Home >  About ISSP >  Publications > Activity Report 2018 > Xxxx Xxxx

Quantum Liquid-Quantum Liquid Transition in a Strong Magnetic Field

Kindo and Tokunaga Groups

In recent years, quantum liquids of quasiparticles, which are disordered states by quantum fluctuations, has attracted much attention. The similarities and differences between quantum and classical liquids are an interesting topic. In the case of classical liquids, the absence of order typically suggests the existence of only a single liquid phase. However, some anomalous molecules, such as H2O, which have locally stable structures, exhibit multiple liquid phases, and liquid-liquid phase transitions have been observed. Due to the involvement of various degrees of freedom in liquid-liquid transitions, its complete understanding is still elusive. For quantum liquids, it has not even been clear whether a quantum liquid state can exhibit athermal transition to a distinctly different quantum liquid state.

We have investigated the organic charge-transfer complex, TTF-QBr3I (tetrathiafulvalene-2-iodo-3,5,6-tri-bromo-p-benzoquinone) that simultaneously exhibits ferroelectric and spin-Peierls (FSP) transition at 5.6 K. As the one-dimensional alternate stack of ionic TTF (cation) and QBr3I (anion) molecules, spin solitons are excited as topological defects in the FSP ordered state, as shown in Fig. 1. Our earlier research in zero magnetic field [1] demonstrated that spin solitons traverse potential barriers by quantum tunneling even at extremely low temperatures. In this study [2], we performed magnetization, dielectric property, and ultrasound measurements of this salt in pulsed high magnetic fields. Given the density and dynamics of spin solitons, we demonstrated that these solitons can be regarded as a quantum liquid at zero field. TTF-QBr3I positions near the quantum critical point in its electronic phase diagram, and the FSP state is strongly influenced by strong quantum fluctuations. We revealed that the quantum liquidity originates from the developed quantum fluctuations.

When a strong magnetic field of 40 T is applied, an anomaly was observed in all measured physical quantities, indicating the emergence of an additional FSP state. In the case of a conventional spin-Peierls state, the strong Zeeman effect leads to a transition to an incommensurate state with an emergent distortion wave vector, known as the soliton-lattice state. Given this analogy, the solidification of solitons due to the lattice formation would be expected. Nevertheless, our results suggested that the presence of the strong quantum fluctuations in TTF-QBr3I preclude the formation of such a soliton lattice, causing the dense solitons to remain in a quantum-mechanically melted state even in high magnetic fields. Namely, the observed transition indicates the realization of a quantum liquid-quantum liquid transition of topological particles by the application of a strong magnetic field.

Even in classical liquids, since liquid-liquid phase transitions appear only in anomalous systems, their origins are still mysterious. In this study, we have for the first time discovered the phenomenon where quasiparticles drifting quantum mechanically undergo a phase transition from one quantum liquid state to another under the influence of a magnetic field. This discovery not only represents a novel phenomenon but also holds potential to contribute to the understanding of classical liquids.


References
  • [1] S. Imajo, A. Miyake, R. Kurihara, M. Tokunaga, K. Kindo, S. Horiuchi, and F. Kagawa, Phys. Rev. B 103, L201117 (2021).
  • [2] S. Imajo, A. Miyake, R. Kurihara, M. Tokunaga, K. Kindo, S. Horiuchi, and F. Kagawa, Phys. Rev. Lett. 132, 096601 (2024).
Authors
  • S. Imajo, A. Miyakea, R Kuriharab, M. Tokunaga, K. Kindo, S. Horiuchic, and F. Kagawad,e
  • aTohoku University
  • bTokyo University of Science
  • cAIST
  • dTokyo Institute of Technology
  • eRIKEN CEMS