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@INPROCEEDINGS{Heinze:1048340,
      author       = {Heinze, Leonie},
      title        = {{Q}uantum criticality and dimensional reduction in the
                      sawtooth chain material atacamite},
      reportid     = {FZJ-2025-04562},
      year         = {2025},
      abstract     = {Quantum magnets with geometrical frustration stand out due
                      to their highly degenerate ground states and their
                      susceptibility to be tuned by applying pressure or magnetic
                      field. Such tuning can lead to quantum phase transitions
                      from ordered to disordered states, or vice versa, with the
                      emergent quantum critical points (QCPs) determining the
                      deformed entropy landscapes in the respective phase
                      diagrams. While, in general, there is fundamental interest
                      in using the properties arising from such distorted entropy
                      landscapes for applications (e.g. the magnetocaloric effect
                      for low-temperature cooling), I address here the role of
                      residual exchange interactions in real materials. I
                      demonstrate that a QCP can develop on a lower energy scale
                      measured against the leading exchange couplings in the
                      system. In this talk, I present the case of the mineral
                      atacamite Cu$_2$Cl(OH)$_3$, a sawtooth-chain compound where
                      the non-uniform antiferromagnetic chain units [J ~ 336 K
                      (basal-basal), J' ~ 102 K (basal-apical)] are embedded into
                      a weak 3D network of interchain couplings. I will show that
                      the magnetic phase diagram of atacamite contains a
                      field-induced quantum critical point at 21.9(1) T (H || c
                      axis) which emerges on a much lower energy scale compared to
                      the leading terms in the spin Hamiltonian derived by means
                      of density-functional theory. The QCP separates field
                      regions with and without long-range magnetic order. In the
                      latter, underpinned by numerical results, the sawtooth
                      chains decompose, but far away from full field
                      polarization.},
      month         = {Oct},
      date          = {2025-10-07},
      organization  = {JCNS Workshop 2025: Trends and
                       Perspectives in Neutron Scattering.
                       Quantum Materials: Theory and
                       Experiments, Tutzing (Germany), 7 Oct
                       2025 - 9 Oct 2025},
      subtyp        = {Invited},
      cin          = {JCNS-4 / JCNS-3 / MLZ / JCNS-FRM-II},
      cid          = {I:(DE-Juel1)JCNS-4-20201012 / I:(DE-Juel1)JCNS-3-20170926 /
                      I:(DE-588b)4597118-3 / I:(DE-Juel1)JCNS-FRM-II-20110218},
      pnm          = {6G4 - Jülich Centre for Neutron Research (JCNS) (FZJ)
                      (POF4-6G4) / 632 - Materials – Quantum, Complex and
                      Functional Materials (POF4-632)},
      pid          = {G:(DE-HGF)POF4-6G4 / G:(DE-HGF)POF4-632},
      experiment   = {EXP:(DE-MLZ)External-20140101},
      typ          = {PUB:(DE-HGF)6},
      url          = {https://juser.fz-juelich.de/record/1048340},
}