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Full-Text Articles in Physics

Phase Transition In Bulk Single Crystals And Thin Films Of Vo2 By Nanoscale Infrared Spectroscopy And Imaging, Mengkun Liu, Aaron J. Sternbach, Martin Wagner, Tetiana V. Slusar, Sergey L. Bud'ko, Salinporn Kittiwatanakul, M. M. Qazilbash, Alexander Mcleod, Zhe Fei, Elsa Abreu, Jingdi Zhang, Michael Goldflam, Siyuan Dai, Guang-Xin Ni, Jiwei Lu, Hans A. Bechtel, Michael C. Martin, Markus B. Raschke, Richard D. Averitt, Stuart A. Wolf, Hyun-Tak Kim, Paul C. Canfield, D. N. Basov Jun 2015

Phase Transition In Bulk Single Crystals And Thin Films Of Vo2 By Nanoscale Infrared Spectroscopy And Imaging, Mengkun Liu, Aaron J. Sternbach, Martin Wagner, Tetiana V. Slusar, Sergey L. Bud'ko, Salinporn Kittiwatanakul, M. M. Qazilbash, Alexander Mcleod, Zhe Fei, Elsa Abreu, Jingdi Zhang, Michael Goldflam, Siyuan Dai, Guang-Xin Ni, Jiwei Lu, Hans A. Bechtel, Michael C. Martin, Markus B. Raschke, Richard D. Averitt, Stuart A. Wolf, Hyun-Tak Kim, Paul C. Canfield, D. N. Basov

Ames Laboratory Publications

We have systematically studied a variety of vanadium dioxide (VO2) crystalline forms, including bulk single crystals and oriented thin films, using infrared (IR) near-field spectroscopic imaging techniques. By measuring the IR spectroscopic responses of electrons and phonons in VO2 with sub-grain-size spatial resolution (∼20nm), we show that epitaxial strain in VO2 thin films not only triggers spontaneous local phase separations, but also leads to intermediate electronic and lattice states that are intrinsically different from those found in bulk. Generalized rules of strain- and symmetry-dependent mesoscopic phase inhomogeneity are also discussed. These results set the stage for a comprehensive understanding of ...


Superconductivity Versus Structural Phase Transition In The Closely Related Bi2rh3.5s2 And Bi2rh3s2, Udhara S. Kaluarachchi, Weiwei Xie, Qisheng Lin, Valentin Taufour, Sergey L. Bud'ko, Gordon J. Miller, Paul C. Canfield May 2015

Superconductivity Versus Structural Phase Transition In The Closely Related Bi2rh3.5s2 And Bi2rh3s2, Udhara S. Kaluarachchi, Weiwei Xie, Qisheng Lin, Valentin Taufour, Sergey L. Bud'ko, Gordon J. Miller, Paul C. Canfield

Ames Laboratory Publications

Single crystals of Bi2Rh3S2 and Bi2Rh3.5S2 were synthesized by solution growth, and the crystal structures and thermodynamic and transport properties of both compounds were studied. In the case ofBi2Rh3S2, a structural first-order transition at around 165 K is identified by single-crystal diffraction experiments, with clear signatures visible in resistivity, magnetization, and specific heat data. No superconducting transition for Bi2Rh3S2 was observed down to 0.5 K. In contrast, no structural phase transition at high temperature was observed for Bi2Rh3.5S2; however, bulk superconductivity with a critical temperature, Tc≈1.7 K, was observed. The Sommerfeld coefficient γ and the ...


Neutron-Scattering Measurements Of Spin Excitations In Lafeaso And Ba(Fe0.953co0.047)2as2: Evidence For A Sharp Enhancement Of Spin Fluctuations By Nematic Order, Qiang Zhang, Rafael M. Fernandes, Jagat Lamsal, Jiaqiang Yan, Songxue Chi, Gregory S. Tucker, Daniel K. Pratt, Jeffrey W. Lynn, R. William Mccallum, Paul C. Canfield, Thomas A. Lograsso, Alan I. Goldman, David Vaknin, Robert J. Mcqueeney Feb 2015

Neutron-Scattering Measurements Of Spin Excitations In Lafeaso And Ba(Fe0.953co0.047)2as2: Evidence For A Sharp Enhancement Of Spin Fluctuations By Nematic Order, Qiang Zhang, Rafael M. Fernandes, Jagat Lamsal, Jiaqiang Yan, Songxue Chi, Gregory S. Tucker, Daniel K. Pratt, Jeffrey W. Lynn, R. William Mccallum, Paul C. Canfield, Thomas A. Lograsso, Alan I. Goldman, David Vaknin, Robert J. Mcqueeney

Ames Laboratory Publications

Inelastic neutron scattering is employed to investigate the impact of electronic nematic order on the magnetic spectra of LaFeAsO and Ba(Fe0.953Co0.047)2As2. These materials are ideal to study the paramagnetic-nematic state, since the nematic order, signaled by the tetragonal-to-orthorhombic transition at TS, sets in well above the stripe antiferromagnetic ordering at TN. We find that the temperature-dependent dynamic susceptibility displays an anomaly at TS followed by a sharp enhancement in the spin-spin correlation length, revealing a strong feedback effect of nematic order on the low-energy magnetic spectrum. Our findings can be consistently described by a model that ...


