Electronic liquid crystal physics of underdoped cuprates

Recent observations of broken symmetries have partly demystified the pseudogap phase. Here we review evidence for long-range intra–unit-cell (IUC) nematic order and its unexpectedly strong coupling to the phase of the fluctuating stripes in the pseudogap states of underdoped Bi2Sr2CaCu2O8+δ. In particular, we focus on the analysis techniques that reveal this evidence in scanning tunneling spectroscopy data, the definition of the extracted IUC nematic order parameter, and a phenomenological theory of the coupling between the IUC nematic order and the previously reported coexisting fluctuating stripes. We also present a microscopic mechanism of IUC nematic order driven by on-site and near-neighbor repulsions. Finally we discuss open questions in the context of these results.

► Long-range intra–unit-cell nematic and disordered stripe were revealed in the pseudo-gap states of underdoped BSCCO.
► The intra–unit-cell nematic order parameter is strongly coupled to the phase fluctuation of disordered stripe.
► A microscopic mechanism of intra–unit-cell nematic driven by on-site and near-neighbor repulsion is presented.