Superoscillations Deliver Superspectroscopy.

In ordinary circumstances the highest frequency present in a wave is the highest frequency in its Fourier decomposition. It is however possible for there to be a spatial or temporal region where the wave locally oscillates at a still greater frequency in a phenomenon known as superoscillation. Superoscillations find application in wide range of disciplines, but at present their generation is based upon constructive approaches that are difficult to implement.

Magneto-optical nonreciprocity without chirality: Archimedean spirals on InSb.

We report the observation of magneto-optical nonreciprocity in Faraday geometry in a hybrid metamaterial consisting of an Archimedean spiral metasurface and semiconductor InSb that serves as the magneto-optical medium. None of the metamaterial constituents possesses chirality, which is usually a necessary ingredient for optical nonreciprocity in natural materials when the light travels along the magnetic field direction. We also find that our metamaterial can serve as an optical element for polarization control via magnetic field.

Ultrafast Neuromorphic Dynamics Using Hidden Phases in the Prototype of Relaxor Ferroelectrics.

Materials possessing multiple states are promising to emulate synaptic and neuronic behaviors. Their operation frequency, typically in or below the GHz range, however, limits the speed of neuromorphic computing. Ultrafast THz electric field excitation has been employed to induce nonequilibrium states of matter, called hidden phases in oxides.

Nonreciprocal Fabry-Perot effect and performance enhancement in a magneto-optical InSb-based Faraday terahertz isolator.

The Faraday effect due to the cyclotron resonance of conduction electrons in semiconductor InSb allows for nonreciprocity of transmitted light in our Faraday THz isolator operating in the presence of a small magnetic field. We select InSb as an efficient medium for our isolator due to its high electron mobility, low electron effective mass, and narrow band gap. Experimental measurements of the isolator performance indicate a maximum achieved isolation power of 18.

High-Temperature Terahertz Optical Diode Effect without Magnetic Order in Polar FeZnMo_{3}O_{8}.

We present a terahertz spectroscopic study of polar ferrimagnet FeZnMo_{3}O_{8}. Our main finding is a giant high-temperature optical diode effect, or nonreciprocal directional dichroism, where the transmitted light intensity in one direction is over 100 times lower than intensity transmitted in the opposite direction. The effect takes place in the paramagnetic phase with no long-range magnetic order in the crystal, which contrasts sharply with all existing reports of the terahertz optical diode effect in other magnetoelectric materials, where the long-range magnetic ordering is a necessary prerequisite.

Giant THz surface plasmon polariton induced by high-index dielectric metasurface.

We use computational approaches to explore the role of a high-refractive-index dielectric TiO grating with deep subwavelength thickness on InSb as a tunable coupler for THz surface plasmons. We find a series of resonances as the grating couples a normally-incident THz wave to standing surface plasmon waves on both thin and thick InSb layers. In a marked contrast with previously-explored metallic gratings, we observe the emergence of a much stronger additional resonance.

Thin InSb layers with metallic gratings: a novel platform for spectrally-selective THz plasmonic sensing.

We present a computational study of terahertz optical properties of a grating-coupled plasmonic structure based on micrometer-thin InSb layers. We find two strong absorption resonances that we interpret as standing surface plasmon modes and investigate their dispersion relations, dependence on InSb thickness, and the spatial distribution of the electric field. The observed surface plasmon modes are well described by a simple theory of the air/InSb/air tri-layer.

Observing the interplay between surface and bulk optical nonlinearities in thin van der Waals crystals.

Van der Waals materials, existing in a range of thicknesses from monolayer to bulk, allow for interplay between surface and bulk nonlinearities, which otherwise dominate only at atomically-thin or bulk extremes, respectively. Here, we observe an unexpected peak in intensity of the generated second harmonic signal versus the thickness of Indium Selenide crystals, in contrast to the quadratic increase expected from thin crystals. We explain this by interference effects between surface and bulk nonlinearities, which offer a new handle on engineering the nonlinear optical response of 2D materials and their heterostructures.

Probing the interplay between quantum charge fluctuations and magnetic ordering in LuFe2O4.

