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Wu G, Greene RL, Reyes AP, Kuhns PL, Moulton WG, Wu B, Wu F, Clark WG. Superconducting anisotropy in the electron-doped high-Tc superconductors Pr2-xCexCuO4-y. J Phys Condens Matter 2014; 26:405701. [PMID: 25219526 DOI: 10.1088/0953-8984/26/40/405701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We report superconducting anisotropy measurements in the electron-doped high-Tc superconductors (HTSCs) Pr(2-x)Ce(x)C(u)O(4-y) (PCCO, x = 0.15 and 0.17) with an applied magnetic field (H0) up to 28 T. Our results show that the upper critical field [H(c2)(T)] of PCCO is highly anisotropic and as the temperature T → 0, the value of it at H0 ∥ c [H(c2,∥c)(0)] is far less than the Pauli limit. The low temperature anisotropic character of PCCO is found to be rather similar to that of hole-doped cuprate HTSCs, but apparently larger than that of typical Fe-based superconductors. This study also proves a new sensitive probe of detecting rich properties of unconventional superconductors with the use of the resonant frequency of an NMR probe circuit.
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Affiliation(s)
- Guoqing Wu
- College of Physics Science and Technology, Yangzhou University, Yangzhou, Jiangsu 225002, People's Republic of China. Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
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Urbano RR, Green EL, Moulton WG, Reyes AP, Kuhns PL, Bittar EM, Adriano C, Garitezi TM, Bufaiçal L, Pagliuso PG. Distinct high-T transitions in underdoped Ba(1-x)KxFe2As2. Phys Rev Lett 2010; 105:107001. [PMID: 20867539 DOI: 10.1103/physrevlett.105.107001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/19/2010] [Indexed: 05/29/2023]
Abstract
In contrast with the simultaneous structural and magnetic first order phase transition T0 previously reported, our detailed investigation on an underdoped Ba(0.84)K(0.16)Fe2As2 single crystal unambiguously revealed that the transitions are not concomitant. The tetragonal (τ: I4/mmm)-orthorhombic (ϑ: Fmmm) structural transition occurs at T(S)≃110 K, followed by an adjacent long-range antiferromagnetic (AFM) transition at T(N)≃102 K. Hysteresis and coexistence of the τ and ϑ phases over a finite temperature range observed by NMR experiments confirm the first order character of the τ-ϑ transition and provide evidence that both T(S) and T(N) are strongly correlated. Our data also show that superconductivity develops in the ϑ phase below T(c)=20 K and coexists with AFM. This new observation, T(S)≠T(N), firmly establishes another similarity between the hole-doped BaFe2As2 and the electron-doped iron-arsenide superconductors.
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Affiliation(s)
- R R Urbano
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306-4005, USA
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Leighton C, Manno M, Cady A, Freeland JW, Wang L, Umemoto K, Wentzcovitch RM, Chen TY, Chien CL, Kuhns PL, Hoch MJR, Reyes AP, Moulton WG, Dahlberg ED, Checkelsky J, Eckert J. Composition controlled spin polarization in Co(1-x)Fe(x)S(2) alloys. J Phys Condens Matter 2007; 19:315219. [PMID: 21694119 DOI: 10.1088/0953-8984/19/31/315219] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The transition metal (TM) chalcogenides of the form TMX(2) (X = S or Se) have been studied for decades due to their interesting electronic and magnetic properties such as metamagnetism and metal-insulator transitions. In particular, the Co(1-x)Fe(x)S(2) alloys were the subject of investigation in the 1970s due to general interest in itinerant ferromagnetism. In recent years (2000-present) it has been shown, both by electronic structure calculations and detailed experimental investigations, that Co(1-x)Fe(x)S(2) is a model system for the investigation of highly spin polarized ferromagnetism. The radically different electronic properties of the two endpoint compounds (CoS(2) is a narrow bandwidth ferromagnetic metal, while FeS(2) is a diamagnetic semiconductor), in a system forming a substitutional solid solution allows for composition control of the Fermi level relative to the spin split bands, and therefore composition-controlled conduction electron spin polarization. In essence, the recent work has shown that the concept of 'band engineering' can be applied to half-metallic ferromagnets and that high spin polarization can be deliberately engineered. Experiments reveal tunability in both sign and magnitude of the spin polarization at the Fermi level, with maximum values obtained to date of 85% at low temperatures. In this paper we review the properties of Co(1-x)Fe(x)S(2) alloys, with an emphasis on properties of relevance to half-metallicity. Crystal structure, electronic structure, synthesis, magnetic properties, transport properties, direct probes of the spin polarization, and measurements of the total density of states at the Fermi level are all discussed. We conclude with a discussion of the factors that influence, or even limit, the spin polarization, along with a discussion of opportunities and problems for future investigation, particularly with regard to fundamental studies of spintronic devices.
