Magnetic-field induced quantum phase transition and critical behavior in a gapped spin system (original) (raw)
Spin dynamics in the high-field phase of quantum-critical S =1/2 TlCuCl 3
Applied Physics A: Materials Science & Processing, 2002
An external magnetic field suppresses the spinenergy gap in singlet ground state S = 1/2 TlCuCl 3. The system becomes quantum-critical at H c ≈ 5.7 T, where the energy of the lowest Zeeman-split triplet excitation crosses the nonmagnetic ground state. Antiferromagnetic ordering is reported above H c , which underlines the three-dimensional nature of the observed quantum phase transition. The intrinsic parameters of S = 1/2 TlCuCl 3 allow us to access the critical region microscopically by neutron scattering. A substantial study of the spin dynamics in the high-field phase of TlCuCl 3 at T = 1.5 K up to H = 12 T was performed for the first time. The results possibly indicate two dynamical regimes, which can be understood within characteristically renormalized triplet modes and a low-lying dynamics of potentially collective origin.
Pressure-induced Magnetic Quantum Phase Transition from Gapped Ground State in TlCuCl 3
Journal of the Physical Society of Japan, 2004
Magnetization measurements under hydrostatic pressure were performed on an S = 1/2 coupled spin dimer system TlCuCl3 with a gapped ground state under magnetic field H parallel to the [2, 0, 1] direction. With increasing applied pressure P , the gap decreases and closes completely at Pc = 0.42 ± 0.05 kbar. For P > Pc, TlCuCl3 undergoes antiferromagnetic ordering. A spin-flop transition was observed at H sf ≃ 0.7 T. The spin-flop field is approximately independent of pressure, although the sublattice magnetization increases with pressure. The gap and Néel temperature are presented as functions of pressure. The occurrence of the pressureinduced quantum phase transition is attributed to the relative enhancement of the interdimer exchange interactions compared with the intradimer exchange interaction.
Magnetic quantum phase transitions from gapped spin liquid state in
Journal of Magnetism and Magnetic Materials, 2007
TlCuCl 3 is composed of spin dimers and has a gapped singlet ground state. This system undergoes antiferromagnetic orderings under both external magnetic field and hydrostatic pressure, which are described as Bose-Einstein condensation and softening of triplet excitations. An overview of the magnetic quantum phase transitions in TlCuCl 3 is given. r
Pressure-Induced Successive Magnetic Phase Transitions in the Spin Gap System TlCuCl 3
Journal of the Physical Society of Japan, 2004
Under the hydrostatic pressure P = 1.48 GPa, polarized neutron elastic scattering experiments have been carried out on the coupled spin dimer system TlCuCl3 with the gapped ground state at ambient pressure. Pressure-induced magnetic ordering occurs at the transition temperature TN = 16.9 K. As in the field-induced and impurity-induced magnetic ordered phases, the ordered moments lie in the a − c plane just below TN. An additional spin reorientation (SR) phase transition was observed at TSR = 10 K, where the ordered moments start to incline toward the b-axis. The temperature variations of the direction and the magnitude of the ordered moments were also investigated.
Magnetic excitations and exchange interactions in the spin-gap system TlCuCl 3
Applied Physics A: Materials Science & Processing, 2002
The magnetic excitations from the gapped ground state in TlCuCl 3 have been investigated by means of inelastic neutron scattering experiments. The excitation data were collected along four different directions in the a *c * plane. A well-defined single magnetic excitation mode was observed. The lowest excitation occurs at Q = (h, 0, l) with integer h and odd l, as observed in KCuCl 3. The dispersion relations were analyzed by the cluster-series expansion up to the sixth order, so that the individual exchange interactions were evaluated. It was demonstrated that TlCuCl 3 is a strongly coupled spin-dimer system.
Magnetic excitations in the spin gap system KCuCl3 and TlCuCl3
Journal of Physics and Chemistry of Solids, 1999
Magnetic excitation spectra of the spin S 1/2 system of the KCuCl 3-family crystals are studied by neutron inelastic scattering experiments. The obtained dispersion curves of KCuCl 3 for Q changed in the a*-c* plane showed that this compound is likely to be a quasi-two-dimensionally coupled antiferromagnetic-dimer spin system.
Magnetic excitations in the spin-gap systemTlCuCl3
Physical Review B, 2002
Single-crystal neutron inelastic scattering was performed in order to investigate the magnetic excitations in the spin gap system TlCuCl 3. The constant-Q energy scan profiles were collected in the a * − c * plane. Three excitations are observed for E≤15 meV. One of the excitations is identified to be magnetic excitation. The lowest magnetic excitation with E ∼ 0.5 meV occurs at Q = (1, 0, 1), as observed in KCuCl 3. The dispersion relation of the magnetic excitation can be fitted to the dispersion formula derived from the weakly coupled dimer model. The intradimer interaction is evaluated as J = 5.23 meV, which coincides with the value estimated from the susceptibility data. However, one of the interdimer interactions obtained is so large that the weakly coupled dimer model is broken down.
Quantum Magnets under Pressure: Controlling Elementary Excitations in TlCuCl3
Physical Review Letters, 2008
We follow the evolution of the elementary excitations of the quantum antiferromagnet TlCuCl3 through the pressure-induced quantum critical point, which separates a dimer-based quantum disordered phase from a phase of long-ranged magnetic order. We demonstrate by neutron spectroscopy the continuous emergence in the weakly ordered state of a low-lying but massive excitation corresponding to longitudinal fluctuations of the magnetic moment. This mode is not present in a classical description of ordered magnets, but is a direct consequence of the quantum critical point.
Physical Review B, 2017
The complete set of hallmarks of the three-dimensional antiferromagnet near the quantum critical point has been recently observed in the spin dimer compound TlCuCl3. Nonetheless, the mechanism, responsible for several distinct features of the experimental data, has remained a puzzle, namely: (i) the paramagnons exhibit remarkable robustness to thermal damping and are stable up to high temperatures, where kBT is comparable with the excitation energy, (ii) the width to mass ratios of the high-temperature paramagnons are, within the error bars, equal to that of the low-temperature amplitude (or Higgs) mode. We propose such a mechanism and identify two principal factors, contributing to the scaling between width to mass ratios of the paramagnon and the amplitude mode: (i) the emergence of the thermal mass scale reorganizing the paramagnon decay processes, and (ii) substantial renormalization of the multi-magnon interactions by thermal fluctuations. The study is carried out for the general case of a D = 3+1 quantum antiferromagnet within the framework of the ϕ 4 model using the hybrid Callan-Symanzik + Wilson thermal renormalization group method. Our approach is tested by demonstrating a good quantitative agreement with available experimental data across the phase diagram of TlCuCl3.