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Quantum critical fluctuations in a transverse-field Ising magnet
A Hauspurg1,2, K Matsuura3, Taka-Hisa Arima3
1Hochfeld-Magnetlabor Dresden (HLD-EMFL) and Würzburg-Dresden Cluster of Excellence ct.qmat, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), 01328 Dresden, Germany.
Summary
Quantum critical fluctuations influence spin-1/2 one-dimensional Ising magnets. Ultrasound measurements in Cobalt Niobate (CoNb2O6) reveal anomalies linked to quantum critical points, providing evidence for predicted magnetic ordering phase diagrams.
Area of Science:
- Condensed Matter Physics
- Magnetism and Magnetic Materials
- Quantum Critical Phenomena
Background:
- Cobalt Niobate (CoNb2O6) serves as a model system for studying spin-1/2 one-dimensional (1D) transverse-field Ising magnets (TFIM).
- This material exhibits a low three-dimensional (3D) Néel ordering temperature (TN = 2.95 K), making it suitable for low-temperature investigations.
- Understanding the interplay between 1D quantum criticality and 3D ordering is crucial for magnetic systems.
Purpose of the Study:
- To investigate the behavior of CoNb2O6 under transverse magnetic fields applied along the b-direction using ultrasound measurements.
- To identify and characterize anomalies in acoustic modes associated with magnetic ordering and quantum critical fluctuations.
- To provide experimental evidence for the predicted generic phase diagram of a TFIM with superimposed 3D ordering.
Main Methods:
- Ultrasound measurements were performed on CoNb2O6 samples at temperatures down to 0.3 K.
- Transverse magnetic fields were applied along the b-direction to probe magnetic phase transitions.
- The transverse acoustic mode c66 was monitored for anomalies, specifically softening, indicative of phase transitions and critical fluctuations.
Main Results:
- Pronounced anomalies were observed in the transverse acoustic mode c66 upon entering the 3D ordered state.
- An almost diverging softening of the c66 mode was detected around 4.7 T between 1.3 K and 1.5 K.
- This softening was significantly reduced at magnetic fields lower and higher than 4.7 T, suggesting the influence of quantum critical fluctuations.
Conclusions:
- The observed acoustic anomalies are interpreted as the influence of quantum critical fluctuations originating from the quantum critical point (QCP) of the 1D Ising spin chains.
- The study identifies a QCP for the 1D chains at approximately 4.75 T, which lies below the QCP for the 3D ordering at approximately 5.4 T.
- These findings provide clear experimental evidence supporting the predicted generic phase diagram for a TFIM system with superimposed 3D ordering.
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