R. C. Rai, J. Cao, S. Brown, J. L. Musfeldt, ∗ D. Kasinathan, D. J. Singh, G. Lawes, N. Rogado, R. J. Cava, and X. Wei Department of Chemistry, University of Tennessee, Knoxville, TN 37996 Department of Physics, University of California Davis, Davis, CA 95616 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge,TN 37831-6032 Department of Physics, Wayne State University, Detroit, MI 48201 DuPont Central Research and Development, Experimental Station, Wilmington, DE 19880-0328 Department of Chemistry and Princeton Materials Institute, Princeton University, Princeton, NJ 08544 National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310

Large high energy magnetodielectric effects are observed in the bilayer manganite (La0.4Pr0.6)1.2Sr1.8Mn2O7, a direct consequence of exploiting magnetoresistance changes associated with the field driven spin-glass insulator to ferromagnetic metal transition and its high temperature remnant. The low temperature magnetodielectric contrast is as large as ∼100% near 0.8eV at 10T and over 10 000% in selected phonon regions. The 300K magnetodielectric contrast is ∼20% near 1.1eV at 30T. The results are potentially useful for magnetic memory applications away from the dc limit.

In this work, the authors present a systematic study on the variation of the structural and the optical properties of GaAsSbN∕GaAs single quantum wells (SQWs) as a function of nitrogen concentration. These SQW layers were grown by the solid source molecular beam epitaxial technique. A maximum reduction of 328meV in the photoluminescence (PL) peak energy of GaAsSbN was observed with respect to the reference GaAsSb QW. 8K and RT PL peak energies of 0.774eV (FWHM of ∼25meV) and 0.729eV (FWHM of ∼67meV) (FWHM denotes full width at half maximum) corresponding to the emission wavelengths of 1.6 and 1.7μm, respectively, have been achieved for a GaAsSbN SQW of N∼1.4%. The pronounced S-curve behavior of the PL spectra at low temperatures is a signature of exciton localization, which is found to decrease from 16to9meV with increasing N concentration of 0.9%–2.5%. The diamagnetic shift of 13meV observed in the magnetophotoluminescence spectra of the nitride sample with N∼1.4% is smaller in comparison to the value of 28meV in the non-nitride sample, indicative of an enhancement in the electron effective mass in the nitride QWs. Electron effective mass of 0.065mo has been estimated for a SQW with N∼1.4% using the band anticrossing model.

We investigate the optical and magneto-optical properties of $\mathrm{Ho}\mathrm{Mn}{\mathrm{O}}_{3}$ in order to elucidate the spin-charge coupling and high-energy magnetodielectric effect. We find that the $\mathrm{Mn}\phantom{\rule{0.2em}{0ex}}d$ to $d$ excitations are sensitive to the cascade of low-temperature magnetic transitions involving the ${\mathrm{Mn}}^{3+}$ moment, direct evidence for spin-charge coupling. An applied magnetic field also modifies the on-site excitations. The high-energy magnetodielectric contrast ($\ensuremath{\sim}8%$ at $20\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ near $1.8\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$) derives from the substantial mixing in this multiferroic system.

In this work, the effects of N incorporation on the optical properties of GaAsSbN∕GaAs single quantum wells (SQWs) have been investigated using temperature, excitation, and magnetic dependencies of photoluminescence (PL) characteristics. These layers were grown in an elemental solid source molecular beam epitaxy system with a rf plasma N source. The N concentrations in the range of 0.5%–2.5% were investigated in this study. The SQW with N∼0.5% exhibits a behavior similar to that in an intermediate regime where the contributions from the localized states in the band gap are dominant. The temperature and excitation dependencies of the PL characteristics indicate that for the N concentration of 0.9% and above, the alloy behavior is analogous to that of a regular alloy and the changes in optical properties are only marginal. The conduction band effective mass (meff) values computed from the magnetophotoluminescence spectra using a variational formalism and the band anticrossing model are in good agreement and indicate enhanced values of meff. However, there is no significant variation in meff values of QWs for N⩾0.9%. Small redshift of about 30–50meV for the temperature variations from 10to300K in conjunction with unusually small blueshift observed in the excitation dependence of PL for N⩾0.9% indicate that this system holds a great promise for laser applications at 1.55μm and beyond.