Morphological Transformations In The Magnetite Biomineralizing Protein Mms6 In Iron Solutions: A Small-Angle X‑Ray Scattering Study, Honghu Zhang, Xunpei Liu, Shuren Feng, Wenjie Wang, Klaus Schmidt-Rohr, Mufit Akinc, Marit Nilsen-Hamilton, David Vaknin, Surya K. Mallapragada Feb 2015

Morphological Transformations In The Magnetite Biomineralizing Protein Mms6 In Iron Solutions: A Small-Angle X‑Ray Scattering Study, Honghu Zhang, Xunpei Liu, Shuren Feng, Wenjie Wang, Klaus Schmidt-Rohr, Mufit Akinc, Marit Nilsen-Hamilton, David Vaknin, Surya K. Mallapragada

Chemical and Biological Engineering Publications

Magnetotactic bacteria that produce magnetic nanocrystals of uniform size and well-defined morphologies have inspired the use of biomineralization protein Mms6 to promote formation of uniform magnetic nanocrystals in vitro. Small angle X-ray scattering (SAXS) studies in physiological solutions reveal that Mms6 forms compact globular threedimensional (3D) micelles (approximately 10 nm in diameter) that are, to a large extent, independent of concentration. In the presence of iron ions in the solutions, the general micellar morphology is preserved, however, with associations among micelles that are induced by iron ions. Compared with Mms6, the m2Mms6 mutant (with the sequence of hydroxyl/carboxyl containing ...


Reconstruction Of Steps On The Cu(111) Surface Induced By Sulfur, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Yousoo Kim, Patricia A. Thiel Jan 2015

Reconstruction Of Steps On The Cu(111) Surface Induced By Sulfur, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Yousoo Kim, Patricia A. Thiel

Chemistry Publications

Arich menagerie of structures is identified at 5Kfollowing adsorption of lowcoverages (≤0.05 monolayers) of S on Cu(111) at room temperature. This paper emphasizes the reconstructions at the steps. The A-type close-packed step has 1 row of S atoms along its lower edge, where S atoms occupy alternating pseudo-fourfold-hollow (p4fh) sites. Additionally, there are 2 rows of S atoms of equal density on the upper edge, bridging a row of extra Cu atoms, together creating an extended chain. The B-type close-packed step exhibits an even more complex reconstruction, in which triangle-shaped groups of Cu atoms shift out of their ...


Self-Organization Of S Adatoms On Au(111): √3r30° Rows At Low Coverage, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Yousoo Kim, Patricia A. Thiel Jan 2015

Self-Organization Of S Adatoms On Au(111): √3r30° Rows At Low Coverage, Holly L. Walen, Da-Jiang Liu, Junepyo Oh, Hyunseob Lim, James W. Evans, Yousoo Kim, Patricia A. Thiel

Chemistry Publications

Using scanning tunneling microscopy, we observe an adlayer structure that is dominated by short rows of S atoms, on unreconstructed regions of a Au(111) surface. This structure forms upon adsorption of low S coverage (less than 0.1 monolayer) on a fully reconstructed clean surface at 300 K, then cooling to 5 K for observation. The rows adopt one of three orientations that are rotated by 30◦ from the close-packed directions of the Au(111) substrate, and adjacent S atoms in the rows are separated by √ 3 times the surface lattice constant, a. Monte Carlo simulations are performed on ...


Determining Whether Metals Nucleate Homogeneously On Graphite: A Case Study With Copper, David Victor Appy, Huaping Lei, Yong Han, Cai-Zhuang Wang, Michael C. Tringides, Dahai Shao, Emma Jane Kwolek, James W. Evans, Patricia A. Thiel Nov 2014

Determining Whether Metals Nucleate Homogeneously On Graphite: A Case Study With Copper, David Victor Appy, Huaping Lei, Yong Han, Cai-Zhuang Wang, Michael C. Tringides, Dahai Shao, Emma Jane Kwolek, James W. Evans, Patricia A. Thiel

Chemistry Publications

We observe that Cu clusters grow on surface terraces of graphite as a result of physical vapor deposition in ultrahigh vacuum. We show that the observation is incompatible with a variety of models incorporating homogeneous nucleation and calculations of atomic-scale energetics. An alternative explanation, ion-mediated heterogeneous nucleation, is proposed and validated, both with theory and experiment. This serves as a case study in identifying when and whether the simple, common observation of metal clusters on carbon-rich surfaces can be interpreted in terms of homogeneous nucleation. We describe a general approach for making system-specific and laboratory-specific predictions.


