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Title: Scanning tunneling microscopy study of morphology and electronic properties in (K{sub 0.7}Na{sub 0.3})Fe{sub 2−y}Se{sub 2} single crystal

Abstract

We investigated the microstructure of the iron selenide superconductor (K{sub 0.7}Na{sub 0.3})Fe{sub 2−y}Se{sub 2} with a T{sub c} = 32 K and a near 100% Meissner screening volume fraction. Topography and electron transport properties were studied using electron microscopy and ultra-high vacuum scanning tunneling microscopy (STM) techniques. Room temperature STM measurements reliably identify spatial variations of the local electronic properties of this material. The studied crystals consist of continuous regions with significantly different shapes of current-voltage curves reflecting different electronic transport properties of these regions. Fitting of the local current-voltage curves with the Simmons model for metal-dielectric-metal structure confirmed a phase separation in the sample to a metal and semiconducting phases. The observed regions have dimensions in the range of several tenths of a micrometer and indicate a phase separation in the sample.

Authors:
;  [1];  [2];  [3];  [4]; ; ;  [5];  [6];  [3];  [2];  [2]
  1. Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, 1(2), Leninskie Gory, GSP-1, Moscow 119991 (Russian Federation)
  2. (Russian Federation)
  3. Low Temperature Physics and Superconductivity Department, Physics Faculty, Lomonosov Moscow State University, 119991 Moscow (Russian Federation)
  4. Institute for Materials Research, Tohoku University, 980-8577 Sendai (Japan)
  5. Department of Chemistry, Lomonosov Moscow State University, 119991 Moscow (Russian Federation)
  6. National Institute for Material Science, Tsukuba 305-0047 (Japan)
Publication Date:
OSTI Identifier:
22308539
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 116; Journal Issue: 4; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; DIELECTRIC MATERIALS; ELECTRIC CONDUCTIVITY; ELECTRICAL PROPERTIES; ELECTRON MICROSCOPY; IRON COMPOUNDS; MICROSTRUCTURE; MONOCRYSTALS; POTASSIUM COMPOUNDS; SCANNING TUNNELING MICROSCOPY; SELENIUM COMPOUNDS; SODIUM COMPOUNDS; SUPERCONDUCTORS; TEMPERATURE RANGE 0013-0065 K; TEMPERATURE RANGE 0273-0400 K; TRANSITION TEMPERATURE

