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Full-Text Articles in Physics

Universal Doping Evolution Of The Superconducting Gap Anisotropy In Single Crystals Of Electron-Doped Ba(Fe1-Xrhx)(2)As-2 From London Penetration Depth Measurements, Hyunsoo Kim, Makariy A. Tanatar, C. Martin, E. C. Blomberg, Ni Ni, Sergey L. Bud’Ko, Paul C. Canfield, Ruslan Prozorov Jun 2018

Universal Doping Evolution Of The Superconducting Gap Anisotropy In Single Crystals Of Electron-Doped Ba(Fe1-Xrhx)(2)As-2 From London Penetration Depth Measurements, Hyunsoo Kim, Makariy A. Tanatar, C. Martin, E. C. Blomberg, Ni Ni, Sergey L. Bud’Ko, Paul C. Canfield, Ruslan Prozorov

Ames Laboratory Accepted Manuscripts

Doping evolution of the superconducting gap anisotropy was studied in single crystals of 4d-electron doped Ba(Fe1-xRhx)(2)As-2 using tunnel diode resonator measurements of the temperature variation of the London penetration depth Delta lambda(T). Single crystals with doping levels representative of an underdoped regime x = 0.039 (T-c = 15.5 K), close to optimal doping x = 0.057 (T-c = 24.4 K) and overdoped x = 0.079 (T-c = 21.5 K) and x = 0.131 (T-c = 4.9 K) were studied. Superconducting energy gap anisotropy was characterized by the exponent, n, by fitting the data to the power-law ...


Pressure Effects On Magnetism And Superconductivity, Udhara Sampath Kaluarachchi Jan 2018

Pressure Effects On Magnetism And Superconductivity, Udhara Sampath Kaluarachchi

Graduate Theses and Dissertations

This thesis summarizes experimental work using high pressure as a tuning parameter in the study of selected correlated electron systems at low temperatures. This thesis contains 8 chapters and 2 appendices. After giving the introduction in Chapter 1, experimental techniques are discussed in Chapter 2. Chapters 3 and 5 are devoted to pressure studies of ferromagnetic materials. In ferromagnetic systems, the appearance of quantum criticality is avoided either by a change of the second order transition to one of the first-order at a tricritical point or by the appearance of modulated, antiferromagnetic, phase. Chapter 3 summarizes the pressure study of ...


Heisenberg Model Analysis On Inelastic Powder Neutron Scattering Data Using Parent And K Doped Bamn2as2 Samples, Mehmet Ramazanoglu, Aashish Sapkota, Abhishek Pandey, Jagat Lamsal, Douglas L. Abernathy, Jennifer L. Niedziela, Matthew B. Stone, R. Salci, D. A. Acar, F. O. Oztirpan, Şener Ozonder, Andreas Kreyssig, Alan I. Goldman, David C. Johnston, Robert J. Mcqueeney Nov 2017

Heisenberg Model Analysis On Inelastic Powder Neutron Scattering Data Using Parent And K Doped Bamn2as2 Samples, Mehmet Ramazanoglu, Aashish Sapkota, Abhishek Pandey, Jagat Lamsal, Douglas L. Abernathy, Jennifer L. Niedziela, Matthew B. Stone, R. Salci, D. A. Acar, F. O. Oztirpan, Şener Ozonder, Andreas Kreyssig, Alan I. Goldman, David C. Johnston, Robert J. Mcqueeney

Ames Laboratory Accepted Manuscripts

Low temperature powder inelastic neutron scattering measurements were performed on three different powder samples; parent BaMn2As2,12.5% K-doped Ba0.875K0.125Mn2As2 and 25% K-doped Ba(0.75)K0.25Mn2As2. The Heisenberg Model involving J1‐J2‐Jz coupling constants were compared to the data by a powder integration routine using Monte Carlo integration methods. The best magnetic parameters were selected using a chi-square test where model intensities were compared to the full (q,E) dependence of magnetic scattering. A key step to this analysis is the characterization of the background which is formed mostly by phonon scattering intensities along with ...


