Can there be “Hidden Order” in transition metals?

Abstract

We examine the conditions required to produce a combined spin and orbital density wave state such as that which has been proposed to describe the “Hidden Order” phase of URu2Si2. By using an idealized tight‐binding model with only nearest‐neighbor hopping processes, we search for factors that could stabilize “Hidden Order” phases in transition metals. It is found that strong anisotropy or reduced dimensionality may stabilize “Hidden Order” over spin‐density wave phases. This suggests the possibility that the enigmatic pseudogap phases reported for the high‐temperature ironpnictide superconductors may also be described by the Hund's rule “Hidden Order” mechanism.

Signatures of broken spin-rotational invariance in the “Hidden Ordered” compound URu2Si2?

“…The simplest versions of the model which involves only one spin-degenerate conduction band, constitutes either the underscreened Anderson Impurity [91,92] or Lattice [93,94] Models. Therefore, we have proposed a theory of "Hidden Order" [95] based on the underscreened Anderson Lattice Model [96,97] which leads to a low-temperature phase that can be described as a spin-dependent orbital density wave. The transition is driven by the Hund's rule interaction and spontaneously breaks spin-rotational invariance.…”

A minimal model for “Hidden Order” in URu2Si2

“…We examine a bare bones version of the model which corresponds to the limit of zero hybridization [23] and the neglect of all Coulomb interactions except for the spin-flip terms of the Hund's rule interaction. In this limit, we find a Hidden Ordered state by using a variational method.…”

Photoemission Imaging of 3D Fermi Surface Pairing at the Hidden Order Transition in URu2Si2

“…This second-order phase transition at T 0 = 17.5 K is marked by a jump in specific heat and removal of significant fraction of total entropy [1,3], however, with no sign of static dipolar magnetic order except under pressure [5,6]. The appearance of a new 5f electronic phase with apparent lack of ordered magnetism has given birth to the mystery of the unknown, or 'hidden' order parameter, addressed so far by a few dozens of theories (e.g., [4,[7][8][9][10][11][12][13][14][15][16]), and has recently been proposed to occur in a wide range of materials [17].…”