Complex Magnetic Ordering In Cege1.76 Studied By Neutron Diffraction, Wageesha T. Jayasekara, W. Tian, Halyna Hodovanets, Paul C. Canfield, Andreas Kreyssig, Alan I. Goldman Oct 2014

Complex Magnetic Ordering In Cege1.76 Studied By Neutron Diffraction, Wageesha T. Jayasekara, W. Tian, Halyna Hodovanets, Paul C. Canfield, Andreas Kreyssig, Alan I. Goldman

Ames Laboratory Publications

Neutron diffraction measurements on a single crystal of CeGe1.76 reveal a complex series of magnetic transitions at low temperature. At TN≈7 K, there is a transition from a paramagnetic state at higher temperature to an incommensurate magnetic structure characterized by a magnetic propagation vector (0 0 τ) with τ≈14 and the magnetic moment along the a axis of the orthorhombic unit cell. Below TLI≈5 K, the magnetic structure locks in to a commensurate structure with τ=14 and the magnetic moment remains along the a axis. Below T☆≈4 K, we find additional half-integer and integer ...


Effect Of Electron Irradiation On Superconductivity In Single Crystals Of Ba(Fe1−Xrux)2as2 (X=0.24), Ruslan Prozorov, M. Kończykowski, Makariy A. Tanatar, Alexander N. Thaler, Sergey L. Bud'ko, Paul C. Canfield, V. Mishra, P. J. Hirschfeld Oct 2014

Effect Of Electron Irradiation On Superconductivity In Single Crystals Of Ba(Fe1−Xrux)2as2 (X=0.24), Ruslan Prozorov, M. Kończykowski, Makariy A. Tanatar, Alexander N. Thaler, Sergey L. Bud'ko, Paul C. Canfield, V. Mishra, P. J. Hirschfeld

Ames Laboratory Publications

A single crystal of isovalently substituted Ba(Fe1−xRux)2As2 (x=0.24) is sequentially irradiated with 2.5 MeV electrons up to a maximum dose of 2.1×1019 e−/cm2. The electrical resistivity is measuredin situ at T=22  K during the irradiation and ex situ as a function of temperature between subsequent irradiation runs. Upon irradiation, the superconducting transition temperature Tc decreases and the residual resistivity ρ0 increases. We find that electron irradiation leads to the fastest suppression of Tccompared to other types of artificially introduced disorder, probably due to the strong short-range potential of the ...


Combined Effects Of Transition Metal (Ni And Rh) Substitution And Annealing/Quenching On The Physical Properties Of Cafe2as2, Sheng Ran, Sergey L. Bud'ko, Warren E. Straszheim, Paul C. Canfield Aug 2014

Combined Effects Of Transition Metal (Ni And Rh) Substitution And Annealing/Quenching On The Physical Properties Of Cafe2as2, Sheng Ran, Sergey L. Bud'ko, Warren E. Straszheim, Paul C. Canfield

Ames Laboratory Publications

We performed systematic studies of the combined effects of annealing/quenching temperature (TA/Q) and T=Ni, Rh substitution (x) on the physical properties of Ca(Fe1−xTx)2As2. We constructed two-dimensional, TA/Q-x phase diagrams for the low-temperature states for both substitutions to map out the relations between ground states and compared them with that of Co substitution. Ni substitution, which brings one more extra electron per substituted atom and suppresses the c-lattice parameter at roughly the same rate as Co substitution, leads to a similar parameter range of antiferromagnetic/orthorhombic phase space in the TA/Q-x space as ...


Magnetic And Transport Properties Of I-R-Cd Icosahedral Quasicrystals (R=Y,Gd-Tm), Tai Kong, Sergey L. Bud'ko, Anton Jesche, John Mcarthur, Andreas Kreyssig, Alan I. Goldman, Paul C. Canfield Jul 2014

Magnetic And Transport Properties Of I-R-Cd Icosahedral Quasicrystals (R=Y,Gd-Tm), Tai Kong, Sergey L. Bud'ko, Anton Jesche, John Mcarthur, Andreas Kreyssig, Alan I. Goldman, Paul C. Canfield

Ames Laboratory Publications

We present a detailed characterization of the recently discovered i-R-Cd (R=Y,Gd-Tm) binary quasicrystals by means of x-ray diffraction, temperature-dependent dc and ac magnetization, temperature-dependent resistance, and temperature-dependent specific heat measurements. Structurally, the broadening of x-ray diffraction peaks found for i-R-Cd is dominated by frozen-in phason strain, which is essentially independent of R. i-Y-Cd is weakly diamagnetic and manifests a temperature-independent susceptibility. i-Gd-Cd can be characterized as a spin glass below 4.6 K via dc magnetization cusp, a third order nonlinear magnetic susceptibility peak, a frequency-dependent freezing temperature, and a broad maximum in the specific heat. i-R-Cd (R ...