Pressure Induced Half-Collapsed-Tetragonal Phase In Cakfe4as4, Udhara Kaluarachchi, Valentin Taufour, Aashish Sapkota, Vladislav Borisov, Tai Kong, W. R. Meier, Karunakar Kothapalli, Benjamin G. Ueland, Andreas Kreyssig, Roser Valenti, Robert J. Mcqueeney, Alan I. Goldman, Sergey L. Bud'ko, Paul C. Canfield Oct 2017

Pressure Induced Half-Collapsed-Tetragonal Phase In Cakfe4as4, Udhara Kaluarachchi, Valentin Taufour, Aashish Sapkota, Vladislav Borisov, Tai Kong, W. R. Meier, Karunakar Kothapalli, Benjamin G. Ueland, Andreas Kreyssig, Roser Valenti, Robert J. Mcqueeney, Alan I. Goldman, Sergey L. Bud'ko, Paul C. Canfield

Ames Laboratory Accepted Manuscripts

We report the temperature-pressure phase diagram of CaKFe4As4 established using high-pressure electrical resistivity, magnetization, and high-energy x-ray diffraction measurements up to 6 GPa. With increasing pressure, both resistivity and magnetization data show that the bulk superconducting transition of CaKFe4As4 is suppressed and then disappears at p≳4 GPa. High-pressure x-ray data clearly indicate a phase transition to a collapsed tetragonal phase in CaKFe4As4 under pressure that coincides with the abrupt loss of bulk superconductivity near 4 GPa. The x-ray data, combined with resistivity data, indicate that the collapsed tetragonal transition line is essentially independent of pressure, occurring at 4.0 ...


Effective One-Dimensional Coupling In The Highly Frustrated Square-Lattice Itinerant Magnet Caco 2 − Y As 2, Aashish Sapkota, B. G. Ueland, V. K. Anand, N. S. Sangeetha, D. L. Abernathy, M. B. Stone, J. L. Niedziela, D. C. Johnston, A. Kreyssig, A. I. Goldman, R. J. Mcqueeney Oct 2017

Effective One-Dimensional Coupling In The Highly Frustrated Square-Lattice Itinerant Magnet Caco 2 − Y As 2, Aashish Sapkota, B. G. Ueland, V. K. Anand, N. S. Sangeetha, D. L. Abernathy, M. B. Stone, J. L. Niedziela, D. C. Johnston, A. Kreyssig, A. I. Goldman, R. J. Mcqueeney

Ames Laboratory Accepted Manuscripts

Inelastic neutron scattering measurements on the itinerant antiferromagnet CaCo2−yAs2 at a temperature of 8 K reveal two orthogonal planes of scattering perpendicular to the Co square lattice in reciprocal space, demonstrating the presence of effective one-dimensional spin interactions. These results are shown to arise from near-perfect bond frustration within the J1-J2 Heisenberg model on a square lattice with ferromagnetic J1 and hence indicate that the extensive previous experimental and theoretical study of the J1-J2 Heisenberg model on local-moment square spin lattices should be expanded to include itinerant spin systems.


Nature Of Magnetic Excitations In The Iron Pnictides And Its Pertinence To Superconductivity As Studied By Inelastic Neutron Scattering, Gregory Scott Tucker Jan 2015

Nature Of Magnetic Excitations In The Iron Pnictides And Its Pertinence To Superconductivity As Studied By Inelastic Neutron Scattering, Gregory Scott Tucker

Graduate Theses and Dissertations

Unconventional superconductivity and antiferromagnetism are often found in close proximity to one another. For the series of compounds Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, which possesses both antiferromagnetism and superconductivity for the under-doped range of composition, this observation is certainly true. The close proximity, and in fact coexistence for under-doped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, of antiferromagnetism and superconductivity has encouraged speculation that antiferromagnetic spin fluctuations may mediate the electron pairing interaction in unconventional superconductors. Previous studies indicated that the spin fluctuations at optimally-doped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2 ...


Combined Effects Of Post-Growth Thermal Treatment And Chemical Substitution On Physical Properties Of Cafe2 As2, Sheng Ran Jan 2014

Combined Effects Of Post-Growth Thermal Treatment And Chemical Substitution On Physical Properties Of Cafe2 As2, Sheng Ran

Graduate Theses and Dissertations

This thesis summarizes experimental work using process of postgrowth thermal treatment and chemical substitution as tuning parameters in the study of physical properties of CaFe2As2. Details of sample preparation and characterization are given as well as various phase diagrams.


Low Temperature London Penetration Depth And Superfluid Density In Fe-Based Superconductors, Hyunsoo Kim Jan 2013

Low Temperature London Penetration Depth And Superfluid Density In Fe-Based Superconductors, Hyunsoo Kim

Graduate Theses and Dissertations

The superconducting gap symmetry of the Fe-based superconductors was studied by measurements and analysis of London penetration depth and superfluid density. Tunnel diode resonator technique for these measurements was implemented in a dilution refrigerator allowing for the temperatures down to 50 mK. For the analysis of the superfluid density, we used both experimental studies of Al-coated samples and original thermodynamic approach based on Rutgers relation. In three systems studied, we found that the superconducting gap at the optimal doping is best described in multi-gap full gap scenario. By performing experiments on samples with artificially introduced disorder with heavy ion irradiation ...


