Magnetic-field-controlled spin fluctuations and quantum criticality in Sr3Ru2O7

TL;DR

This study investigates how magnetic fields influence spin fluctuations and quantum criticality in Sr3Ru2O7, revealing critical spin dynamics and their role in strange metal behavior near a quantum critical point.

Contribution

It provides the first direct evidence of collective spin fluctuations near the quantum critical point in Sr3Ru2O7 using inelastic neutron scattering.

Findings

Spin fluctuations show nearly singular variation with magnetic field.

Electronic heat capacity and entropy are explained by electron scattering off spin fluctuations.

Fluctuations intensify in the spin density wave phase, indicating an 'order-by-disorder' stabilization mechanism.

Abstract

When the transition temperature of a continuous phase transition is tuned to absolute zero, new ordered phases and physical behaviour emerge in the vicinity of the resulting quantum critical point. Sr3Ru2O7 can be tuned through quantum criticality with magnetic field at low temperature. Near its critical field Bc it displays the hallmark T-linear resistivity and a T log(1/T) electronic heat capacity behaviour of strange metals. However, these behaviours have not been related to any critical fluctuations. Here we use inelastic neutron scattering to reveal the presence of collective spin fluctuations whose relaxation time and strength show a nearly singular variation with magnetic field as Bc is approached. The large increase in the electronic heat capacity and entropy near Bc can be understood quantitatively in terms of the scattering of conduction electrons by these spin-fluctuations. On entering the spin density wave (SDW) phase present near Bc, the fluctuations become stronger suggesting that the SDW order is stabilised through an "order-by-disorder" mechanism.