Do you want to know about the read-head inside your computer works? Why some butterflis are blue, yellow and multi-colored? The arrangement of spins in magnetic nanostructures and how they fluctuate? How your TV remote control works? How information is stored and read in your “pen drives” and flash memory? The quantum fluctuations of atoms in single crystals of solid Helium at temperatures near absolute zero? Or the structure and dynamics of stripe domains and puddles in ferroelectric, ferromagnetic and superconducting phases? These topics and more are investigated by the Fohtung Group, primarily using the interaction of radiation (photons, neutrons ans ions) with condensed matter systems. The focus of our research is the study of the structure and dynamics of condensed matter.
Our We investigate the quantum interaction between electromagnetic radiation (photons and neutrons) with condensed and soft matter at the nanoscale. To this end, we are interested in developing novel optical metrology (lens-less microscopy, coherent diffraction imaging with photons at synchrotrons and XFELs) and neutron scattering techniques to probe spatial and temporal dynamics due to competing charge-, spin-, orbital and lattice degree of freedoms at the nanoscale. Applications of our research includes Magneto-electric based nano-mechanical oscillators, sensing, quantum photonics, Magneto-electric conversion of optical energy to electricity, transparent ceramics and biomimetics. We also focus on training the next generation of innovative students/scientists. We aim to foster an environment that is conducive to learning, creativity, and personal development.
Our group is broadly engaged in the study of the structure and dynamics of condensed matter using the techniques of optical, x-ray and neutron scattering. For this purpose, we use in-house x-ray sources and diffractometers, Optical Metrology, while most of our studies require an intensity that can only be provided at synchrotron sources and XFELs.
Towards quantum biomemetics and bio-inspired quantum devices
For decades, humans have mimicked nature for inspiration to create or optimize devices and machines, as well as industrial fabrication, characterization processes and strategies. Besides studying quantized plasma oscillations (plasmons) in metallic nanostructures and at interfaces between metals and dielectrics, we dwell into a branch of science which designs materials and machines inspired in the structure and function of biological systems. Since nature possesses a diversity of photonic structures that have been fine-tuned over millions of years by trial and error; we study a range of bio-inspired features such as structural color vs pigmentary color with the aim of building new photonic devices.
A Conventional broadband reflection microscope with different angles of illumination (a) is used to image the bright metallic blue colored structures of the Morpho Marcus butterfly wing with illumination from all angles (b) and to show the directional dependency of the reflected light with blue wavelength synthesized in a pseudo-color image (c) where blue channel of the 2pm illumination image is assigned to a blue channel of the synthesized image, blue channel of the 8pm illumination image is assigned to red channel of the synthesized image and blue channel of 5pm illumination image is assigned to the green channel of the synthesized image. This is a direct evidence of structural coloring.
As an alternative to electronic charge, the storage and transport of electronic spin in semiconductor devices – “spintronics”, may revolutionize the electronic device industry, with spin based transistors , opto-electronic devices, and memory. Moreover, the ability to preserve coherent spin states in conventional semiconductors and quantum dots may eventually enable quantum computing in the solid state.
In the so-called intrinsic multiferroics (those that naturally combine magnetic and electric order parameters), the magnetoelectric coupling is however often weak and heterogeneous multiferroics (composite materials) are currently developed to optimize order parameter coupling. Magnetic and ferroelectric materials are thus artificially combined and two main paths are followed to achieve the magnetoelectric coupling: either strains or modulation of charge carrier density. Several works have been recently reported on strains-driven magnetoelectric coupling, generally achieved when combining magnetostrictive and piezoelectric materials and on the control of ferromagnetic properties achieved through the modulation of the carrier density by applying a gate voltage. In this domain, the effects on ferromagnetic semiconductors have been intensively investigated because its ferromagnetic properties are function of carrier concentration; But electric field control of coercivity, anisotropy, Curie temperature in ferromagnetic metallic layers have also been recently reported. Complex magnetic oxides are other interesting candidates for charge-driven magnetoelectric coupling because of high sensitivity of strongly correlated magnetic systems to competing electronic ground states. Charge plays especially a prominent role in double exchange, hopping and orbital overlap. A large charge-driven magnetoelectric coupling effect has thus been reported in Sr-doped lanthanum manganite (LSMO)/ferroelectric (PZT) composite structure.
We aim at taking an alternative path to multiferroics by designing a piezoelectric-ferromagnetic-semiconductor heterostructures or nanoscale devices in which the applied electric field induces strain field that propagates into the ferromagnetic material and alters the its magnetization.
In magneto-electronic materials such as multiferroics an external electric field displaces ions from their equilibrium positions, which alters the magnetostatic and exchange interactions yielding magnetoelectric coupling. There has been extensive effort to realize multiferroic materials in thin films and nanostructures. In ferromagnetic/piezoelectric composite structures (which is the focus of this proposal), electric field induced strain in the piezoelectric material can alter the magnetization of the ferromagnetic material due to magnetostrictive effects. Recent theoretical calculations suggest that in ferroelectric insulator/ferromagnetic heterostructures that ferroelectric displacements of the interfacial atoms may be reversed by electric fields, significantly altering the interfacial moment or anisotropy. More generally magneto-electric effects may be a common feature of interfaces between dielectrics and metals. Understanding and control of these effects may ultimately lead to new memory and spintronics logic elements.