We use a combination of optical spectroscopy, first-principles calculations, and energy-dependent magnetooptical measurements to investigate the high-energy magnetodielectric effect in the frustrated kagome staircase compound Co3V2O8 and develop structure-property relations in this family of materials. The optical spectra show two distinct Co on-site d to d excitations that can be assigned as deriving from spine and cross-tie sites, respectively. The energy separation between these features is substantially larger in Co3V2O8 than in quasiisostructural Ni3V2O8, indicating that the spine and cross-tie crystal field environments are more dissimilar in the Co compound compared with those in the Ni analog. Despite the similar appearance of the spectra, orbital correlation effects seem to dominate the optical properties of Co3V2O8, different from Ni3V2O8. Through the 6.2 K ferromagnetic transition temperature, Co3V2O8 displays 2% dielectric contrast near 1.5 eV, larger than that observed in the static dielectric constant. Co3V2O8 also shows a high-energy magnetodielectric contrast of 2% near 1.4 eV at 30 T, smaller than that of Ni3V2O8 16% near 1.3 eV at 30 T. We attribute this result to the lack of strong lattice coupling at the low temperature magnetic phase boundaries.

Cooperative spontaneous recombination (superfluorescence) of electron-hole plasmas in semiconductors has been a challenge to observe due to ultrafast decoherence. We argue that superfluorescence can be achieved in quantum-confined semiconductor systems and present experimental evidence for superfluorescence from high-density photoexcited electronhole plasmas in magnetized quantum wells. At a critical magnetic field strength and excitation fluence, we observe a clear transition in the band-edge photoluminescence from omnidirectional output to a randomly directed but highly collimated beam. Changes in the linewidth, carrier density, and magnetic field scaling of the emission spectra correlate precisely with the onset of random directionality and are consistent with cooperative recombination.

We use a combination of optical spectra, first principles calculations, and energy dependent magneto-optical measurements to elucidate the electronic structure and to study the phase diagram of Ni_3V_2O_8. We find a remarkable interplay of magnetic field and optical properties that reveals additional high magnetic field phases and an unexpected electronic structure which we associate with the strong magneto-dielectric couplings in this material over a wide energy range. Specifically, we observed several prominent magneto-dielectric effects that derive from changes in crystal field environment around Ni spine and cross-tie centers. This effect is consistent with a field-induced modification of local structure. Symmetry-breaking effects are also evident with temperature. We find Ni_3V_2O_8 to be an intermediate gap, local moment band insulator. This electronic structure is particularly favorable for magneto-dielectric couplings, because the material is not subject to the spin charge separation characteristic of strongly correlated large gap Mott insulators, while at the same time remaining a magnetic insulator independent of the particular spin order and temperature.

We observed a large HEMD effect in the bilayer manganite (La$_{0.4}$Pr$_{0.6}$)$_{1.2}$Sr$_{1.8}$Mn$_2$O$_7$, a direct consequence of field driven spin-glass insulator to ferromagnetic metal transition. The remnants of the transition can be used to achieve dielectric contrast at room temperature. This discovery suggests that electronic mechanisms such as the metal-insulator transition, charge ordering, and orbital ordering can be exploited to give substantial dielectric contrast in other materials.

We report the optical and magneto-optical properties of K2V3O8, an S=1/2 quasi-two-dimensional Heisenberg antiferromagnet. Local spin density approximation electronic structure calculations are used to assign the observed excitations and analyze the field dependent features. Two large magneto-optical effects, centered at ~1.19 and 2.5 eV, are attributed to field-induced changes in the V 4+ d to d on-site excitations due to modification of the local crystal field environment of the VO5 square pyramids with applied magnetic field. Taken together, the evidence for a soft lattice, the presence of vibrational fine structure on the sharp 1.19 eV magneto-optical feature,and the fact that these optical excitations are due to transitions from a nearly pure spin polarized V d state to hybridized states involving both V and O, suggest that the magneto-dielectric effect in K2V3O8 is driven by strong lattice coupling.

We investigate the bulk magnetic, electron paramagnetic resonance, and magneto-optical properties of {Ni4Mo12}, a magnetic molecule with antiferromagnetically coupled tetrahedral {Ni4Mo12} in a diamagnetic molybdenum matrix. The low-temperature magnetization exhibits steps at irregular field intervals, a result that cannot be explained using a Heisenberg model even if it is augmented by magnetic anisotropy and biquadratic terms. Allowing the exchange and anisotropy parameters to depend on the magnetic field provides the best fit to our data, suggesting that the molecular structure (and thus the interactions between spins) may be changing with applied magnetic field.

