| The presence or absence of a quantum critical point and its location in the phase diagram of high temperature superconductors continues to divide the community. Crucially, clear manifestations of this critical behaviour in the transport properties have been particularly hard to pin down largely due to difficulties in accessing the limiting low-temperature region hidden deep inside the superconducting dome. In this talk, we will describe combined measurements of anisotropic magnetoresistance and electrical resistivity in persistent and pulsed high magnetic fields that reveal the presence of a critical doping concentration at which the charge dynamics undergo a profound change. Surprisingly, the form of the criticality is unlike anything seen in other quantum critical systems, establishing the cuprates as a new paradigm in the field of strongly correlated electron physics in which the critical point, and with it the development of the pseudogap, are defined by the onset of temperature-invariant but momentum-dependent incoherence. |
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