Helical nanostructures – growth, cooperative & anisotropic electronics/optics in the PT-violating regime (Prof. Krstić)

Helical systems such as (nano)helices violate parity reversal symmetry (P). They represent non-linear systems with electromagnetic response functions that depend on a magnetic field vector (breaking of time reversal symmetry T). That is, their response function has spatial dispersion and (magnetic) anisotropy. Consequently, the electronic and optical properties of chiral (P-violating) systems in magnetic fields are nonlinear and anisotropic.
Furthermore, such structures can in principle have exhibit field-controlled metal to insulator transitions and (topological) charge order effects. They are prototypes of quantum optical systems for second harmonic generation, for the generation of entangled quantum states and also represent a photonic topological material. In terms of applications, such structures can be used, for example, as optical isolators or negative refractive index material.
Interestingly, the physics of such helical systems can be mapped (at least in part) to the same physics of other PT-violating systems, for example to chiral Weyl fermions exposed to an electromagnetic field or to phenomena in axion electrodynamics.
We grow nanohelix systems from different materials (Ge, Si, Ni, Ag) and achieve characteristic structural parameters < 100 nm, which leverage such nanohelix systems into the quantum regime. We investigate the properties of the nanohelix systems by means of electrical transport and optical methods in regard of PT-violation consequences and quantum-cooperative properties.


We study quantum cooperative effects in the linear and nonlinear optical response of helical metafilms. In particular, by tuning the characteristics of the metafilms, we aim to obtain a high value of the second-order nonlinear susceptibility. This property will be used to efficiently generate entangled photon pairs through spontaneous parametric down-conversion. Further, we will spatially modulate the properties of the metafilms, to vary and control the entanglement of the photon pairs, in particular in orbital angular momentum.

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