Pressure Effects On Selected Correlated Electron Systems, Stella Kim Jan 2013

Pressure Effects On Selected Correlated Electron Systems, Stella Kim

Graduate Theses and Dissertations

This thesis summarizes experimental work using high pressure for materials synthesis and also as a tuning parameter in the study of selected correlated electron systems at low temperatures. Details of materials growth at high pressure and high temperature are given as well as the details of the assembly and use of the high pressure modified Bridgman anvil cell (mBAC) for resistivity measurements. The mBAC was used to tune the various ground states of several correlated electron systems: the metal-to-insulator transition in V6O11, the spin density wave antiferromagnetism in V7O13 as well as members of ...


In-Plane Structural And Electronic Anisotropy Of Iron-Based Superconductors, Erick Blomberg Jan 2013

In-Plane Structural And Electronic Anisotropy Of Iron-Based Superconductors, Erick Blomberg

Graduate Theses and Dissertations

\specialchapt{ABSTRACT}

Many iron-based superconductors undergo a tetragonal to orthorhombic change of their crystallographic lattice symmetry, as well as paramagnetic to anti-ferromagnetic ordering upon cooling through a characteristic temperature $T_N$. The anisotropic structure of the orthorhombic crystal symmetry would naturally lead one to expect to find in-plane electronic anisotropy.

Upon cooling through $T_s$, and going into the orthorhombic symmetry, crystals divide into many small \textit{twin domains}. Although crystallographically identical, the twin domains express four different rotations of the orthorhombic lattice within the $\bf{ab}$-plane making direct measurements along an individual orthorhombic axis impossible. This complication lead to the ...


Structural And Magnetic Properties And Superconductivity In Ba(Fe1−Xtmx)2as2 (Tm=Ru, Mn, Cr/Co, Mn/Co) Single Crystals, Alexander Nicholas Thaler Jan 2012

Structural And Magnetic Properties And Superconductivity In Ba(Fe1−Xtmx)2as2 (Tm=Ru, Mn, Cr/Co, Mn/Co) Single Crystals, Alexander Nicholas Thaler

Graduate Theses and Dissertations

Transition metal substitutions of BaFe2As2 have been characterized by structural and magnetic measurements. Particular focus has been paid to magnetic ordering, SDW suppression and emergence of superconductivity. Details of sample synthesis are given for all substitutions. Phase diagrams of the resulting systems are presented and discussed.


Millimeter-Wave Study Of London Penetration Depth Temperature Dependence In Ba(Fe0.926co0.074)2as2 Single Crystal, A. A. Barannik, N. T. Cherpak, Ni Ni, Makariy A. Tanatar, S. A. Vitusevich, V. N. Skresanov, Paul C. Canfield, Ruslan Prozorov, V. V. Glamazdin, K. I. Torokhtii Jan 2011

Millimeter-Wave Study Of London Penetration Depth Temperature Dependence In Ba(Fe0.926co0.074)2as2 Single Crystal, A. A. Barannik, N. T. Cherpak, Ni Ni, Makariy A. Tanatar, S. A. Vitusevich, V. N. Skresanov, Paul C. Canfield, Ruslan Prozorov, V. V. Glamazdin, K. I. Torokhtii

Ames Laboratory Publications

In-plane surface Ka-band microwave impedance of optimally dopedsingle crystals of the Fe-based superconductor Ba(Fe0.926Co0.074)2As2 (Tc  = 22.8 K) was measured. Sensitive sapphire disk quasi-optical resonator with high-Tc cuprate conducting endplates was developed specially for Fe-pnictide superconductors. It allowed finding temperature variation of London penetration depth in a form of power law, namely Δλ(T) ∼ Tn with n = 2.8 from low temperatures up to at least 0.6Tc consisted with radio-frequency measurements. This exponent points towards nodeless state with pairbreaking scattering, which can support one ...


London Penetration Depth Measurements In Ba(Fe1-Xtx)2as2 (T=Co,Ni,Ru,Rh,Pd,Pt,Co+Cu) Superconductors, Ryan Todd Gordon Jan 2011

London Penetration Depth Measurements In Ba(Fe1-Xtx)2as2 (T=Co,Ni,Ru,Rh,Pd,Pt,Co+Cu) Superconductors, Ryan Todd Gordon

Graduate Theses and Dissertations

The London penetration depth has been measured in various doping levels of single crystals of Ba(Fe1-xTx)2As2 (T=Co,Ni,Ru,Rh,Pd,Pt,Co+Cu) superconductors by utilizing a tunnel diode resonator (TDR) apparatus. All in-plane penetration depth measurements exhibit a power law temperature dependence, indicating the existence of low-temperature, normal state quasiparticles all the way down to the lowest measured temperature, which was typically 500 mK. Several different doping concentrations from the Ba(Fe1-xTx)2As2 (T=Co,Ni) systems have been measured and the doping dependence of the power law exponent, n, is compared to results from ...


