Magnetic and phononic dynamics in the two-ladder quantum magnet (C5H9NH3)2CuBr4
Journal article, 2026
In quantum magnetic materials it is common to observe both static and dynamic lattice effects on the magnetic excitation spectrum. Less common is to find that the magnetic correlations have a significant impact on the phonon spectrum. Here we study the metal-organic material (C5H9NH3)2CuBr4(Cu-CPA), in which an explanation of the low-lying excitations depends crucially on a full understanding of both the spin and lattice subsystems. We report high-resolution neutron spectroscopy enabled by large, deuterated single crystals that reveal how both sectors are affected by the recently discovered structural phase transition. By measuring over several Brillouin zones, we disentangle the vibrational contribution to the spectrum in order to obtain an accurate estimate of the quasi-one-dimensional magnetic signal. The low-energy magnetic excitations are dominated by two gaps, Δb = 0.41 meV and Δa = 0.55 meV, which contribute with equal intensity ratios, confirming that Cu-CPA realizes a two-ladder spin Hamiltonian, and we deduce the magnetic interaction parameters of both ladders. The phonon spectrum contains highly localized modes at an anomalously low energy around 2 meV. For half of these modes, this characteristic frequency drops by approximately 5% as magnetic correlations become established with decreasing temperature, and we connect this apparent “elastomagnetic” behavior with the location and structure of the cyclopentylammonium rings.
Author
J. Philippe
Paul Scherrer Institut
University of Zürich
Frank Elson
Royal Institute of Technology (KTH)
T. Arh
Paul Scherrer Institut
S. Sanz
Jülich Research Centre
M. Metzelaars
Jülich Research Centre
RWTH Aachen University
D. W. Tam
Royal Institute of Technology (KTH)
Ola Kenji Forslund
University of Zürich
Uppsala University
O. Shliakhtun
University of Zürich
Paul Scherrer Institut
C. Jiang
Royal Institute of Technology (KTH)
Jakob Lass
Paul Scherrer Institut
Manh Duc Le
STFC Rutherford Appleton Laboratory
J. Ollivier
Institut Laue-Langevin
P. Bouillot
University of Geneva
T. Giamarchi
University of Geneva
M. Bartkowiak
Paul Scherrer Institut
Daniel G. Mazzone
Paul Scherrer Institut
Paul Kögerler
RWTH Aachen University
Martin Månsson
Royal Institute of Technology (KTH)
A. M. Läuchli
Paul Scherrer Institut
Swiss Federal Institute of Technology in Lausanne (EPFL)
Yasmine Sassa
Chalmers, Physics, Materials Physics
Royal Institute of Technology (KTH)
Marc Janoschek
Paul Scherrer Institut
University of Zürich
B. Normand
Paul Scherrer Institut
Gediminas Simutis
Paul Scherrer Institut
Physical Review B
2469-9950 (ISSN) 2469-9969 (eISSN)
Vol. 113 13 134438Subject Categories (SSIF 2025)
Condensed Matter Physics
DOI
10.1103/89JZ-CF9Z