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Affiliation(s)
- C Leighton
- Department of Chemical Engineering and Materials Science, University of Minnesota, USA
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Kuhns PL, Hoch MJR, Reyes AP, Moulton WG, Wang L, Leighton C. Evolution with composition of the d-band density of states at the Fermi level in highly spin polarized Co1-xFexS2. Phys Rev Lett 2006; 96:167208. [PMID: 16712272 DOI: 10.1103/physrevlett.96.167208] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2005] [Revised: 01/30/2006] [Indexed: 05/09/2023]
Abstract
Highly spin polarized (SP) and half-metallic ferromagnetic systems are of considerable current interest and of potential importance for spintronic applications. Recent work has demonstrated that Co1-xFexS2 is a highly polarized ferromagnet (FM) where the spin polarization can be tuned by alloy composition. Using 59Co FM-NMR as a probe, we have measured the low-temperature spin relaxation in this system in magnetic fields from 0 to 1.0 T for 0<or=x<or=0.3. The 59Co spin-lattice relaxation rates follow a linear T dependence. Analysis of the data, using expressions for a FM system, permits information to be obtained on the d-band density of states at the Fermi level. The results are compared with independent density of states values inferred from electronic specific heat measurements and band structure calculations. It is shown that FM-NMR can be an important method for investigating highly SP systems.
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Affiliation(s)
- P L Kuhns
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA
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Gervais G, Stormer HL, Tsui DC, Kuhns PL, Moulton WG, Reyes AP, Pfeiffer LN, Baldwin KW, West KW. Evidence for skyrmion crystallization from NMR relaxation experiments. Phys Rev Lett 2005; 94:196803. [PMID: 16090197 DOI: 10.1103/physrevlett.94.196803] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2004] [Indexed: 05/03/2023]
Abstract
A resistively detected NMR technique was used to probe the two-dimensional electron gas in a GaAs/AlGaAs quantum well. The spin-lattice relaxation rate (1/T(1)) was extracted at near complete filling of the first Landau level by electrons. The nuclear spin of (75)As is found to relax much more efficiently with T --> 0 and when a well developed quantum Hall state with R(xx) approximately 0 occurs. The data show a remarkable correlation between the nuclear spin relaxation and localization. This suggests that the magnetic ground state near complete filling of the first Landau level may contain a lattice of topological spin texture, i.e., a Skyrmion crystal.
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Affiliation(s)
- G Gervais
- Department of Physics, Columbia University, New York, New York 10027 USA
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Kuhns PL, Hoch MJR, Moulton WG, Reyes AP, Wu J, Leighton C. Magnetic phase separation in La1-xSrxCoO3 by 59Co nuclear magnetic resonance. Phys Rev Lett 2003; 91:127202. [PMID: 14525396 DOI: 10.1103/physrevlett.91.127202] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2003] [Indexed: 05/24/2023]
Abstract
59Co NMR measurements on La1-xSrxCoO3 reported here establish unequivocally, for the first time, the coexistence of ferromagnetic regions, spin-glass regions, and hole-poor low spin regions at all x values from 0.1 to 0.5. A zero external field NMR spectrum, which is assigned to the ferromagnetic regions, has a spectral shape that is nearly x independent at 1.9 K, as are the relaxation times, T1 and T2. The integrated spectral area increases rapidly with x up to x = 0.2 and then decreases slightly for larger x. In a field of 9.97 T, a narrow NMR line is observed at 102 MHz, identical to that found in x = 0 samples in previous work. The integrated intensity of this spectrum decreases rapidly with increasing x, and is ascribed to hole-poor low spin regions. Beneath this spectrum, a third broad line, with a peak at 100 MHz, is assigned to a spin- or cluster-glass-like phase.
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Affiliation(s)
- P L Kuhns
- National High Magnetic Field Laboratory, Tallahassee, Florida 32310, USA
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Zheng GQ, Ozaki H, Kitaoka Y, Kuhns P, Reyes AP, Moulton WG. Delocalized quasiparticles in the vortex state of an overdoped high-T(c) superconductor probed by 63Cu NMR. Phys Rev Lett 2002; 88:077003. [PMID: 11863931 DOI: 10.1103/physrevlett.88.077003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2001] [Indexed: 05/23/2023]
Abstract
We report the spin Knight shift (K(s)) and the nuclear spin-lattice relaxation rate (1/T1) in the vortex state as a function of magnetic field (H) up to 28 T in the high-Tc superconductor TlSr2CaCu2O6.8 (Tc = 68 K). At low temperatures well below Tc, both K(s) and 1/T1 measured around the middle point between the two nearest vortices (saddle point) increase substantially with increasing field, which indicate that the quasiparticle states with an ungapped spectrum are extended outside the vortex cores in a d-wave superconductor. The density of states (DOS) around the saddle point is found to be kappaN(0)square root[H/H(c2)], with kappa = 0.5-0.7 and N0 being the normal-state DOS.
