ghiringhelli, and S. Caprara, Strange metal behaviour from charge density fluctuations in cuprates, Commun. Phys. 4, 7 (2021).
[4] Michon, et al, Thermodynamic signatures of quantum criticality in cuprate superconductors, Nature 567, 218222 (2019)
[5] S. Caprara, C. Di Castro, G. Mirarchi, G. Seibold and M. Grilli
Dissipation-driven strange metal behavior, Commun. Phys. 5, 10 (2022). 
[6] R. Arpaia et al. Signature of quantum criticality in cuprates by charge density fluctuations. Nat Commun 14, 7198 (2023).

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