Evidence for Dimer Crystal Melting in the Frustrated Spin-Ladder BiCu2PO6

Abstract

In the spin ladder compound BiCu${}_2$PO${}_6$ there exists a decisive dynamics of spin excitations that we classify and characterize using inelastic light scattering. We observe low-energy singlets and a broad triplon continuum extending from 36 cm${}^{-1}$ to 700 cm${}^{-1}$ in ($aa$), ($bb$), and ($cc$) light scattering polarizations. Though isolated spin ladder physics can roughly account for the observed excitations at high energies, frustration and interladder interactions need to be considered to fully describe the spectral distribution and scattering selection rules at low and intermediate energies. More significantly, an interladder singlet bound mode at 24 cm${}^{-1}$, lying below the continuum, shows its largest scattering intensity in interladder ($ab$) polarization. In contrast, two intraladder bound states at 62 cm${}^{-1}$ and 108 cm${}^{-1}$ with energies comparable to the continuum are observed with light polarization along the leg ($bb$) and the rung ($cc$). We attribute the rich spectrum of singlet bound modes to a melting of a dimer crystal. Our study provides evidence for a Z${}_2$ quantum phase transition from a dimer to a resonating valence bond state driven by singlet fluctuations.

14 pages, 4 figures, Accepted for publication in PRL

References in corpus (9)

• Controlling Luttinger liquid physics in spin ladders under a magnetic field
• Direct Observation of Magnon Fractionalization in the Quantum Spin Ladder
• Field-induced Tomonaga-Luttinger liquid phase of a two-leg spin-1/2 ladder with strong leg interactions
• Spectral and thermodynamic properties of a strong-leg quantum spin ladder
• Bridging frustrated-spin-chain and spin-ladder physics: quasi-one-dimensional magnetism of BiCu2PO6
• Wilson ratio of a Tomonaga-Luttinger liquid in a spin-1/2 Heisenberg ladder
• Quantum-critical spin dynamics in quasi-one-dimensional antiferromagnets
• Spin-gap behaviour in the 2-leg spin-ladder BiCu2PO6
• Direct observation of impurity-induced magnetism in an S = 1/2 antiferromagnetic Heisenberg 2-leg spin ladder

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• Tellurium-bridged two-leg spin ladder in Ba${}_2$CuTeO${}_6$
• Quantum criticality in the coupled two-leg spin ladder Ba2CuTeO6
• Theory of triplon dynamics in the quantum magnet BiCu${}_2$PO${}_6$
• Magnetic responses of randomly depleted spin ladders
• Thermally populated versus field-induced triplon bound states in the Shastry-Sutherland lattice SrCu${}_2$(BO${}_3$)${}_2$
• Raman study of spin excitations in the tunable quantum spin ladder Cu(Qnx)(Cl${}_{1-x}$Br${}_x$)${}_2$
• Two Coupled Chains are Simpler than One: Field-induced Chirality in a Frustrated Quantum Spin Ladder
• Honeycomb Heisenberg Spin Ladder: Unusual Ground State and Thermodynamic Properties
• Low-energy spin excitations in field-induced phases of the spin-ladder antiferromagnet BiCu${}_2$PO${}_6$