Condensed Matter Physics Seminar

Is the 'Hidden Electronic Order' in the Cuprates neither Hidden nor Ordered?

Seamus Davis
Cornell University
Tuesday, November 1, 2005
Higgins 235, 3pm

Does a ‘hidden’ ordered electronic state exist in the underdoped ‘pseudogap’ regime of the cuprate phase diagram? This question has been the focus of intensive research worldwide. But after more than a decade of searches, no long range ordered state has been detected there.

Our spectroscopic imaging STM studies of Ca_2-xNa_xCuO₂Cl₂ in that regime did reveal a 4a₀X4a₀ ‘checkerboard’ pattern of density-of-state modulations¹ which persisted into the low doped superconducting region. But the actual charge density modulation in the ‘checkerboard’ pattern is negligible.

So, to examine the doped-hole density in Ca_2-xNa_xCuO₂Cl₂ directly, we have recently developed new imaging techniques. We find atomic-scale variations in hole-density which have no long range order but, instead, look like a ‘hole glass’ with short range 4a₀X4a₀ correlations. Embedded in this ‘hole glass’ are more ordered nano-regions of dimensions ~4a₀X16a₀. It seems plausible that the ‘checkerboard’ density-of-state modulations are due to scattering of quasiparticles by the Coulomb potential of this 4a₀X4a₀ correlated ‘hole glass’.

I will discuss the relationship of these observations to results from other probes and argue that the electronic state in lightly-doped cuprates has not been hidden, merely overlooked. I will also discuss the likelihood that this type of ‘hole glass’ is, in fact, the native state of lightly doped cuprates (when dopant disorder is present).

¹Hanaguri et al., Nature 430, 1001 (2004)