Neutron spectroscopy

Schematic phase diagram of a quantum critical point (QCP) with the occurrence of novel phases near the QCP from an antiferromagnetically (AF)/ ferromagnetically (FM) ordered ground state to a disordered paramagnetic (PM) ground state at zero temperature.

Spin textures in PrPtAl, a compound close to FM quantum criticality


Magnetic quantum critical points (QCPs), i.e. continuous phase transitions at absolute zero temperature separating a magnetically ordered from a disordered ground state, display itself in unusual low-temperature properties (e.g. non-Fermi-liquid behavior) and are quite often the result of competing interactions. These competing interactions can also give rise to novel ordering phenomena in the vicinity to the QCP. The (quantum-) critical spin fluctuations are at the origin of the peculiar behavior seen in the physical properties. Strongly correlated electron compounds are good model systems since their ground state can often be easily tuned by an external control parameter, such as compositional variation, pressure or magnetic field.

We employ neutron scattering to study those critical spin dynamics and the magnetic ordering phenomena close to QCPs to shed light on to the nature of the quantum criticality and the (novel) phases involved. In particular, e.g. we look at spin textures close to ferromagnetic QCPs, investigate the spin fluctuations near antiferromagnetic quantum criticality, but also study the spin dynamics in systems exhibiting e.g. unconventional superconductivity in the vicinity of QCPs.

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