Gapless spin liquids on the three dimensional hyper-kagome lattice of Na$_4$Ir$_3$O$_8$

TL;DR

This paper proposes a gapless quantum spin liquid with spinon Fermi surfaces as the ground state for Na$_4$Ir$_3$O$_8$, supported by theoretical methods and consistent with experimental indications of gapless excitations.

Contribution

It introduces a novel candidate spin liquid state on the hyper-kagome lattice using a combination of theoretical techniques, including exact diagonalization and variational wavefunctions.

Findings

Proposes a spinon Fermi surface spin liquid as the ground state.

Provides a mean field theory for specific heat behavior.

Discusses potential low-temperature instabilities of the spinon Fermi surfaces.

Abstract

Recent experiments indicate that Na$_4$Ir$_3$O$_8$, a material in which s=1/2 iridium local moments form a three dimensional network of corner-sharing triangles, may have a quantum spin liquid ground state with gapless spin excitations. Using a combination of exact diagonalization, symmetry analysis of fermionic mean field ground states and Gutzwiller projected variational wavefunction studies, we propose a quantum spin liquid with spinon Fermi surfaces as a favorable candidate for the ground state of the Heisenberg model on the hyper-kagome lattice of Na$_4$Ir$_3$O$_8$. We present a renormalized mean field theory of the specific heat of this spin liquid and also discuss possible low temperature instabilities of the spinon Fermi surfaces.