Quantum Criticality
Phase transitions are most commonly known to occur between solid, liquid, and gaseous states of matter. They also occur when magnetic and superconducting states form. Researchers at the University of Bristol study phase transitions close to zero temperature.
Here, thermal fluctuations are absent and phase transitions are dominated by quantum fluctuations. This gives rise to completely new behaviour arising from a so-called quantum critical point (QCP). Often superconductivity is found to emerge from quantum critical points.
A quantum critical point (QCP) is accessed by suppressing a finite-temperature phase transition to zero temperature, e.g. by applying pressure
Quantum Tricritical Points
Sven Friedemann and his collaborators studied what happens when the second-order transition of a ferromagnet is suppressed to zero temperature. They used detailed magnetic measurements combined with very clear-cut modelling to do this.
The researchers discovered quantum tricritical points with both ferromagnetic and antiferromagnetic quantum fluctuations. The team used a very general approach in their analysis. Thus, it is expected that the results apply to a whole class of ferromagnets and other materials with two competing orders.
Three dimensional phase diagram of NbFe2 with the newly discovered quantum tricritical points (QCTP)