Fermi Surface Reconstruction In (Ba1−Xkx)Fe2as2 (0.44≤X≤1) Probed By Thermoelectric Power Measurements, Halyna Hodovanets, Yong Liu, Anton Jesche, Sheng Ran, Eun Deok Mun, Thomas A. Lograsso, Sergey L. Bud'ko, Paul C. Canfield Jun 2014

Fermi Surface Reconstruction In (Ba1−Xkx)Fe2as2 (0.44≤X≤1) Probed By Thermoelectric Power Measurements, Halyna Hodovanets, Yong Liu, Anton Jesche, Sheng Ran, Eun Deok Mun, Thomas A. Lograsso, Sergey L. Bud'ko, Paul C. Canfield

Ames Laboratory Publications

We report in-plane thermoelectric power measurements on single crystals of (Ba1−xKx)Fe2As2(0.44≤x≤1). We observe a minimum in the S|T=const versus x at x∼0.55 that can be associated with the change in the topology of the Fermi surface, a Lifshitz transition, related to the electron pockets at the center of M point crossing the Fermi level. This feature is clearly observable below ∼75 K. Thermoelectric power also shows a change in the x∼0.8–0.9 range, where the maximum in the thermoelectric power collapses into a plateau. This Lifshitz transition ...


Upper Critical Field Of Kfe2as2 Under Pressure: A Test For The Change In The Superconducting Gap Structure, Valentin Taufour, Neda Foroozani, Makariy A. Tanatar, Jinhyuk Lim, Udhara S. Kaluarachchi, Stella K. Kim, Yong Liu, Thomas A. Lograsso, Vladimir G. Kogan, Ruslan Prozorov, Sergey L. Bud'ko, James S. Schilling, Paul C. Canfield Jun 2014

Upper Critical Field Of Kfe2as2 Under Pressure: A Test For The Change In The Superconducting Gap Structure, Valentin Taufour, Neda Foroozani, Makariy A. Tanatar, Jinhyuk Lim, Udhara S. Kaluarachchi, Stella K. Kim, Yong Liu, Thomas A. Lograsso, Vladimir G. Kogan, Ruslan Prozorov, Sergey L. Bud'ko, James S. Schilling, Paul C. Canfield

Ames Laboratory Publications

ARTICLE TEXT
SUPPLEMENTAL MATERIAL
REFERENCES

ABSTRACT

We report measurements of electrical resistivity under pressure to 5.8 GPa, magnetization to 6.7 GPa, and ac susceptibility to 7.1 GPa in KFe2As2. The previously reported change of slope in the pressure dependence of the superconducting transition temperature Tc(p) at a pressure p∗∼1.8 GPa is confirmed, and Tc(p) is found to be nearly constant above p∗ up to 7.1 GPa. The T−p phase diagram is very sensitive to the pressure conditions as a consequence of the anisotropic uniaxial pressure dependence of Tc. Across p∗, a ...


Soft Lithography Microlens Fabrication And Array For Enhanced Light Extraction From Organic Light Emitting Diodes (Oleds), Wai Y. Leung, Joong-Mok Park, Zhengqing Gan, Kristen P. Constant, Joseph Shinar, Ruth Shinar, Kai-Ming Ho Jun 2014

Soft Lithography Microlens Fabrication And Array For Enhanced Light Extraction From Organic Light Emitting Diodes (Oleds), Wai Y. Leung, Joong-Mok Park, Zhengqing Gan, Kristen P. Constant, Joseph Shinar, Ruth Shinar, Kai-Ming Ho

Iowa State University Patents

Provided are microlens arrays for use on the substrate of OLEDs to extract more light that is trapped in waveguided modes inside the devices and methods of manufacturing same. Light extraction with microlens arrays is not limited to the light emitting area, but is also efficient in extracting light from the whole microlens patterned area where waveguiding occurs. Large microlens array, compared to the size of the light emitting area, extract more light and result in over 100% enhancement. Such a microlens array is not limited to (O)LEDs of specific emission, configuration, pixel size, or pixel shape. It is ...


