SIGNATURES OF INCOHERENT TRANSPORT IN THE STRANGE-METAL REGIME OF HIGH-T_C CUPRATES

Jake Ayres, University of Bristol, Maarten Berben and Nigel Hussey, HFML Nijmegen.

Researchers from HFML-EMFL, UK, Netherlands, and Japan studied the high-field magnetotransport properties of overdoped high-T_c cuprates and found behavior that is strikingly different from that of ordinary metals. For the latter, the resistivity increases quadratically with temperature and magnetic field. In cuprates, however, a novel ‘strange-metal’ phase exists in which the resistivity depends linearly on both temperature and field. Curiously, this behavior is found to persist over a large range of parameters. Combined linear-in-temperature and linear-in field resistivity had only been observed previously at a singular quantum critical point where a second-order phase transition is suppressed to absolute zero. In the two cuprate families studied, however, this behavior was observed over an extended range of doping. Moreover, the strength of the magnetoresistance was found to be two orders of magnitude larger than expected from conventional orbital motion and insensitive to the level of disorder in the material as well as to the direction of the magnetic field relative to the electrical current. These features in the data, coupled with the temperature-field scaling properties, imply that the origin of this unusual magnetoresistance may not be the coherent orbital motion of conventional metallic charge carriers, but rather a non-orbital, incoherent motion from a different type of charge carrier whose energy is being dissipated at the maximal rate allowed by quantum mechanics. Taking into account earlier Hall-effect measurements, the team believes they have uncovered compelling evidence for two distinct charge-carrier types in cuprates – one coherent, the other incoherent.  The key question to address now is which type is responsible for high-temperature superconductivity? Were it to be the latter, then this would signal an entirely new paradigm for superconductivity, one in which the strange metal takes center stage.

Figure: Scaled derivatives of the in-plane MR at different fixed temperatures between 4.2 and 60 K for various Tl₂Ba₂CuO_6+δ (Tl2201) and La/Pb-doped Bi₂Sr₂CuO_6+δ (Bi2201) single crystals with T_c values as indicated. To emphasize the similarity of the MR response of all the measured samples, both axes have been normalized. In this way, all the data collapse onto the same form given by the derivative of the function y=√1+x² as indicated by dashed lines. Note that the sections of individual curves that reside within the vortex state are here plotted faintly, since only in the normal state can the quadrature MR be probed.

Incoherent transport across the strangemetal regime of overdoped cuprates, J. Ayres, M. Berben, M. Čulo, Y.-T. Hsu, E. van Heumen, Y. Huang, J. Zaanen, T. Kondo, T. Takeuchi, J. R. Cooper, C. Putzke, S. Friedemann, A. Carrington, and N. E. Hussey,

Nature 595, 661 (2021).

https://www.nature.com/articles/s41586-021-03622-z?proof=t#Fig1

Contact: jake.ayres@bristol.ac.uk  maarten.berben@gmail.com  nigel.hussey@ru.nl