Structural / Magnetic Phase Transitions And Superconductivity In Ba(Fe1-XTmX)2As2 Single Crystals, Ni Ni Jan 2009

Structural / Magnetic Phase Transitions And Superconductivity In Ba(Fe1-XTmX)2As2 Single Crystals, Ni Ni

Graduate Theses and Dissertations

BaFe2As2 single crystal undergoes strongly coupled tetragonal to orthorhombic / paramagnetic to antiferromagnetic phase transitions at 134 K and can become superconducting under doping. To study the correlations between the structural / magnetic phase transitions and the superconductivity, seven transition metal electron

doped series : Ba(Fe1-xTMx)2As2 (TM=Co, Ni, Cu, Co / Cu, Rh and Pd) were grown and characterized by microscopic, transport and thermodynamic measurements.

It was found that the structural and magnetic phase transitions (upper transitions) at 134 K in pure BaFe2As2 are monotonically suppressed and increasingly separated in ...


Nqr Study Of Local Structure And Cooling Rate‐Dependent Superconductivity In La2cuo4+Δ, A. P. Reyes, E. T. Ahrens, P. C. Hammel, J. D. Thompson, Paul C. Canfield, Z. Fisk, R. H. Heffner, J. E. Schirber Jan 1993

Nqr Study Of Local Structure And Cooling Rate‐Dependent Superconductivity In La2cuo4+Δ, A. P. Reyes, E. T. Ahrens, P. C. Hammel, J. D. Thompson, Paul C. Canfield, Z. Fisk, R. H. Heffner, J. E. Schirber

Paul C. Canfield

Preliminary results of structural studies in oxygen‐annealed La2CuO4+δ(δ∼0.03) using 139La nuclear quadrupole resonance (NQR) spectroscopy are reported. Superconducting critical temperatures were found to depend on the rate of cooling through a narrow temperature range near 195 K. Analysis of the 139La NQR spectra reveal that lanthanum atoms in the oxygen‐rich metallic region occupy two sites having different local environments. One site has a structural configuration closely related to the stoichiometric oxygen‐poor compound. The second appears only below 200 K and exhibits a large shift and broad distribution of NQR frequency ν Q . Shifts ...


Surface Superconductivity In Niobium And Niobium-Tantalum Alloys , John Raymond Hopkins Jan 1972

Surface Superconductivity In Niobium And Niobium-Tantalum Alloys , John Raymond Hopkins

Retrospective Theses and Dissertations

No abstract provided.


Electron Tunneling Measurements On Pure Bulk Thorium , Brent Alan Haskell Jan 1971

Electron Tunneling Measurements On Pure Bulk Thorium , Brent Alan Haskell

Retrospective Theses and Dissertations

No abstract provided.


Superconductivity Of Pb-Bi Alloys Under High Pressure , Robert Edwin Jones Jr. Jan 1971

Superconductivity Of Pb-Bi Alloys Under High Pressure , Robert Edwin Jones Jr.

Retrospective Theses and Dissertations

No abstract provided.


Superconductivity And Magnetic Order In La-Ce Alloys , John Jerome Wollan Jan 1970

Superconductivity And Magnetic Order In La-Ce Alloys , John Jerome Wollan

Retrospective Theses and Dissertations

No abstract provided.


Spin Scattering In Superconductors , Larry John Williams Jan 1969

Spin Scattering In Superconductors , Larry John Williams

Retrospective Theses and Dissertations

No abstract provided.


Specific Heat Of Fcc And D-Hcp Lanthanum From 1.0-10.0°K , David Lee Johnson Jan 1966

Specific Heat Of Fcc And D-Hcp Lanthanum From 1.0-10.0°K , David Lee Johnson

Retrospective Theses and Dissertations

No abstract provided.


The Superconducting Properties Of High Purity Niobium , Thorsten Fredrick Stromberg Jan 1965

The Superconducting Properties Of High Purity Niobium , Thorsten Fredrick Stromberg

Retrospective Theses and Dissertations

No abstract provided.


Some Properties Of [Beta]-Mercury , James Emmanuel Schirber Jan 1960

Some Properties Of [Beta]-Mercury , James Emmanuel Schirber

Retrospective Theses and Dissertations

No abstract provided.