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Affiliation(s)
- G-q Zheng
- Department of Physical Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
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Mitrović VF, Sigmund EE, Eschrig M, Bachman HN, Halperin WP, Reyes AP, Kuhns P, Moulton WG. Spatially resolved electronic structure inside and outside the vortex cores of a high-temperature superconductor. Nature 2001; 413:501-4. [PMID: 11586354 DOI: 10.1038/35097039] [Citation(s) in RCA: 163] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Puzzling aspects of high-transition-temperature (high-Tc) superconductors include the prevalence of magnetism in the normal state and the persistence of superconductivity in high magnetic fields. Superconductivity and magnetism generally are thought to be incompatible, based on what is known about conventional superconductors. Recent results, however, indicate that antiferromagnetism can appear in the superconducting state of a high-Tc superconductor in the presence of an applied magnetic field. Magnetic fields penetrate a superconductor in the form of quantized flux lines, each of which represents a vortex of supercurrents. Superconductivity is suppressed in the core of the vortex and it has been suggested that antiferromagnetism might develop there. Here we report the results of a high-field nuclear-magnetic-resonance (NMR) imaging experiment in which we spatially resolve the electronic structure of near-optimally doped YBa2Cu3O7-delta inside and outside vortex cores. Outside the cores, we find strong antiferromagnetic fluctuations, whereas inside we detect electronic states that are rather different from those found in conventional superconductors.
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Affiliation(s)
- V F Mitrović
- Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208, USA
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Zheng G, Ozaki H, Clark WG, Kitaoka Y, Kuhns P, Reyes AP, Moulton WG, Kondo T, Shimakawa Y, Kubo Y. Superconducting fluctuations and the pseudogap in the slightly overdoped high- T(c) superconductor TlSr2CaCu2O6.8: high magnetic field NMR studies. Phys Rev Lett 2000; 85:405-408. [PMID: 10991294 DOI: 10.1103/physrevlett.85.405] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2000] [Indexed: 05/23/2023]
Abstract
From measurements of the 63Cu Knight shift ( K) and the nuclear spin-lattice relaxation rate ( 1/T1) under magnetic fields from zero up to 28 T in the slightly overdoped high- T(c) superconductor TlSr2CaCu2O6.8 ( T(c) = 68 K), we find that the pseudogap behavior, i.e., the reductions of 1/T1T and K above T(c) from the values expected from the normal state at high T, is strongly field dependent and follows a scaling relation. We show that this scaling is consistent with the effects of the Cooper pair density fluctuations. The present finding contrasts sharply with the pseudogap property reported previously in the underdoped regime where no field effect was seen up to 23.2 T. The implications are discussed.
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Affiliation(s)
- Gq Zheng
- Department of Physical Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
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Kwok WK, Olsson RJ, Karapetrov G, Paulius LM, Moulton WG, Hofman DJ, Crabtree GW. Critical points in heavy ion irradiated untwinned YBa(2)Cu3O(7-delta) crystals. Phys Rev Lett 2000; 84:3706-3709. [PMID: 11019182 DOI: 10.1103/physrevlett.84.3706] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/1999] [Indexed: 05/23/2023]
Abstract
The critical points in untwinned YBa(2)Cu(3)O(7-delta) crystals with dilute columnar defects are investigated. We find a convergence of a first order vortex melting line with an irreversibility line associated with the onset of the Bose glass critical regime at the lower critical point. In addition, we find that columnar defects raise the upper critical point, implying that vortex line meandering is a basic feature controlling its position.
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Affiliation(s)
- WK Kwok
- Materials Science Division and Science and Technology Center for Superconductivity, Argonne National Laboratory, Argonne, Illinois 60439, USA
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Kleinhammes A, Chang CL, Moulton WG, Testardi LR. Nonbolometric laser-induced voltage signals in YBa2Cu3O7- delta thin films at room temperature. Phys Rev B Condens Matter 1991; 44:2313-2319. [PMID: 9999784 DOI: 10.1103/physrevb.44.2313] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Chang CL, Kleinhammes A, Moulton WG, Testardi LR. Symmetry-forbidden laser-induced voltages in YBa2Cu3O7. Phys Rev B Condens Matter 1990; 41:11564-11567. [PMID: 9993578 DOI: 10.1103/physrevb.41.11564] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Goldstein MJ, Moulton WG. Thermally induced flux motion and the elementary pinning force in Nb thin films. Phys Rev B Condens Matter 1989; 40:8714-8719. [PMID: 9991349 DOI: 10.1103/physrevb.40.8714] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Testardi LR, Moulton WG, Mathias H, Ng HK, Rey CM. Large static dielectric constant in the high-temperature phase of polycrystalline YBa2Cu3Ox. Phys Rev B Condens Matter 1988; 37:2324-2325. [PMID: 9944765 DOI: 10.1103/physrevb.37.2324] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/11/2023]
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Testardi LR, Moulton WG, Mathias H, Ng HK, Rey CM, Kennedy RJ. Superconducting and nonsuperconducting phases of YBa2Cu. Phys Rev B Condens Matter 1987; 36:8816-8818. [PMID: 9942717 DOI: 10.1103/physrevb.36.8816] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/11/2023]
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Mathias H, Moulton W, Ng HK, Pan SJ, Pan KK, Peirce LH, Testardi LR, Kennedy RJ. Large "forbidden" change in elastic modulus at the superconducting transition of Y1Ba2Cu3O9-x. Phys Rev B Condens Matter 1987; 36:2411-2413. [PMID: 9943116 DOI: 10.1103/physrevb.36.2411] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/11/2023]
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