Magnetic Excitations And Anomalous Spin-Wave Broadening In Multiferroic Fev2o4, Qiang Zhang, Mehmet Ramazanoglu, Songxue Chi, Yong Liu, Thomas A. Lograsso, David Vaknin Jun 2014

Magnetic Excitations And Anomalous Spin-Wave Broadening In Multiferroic Fev2o4, Qiang Zhang, Mehmet Ramazanoglu, Songxue Chi, Yong Liu, Thomas A. Lograsso, David Vaknin

Ames Laboratory Publications

We report on the different roles of two orbital-active Fe2+ at the A site and V3+ at the B site in the magnetic excitations and on the anomalous spin-wave broadening in FeV2O4. FeV2O4 exhibits three structural transitions and successive paramagnetic (PM)–collinear ferrimagnetic (CFI)–noncollinear ferrimagnetic (NCFI)/ferroelectric transitions. The high-temperature tetragonal/PM–orthorhombic/CFI transition is accompanied by the appearance of a large energy gap in the magnetic excitations due to strong spin-orbit-coupling-induced anisotropy at the Fe2+ site. While there is no measurable increase in the energy gap from the orbital ordering of V3+ at the orthorhombic/CFI–tetragonal ...


Fragile Antiferromagnetism In The Heavy-Fermion Compound Ybbipt, Benjamin G. Ueland, Andreas Kreyssig, K. Prokeš, J. W. Lynn, L. W. Harriger, D. K. Pratt, D. K. Singh, T. W. Heitmann, S. Sauerbrei, Scott M. Saunders, E. D. Mun, Sergey L. Bud'ko, Robert J. Mcqueeney, Paul C. Canfield, Alan I. Goldman May 2014

Fragile Antiferromagnetism In The Heavy-Fermion Compound Ybbipt, Benjamin G. Ueland, Andreas Kreyssig, K. Prokeš, J. W. Lynn, L. W. Harriger, D. K. Pratt, D. K. Singh, T. W. Heitmann, S. Sauerbrei, Scott M. Saunders, E. D. Mun, Sergey L. Bud'ko, Robert J. Mcqueeney, Paul C. Canfield, Alan I. Goldman

Ames Laboratory Publications

We report results from neutron scattering experiments on single crystals of YbBiPt that demonstrate antiferromagnetic order characterized by a propagation vector, τAFM = (121212), and ordered moments that align along the [1 1 1] direction of the cubic unit cell. We describe the scattering in terms of a two-Gaussian peak fit, which consists of a narrower component that appears below TN≈0.4 K and corresponds to a magnetic correlation length of ξn≈ 80 Å, and a broad component that persists up to T∗≈ 0.7 K and corresponds to antiferromagnetic correlations extending over ξb≈ 20 Å. Our results illustrate the ...


Suppression Of Electron Correlations In The Collapsed Tetragonal Phase Of Cafe2as2 Under Ambient Pressure Demonstrated By As75 Nmr/Nqr Measurements, Yuji Furukawa, B. Roy, S. Ran, Sergey L. Bud'ko, Paul C. Canfield Mar 2014

Suppression Of Electron Correlations In The Collapsed Tetragonal Phase Of Cafe2as2 Under Ambient Pressure Demonstrated By As75 Nmr/Nqr Measurements, Yuji Furukawa, B. Roy, S. Ran, Sergey L. Bud'ko, Paul C. Canfield

Ames Laboratory Publications

The static and the dynamic spin correlations in the low-temperature collapsed tetragonal and the high-temperature tetragonal phase in CaFe2As2 have been investigated by As75 nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements. Through the temperature (T) dependence of the nuclear spin lattice relaxation rates (1/T1) and the Knight shifts, although stripe-type antiferromagnetic (AFM) spin correlations are realized in the high-temperature tetragonal phase, no trace of the AFM spin correlations can be found in the nonsuperconducting, low-temperature, collapsed tetragonal (cT) phase. Given that there is no magnetic broadening in As75 NMR spectra, together with the T-independent behavior of ...


Heat Capacity Jump At Tc And Pressure Derivatives Of Superconducting Transition Temperature In The Ba1−Xnaxfe2as2 (0.1≤X≤0.9) Series, Sergey L. Bud'ko, Duck Young Chung, Daniel Bugaris, Helmut Claus, Mercouri G. Kanatzdis, Paul C. Canfield Jan 2014

Heat Capacity Jump At Tc And Pressure Derivatives Of Superconducting Transition Temperature In The Ba1−Xnaxfe2as2 (0.1≤X≤0.9) Series, Sergey L. Bud'ko, Duck Young Chung, Daniel Bugaris, Helmut Claus, Mercouri G. Kanatzdis, Paul C. Canfield

Ames Laboratory Publications

We present the evolution of the initial (up to ∼10 kbar) hydrostatic pressure dependencies of Tc and of the ambient pressure, and the jump in the heat capacity associated with the superconducting transition as a function of Na doping in the Ba1−xNaxFe2As2 family of iron-based superconductors. For Na concentrations 0.15≤x≤0.9, the jump in specific heat at Tc, ΔCp∣∣Tc, follows the ΔCp∝T3 (the so-called BNC scaling) found for most BaFe2As2-based superconductors. This finding suggests that, unlike the related Ba1−xKxFe2As2 series, there is no significant modification of the superconducting state (e.g., change in ...


