Thermal and quantum melting of the magnetic
order in TlCuCl3. In the limit of zero temperature T and zero pressure P the
quantum fluctuations in TlCuCl3 are severe enough to prevent the onset of any
magnetic order. Increasing the pressure at zero temperature acts to reduce
quantum fluctuations. The system eventually passes through a quantum critical
point (QCP) and becomes magnetic. The effects of thermal and quantum fluctuations
can then be disentangled by varying T and P. The coloured panels show neutron cattering data at fixed pressure where the critical fluctuations driving the
melting of the order can be studied as a function of energy and temperature.
An international team of researchers including a group from the London Centre for Nanotechnology (LCN) at UCL have uncovered vital information regarding the "quantum melting" of the magnetic structure of Thallium Copper Trichloride (TlCuCl3), reports Nature Physics. The findings of team from the UK, Switzerland, France and China establish for the first time that thermal and quantum routes to melting behave largely independently of one another. At sufficiently high temperature the particles contained within a material will move increasingly vigorously until the forces between them are eventually no longer strong enough to hold them together, causing it to melt. This familiar idea suggests that freezing should occur as solids are cooled towards absolute zero where all thermal motion ceases. Various important classes of materials exist, however, whose low-temperature properties are also dominated by the effects of quantum mechanics. In such quantum matter, melting may proceed at zero temperature due to quantum rather than thermal fluctuations. Understanding the role of quantum melting, an example of a quantum phase transition, is believed to lie at the heart of many of the outstanding problems in physics, including high-temperature superconductivity.
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