Experiments on ladders reveal a complex interplay between a spin-gapped normal state and superconductivity

Abstract

In recent years, the study of ladder materials has developed into a well-established area of research within the general context of strongly correlated electrons. This effort has been triggered by an unusual cross-fertilization between theory and experiments. In this paper, the main experimental results obtained in the context of ladders are reviewed from the perspective of a theorist. Emphasis is given to the many similarities between the two-dimensional high-T c cuprates and the two-leg ladder compounds, including Sr 14−x Ca x Cu 24 O 41 ([14-24-41]) which has a superconducting phase at high pressure and a small hole density. Examples of these similarities include regimes of linear resistivity versus temperature in metallic ladders and a normal state with spin gap or pseudogap characteristics. It is remarked that the ladder [14-24-41] is the first superconducting Cu oxide material with a non-square-lattice layered arrangement, and certainly much can be learned from a careful analysis of this compound. A short summary of the main theoretical developments in this field is also included, as well as a brief description of the properties of non-Cu-oxide ladders. Suggestions by the author on possible experiments are described in the text. Overall, it is concluded that the enormous experimental effort carried out on ladders has already unveiled quite challenging and interesting physics that adds to the rich behaviour of electrons in transition metal-oxides, and in addition contributes to the understanding of the two-dimensional cuprates. However, considerable work still needs to be carried out to fully understand the interplay between charge and spin degrees of freedom in these materials.

Symmetry disquisition on theTiOXphase diagram(X=Br,Cl)Fausti1, Lummen2, Angelescu3 et al. 2007Phys. Rev. B274271View full textAdd to dashboardCite

“…Only short range interactions between nearest neighbor ions are taken into account. Considering the forces to be central forces, the number of parameters is reduced to two for each atomic interaction: the longitudinal and transversal forces, respectively, defined as L = d 2 V͑r i,j ͒ dr 2 and T = 1 r dV͑r i,j ͒ dr . A custom-made program was interfaced with UNISOFT to optimize the elastic constants.…”

Series expansion analysis of a frustrated four-spin tube

“…Two-leg ladders, such as Sr 14−x Ca x Cu 24 O 41 2 , have been under intense scrutiny mainly because of the potential interplay between their spin-gaped ground state and the occurrence of superconductivity 3,4 . N-leg ladders with N > 2 are of particular relevance, not only because they allow for a generalized test of Haldane's conjecture 5 , but also because new, tube-like lattice structures can be realized if periodic transverse boundary conditions apply, such as in [(CuCl 2 tachH) 3 Cl]Cl 2 6 and CsCrF 4 7 with N = 3, Cu 2 Cl 4 ·D 8 C 4 SO 2 8,9 with N = 4, and Na 2 V 3 O 7 10 with N = 9. For N = 3, magnetic frustration surfaces as an additional ingredient, already for tubes with only nearest neighbor exchange, leading to a rich variety of phenomena not present in two-leg ladders [11][12][13][14][15] .…”

Electronic structure of the spin-12quantum magnet TiOCl

“…1,2 This applies in particular to one-dimensional systems for which exactly solvable many-body models exist. 3 Meanwhile the narrowed view on the isolated subsystems, e.g.…”