Issue
EPL
Volume 82, Number 6, June 2008
Article Number 60004
Number of page(s) 6
Section General
DOI http://dx.doi.org/10.1209/0295-5075/82/60004
Published online 30 May 2008
EPL, 82 (2008) 60004
DOI: 10.1209/0295-5075/82/60004

Pressure-induced quantum phase transitions

G. A. Gehring

Department of Physics and Astronomy, University of Sheffield - Sheffield S3 7RH UK, EU

g.gehring@shef.ac.uk

received 10 October 2007; accepted in final form 30 April 2008; published June 2008
published online 30 May 2008

Abstract
A quantum critical point is approached by applying pressure in a number of ferromagnetic and antiferromagnetic metals. The observed dependence of Tc on pressure necessarily means that the magnetic energy is coupled to the lattice. A first-order phase transition occurs if this coupling exceeds a critical value: this is inevitable if $\frac{\partial T_c}{\partial p}$ diverges as Tc approaches zero. It is argued that this is the cause of the first-order transition that is observed in many systems. Landau theory is used to obtain the phase diagram and also to predict the regions where metastable phases occur that agree well with experiments done on MnSi and other materials. The theory can be used to obtain very approximate values for the temperature and pressure at the tricritical point in terms of measured quantities. The values of the tricritical temperature for various materials obtained from Landau theory are too low but it is shown that the predicted values will rise if the effects of fluctuations are included.

PACS
05.70.Fh - Phase transitions: general studies.
64.70.Tg - Quantum phase transitions.
75.20.En - Metals and alloys.

© EPLA 2008