Page 72 - ILLS Annual Report 2018

THEORY
Mariya Gvozdikova. Ukranian
High Magnetic Field Laboratory (LNCMI) and INAC-CEA, Grenoble
‘I have a PhD in Theoretical Physics. Today I hold post-doctoral positions at the Grenoble High Magnetic Field Laboratory (LNCMI) and in the INAC, CEA-Grenoble. I worked on
several collaborations with theorists at the ILL, and it was during one of my visits that this study was completed.’
Multipoles versus dipole fans near a quantum critical point
One of the holy grails of modern magnetism is the phases of spins that constitute really exotic states of matter and whose properties are dominated
by quantum fluctuations even from macroscopically large samples. The observation of such phases is often claimed, in some cases prematurely,
on the basis of evidence that admits
an exotic explanation but is really incomplete: the actual structure is seen only indirectly through its relation to the observed properties, and the attribution to one state rather than another depends on theory that relates the observables uniquely to the new phase.
AUTHORS
M. Gvodzikova and T. Ziman (ILL)
M. Zhitomirsky (CEA-INAC, Grenoble)
ARTICLE FROM
Phys. Rev. Lett. (2018) —doi: 10.1103/PhysRevLett.120.067203
REFERENCES
[1] B. Willenberg et al., Phys. Rev. Lett. 116 (2016) 047202 [2] E. Cemal et al., Phys. Rev. Lett. 120 (2018) 067203
The advantage of neutron experiments is that both statics and dynamics can be seen rather directly and completely, providing for real confrontation between experiment
and theory. A recent example of this is provided by the detailed experiments carried out on a frustrated linear magnet, a mineral called linarite PbCuSO4(OH)2. This
is promising as it is known to be, up to small corrections, almost but not quite described by a model at a quantum critical point, i.e. it is close to a state that is known mathematically to have large quantum fluctuations but
not the normal order based on some regular pattern of the magnetic dipoles. The slight departures from criticality are thought to make it a candidate for an unusual state, where the order in the magnetic dipoles present on
each copper atom is lost to each site to fluctuation but a higher, multipolar order involving entanglement of pairs of magnetic moments on adjacent sites prevails. The question is, which of the many possible ordered, or disordered, states prevails in the real mineral? Elastic and inelastic scattering of neutrons in a magnetic field can resolve the question—with the help of theory.
Figure 1
Schematic phase sequence in the vicinity of a quantum critical point.
ANNUAL REPORT 2018