PressureTuned Classical–Quantum Crossover in Magnetic FieldInduced Quantum Phase Transitions of a TriangularLattice Antiferromagnet
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FieldInduced Quantum Phase Transitions in the PressureTuned TriangularLattice Antiferromagnet CsCuCl_{3}
J. Phys. Soc. Jpn. 93, 084704 (2024).
The correspondence principle states that as quantum numbers approach infinity, the nature of a system described by quantum mechanics should match that described by classical mechanics. Quantum phenomena, such as quantum superposition and quantum correlation, generally become unobservable when a system approaches this regime. Conversely, as quantum numbers decrease, classical descriptions give way to observable quantum effects. The external approach to classical–quantum crossover has attracted research interest. This study aims to demonstrate a method for achieving such control in materials.
The highpressure application is an experimental means to significantly alter the microscopic physical parameters of a material. At ambient pressure, these physical parameters generally do not change significantly, regardless of the temperature. Recently, the effects of high pressure have been studied across a broad area of condensed matter physics, including pressuredriven hightemperature superconductivity and topological phases. Frustrated quantum magnets are expected to be significantly affected by pressure because frustration due to competing interactions gives rise to many lowenergy states with small energy differences. Additionally, small quantum fluctuations play an important role in manifesting unconventional physical phenomena, such as unconventional quantum phases. Therefore, applying external pressure to frustrated quantum materials enables the manipulation of quantum correlations across the classical and quantum mechanical regimes, facilitating the exploration of exotic phenomena along the crossover.
This study explores an exciting example of a frustrated antiferromagnet—triangularlattice compound CsCuCl_{3}. To generate the phase diagram of magnetic field vs. pressure for this compound, we utilized our newly developed proximity detector oscillator system and highpressure cell to measure magnetic susceptibility in pulsed magnetic fields exceeding the saturation field up to 55 T, under pressures of up to 2.08 GPa. We observed the fieldinduced quantum phase transitions from umbrella to upupdown (UUD) and Ycoplanar phase immediately below the UUD phase above 0.90 and 1.7 GPa, respectively. Moreover, we calculated the pressure dependence of the transition fields, including the saturation field, and reliably determined the exchange interaction and easyplane anisotropy parameters under pressure. With increasing pressure, the magnitude of the interchain antiferromagnetic exchange interaction increased linearly, whereas the magnitude of the intrachain ferromagnetic exchange interaction decreased significantly. Consequently, the ratio of the intra to interchain exchange interactions decreased substantially with increasing pressure, indicating that the largely coupled ferromagnetic spins, regarded as semiclassical spins, became quantum spins. This suggests that the occurrence of the UUD and Ycoplanar phases is accompanied by a crossover from semiclassical to quantum spins in CsCuCl_{3}.
(Written by Masayuki Hagiwara on behalf of all authors)
FieldInduced Quantum Phase Transitions in the PressureTuned TriangularLattice Antiferromagnet CsCuCl_{3}
J. Phys. Soc. Jpn. 93, 084704 (2024).
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