Electrical Resistivity Study Of Cezn11: Magnetic Field And Pressure Phase Diagram Up To 5 Gpa, Valentin Taufour, Halyna Hodovanets, Stella K. Kim, Sergey L. Bud'ko, Paul C. Canfield Nov 2013

Electrical Resistivity Study Of Cezn11: Magnetic Field And Pressure Phase Diagram Up To 5 Gpa, Valentin Taufour, Halyna Hodovanets, Stella K. Kim, Sergey L. Bud'ko, Paul C. Canfield

Ames Laboratory Publications

Thorough resistivity measurements on single crystals of CeZn11 under pressure p and magnetic field H are presented. At ambient pressure, CeZn11 orders antiferromagnetically at TN=2 K. The pressure dependence of the resistivity reveals an increase of the Kondo effect. We determine the pressure evolution of the magnetic exchange interaction between conduction and localized 4f electrons. It qualitatively reproduces the pressure evolution of the magnetic ordering temperature TO1 (with TO1=TN at ambient pressure). In addition to TO1, a new anomaly TO2appears under pressure. Both anomalies are found to increase with applied pressure up to 4.9 GPa, indicating that ...


Suppression Of Ferromagnetism In The Lavxcr1−Xge3 System, Xiao Lin, Valentin Taufour, Sergey L. Bud'ko, Paul C. Canfield Sep 2013

Suppression Of Ferromagnetism In The Lavxcr1−Xge3 System, Xiao Lin, Valentin Taufour, Sergey L. Bud'ko, Paul C. Canfield

Ames Laboratory Publications

We report the synthesis of hexagonal LaVxCr1−xGe3 (x=0–0.21, 1.00) single crystals and present a systematic study of this series by measurements of temperature- and field-dependent magnetic susceptibility, magnetization, resistivity, and specific heat. Ferromagnetism has been observed for x=0–0.21. The Curie temperature declines monotonically as the V concentration increases. Single-crystalline samples could only be grown for x values up to 0.21 for which the transition temperature was suppressed down to 36 K. Although we could not fully suppress TC via V substitution, for x=0.16, we performed magnetization measurements under pressure ...


Thermal Expansion Of Cafe2as2: Effect Of Cobalt Doping And Postgrowth Thermal Treatment, Sergey L. Bud'ko, Sheng Ran, Paul C. Canfield Aug 2013

Thermal Expansion Of Cafe2as2: Effect Of Cobalt Doping And Postgrowth Thermal Treatment, Sergey L. Bud'ko, Sheng Ran, Paul C. Canfield

Ames Laboratory Publications

We report thermal expansion measurements on Ca(Fe1−xCox)2As2 single crystals with different thermal treatment, with samples chosen to represent four different ground states observed in this family. For all samples, thermal expansion is anisotropic with different signs of the in-plane and c-axis thermal expansion coefficients in the high temperature, tetragonal phase. The features in thermal expansion associated with the phase transitions are of opposite signs as well, pointing to a different response of transition temperatures to the in-plane and the c-axis stress. These features, and consequently the inferred pressure derivatives, are very large, clearly and substantially exceeding those ...


Multi-Channel Polarized Thermal Emitter, Jae-Hwang Lee, Kai-Ming Ho, Kristen P. Constant Jul 2013

Multi-Channel Polarized Thermal Emitter, Jae-Hwang Lee, Kai-Ming Ho, Kristen P. Constant

Iowa State University Patents

A multi-channel polarized thermal emitter (PTE) is presented. The multi-channelPTE can emit polarized thermal radiation without using a polarizer at normal emergence. The multi-channel PTE consists of two layers of metallic gratings on a monolithic and homogeneous metallic plate. It can be fabricated by a low-cost soft lithography technique called two-polymer microtransfer molding. The spectral positions of the mid-infrared (MIR) radiation peaks can be tuned by changing the periodicity of the gratings and the spectral separation between peaks are tuned by changing the mutual angle between the orientations of the two gratings.