The mechanisms producing strong coupling between electric and magnetic order in multiferroics are not always well understood, since their microscopic origins can be quite different. Hence, gaining a deeper understanding of magnetoelectric coupling in these materials is the key to their rational design. Here, we use ultrafast optical spectroscopy to show that the influence of magnetic ordering on quantum charge fluctuations via the double-exchange mechanism can govern the interplay between electric polarization and magnetism in the charge-ordered multiferroic LuFe2O4.

Terahertz spectroscopy of spin waves in multiferroic BiFeO3 in high magnetic fields.

We have studied the magnetic field dependence of far-infrared active magnetic modes in a single ferroelectric domain BiFeO3 crystal at low temperature. The modes soften close to the critical field of 18.8 T along the [001] (pseudocubic) axis, where the cycloidal structure changes to the homogeneous canted antiferromagnetic state and a new strong mode with linear field dependence appears that persists at least up to 31 T.

Coherent spin precession via photoinduced antiferromagnetic interactions in La0.67Ca0.33MnO3.

Pronounced spin precessions are observed in a geometry with negligible canting of the magnetization in ferromagnetic La(0.67)Ca(0.33)MnO(3) thin films using the time-resolved magneto-optical Kerr effect.

Hybridization and superconducting gaps in the heavy-fermion superconductor PuCoGa5 probed via the dynamics of photoinduced quasiparticles.

We have examined the relaxation of photoinduced quasiparticles in the heavy-fermion superconductor PuCoGa5. The deduced electron-phonon coupling constant is incompatible with the measured superconducting transition temperature Tc=18.5  K, which speaks against phonon-mediated superconductivity.

Ultrafast pump-probe study of phase separation and competing orders in the underdoped (Ba,K)Fe2As2 superconductor.

We report measurements of quasiparticle relaxation dynamics in the high-temperature superconductor (Ba,K)Fe2As2 in optimally doped, underdoped, and undoped regimes. In the underdoped sample, spin-density wave (SDW) order forms at approximately 85 K, followed by superconductivity at approximately 28 K. We find the emergence of a normal-state order that suppresses SDW at a temperature T{*} approximately 60 K and argue that this normal-state order is a precursor to superconductivity.

Magnetic exchange interaction between rare-earth and Mn ions in multiferroic hexagonal manganites.

We report a study of magnetic dynamics in multiferroic hexagonal manganite HoMnO3 by far-infrared spectroscopy. The low-temperature magnetic excitation spectrum of HoMnO3 consists of magnetic-dipole transitions of Ho ions within the crystal-field split J = 8 manifold and of the triangular antiferromagnetic resonance of Mn ions. We determine the effective spin Hamiltonian for the Ho ion ground state.

Detection of coherent magnons via ultrafast pump-probe reflectance spectroscopy in multiferroic Ba0.6Sr1.4Zn2Fe12O22.

We report the detection of a magnetic resonance mode in multiferroic Ba0.6Sr1.4Zn2Fe12O22 using time-domain pump-probe reflectance spectroscopy.

Coupling between an optical phonon and the Kondo effect.

We explore the ultrafast optical response of Yb14MnSb11, providing further evidence that this compound is the first d-electron, ferromagnetic, underscreened Kondo lattice. These results also provide the first demonstration of coupling between an optical phonon mode and the Kondo effect.

Observation of competing order in a high-Tc superconductor using femtosecond optical pulses.

We present studies of the photoexcited quasiparticle dynamics in Tl(2)Ba(2)Ca(2)Cu(3)O(y) (Tl-2223) using femtosecond optical techniques. Deep into the superconducting state (below 40 K), a dramatic change occurs in the temporal dynamics associated with photoexcited quasiparticles rejoining the condensate. This is suggestive of entry into a coexistence phase which, as our analysis reveals, opens a gap in the density of states (in addition to the superconducting gap), and furthermore, competes with superconductivity resulting in a depression of the superconducting gap.

Interface magnetization reversal and anisotropy in Fe/AlGaAs(001).

The reversal process of the Fe interface layer magnetization in Fe/AlGaAs heterostructures is measured directly using magnetization-induced second-harmonic generation, and is compared with the reversal of the bulk magnetization as obtained from magneto-optic Kerr effect. The switching characteristics are distinctly different due to interface-derived anisotropy--single step switching occurs at the interface layer, while two-jump switching occurs in the bulk Fe for the magnetic field orientations employed. The angle between the interface and bulk magnetization may be as large as 40-85 degrees.