Emergent spin-$1$ Haldane gap and ferroelectricity in a frustrated spin-$1/2$ ladder

Hiroshi Ueda, Shigeki Onoda, Yasuhiro Yamaguchi +19

We report experimental and theoretical evidence that Rb${}_2$Cu${}_2$Mo${}_3$O${}_{12}$ has a nonmagnetic tetramer ground state of a two-leg ladder comprising antiferromagnetically coupled…