Low Resistivity Contact To Iron-Pnictide Superconductors, Makariy A. Tanatar, Ruslan Prozorov, Ni Ni, Sergey L. Bud'ko, Paul C. Canfield May 2013

Low Resistivity Contact To Iron-Pnictide Superconductors, Makariy A. Tanatar, Ruslan Prozorov, Ni Ni, Sergey L. Bud'ko, Paul C. Canfield

Iowa State University Patents

Method of making a low resistivity electrical connection between an electrical conductor and an iron pnictide superconductor involves connecting the electrical conductor and superconductor using a tin or tin-based material therebetween, such as using a tin or tin-based solder. The superconductor can be based on doped AFe2As2, where A can be Ca, Sr, Ba, Eu or combinations thereof for purposes of illustration only.


Two-Dimensional Magnetic Interactions In Lafeaso, Mehmet Ramazanoglu, J. Lamsal, Gregory S. Tucker, J.-Q. Yan, S. Calder, T. Guidi, T. Perring, R. William Mccallum, Thomas A. Lograsso, Andreas Kreyssig, Robert J. Mcqueeney Apr 2013

Two-Dimensional Magnetic Interactions In Lafeaso, Mehmet Ramazanoglu, J. Lamsal, Gregory S. Tucker, J.-Q. Yan, S. Calder, T. Guidi, T. Perring, R. William Mccallum, Thomas A. Lograsso, Andreas Kreyssig, Robert J. Mcqueeney

Ames Laboratory Publications

Inelastic neutron scattering measurements demonstrate that the magnetic interactions in antiferromagnetic LaFeAsO are two dimensional. Spin-wave velocities within the Fe layer and the magnitude of the spin gap are similar to the AFe2As2 based materials. However, the ratio of interlayer and intralayer exchange is found to be less than ∼10−4 in LaFeAsO, very similar to the cuprates, and ∼100 times smaller than that found in AFe2As2 compounds. The results suggest that the effective dimensionality of the magnetic system is highly variable in the parent compounds of the iron arsenides and weak three-dimensional interactions ...


Upper Critical Field Of High-Quality Single Crystals Of Kfe2as2, Yong Liu, Makariy A. Tanatar, Vladimir G. Kogan, Hyunsoo Kim, Thomas A. Lograsso, Ruslan Prozorov Apr 2013

Upper Critical Field Of High-Quality Single Crystals Of Kfe2as2, Yong Liu, Makariy A. Tanatar, Vladimir G. Kogan, Hyunsoo Kim, Thomas A. Lograsso, Ruslan Prozorov

Ames Laboratory Publications

Measurements of temperature-dependent in-plane resistivity ρ(T) were used to determine the upper critical field and its anisotropy in high-quality single crystals of the stoichiometric iron arsenide superconductor KFe2As2. The crystals were characterized by the residual resistivity ratio ρ(300 K)/ρ(0) up to 3000 and the resistive transition midpoint temperature Tc=3.8 K, significantly higher than in previous studies on the same material. We find increased Hc2(T) for both directions of the magnetic field, which scale with the increased Tc. This unusual linear Hc2(Tc) scaling is not ...


Magnetism Dependent Phonon Anomaly In Lafeaso Observed Via Inelastic X-Ray Scattering, Steven E. Hahn, Gregory S. Tucker, J.-Q. Yan, A. H. Said, B. M. Leu, R. William Mccallum, E. E. Alp, Thomas A. Lograsso, Robert J. Mcqueeney, Bruce N. Harmon Apr 2013

Magnetism Dependent Phonon Anomaly In Lafeaso Observed Via Inelastic X-Ray Scattering, Steven E. Hahn, Gregory S. Tucker, J.-Q. Yan, A. H. Said, B. M. Leu, R. William Mccallum, E. E. Alp, Thomas A. Lograsso, Robert J. Mcqueeney, Bruce N. Harmon

Ames Laboratory Conference Papers, Posters, and Presentations

The phonon dispersion was measured at room temperature (above the Néel temperature TN) along (0,0,L) in the tetragonal phase of LaFeAsO using inelastic x-ray scattering. Magnetostructural effects are well documented in the AFe2As2-based (A = Ca, Sr, Ba, Eu) systems. Only recently have single crystals of LaFeAsO become available. The experimentally observed splitting between two A1g phonon modes at 22 and 26 meV is only reproduced in spin-polarized calculations. Magnetostructural effects similar to those observed in the AFe2As2 materials are confirmed to be present in LaFeAsO. This is discussed ...


