391 research outputs found
Magnetic excitations in the S = 1/2 antiferromagnetic-ferromagnetic chain compound BaCu2V2O8 at zero and finite temperature
Unlike most quantum systems which rapidly become incoherent as temperature is
raised, strong correlations persist at elevated temperatures in dimer
magnets, as revealed by the unusual asymmetric lineshape of their excitations
at finite temperatures. Here we quantitatively explore and parameterize the
strongly correlated magnetic excitations at finite temperatures using the high
resolution inelastic neutron scattering on the model compound
BaCuVO which we show to be an alternating
antiferromagnetic-ferromagnetic spin chain. Comparison to state of the
art computational techniques shows excellent agreement over a wide temperature
range. Our findings hence demonstrate the possibility to quantitatively predict
coherent behavior at elevated temperatures in quantum magnets.Comment: 5 pages + 6 pages supplement; problems with list of references are
fixe
Mutual induction of magnetic 3d and 4f order in multiferroic hexagonal ErMnO3
The complex interplay between the 3d and 4f moments in hexagonal ErMnO3 is
investigated by magnetization, optical second harmonic generation, and
neutron-diffraction measurements. We revise the phase diagram and provide a
microscopic model for the emergent spin structures with a special focus on the
intermediary phase transitions. Our measurements reveal that the 3d exchange
between Mn^{3+} ions dominates the magnetic symmetry at 10 K < T < T_N with
Mn^3+ order according to the Gamma_4 representation triggering 4f ordering
according to the same representation on the Er^{3+}(4b) site. Below 10 K the
magnetic order is governed by 4f exchange interactions of Er^{3+} ions on the
2a site. The magnetic Er^{3+}(2a) order according to the representation Gamma_2
induces a magnetic reorientation (Gamma_4 --> Gamma_2) at the Er^{3+}(4b) and
the Mn^{3+} sites. Our findings highlight the fundamentally different roles the
Mn^{3+}, R^{3+}(2a), and R^{3+}(4b) magnetism play in establishing the magnetic
phase diagram of the hexagonal RMnO3 system
Direct observation of the Higgs amplitude mode in a two-dimensional quantum antiferromagnet near the quantum critical point
Spontaneous symmetry-breaking quantum phase transitions play an essential
role in condensed matter physics. The collective excitations in the
broken-symmetry phase near the quantum critical point can be characterized by
fluctuations of phase and amplitude of the order parameter. The phase
oscillations correspond to the massless NambuGoldstone modes whereas the
massive amplitude mode, analogous to the Higgs boson in particle physics, is
prone to decay into a pair of low-energy NambuGoldstone modes in low
dimensions. Especially, observation of a Higgs amplitude mode in two dimensions
is an outstanding experimental challenge. Here, using the inelastic neutron
scattering and applying the bond-operator theory, we directly and unambiguously
identify the Higgs amplitude mode in a two-dimensional S=1/2 quantum
antiferromagnet CHNCuBr near a quantum critical point in two
dimensions. Owing to an anisotropic energy gap, it kinematically prevents such
decay and the Higgs amplitude mode acquires an infinite lifetime.Comment: 12 pages, 4 figures in the main text+3 figures in Supplementary
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