Lukas Hellbrück1,Ji Dai1,Michele Puppin1,Alberto Crepaldi1,Edoardo Martino1,Yong Liu1,Arnaud Magrez1,László Forró1,Marco Grioni1,Siham Benhabib1,Fabrizio Carbone1
École Polytechnique Fédérale de Lausanne1
Lukas Hellbrück1,Ji Dai1,Michele Puppin1,Alberto Crepaldi1,Edoardo Martino1,Yong Liu1,Arnaud Magrez1,László Forró1,Marco Grioni1,Siham Benhabib1,Fabrizio Carbone1
École Polytechnique Fédérale de Lausanne1
Cuprates as a class of high T<sub>c</sub> superconductors host multiple unconventional phases that require further studies to fully understand. Studying the time dependent response of these materials can enhance our understanding of excitations, light-matter interaction, electron-phonon coupling and the electronic response in different phases. Here we focus on the relationship between the pseudogap and superconducting phases. To study this, we employ time and angle resolved photoemission spectroscopy (trARPES). We directly probe the Fermi surface and electron dispersion, giving us access to the spectral function at different momenta and the dynamics of quasi particles. Relating this information about the quasi particles to the pseudogap and superconducting phase respectively can help us understand the underlying mechanism of superconductivity in these compounds.<br/>The pseudogap phase is characterized by a low density of states (DOS) at the Fermi level, a loss of states in the Fermi surface compared to the superconducting phase and the loss of one hole contributing to the charge transport. Doping dependent studies on the bi-layer high T<sub>c</sub> superconductor Bi2212 reveal a change in the topology of its Fermi surface [1,2,3]. At a hole doping of 22% the topology changes from a hole- to electron-like Fermi surface, which is usually called a Lifshitz transition. We find that for the optimally doped Bi2212 (16% hole doping), we are able to induce this Lifshiftz transition by irradiating the sample with high fluence femtosecond laser excitation. The induced transition persists for multiple picoseconds and is of reversible nature.<br/>Exploiting this effect could allow for a controlled manipulation of the phase diagram through the use of laser radiation.<br/><br/>[1] A. Kaminski, et al., <i>Phys. Rev. B</i> <b>73</b>, 174511 (2006)<br/>[2] S. Benhabib, et al., <i>PRL</i> <b>114</b>, 147001 (2015)<br/>[3] N. Doiron-Leyraud, et al., <i>Nat Commun</i> <b>8, </b>2044 (2017)