Magnetism-Dependent Phonon Anomaly In Lafeaso Observed Via Inelastic X-Ray Scattering, S. E. Hahn, Gregory S. Tucker, J.-Q. Yan, A. H. Said, B. M. Leu, R. William Mccallum, E. E. Alp, Thomas A. Lograsso, Robert J. Mcqueeney, Bruce N. Harmon Mar 2013

Magnetism-Dependent Phonon Anomaly In Lafeaso Observed Via Inelastic X-Ray Scattering, S. E. Hahn, Gregory S. Tucker, J.-Q. Yan, A. H. Said, B. M. Leu, R. William Mccallum, E. E. Alp, Thomas A. Lograsso, Robert J. Mcqueeney, Bruce N. Harmon

Ames Laboratory Publications

The phonon dispersion was measured at room temperature along (0,0,L) in the tetragonal phase of LaFeAsO using inelastic x-ray scattering. Spin-polarized first-principles calculations imposing various types of antiferromagnetic order are in better agreement with the experimental results than nonmagnetic calculations, although the measurements were made well above the magnetic ordering temperature, TN. Splitting observed between two A1g phonon modes at 22 and 26 meV is only reproduced in spin-polarized calculations. Magnetostructural effects similar to those observed in the AFe2As2 (A=Ca,Sr,Ba,Eu) materials are present in LaFeAsO. The inclusion of Fe ...


Magnetoelastic Coupling And Charge Correlation Lengths In A Twin Domain Of Ba(Fe1−Xcox)2as2 (X=0.047): A High-Resolution X-Ray Diffraction Study, Qiang Zhang, Wenjie Wang, Jong-Woo Kim, Benjamin Hansen, Ni Ni, Sergey L. Bud'ko, Paul C. Canfield, Robert J. Mcqueeney, David Vaknin Mar 2013

Magnetoelastic Coupling And Charge Correlation Lengths In A Twin Domain Of Ba(Fe1−Xcox)2as2 (X=0.047): A High-Resolution X-Ray Diffraction Study, Qiang Zhang, Wenjie Wang, Jong-Woo Kim, Benjamin Hansen, Ni Ni, Sergey L. Bud'ko, Paul C. Canfield, Robert J. Mcqueeney, David Vaknin

Ames Laboratory Publications

The interplay between structure, magnetism, and superconductivity in single crystal Ba(Fe1−xCox)2As2 (x=0.047) has been studied using high-resolution x-ray diffraction by monitoring charge Bragg reflections in each twin domain separately. The emergence of the superconducting state is correlated with the suppression of the orthorhombic distortion around TC, exhibiting competition between orthorhombicity and superconductivity. Above TS, the in-plane charge correlation length increases with the decrease of temperature, possibly induced by nematic fluctuations in the paramagnetic tetragonal phase. Upon cooling, anomalies in the in-plane charge correlation lengths along a (ξa) and baxes (ξb) are observed at TS and ...


Native Defects In Tetradymite Bi2(Texse3−X) Topological Insulators, Linlin Wang, Mianliang Huang, Srinivasa Thimmaiah, Aftab Alam, Sergey L. Bud'ko, Adam Kaminski, Thomas A. Lograsso, Paul C. Canfield, Duane D. Johnson Mar 2013

Native Defects In Tetradymite Bi2(Texse3−X) Topological Insulators, Linlin Wang, Mianliang Huang, Srinivasa Thimmaiah, Aftab Alam, Sergey L. Bud'ko, Adam Kaminski, Thomas A. Lograsso, Paul C. Canfield, Duane D. Johnson

Ames Laboratory Publications

Formation energies of native defects in Bi2(TexSe3−x), with comparison to ideal Bi2Te2S, are calculated in density-functional theory to assess transport properties. Bi2Se3 is found to be n type for both Bi- and Se-rich growth conditions, while Bi2Te3 changes fromn to p type going from Te- to Bi-rich conditions, as observed. Bi2Te2Se and Bi2Te2S are generally n type, explaining observed heavily doped n-type behavior in most samples. A (0/−) transition level at 16 meV above valence-band maximum ...


Manufacturing Method Of Photonic Crystal, In Sung Park, Tae Ho Lee, Jin Ho Ahn, Rana Biswas, Kristen P. Constant, Kai-Ming Ho, Jae-Hwang Lee Jan 2013

Manufacturing Method Of Photonic Crystal, In Sung Park, Tae Ho Lee, Jin Ho Ahn, Rana Biswas, Kristen P. Constant, Kai-Ming Ho, Jae-Hwang Lee

Iowa State University Patents

A manufacturing method of a photonic crystal is provided. In the method, a high-refractive-index material is conformally deposited on an exposed portion of a periodic template composed of a low-refractive-index material by an atomic layer deposition process so that a difference in refractive indices or dielectric constants between the template and adjacent air becomes greater, which makes it possible to form a three-dimensional photonic crystal having a superior photonic bandgap. Herein, the three-dimensional structure may be prepared by a layer-by-layer method.