|Speaker||Dr. Matthew Coak (University of Cambridge)|
|Date & Time||2017.04.05, 15:00~16:00|
|Place||Bldg. 19, Rm. 210|
|Title||High pressure as a probe of quantum critical systems and emergent phases|
This talk will give an overview of the high pressure and low temperature techniques used in our group to tune long range ordered systems to quantum critical points and new phases. Two example materials will be discussed:
A quantum critical point occurs when a second order phase transition is tuned to zero temperature. In the vicinity of such a critical point, physical quantities like resistivity, magnetisation and dielectric constant change into unconventional forms due to the fluctuations experienced in this region giving rise to new kinds of ordered states including superconductivity in metallic systems. Metallic and magnetic quantum critical systems are complex to model and understand however, so ferroelectric systems are here used for the first time to test predictions of the underlying mechanics of quantum criticality. Perovskite quantum paraelectric SrTiO 3 at ambient pressure is shown to border a ferroelectric quantum critical point and the application of pressure to push the system away from criticality and suppresses the effect of quantum fluctuations, while also allowing the emergence of a novel low-temperature phase.
Low-dimensional insulating antiferromagnetic systems are interesting to tune, as they are directly comparable to certain unconventional high-temperature superconductors where tuning causes the superconducting state to emerge from such a phase. Measurements of magnetisation and resistivity under pressure in layered antiferromagnet FePS 3 show the Néel Temperature to be increased by applying pressure, and the resistivity to switch from a gapped insulating behaviour to a novel metallic state at high pressures.
Host : Prof. Je-Geun Park