We present a comprehensive theoretical study of the magnetic field dependence of the near-field radiative heat transfer (NFRHT) between two parallel plates. We show that when the plates are made of doped semiconductors, the near-field thermal radiation can be severely affected by the application of a static magnetic field. We find that irrespective of its direction, the presence of a magnetic field reduces the radiative heat conductance, and dramatic reductions up to 700% can be found with fields of about 6 T at room temperature. We show that this striking behavior is due to the fact that the magnetic field radically changes the nature of the NFRHT. The field not only affects the electromagnetic surface waves (both plasmons and phonon polaritons) that normally dominate the near-field radiation in doped semiconductors, but it also induces hyperbolic modes that progressively dominate the heat transfer as the field increases. In particular, we show that when the field is perpendicular to the plates, the semiconductors become ideal hyperbolic near-field emitters. More importantly, by changing the magnetic field, the system can be continuously tuned from a situation where the surface waves dominate the heat transfer to a situation where hyperbolic modes completely govern the near-field thermal radiation. We show that this high tunability can be achieved with accessible magnetic fields and very common materials like n-doped InSb or Si. Our study paves the way for an active control of NFRHT and it opens the possibility to study unique hyperbolic thermal emitters without the need to resort to complicated metamaterials.

We show here the design of a magnetoplasmonic sensing platform consisting of a bilayer of a transparent conducting oxide and a gold film grown on a ferromagnetic substrate. Near the bulk plasmon frequency (ε ≈ 0) of the oxide film, sharp resonances are observed for the transverse magneto-optical Kerr effect, which are used for sensing permittivity changes. As a proof of concept, we demonstrate that the proposed architecture is able to detect glucose at millimolar concentration levels in aqueous media, even without any surface functionalization. Because no prism coupler is needed, the sensing platform may be miniaturized and employed in microfluidic systems for point-of-care devices.

One of the main challenges in the field of thermal radiation is to actively control the near-field radiative heat transfer (NFRHT) between closely spaced bodies. In this context, the use of an external magnetic field has emerged as a very attractive possibility and a plethora of physical phenomena have been put forward in the last few years. Here, we predict some additional magneticfield-induced phenomena that can take place in the context of NFRHT between planar layered structures containing magneto-optical (MO) materials (mainly doped semiconductors like InSb). In particular, we predict the possibility of increasing the NFRHT upon applying an external magnetic field in an asymmetric structure consisting of two infinite plates made of InSb and Au. We also study the impact of a magnetic field in the NFRHT between structures containing MO thin films and show that the effect is more drastic than in their bulk counterparts. Finally, we systematically investigate the anisotropic thermal magnetoresistance, i.e., the dependence of the radiative heat conductance on the orientation of an external magnetic field, in the case of two infinite plates made of InSb and show that one can strongly modulate the NFRHT by simply changing the orientation of the magnetic field. All the phenomena predicted in this work can be experimentally tested with existent technology and provide a new insight into the topic of active control of NFRHT.

In recent years there has been a number of proposals of thermal devices operating in the near-field regime that make use of phase-transition materials. Here, we present a theoretical study of near-field thermal diodes and transistors that combine superconducting materials with normal (nonsuperconducting) metals. To be precise, we show that a system formed by two parallel plates made of Nb and Au can exhibit unprecedented rectification ratios very close to unity at temperatures around the Nb superconducting critical temperature and for a wide range of gap size values within the near-field regime. Moreover, we also show that a superconducting Nb layer placed between Au plates can operate as a near-field thermal transistor where the amplification factor can be greatly tuned by varying different parameters such as the temperature and thickness of the Nb layer or the distance between the Nb layer and the Au plates. Overall, our work shows the potential of the use of superconductors for the realization of near-field thermal devices.

We present a theoretical study of the effect of an external dc magnetic field in the near-field radiative heat transfer between two one-dimensional magnetophotonic crystals with unit cells comprising a magneto-optical layer made of n-doped InSb and a dielectric layer. We find that in the absence of an external field, and depending on the gap size, the radiative heat transfer between these multilayer structures can be larger or smaller than that of the case of two InSb infinite plates. On the other hand, when an external magnetic field is applied, the near-field radiative heat transfer is reduced as a consequence of the suppression of hybridized surface polariton waves that are supported for transverse magnetic polarized light. We show that such reduction is exclusively due to the appearance of magnetic-field induced hyperbolic modes and not to the polarization conversion in this magneto-optical system.