Electronic structure of cuprate superconductors close to their ground state.

• Applicants: Dr. Sergey Borisenko; Professor Dr. Bernd Büchner
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 281518034

• Final Report Year: 2020

Final Report Abstract

We have studied the electronic structure of the main representatives of the cuprate family of high-temperature superconductors as well as of other related superconductors at very low temperatures. We have obtained many new and surprising results which put strong constraints on existing theories of superconductivity. Topology of the Fermi surface in BSCCO seems to define the pseudogap phase in a way that after some critical doping level the antibonding sheet of the former becomes gapless. This is confirmed by the Raman experiments on the same samples. The symmetry and structure of the order parameter, long time considered to be purely of d-wave character, may turn out to deviate from this paradigm. Our ultra-high resolution measurements near the „nodal“ points in BSCCO show that a small superconducting gap of the order of 1-2 meV is present in a finite range of k-values, thus implying the absence of the real nodes in the gap function. Nodeless behavior is also confirmed in iron-based superconductors in the whole 3D k-space and comparison implies a close relationship between the underlying mechanisms in both classes of materials. Influence of nematicity on the electronic structure has been carefully studied in ironbased superconductors. Surprisingly, we found the evidence for the diagonal nematic order also in Hg-based cuprates, which is in agreement with other recent report based on thermodynamic measurements. At the same time, the role of nematic fluctuations in the mechanism of high-temperature superconductivity itself is most likely a secondary one. As for the relationship between the superconductivity and charge-density waves, we argue that it is particular fermiology of the material which is responsible for each phenomenon thus explaining their persistent proximity as phases. ARPES experiments carried out during the project led to the invention of a new type of electron spectrometer which allows the fastest high-resolution mapping of the Fermi surface, in particular of the high-temperature superconducting cuprates. First measurements of the Fermi surface of BSCCO demonstrate the potential of this novel approach.

Publications

• (2020) Turning charge-density waves into Cooper pairs. npj Quantum Mater. (npj Quantum Materials) 5 (1) 22
  Chikina, Alla; Fedorov, Alexander; Bhoi, Dilipkumar; Voroshnin, Vladimir; Haubold, Erik; Kushnirenko, Yevhen; Kim, Kee Hoon; Borisenko, Sergey
  
• Stripe order of La1.64Eu0.2Sr0.16CuO4 in magnetic fields studied by resonant soft x-ray scattering. Phys. Rev. B 94, 165157 (2016)
  M. Zwiebler, E. Schierle, E. Weschke, B. Büchner, A. Revcolevschi, Patrick Ribeiro, J. Geck, and J. Fink
  
• Anomalous temperature evolution of the electronic structure of FeSe. Phys. Rev. B 96, 100504(R) (2017)
  Y. S. Kushnirenko, A. A. Kordyuk, A. V. Fedorov, E. Haubold, T. Wolf, B. Büchner, and S. V. Borisenk
  
• Low-energy spin dynamics and critical hole concentrations in La2−xSrxCuO4 (0.07≤x≤0.2) revealed by 139La and 63Cu nuclear magnetic resonance. Phys. Rev. B 96, 094519 (2017)
  S.-H. Baek, A. Erb, and B. Büchner
  
• Mass Enhancements and Band Shifts in Strongly Hole-Overdoped Fe Based Pnictide Superconductors: KFe2As2 and CsFe2As2. Journal of Superconductivity and Novel Magnetism volume 31, 777 (2018)
  S.-L. Drechsler, H. Rosner, V. Grinenko, S. Aswartham, I. Morozov, M. Liu, A. Boltalin, K. Kihou, C. H. Lee, T. Kim, D. Evtushinsky, J. M. Tomczak, S. Johnston, and S. V. Borisenko
  
• Raman and ARPES combined study on the connection between the existence of the pseudogap and the topology of the Fermi surface in Bi2Sr2CaCu2O8+δ. Phys. Rev. B 97, 174521 (2018)
  B. Loret, Y. Gallais, M. Cazayous, R. D. Zhong, J. Schneeloch, G. D. Gu, A. Fedorov, T. K. Kim, S. V. Borisenko, and A. Sacuto
  
• Superconductivity-induced nematicity
  Y. S. Kushnirenko, D. V. Evtushinsky, T. K. Kim, I.V. Morozov, L. Harnagea, S. Wurmehl, S. Aswartham, A.V. Chubukov, and S. V. Borisenko
  
• Three-dimensional superconducting gap in FeSe from angle-resolved photoemission spectroscopy. Phys. Rev. B 97, 180501(R) (2018)
  Y. S. Kushnirenko, A. V. Fedorov, E. Haubold, S. Thirupathaiah, T. Wolf, S. Aswartham, I. Morozov, T. K. Kim, B. Büchner, and S. V. Borisenko
  
• Energy scale of nematic ordering in the parent iron-based superconductor BaFe2As2. Phys. Rev. B 100, 024517 (2019)
  Alexander Fedorov, Alexander Yaresko, Erik Haubold, Yevhen Kushnirenko, Timur Kim, Bernd Büchner, Saicharan Aswartham, Sabine Wurmehl, and Sergey Borisenko