A new type of non-Fermi-liquid near the ferromagnetic transition in a 2D metal

Expositor:  Dr. Chris Hooley – SUPA, St Andrews University, United Kingdom

Fecha: Martes 22/03/2016 – 10.30 hs.

In this seminar I shall consider the low-temperature behaviour of a two-dimensional metal near a second-order transition to ferromagnetism. This is a particular example of the type of problem referred to by the phrase ‘quantum criticality’. In general, magnetic fluctuations near such a quantum critical point are subject to Landau damping due to their coupling to the conduction electrons. However, in the ferromagnetic case this damping must vanish as the wavevector of the fluctuation tends to zero, since uniform magnetisation (being a conserved quantity of the model) cannot be damped.

It is usually assumed [1,2], on the basis of a perturbative calculation, that the Landau-damping rate is proportional to the modulus of the wavevector, i.e. goes as |q|. However, in this seminar I shall describe a calculation (carried out using the functional renormalisation group) that suggests that this is not the case. Instead, we find a new type of low-energy fixed-point that corresponds to a strongly interacting non-Fermi-liquid in which the Landau damping rate goes as |q|^(3/5), and the specific heat as T^(10/13). I shall discuss the physics of this fixed point and where it might be seen in nature, the relationship of our calculation to other works on nearly ferromagnetic metals, and possible avenues of future investigation.

This work was done in collaboration with my PhD student Sam Ridgway; details are available in S.P. Ridgway and CAH, Phys. Rev. Lett. 114, 226404 (2015).

[1] J.A. Hertz, Phys. Rev. B 14, 1165 (1976).
[2] A.J. Millis, Phys. Rev. B 48, 7183 (1993).

¡L@s esperamos a partir de las 10.15 hs con café y facturas!