Emergent many-body composite excitations of interacting spin-1/2 trimers

Abstract

Understanding exotic forms of magnetism in quantum spin systems is an emergent topic of modern condensed matter physics. Quantum dynamics can be described by particle-like carriers of information, known-as quasiparticles that appear from the collective behaviour of the underlying system. Spinon excitations, governing the excitations of quantum spin-systems, have been accurately calculated and precisely verified experimentally for the antiferromagnetic chain model. However, identification and characterization of novel quasiparticles emerging from the topological excitations of the spin system having periodic exchange interactions are yet to be obtained. Here, we report the identification of emergent composite excitations of the novel quasiparticles doublons and quartons in spin-1/2 trimer-chain antiferromagnet Na2Cu3Ge4O12 (having periodic intrachain exchange interactions J1-J1-J2) and its topologically protected quantum 1/3 magnetization-plateau state. The characteristic energies, dispersion relations, and dynamical structure factor of neutron scattering as well as macroscopic quantum 1/3 magnetization-plateau state are in good agreement with the state-of-the-art dynamical density matrix renormalization group calculations.

Quantum phase transitions and composite excitations of antiferromagnetic quantum spin trimer chains in a magnetic field

“…When J 2 = J 1 , the trimer chain reduces to the conventional HAC with the two-spinon continuum, indicating that the low-energy spinons reside in different Brillouin zones. Most interestingly, when J 2 /J 1 ≪ 1, the composite excitations of the novel quasi-particles, doublons and quartons have been predicted at the intermediate-energy and high-energy spectra, respectively, and immediately confirmed in the inelastic neutron scattering measurements on Na 2 Cu 3 Ge 4 O 12 [24]. As J 2 /J 1 → 1, the doublons and quartons lose their identity and fractionalize into the standard HAC spinon continuum.…”

“…in the spin chain with trimer structure that is closely associated with the quantum magnet Na 2 Cu 3 Ge 4 O 12 [24]. The magnetic field tuns the lower quarton to approach zero energy, indicating the magnetic-field-induced quarton Bose-Einstein condensation (BEC).…”

Role of Crystal Structure on the Ionic Conduction and Electrical Properties of Germanate Compounds A2Cu3Ge4O12 (A = Na, K)

“…The high purity precursors were mixed thoroughly with the help of agate mortar and pestle for an hour. The mixed powder was then heated in alumina crucible at high temperature (∼1073 K) in air − for 48 h. A 2 CO 3 + 3CuO + 4GeO 2 = A 2 Cu 3 Ge 4 normalO 12 + CO 2 false↑ …”

“…Such excitations are manifestations of quantum spin entangled ground state. These excitations are found to be stable against temperature and persist up to near room temperature (∼250 K), which has a special importance for practical device applications in the upcoming quantum technology. The iso-formula compound with A = K, i.e., K 2 Cu 3 Ge 4 O 12 (KCGO) was first reported by Stoll et al .…”

“…These studies revealed that Na + and K + ion based inorganic compounds could be possible candidates for the development of the new ionic conductors. In the present study, our interest is on the compounds A 2 Cu 3 Ge 4 O 12 ( A = Na, K) ( A CGO) due to their special crystal structures where Na/K ions are located within channels between (Cu/Ge)­O 4 polyhedra. − The compounds A 2 Cu 3 Ge 4 O 12 ( A = Na, K) ( A CGO), consisting of trimer spin-chains of Cu 2+ ions, are known for their interesting magnetic properties. The compound with A = Na, i.e., Na 2 Cu 3 Ge 4 O 12 (NCGO) was first reported by Yasui et al Recently, based on the inelastic neutron scattering study, our group reported the fractional and composite magnetic quasi-particle excitations in NCGO.…”