The Resonating Valence Bond State in La ₂ CuO ₄ and Superconductivity

Abstract

The oxide superconductors, particularly those recently discovered that are based on La(2)CuO(4), have a set of peculiarities that suggest a common, unique mechanism: they tend in every case to occur near a metal-insulator transition into an odd-electron insulator with peculiar magnetic properties. This insulating phase is proposed to be the long-sought "resonating-valence-bond" state or "quantum spin liquid" hypothesized in 1973. This insulating magnetic phase is favored by low spin, low dimensionality, and magnetic frustration. The preexisting magnetic singlet pairs of the insulating state become charged superconducting pairs when the insulator is doped sufficiently strongly. The mechanism for superconductivity is hence predominantly electronic and magnetic, although weak phonon interactions may favor the state. Many unusual properties are predicted, especially of the insulating state.

A two-dimensional spin liquid in quantum kagome ice

“…One is a confined phase, corresponding to a conventional spin-ordered state; the other is a deconfined Z 2 QSL phase 20,21,33 . From these simple arguments it is conceivable that these two phases exist in the phase diagram of equation (1). In the next section, we set J ± ¼ 0 and explore this possibility for all parameter regimes J ±± /J z and h/J z , using nonperturbative, unbiased QMC simulations.…”

Non-Fermi-liquid d-wave metal phase of strongly interacting electrons

“…Pioneering early theoretical work on the cuprates relied on two main premises, 3,[13][14][15][16][17] from which we will be guided but not constrained in our pursuit and understanding of a particular non-Fermi liquid metal: (1) that the microscopics can be described by the square lattice Hubbard model with on-site Coulomb repulsion, which at strong coupling reduces in its simplest form to the t-J model; and (2) that the physics of the system can be faithfully represented by the "slave-boson" technique, wherein the physical electron operator is written as a product of a slave boson ("chargon"), which carries the electronic charge, and a spin-1/2 fermionic "spinon," 18 which carries the spin, both strongly coupled to an emergent gauge field. However, within the slave-boson formulation, it has been difficult to access non-Fermi liquid physics at low temperatures because this requires the chargons to be in an uncondensed, yet conducting, quantum phase, 19 i.e., some sort of the elusive "Bose metal."…”

Topologically protected quantum bits using Josephson junction arrays

“…Tuning the chemical potential µ from ∞ to 0, diagonal dimer flips proliferate and we can study the evolution of the dimer model as we go from a square to a triangular lattice [21]. The above type of quantum dimer models has been actively discussed in the context of short-range resonatingvalence-bond (RVB) models [22] for high temperature superconductivity [14]. In order to gain more insight into its physical properties we exploit a mapping to an 'electrodynamic' analogue [20,21,23]: We decorate the bipartite square lattice (sublattices A and B) with static charges ρ ✷ = ±1, placing all positive charges on the sublattice A, see Fig.…”