Fumiko Yamada

Magnetic-Field Induced Bose–Einstein Condensation of Magnons and Critical Behavior in Interacting Spin Dimer System TlCuCl3

Magnetization measurements were performed to investigate the critical behavior of the field-induced magnetic ordering in gapped spin system TlCuCl 3 . The critical density of the magnons was obtained as a function of temperature and the magnon-magnon interaction constant was evaluated. The experimental phase boundary for T < 5 K agrees almost perfectly with the magnon Bose–Einstein condensation (BEC) theory based on the Hartree–Fock approximation with realistic dispersion relations. The phase boundary can be described by the power law [ H N ( T )- H c ] ∝ T φ . With decreasing fitting temperature range, the critical exponent φ decreases and converges at φ BEC = 3/2 predicted by the magnon BEC theory.

Magnetic field induced one-magnon Raman scattering in the magnon Bose-Einstein condensation phase of TlCuCl 3

We report the observation of the

Longitudinal magnetic excitation in KCuCl3 studied by Raman scattering under hydrostatic pressures

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Spin Fluctuations in the Ground State of Doped Quantum Spin System TlCu1-xMg xCl3 with x=0.0047 Probed by Muon-Spin-Relaxation Technique

-symmetric one-magnon Raman peak in the magnon Bose-Einstein condensation phase of TlCuCl

The effect of randomness on the quantum spin system Tl1- xKxCuCl3 with x = 0.44 studied by the zero-field muon-spin-relaxation (ZF-μSR) method

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Magnetic-field induced quantum phase transition and critical behavior in a gapped spin system TlCuCl3

. Its Raman shift traces the one-magnon energy at the magnetic

Pressure-induced new magnetic phase in Tl(Cu0.985Mg0.015)Cl3 probed by muon spin rotation

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Anticrossing effect between magnon and phonon in Bose-Einstein condensation phase of TlCuCl3

point, and its intensity is proportional to the squared transverse magnetization. The appearance of the one-magnon Raman scattering originates from the exchange magnon Raman process and reflects the change of the magnetic-state symmetry. Using the bond-operator representation, we theoretically clarify the Raman selection rules, being consistent with the experimental results.

Pressure-induced reentrant oblique antiferromagnetic phase in the spin-dimer system TlCuCl3

We measure Raman scattering in an interacting spin-dimer system KCuCl3 under hydrostatic pressures up to 5 GPa mediated by He gas. In the pressure-induced quantum phase, we observe a one-magnon Raman peak, which originates from the longitudinal magnetic excitation and is observable through the second-order exchange interaction Raman process. We report the pressure dependence of the frequency, halfwidth and Raman intensity of this mode.

Gradual evolution in spin dynamics of TlCu1−xMgxCl3 probed by muon-spin-relaxation (μSR) technique

Zero- and longitudinal-field muon-spin-relaxation (ZF- and LF-µSR) measurements were carried out down to T =20 mK on the slightly doped quantum spin system TlCu 1- x Mg x Cl 3 with x =0.0047, in which a magnetic phase transition is observed at 0.70 K by specific heat measurement. LF-µSR measurements above and below the phase transition temperature revealed that the impurity-induced magnetic moments of the Cu-3 d spins slowly fluctuate at a frequency of 0.74 MHz at T =20 mK, far below the magnetic phase transition temperature. It is possible that the impurity-induced magnetic moments are in an exotic state where they fluctuate while preserving their wave vector and relative phase, i.e., a coherently fluctuating state .