Anisotropic Thermal Magnetoresistance in Radiative Heat Transfer

The possibility to create and manipulate nanostructured materials encouraged the exploration of new strategies to control the electromagnetic properties without the need to modify its physical structure, i.e. by means of an external agent. An approach is the combination of magneto-optically active and resonant materials (e.g. plasmonic modes), where it is feasible to control the optical properties with magnetic fields in connection to the excitation of resonances [1] (magnetoplasmonics). It has been shown that these nanostructures can be employed to modulate the propagation wavevector of SPPs [2], which allows the development of label free sensors with enhanced capabilities [3-5] or to enhance the magneto-optical response in isolated entities as well as films, in connection with a strong localization of the electromagnetic field [6-8].<br/>Here we will show that they also play a crucial role in the active control of thermal emission and the radiative heat transfer (RHT) [9-11]. In particular Near Field RHT between two MO particles can be efficiently controlled by changing the direction of the magnetic field, in the spirit of the Anisotropic Magneto Resistance in spintronics [11]. This phenomenon, which we term anisotropic thermal magnetoresistance (ATMR), stems from the anisotropy of the photon tunneling induced by the magnetic field. We discuss this effect through the analysis of the radiative heat exchange between two InSb particles, and show that the ATMR can reach amplitudes of 100% for fields on the order of 1 T and up to 1000% for a magnetic field of 6 T. These values are several orders of magnitude larger than in standard spintronic devices. More importantly, this thermomagnetic effect paves the way for exploring heat transfer physics at pico- and even subpicosecond time scales, which are even shorter than the relaxation time of heat carriers. Moreover, we show that the heat flux is very sensitive to the magnetic field direction, which makes this effect very promising for the development of a new generation of thermal and magnetic sensors.<br/><br/><b>References:</b><br/>[1] G. Armelles, et al., Adv. Opt. Mat. <b>1</b>, 10 (2013)<br/>[2] V.V. Temnov et al., Nat. Photon. <b>4</b>, 107 (2010)<br/>[3] B. Sepuulveda, et al., Opt. Lett. <b>31</b>, 1085 (2006)<br/>[4] M.G. Manera, et al., Biosens. Bioelectron. <b>58</b>, 114 (2014)<br/>[5] B. Caballero, et al., ACS Photonics <b>3</b>, 203 (2016),<br/>[6] N. de Sousa et al., Phys. Rev. B <b>89</b>, 205419 (2014)<br/>[7] N. de Sousa et al., Sci. Rep. <b>6</b>, 30803 (2016)<br/>[8] M. Rollinger et al., Nano Lett. <b>16</b>, 2432-2438 (2016)<br/>[9] E. Moncada-Villa, et al., Phys. Rev. B <b>92</b>, 125418 (2015).<br/>[10] R. M. Abraham Ekeroth, et al., Phys. Rev. B <b>95</b>, 235428 (2017)<br/>[11] R. M. Abraham Ekeroth, et al., ACS Photonics <b>5</b>, 705 (2018).