D. Hüvonen

Field-induced criticality in a gapped quantum magnet with bond disorder

Neutron diffraction and calorimetricmeasurements are used to study the field-induced quantum phase transition in piperazinium-Cu-2( Cl1-xBrx) 6 ( x = 0, 3.5%, and 7.5%), a prototypical quantum antiferromagnet with random bonds. The critical indexes phi and beta are determined. The findings contradict some original predictions for Bose glass based on the assumption z = d, but are consistent with recent theoretical results implying z <= d. Inelastic neutron experiments reveal that disorder has a profound effect on the lowest-energy magnetic gap excitation in the system.

Excitations in a quantum spin liquid with random bonds

We present the results of an inelastic neutron-scattering study on two bond disordered quasi-two-dimensional quantum magnets (C4H12N2)Cu-2(Cl1-xBrx)(6) with x = 0.035 and 0.075. We observe an increase of spin gap, a reduction of magnon bandwidth, and a decrease of magnon lifetimes compared to the x = 0 sample. Additional magnon damping is observed at higher energies away from the zone center, which is found to follow the density of single-particle states. DOI: 10.1103/PhysRevB.86.214408

Criticality in a disordered quantum antiferromagnet studied by neutron diffraction

E. Wulf, D. Hüvonen, J.-W. Kim, 3 A. Paduan-Filho, E. Ressouche, S. Gvasaliya, V. Zapf, and A. Zheludev ∗ Neutron Scattering and Magnetism, Laboratory for Solid State Physics, ETH Zürich, Zürich, Switzerland. National High Magnetic Field Laboratory, MPA-CMMS group, Los Alamos National Lab (LANL), Los Alamos, NM 87545, USA. Lujan Center for Neutron Scattering, LANL, Los Alamos, NM 87545, USA. High Magnetic Field Laboratory, University of São Paulo, 05315-970, São Paulo, Brazil. INAC/SPSMS-MDN, CEA/Grenoble, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France. (Dated: October 4, 2013)

Pressure-Induced Quantum Critical and Multicritical Points in a Frustrated Spin Liquid

The quantum spin-liquid compound (C4H12N2)Cu2Cl6 is studied by muon spin relaxation under hydrostatic pressures up to 23.6 kbar. At low temperatures, pressure-induced incommensurate magnetic order is detected beyond a quantum critical point at P-c similar to 4.3 kbar. An additional phase transition to a different ordered phase is observed at P-1 similar to 13.4 kbar. The data indicate that the high-pressure phase may be a commensurate one. The established (P-T) phase diagram reveals the corresponding pressure-induced multicritical point at P-1, T-1 = 2.0 K.

Crystals for neutron scattering studies of quantum magnetism

We review a strategy for targeted synthesis of large single crystal samples of prototype quantum magnets for inelastic neutron scattering experiments. Four case studies of organic copper halogenide S = 1/2 systems are presented. They are meant to illustrate that exciting experimental results pertaining to the forefront of many-body quantum physics can be obtained on samples grown using very simple techniques, standard laboratory equipment, and almost no experience in advanced crystal growth techniques.

Spin dynamics in pressure-induced magnetically ordered phases in (C4H12N2)Cu2Cl6

In this paper, we present inelastic neutron-scattering experiments on the S=1/2 frustrated gapped quantum magnet piperazinium hexachlorodicuprate (PHCC) under applied hydrostatic pressure. These results show that at 9 kbar the magnetic triplet excitations in the system are gapless, contrary to what was previously reported. Our results are in agreement with recent muon-spin relaxation experiments which found magnetic order above a quantum-critical point at 4.3 kbar. Finally, we show that the changes in the excitation spectrum can be primarily attributed to the change in a single exchange pathway.

Finite-temperature scaling of spin correlations in a partially magnetized Heisenberg

Inelastic neutron scattering is employed to study transverse spin correlations of a Heisenberg

S=1/2

S=1/2

chain

chain compound in a magnetic field of 7.5 T. The target compound is the antiferromagnetic Heisenberg

Effect of disorder on a pressure-induced z = 1 magnetic quantum phase transition

S=1/2