Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

Abstract: Optical magneto-spectroscopy methods (Raman scattering, far-infrared transmission, and photoluminescence) have been applied to investigate the properties of the NiPS3 semiconducting antiferromagnet. The fundamental magnon gap excitation in this van der Waals material has been found to be split into two components, in support of the biaxial character of the NiPS3 antiferromagnet. Photoluminescence measurements in the near-infrared spectral range show that the intriguing 1.475 eV-excitation unique to the NiPS3 antiferromagnetic phase splits upon the application of the in-plane magnetic field. The observed splitting patterns are correlated with properties of magnon excitations and reproduced with the simple model proposed. Possible routes toward a firm identification of the spin-entangled 1.475 eV-optical excitation in NiPS3, which can hardly be recognized as a coherent Zhang-Rice exciton, are discussed.

Abstract: The formation of a topological superconducting phase in a quantum-dot-based Kitaev chain requires nearest neighbor crossed Andreev reflection and elastic co-tunneling. Here we report on a hybrid InSb nanowire in a three-site Kitaev chain geometry - the smallest system with well-defined bulk and edge - where two superconductor-semiconductor hybrids separate three quantum dots. We demonstrate pairwise crossed Andreev reflection and elastic co-tunneling between both pairs of neighboring dots and show sequential tunneling processes involving all three quantum dots. These results are the next step towards the realization of topological superconductivity in long Kitaev chain devices with many coupled quantum dots.

Abstract: The ferromagnetic Weyl semimetals (WSM), such as Co3Sn2S2, are three-dimensional topological states of matter possessing pairs of Weyl points characterized by the opposite chiralities.We model ferromagnetic WSM by a time reversal symmetry(TRS) broken and inversion symmetry protected Bloch Hamiltonian involving index specifying the chirality of the Weyl points, energy parameter determining the shift of the Weyl nodes, terms capturing the tunnelling effect, exchange field in order to take care of the ferromagnetic(FM) order, and the angle formed by the spin moments and the axis perpendicular to the plane of the system. For the FM order along this axis, the bands of opposite chirality almost linearly cross each other (with band inversion) at Weyl points above and below the Fermi level. The in-plane spin order, however, lacks the presence of the Weyl nodes at some points in the Brillouin zone. We also show that, under certain conditions, the incidence of the circularly polarized optical field (CPOF) leads to the emergence of Weyl semimetals from Dirac semimetals due to broken time-reversal symmetry.

Abstract: We study radiative heat transfer between two nanoemitters placed inside different types of closed cavities by means of a fluctuational-electrodynamics approach. We highlight a very sharp dependence of this transfer on cavity width, and connect this to the matching between the material-induced resonance and the resonant modes of the cavity. In resonant configurations, this allows for an energy-flux amplification of several orders of magnitude with respect to the one exchanged between two emitters in vacuum as well as between two black-bodies, even at separation distances much larger than the thermal wavelength. On the other hand, variations of the cavity width by a few percent allow a reduction of the flux by several orders of magnitude and even a transition to inhibition compared to the vacuum scenario. Our results pave the way to the design of thermal waveguides for the long-distance transport of super-Planckian heat flux and selective heat-transfer in many-body system.