We measured the magneto-optical response of ${({\mathrm{La}}_{0.4}{\mathrm{Pr}}_{0.6})}_{1.2}{\mathrm{Sr}}_{1.8}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ in order to investigate the microscopic aspects of the magnetic-field-driven spin-glass-insulator to ferromagnetic-metal transition. Application of a magnetic field recovers the ferromagnetic state with an overall redshift of the electronic structure, growth of the bound carrier localization associated with ferromagnetic domains, development of a pseudogap, and softening of the Mn-O stretching and bending modes. We discuss field- and temperature-induced trends within the framework of the Tomioka-Tokura global electronic phase diagram picture and suggest that controlled disorder near a phase boundary can be used to tune the magnetodielectric response. Remnants of the spin-glass-insulator to ferromagnetic-metal transition can also drive $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ color changes in ${({\mathrm{La}}_{0.4}{\mathrm{Pr}}_{0.6})}_{1.2}{\mathrm{Sr}}_{1.8}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$.

We investigate photoluminescence from a high-density electron-hole plasma in semiconductor quantum wells created via intense femtosecond excitation in a strong perpendicular magnetic field, a fully quantized and tunable system. At a critical magnetic field strength and excitation fluence, we observe a clear transition in the band-edge photoluminescence from omnidirectional output to a randomly directed but highly collimated beam. In addition, changes in the linewidth, carrier density, and magnetic field scaling of the photoluminescence spectral features correlate precisely with the onset of random directionality, indicative of cooperative recombination from a high-density population of free carriers in a semiconductor environment.

Near-infrared magneto-optical spectroscopy of single-walled carbon nanotubes reveals two absorption peaks with an equal strength at high magnetic fields (>55 T). We show that the peak separation is determined by the Aharonov-Bohm phase due to the tube-threading magnetic flux, which breaks the time-reversal symmetry and lifts the valley degeneracy. This field-induced symmetry breaking thus overcomes the Coulomb-induced intervalley mixing which is predicted to make the lowest exciton state optically inactive (or dark).

Foundations of Quantum Mechanics in the Light of New Technology, pp. 234-241 (2006) No AccessOPTICAL PROCESSES IN SINGLE-WALLED CARBON NANOTUBES THREADED BY A MAGNETIC FLUXJ. KONO, S. ZARIC, J. SHAVER, X. WEI, S. A. CROOKER, O. PORTUGALL, G. L. J. A. RIKKEN, R. H. HAUGE, and R. E. SMALLEYJ. KONODepartment of Electrical and Computer Engineering, Rice University, Houston, Texas 77005, U.S.A., S. ZARICDepartment of Electrical and Computer Engineering, Rice University, Houston, Texas 77005, U.S.A., J. SHAVERDepartment of Electrical and Computer Engineering, Rice University, Houston, Texas 77005, U.S.A., X. WEINational High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, U.S.A., S. A. CROOKERNational High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, U.S.A., O. PORTUGALLLaboratoire National des Champs Magnétiques Pulsés, 31432 Toulouse Cedex 04, France, G. L. J. A. RIKKENLaboratoire National des Champs Magnétiques Pulsés, 31432 Toulouse Cedex 04, France, R. H. HAUGEDepartment of Chemistry, Rice University, Houston, Texas 77005, U.S.A., and R. E. SMALLEYDepartment of Chemistry, Rice University, Houston, Texas 77005, U.S.A.https://doi.org/10.1142/9789812773210_0050Cited by:0 (Source: Crossref) PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Abstract: Single-walled carbon nanotubes threaded by a magnetic flux φ are predicted to posses novel magnetic and optical properties, critically depending on the value of φ/φ0 where φ0 is the magnetic flux quantum. This is a consequence of the Aharonov-Bohm phase 2πφ/φ0 influencing the boundary conditions on the Bloch wavefunctions. Here we report results of a series of magneto-optical studies of micelle-suspended single-walled carbon nanotubes in aqueous solutions in high magnetic fields. Their exotic magnetic properties manifest themselves in near-infrared magneto-absorption and magneto-photoluminescence spectra, including static and dynamic magnetic linear dichroism, splittings of exciton peaks, and field-induced band gap shrinkage. We show that these observations are quantitatively consistent with existing theories based on the Aharonov-Bohm effect. Keywords: carbon nanotubesAharonov-Bohm effectmagnetic flux quantum FiguresReferencesRelatedDetails Recommended Foundations of Quantum Mechanics in the Light of New TechnologyMetrics History Keywordscarbon nanotubesAharonov-Bohm effectmagnetic flux quantumPDF download

Ultrafast optical excitation of a dense electron–hole plasma in In x Ga 1−x As multiple quantum wells in high magnetic fields (>20T) produces cooperative radiative recombination between conduction and valence band Landau levels (LL). Above a critical threshold, the emission is characterized by very narrow LL line widths, superlinear increase with increasing field and laser excitation fluence, and stochastic directionality from shot to shot. Here, we investigate the effects of temperature and excitation geometry on the emission properties.