Quantum Critical Dynamics in Magnetoelectric Multiferroics

• Applicant: Professor Dr. Joachim Hemberger
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2013 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 233992164

In this project we will examine the magneto-electric properties of transition-metal oxides by means of broadband dielectric spectroscopy. The efforts shall focus on the dynamics in the vicinity of critical end-points which at low temperatures are determined by quantum fluctuations. In the respected class of materials complex magnetic order is coupled to the onset of electric polarization or at least polarizability. Thus the external magnetic field can be utilized as control parameter for the ground state while the coupled magnetoelectric excitations can be examined via electric-field spectroscopy. For this purpose during the last years an experimental setup was developed to perform measurements of the complex permittivity in the frequency range from 1 mHz to 10 GHz, in external magnetic fields up to 15 T, and for temperatures down to 25 mK.The exceptional experimental sensitivity of this setup allows for the investigation of dynamical processes in the regarded temperature and energy range (1 GHz ~ 50 mK ~ 4 Micro-eV) which is not reachable by other methods, especially considering the width of the possible frequency range. The material basis which is to be studied reaches from the multiferroic quantum-spin chain LiCuVO4 or the ferromagnetic and magnetoelectric system Cu2OSeO3 to the spin-ice Dy2Ti2O7 for which a coupling of the magnetic monopole excitations to electric dipole moments was postulated. The particular combination of experimental methodology and material class can open unrivaled prospects for the understanding of the so far only sparely examined dynamical aspects in the vicinity of quantum phase transitions.

• DFG Programme: Research Grants