Citation Formats

Trifonov, A. S., E-mail: trifonov.artem@phys.msu.ru, Presnov, D. E., Low Temperature Physics and Superconductivity Department, Physics Faculty, Lomonosov Moscow State University, 119991 Moscow, Ovchenkov, Y. A., Belosludov, R., Boltalin, A. I., Liu, M., Morozov, I. V., Nejo, H., Vasiliev, A. N., Theoretical Physics and Applied Mathematics Department, Institute of Physics and Technology, Ural Federal University, Ekaterinburg 620002, and National University of Science and Technology 'MISiS', Moscow 119049. Scanning tunneling microscopy study of morphology and electronic properties in (K{sub 0.7}Na{sub 0.3})Fe{sub 2−y}Se{sub 2} single crystal. United States: N. p., 2014. Web. doi:10.1063/1.4891227.
Trifonov, A. S., E-mail: trifonov.artem@phys.msu.ru, Presnov, D. E., Low Temperature Physics and Superconductivity Department, Physics Faculty, Lomonosov Moscow State University, 119991 Moscow, Ovchenkov, Y. A., Belosludov, R., Boltalin, A. I., Liu, M., Morozov, I. V., Nejo, H., Vasiliev, A. N., Theoretical Physics and Applied Mathematics Department, Institute of Physics and Technology, Ural Federal University, Ekaterinburg 620002, & National University of Science and Technology 'MISiS', Moscow 119049. Scanning tunneling microscopy study of morphology and electronic properties in (K{sub 0.7}Na{sub 0.3})Fe{sub 2−y}Se{sub 2} single crystal. United States. doi:10.1063/1.4891227.
Trifonov, A. S., E-mail: trifonov.artem@phys.msu.ru, Presnov, D. E., Low Temperature Physics and Superconductivity Department, Physics Faculty, Lomonosov Moscow State University, 119991 Moscow, Ovchenkov, Y. A., Belosludov, R., Boltalin, A. I., Liu, M., Morozov, I. V., Nejo, H., Vasiliev, A. N., Theoretical Physics and Applied Mathematics Department, Institute of Physics and Technology, Ural Federal University, Ekaterinburg 620002, and National University of Science and Technology 'MISiS', Moscow 119049. Mon . "Scanning tunneling microscopy study of morphology and electronic properties in (K{sub 0.7}Na{sub 0.3})Fe{sub 2−y}Se{sub 2} single crystal". United States. doi:10.1063/1.4891227.
@article{osti_22308539,
title = {Scanning tunneling microscopy study of morphology and electronic properties in (K{sub 0.7}Na{sub 0.3})Fe{sub 2−y}Se{sub 2} single crystal},
author = {Trifonov, A. S., E-mail: trifonov.artem@phys.msu.ru and Presnov, D. E. and Low Temperature Physics and Superconductivity Department, Physics Faculty, Lomonosov Moscow State University, 119991 Moscow and Ovchenkov, Y. A. and Belosludov, R. and Boltalin, A. I. and Liu, M. and Morozov, I. V. and Nejo, H. and Vasiliev, A. N. and Theoretical Physics and Applied Mathematics Department, Institute of Physics and Technology, Ural Federal University, Ekaterinburg 620002 and National University of Science and Technology 'MISiS', Moscow 119049},
abstractNote = {We investigated the microstructure of the iron selenide superconductor (K{sub 0.7}Na{sub 0.3})Fe{sub 2−y}Se{sub 2} with a T{sub c} = 32 K and a near 100% Meissner screening volume fraction. Topography and electron transport properties were studied using electron microscopy and ultra-high vacuum scanning tunneling microscopy (STM) techniques. Room temperature STM measurements reliably identify spatial variations of the local electronic properties of this material. The studied crystals consist of continuous regions with significantly different shapes of current-voltage curves reflecting different electronic transport properties of these regions. Fitting of the local current-voltage curves with the Simmons model for metal-dielectric-metal structure confirmed a phase separation in the sample to a metal and semiconducting phases. The observed regions have dimensions in the range of several tenths of a micrometer and indicate a phase separation in the sample.},
doi = {10.1063/1.4891227},
journal = {Journal of Applied Physics},
number = 4,
volume = 116,
place = {United States},
year = {Mon Jul 28 00:00:00 EDT 2014},
month = {Mon Jul 28 00:00:00 EDT 2014}
}
  • Scanning tunneling microscopy is used to study the surface structural and electronic properties of cleaved single crystals of Bi/sub 2.15/Sr/sub 1.7/CaCu/sub 2/O/sub 8+/delta// Images with atomic resolution reveal atomic chains with sinusoidal modulations running along the perovskite cell axis with a periodicity of 9 to 10 unit cells. These atomic chains stack along the /bold b/ direction with a translational vector of one unit, resulting in an incommensurate periodicity of about 4.75 units along the /bold a/ direction. In contrast to other reports, no evidence of ''missing Bi-atom rows'' is found. Spectroscopic studies show zero density of states at themore » Fermi level, implying that the surface Bi-O layer is nonmetallic.« less
