Pseudogap state near a quantum critical point

By K. Efetov, H. Meier, C. P'epin. Nature Physics, 2012

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In the standard picture of a quantum phase transition, a single quantum critical point separates the phases at zero temperature. Here we show that the two-dimensional case is considerably more complex. Instead of the single point separating the antiferromagnet from the normal metal, we have discovered a broad region between these two phases where the magnetic order is destroyed but certain areas of the Fermi surface are closed by a large gap. This gap reflects the formation of a quantum state characterized by a superposition of d-wave superconductivity and a quadrupole density wave, which builds a chequerboard pattern with a period incommensurate with that of the original spin-density wave. At moderate temperatures both orders coexist over comparatively large distances but thermal fluctuations destroy the long-range order. Below a critical temperature the fluctuations are less essential and superconductivity becomes stable. This phenomenon may help to explain the origin of the mysterious pseudogap state and of the high-temperature transition into the superconducting state in the cuprates. In particular, we show that spectroscopic probes on the oxygen and copper sites reveal chequerboard order. Near a quantum critical point there are strong critical fluctuations that destroy standard metallic behaviour. Calculations now show that a pseudogap state can arise in the vicinity of an antiferromagnetic quantum critical point, which might be relevant to the cuprate superconductors.

Subfields: Atomic and Molecular Physics, and Optics, Condensed Matter Physics

View Paper: https://www.semanticscholar.org/paper/202fc1bef567111aed083c6e34456ee2eda711bc