Elementary excitation in the spin-stripe phase in quantum chains

Matej Pregelj,Matjaž Gomilšek,Jonathan S White,Denis Arčon,David Rivas Góngora,Oksana Zaharko,Helmuth Berger,Hubertus Luetkens,Andrej Zorko,Martin Klanjšek,Tomislav Ivek,Fiona Coomer

doi:10.1038/s41535-019-0160-5

Abstract

Elementary excitations in condensed matter capture the complex many-body dynamics of interacting basic entities in a simple quasiparticle picture. In magnetic systems the most established quasiparticles are magnons, collective excitations that reside in ordered spin structures, and spinons, their fractional counterparts that emerge in disordered, yet correlated spin states. Here we report on the discovery of elementary excitation inherent to spin-stripe order that represents a bound state of two phason quasiparticles, resulting in a wiggling-like motion of the magnetic moments. We observe these excitations, which we dub “wigglons”, in the frustrated zigzag spin-1/2 chain compound β-TeVO4, where they give rise to unusual low-frequency spin dynamics in the spin-stripe phase. This result provides insights into the stripe physics of strongly-correlated electron systems.

Highlights

The concept of elementary excitations provides an elegant description of dynamical processes in condensed matter.[1]
We explore the spin dynamics in these phases by employing the local-probe muon-spin-relaxation technique, which is extremely sensitive to internal magnetic fields and can distinguish between fluctuating and static magnetism in a broad frequency range.[26]
We find dielectric dynamics, which peaks at ~0.4 MHz and is most pronounced in the multiferroic VC phase

Summary

Introduction

The concept of elementary excitations provides an elegant description of dynamical processes in condensed matter.[1]. Its use is widespread and represents the theoretical foundation for our understanding of vibrational motions of atoms in crystals as phonons,[1] the excitations of the valence electrons in metals as plasmons,[2] the bound states of an electron and an electron hole in semiconductors as excitons,[3] etc. In magnetic systems, this approach inspired the spinon picture of fractional excitations in spin liquids,[4] the phason description of the modulation-phase oscillations in amplitude modulated structures,[5] and the magnon picture of collective spin excitations in ordered states.[6]. A prominent example are the elusive excitations that cause the melting of charge-stripe order in hightemperature superconductors[9–15] and promote enigmatic charge fluctuating-stripe (nematic) states.[14–16]

Methods

Results

Conclusion