  • The (NH{sub 4})[Fe(AsO{sub 4}){sub 1-x}(PO{sub 4}){sub x}F] (x=0.3, 0.6, 0.8) series of compounds has been synthesized under mild hydrothermal conditions. The compounds crystallize in the orthorhombic Pna2{sub 1} space group, with the unit-cell parameters a=13.1718(1), b=6.5966(6), c=10.797(1) A for x=0.3; a=13.081(1), b=6.5341(6), c=10.713(1) A for x=0.6 and a=13.0329(9), b=6.4994(4), c=10.6702(6) A for x=0.8, with the volumes 938.6(1), 915.7(1) and 903.8(1) A{sup 3}, respectively, with Z=8. Single crystals of (NH{sub 4})[Fe(AsO{sub 4}){sub 0.7}(PO{sub 4}){sub 0.3}F] heated under air atmosphere at 465 deg. C remain as single crystals, changing the composition to Fe(AsO{sub 4}){sub 0.7}(PO{sub 4}){sub 0.3}. This later phase belongs tomore » the orthorhombic Imam space group, with the unit cell parameters a=13.328(2), b=6.5114(5), c=10.703(1) A, V=928.9(2) A{sup 3} and Z=12. The crystal structure of the ammonium phases consists of a KTP three-dimensional framework constructed by chains formed by alternating Fe(2)O{sub 4}F{sub 2} or Fe(1)O{sub 4}F{sub 2} octahedra and As/P(2)O{sub 4} or As/P(1)O{sub 4} tetrahedra, respectively. These octahedra and tetrahedra are linked by a common oxygen vertex. The chains run along the 'a' and 'b' crystallographic axes. The crystal structure of Fe(AsO{sub 4}){sub 0.7}(PO{sub 4}){sub 0.3} is a three-dimensional skeleton derived from that of the precursor, formed from (100) sheets stacked along the [001] direction, and interconnected by chains of alternating Fe(2)O{sub 6} octahedra and As/P(2)O{sub 4} tetrahedra sharing a vertex in the 'a' direction. Transmission electronic microscopy of this compound indicates the existence of unconnected external cavities with a BET surface area of 3.91(3) m{sup 2} g{sup -1}. The diffuse reflectance spectra in the visible region show the forbidden electronic transitions characteristic of the Fe(III) d{sup 5}-high spin cation in slightly distorted octahedral geometry, for all the compounds. The ESR spectra for all the compounds, carried out from room temperature to 4.2 K, remain isotropic with variation in temperature; the g-value is 1.99(1). Magnetic measurements indicate the predominance of antiferromagnetic interactions, with Neel temperatures near to 70.0 and 50.0 K for the ammonium phases and Fe(AsO{sub 4}){sub 0.7}(PO{sub 4}){sub 0.30}, respectively. At low temperatures a spin canting phenomenon for Fe(AsO{sub 4}){sub 0.7}(PO{sub 4}){sub 0.30} is detected. - Graphical abstract: The relationship between the |100| and |010| chains in (NH{sub 4})[Fe(AsO{sub 4}){sub 1-x}(PO{sub 4}){sub x}F] left and the |100| chains and the (001) sheets in Fe(AsO{sub 4}){sub 0.7}(PO{sub 4}){sub 0.3}.« less
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  • The structure, Curie temperature, and magnetostriction of R{sub 1{minus}{ital x}}Pr{sub {ital x}}Fe{sub 1.85} and R{sub 0.7}Pr{sub 0.3}Fe{sub {ital y}} ({ital R}=Dy{sub 0.7}Tb{sub 0.3}, {ital x}{le}0.5, 1.55{le}{ital y}{le}1.85) alloys were investigated. The matrix of R{sub 1{minus}{ital x}}Pr{sub {ital x}}Fe{sub 1.85} alloys is the MgCu{sub 2}-type cubic (Dy,Tb,Pr) Fe{sub 2} and the second phase was found to be (Dy,Tb,Pr) Fe{sub 3} when {ital x}{le}0.3. When {ital x}{gt}0.4, (Dy,Tb,Pr)Fe{sub 3} is the main phase with the PuNi{sub 3}-type structure and (Dy,Tb,Pr) Fe{sub 2} becomes the minority phase. In the range of 0.3{lt}{ital x}{le}0.4, both MgCu{sub 2}- and PuNi{sub 3}-type structures coexist. The R{submore » 0.7}Pr{sub 0.3}Fe{sub {ital y}} alloys contain a small amount of (Dy,Tb,Pr) Fe{sub 3} phase when {ital y}{gt}1.55, which increases with increasing {ital y}. When {ital y}=1.55, the alloy is essentially single phase with the MgCu{sub 2}-type cubic structure. The lattice parameter of (Dy,Tb,Pr)Fe{sub 2} compound for R{sub 1{minus}{ital x}}Pr{sub {ital x}}Fe{sub 1.85} alloys increases slowly with increasing {ital x} when {ital x}{le}0.3, and sharply increases when {ital x}{gt}0.3. The Curie temperature of the alloys decreases steadily with increasing Pr content. The magnetostrictions of R{sub 1{minus}{ital x}}Pr{sub {ital x}}Fe{sub 1.85} and R{sub 0.7}Pr{sub 0.3}Fe{sub {ital y}} alloys decrease with increasing Pr content and Fe content, respectively. The largest magnetostriction at room temperature was found in the alloy R{sub 0.7}Pr{sub 0.3}Fe{sub 1.55} (1480{times}10{sup {minus}6} at {ital H}=796 kA/m). {copyright} {ital 1996 American Institute of Physics.}« less