Thermal transport in quantum magnets

• Grant number: 18/23249-8
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: February 01, 2019
• End date: June 30, 2019
• Field of knowledge: Physical Sciences and Mathematics - Physics - Condensed Matter Physics
• Principal Investigator: Armando Paduan Filho
• Grantee: Valentina Martelli
• Host Institution: Instituto de Física (IF). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 15/16191-5 - The research in new materials involving high magnetic fields and low temperatures, AP.TEM

Abstract

The investigation of quantum magnetism at low temperatures reveals a plethora of exotic states of matter that can host unexpected physics due to competing forces among degrees of freedom and due to a manifold energetic degeneracy. Advancing the understanding of the physical behaviours of those states can impact several application fields based on magnetic properties. Pyrochlores are a wide class of magnetic materials that present a geometric frustration given by their crystal structures. Depending on which atoms are selected to compose the structure, peculiar physical properties are observed below the transition temperature where the frustration plays a relevant role. Here we want to explore the low temperature thermal transport in selected groups of pyrochlores across their transition temperature, under the application of magnetic field. We propose to investigate spin-ices (Dy2Ti2O7 and Ho2Ti2O7), antiferromagnetic-type pyrochlores (Sm2Ti2O7 and Nd2Ti2O7) and other pyrochlores (Gd2Ti2O7, Gd2Zr2O7, Er2Ti2-xSnxO7). The investigation of the quantum magnet displaying Bose-Einstein Condensation (BEC) state (NiCl2-4SC(NH2)2), DTN, attracted lots of attention for the possibility of disorder effect or impurities that may leads to an unexpected quantum coherence emerging from localized impurity states. Here, we will investigate the Spin-Seebeck effect across the phase diagram to determine the spin current, in DTN and DTN-doped, that can be generated by means of the inverse spin Hall effect, since it is an electric isolant with large magnetic moment at the BEC phase.Thermal transport is an appropriate tool of investigation in the proposed compounds as they are electrical insulators. By studying thermal transport under magnetic field, we can study magnons transport and their interaction with crystalline vibrations (phonons). Additionally, we will investigate the less explored Spin-Seebeck and the Righi-Leduc effect (or thermal Hall effect), where the effect of the magnetic field shall select the magnetic contribution to thermal transport and, through power-law investigation in the proposed classes of compounds, we shall find a signature of magnons transport and their scattering contribution off elastic vibrations. We plan to carry out the proposed investigation using the facility available at USP and, additionally, to develop a new probe dedicated to thermal transport coefficients at low temperature and under magnetic field. We aim at establishing an effective communication with all participants of the thematic project so that additional users may benefit from the new installed facility. (AU)