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ABSTRACT: The surfaces of a ten years aged crystal and a freshly prepared κ-(BEDT-TTF)2Cu(NCS)2 crystal were compared by scanning tunneling microscopy (STM). The molecularly-resolved STM images of the bc plane of the crystals agree with each other and with the electronic contrast obtained by new density functional theory (DFT)
based simulations. Even after ten years STM images of the molecular stacking of BEDT-TTF display a variation in brightness
at the positions of different molecules. We attribute this symmetry breaking concerning the brightness in the STM images of
the otherwise equivalent BEDT-TTF dimers to the electronic states of a relaxed surface.
PACS68.37.Ef Scanning tunneling microscopy-74.70.Kn Organic superconductors-71.15.Mb Density functional theory, local density approximation, gradient and other corrections
Physics of Condensed Matter 04/2012; 69(2):167-171. · 1.53 Impact Factor
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M. V. Kartsovnik,
T. Helm,
C. Putzke,
F. Wolff-Fabris,
I. Sheikin,
S. Lepault,
C. Proust,
D. Vignolles,
N. Bittner,
W. Biberacher,
A. Erb,
J. Wosnitza, R Gross
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ABSTRACT: We report on the study of the Fermi surface of the electron-doped cuprate
superconductor Nd$_{2-x}$Ce$_x$CuO$_{4}$ by measuring the interlayer
magnetoresistance as a function of the strength and orientation of the applied
magnetic field. We performed experiments in both steady and pulsed magnetic
fields on high-quality single crystals with Ce concentrations of $x=0.13$ to
0.17. In the overdoped regime of $x > 0.15$ we found both semiclassical
angle-dependent magnetoresistance oscillations (AMRO) and Shubnikov-de Haas
(SdH) oscillations. The combined AMRO and SdH data clearly show that the
appearance of fast SdH oscillations in strongly overdoped samples is caused by
magnetic breakdown. This observation provides clear evidence for a
reconstructed multiply-connected Fermi surface up to the very end of the
overdoped regime at $x\simeq 0.17$. The strength of the superlattice potential
responsible for the reconstructed Fermi surface is found to decrease with
increasing doping level and likely vanishes at the same carrier concentration
as superconductivity, suggesting a close relation between translational
symmetry breaking and superconducting pairing. A detailed analysis of the
high-resolution SdH data allowed us to determine the effective cyclotron mass
and Dingle temperature, as well as to estimate the magnetic breakdown field in
the overdoped regime.
04/2011;
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M V Kartsovnik,
T Helm,
C Putzke,
F Wolff-Fabris,
I Sheikin,
S Lepault,
C Proust,
D Vignolles,
N Bittner,
W Biberacher,
A Erb,
J Wosnitza, R Gross
[show abstract]
[hide abstract]
ABSTRACT: We report on the study of the Fermi surface of the electron-doped cuprate superconductor Nd2−xCexCuO4 by measuring the interlayer magnetoresistance as a function of the strength and orientation of the applied magnetic field. We performed experiments in both steady and pulsed magnetic fields on high-quality single crystals with Ce concentrations of x=0.13–0.17. In the overdoped regime of x>0.15, we found both semiclassical angle-dependent magnetoresistance oscillations (AMROs) and Shubnikov–de Haas (SdH) oscillations. The combined AMROs and SdH data clearly show that the appearance of fast SdH oscillations in strongly overdoped samples is caused by magnetic breakdown. This observation provides clear evidence for a reconstructed multiply connected Fermi surface up to the very end of the overdoped regime at x0.17. The strength of the superlattice potential responsible for the reconstructed Fermi surface is found to decrease with increasing doping level and likely vanishes at the same carrier concentration as superconductivity, suggesting a close relation between translational symmetry breaking and superconducting pairing. A detailed analysis of the high-resolution SdH data allowed us to determine the effective cyclotron mass and Dingle temperature, as well as to estimate the magnetic breakdown field in the overdoped regime.
New Journal of Physics 01/2011; 13(1):015001. · 4.18 Impact Factor
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M V Kartsovnik,
T Helm,
C Putzke,
F Wolff-Fabris,
I Sheikin,
S Lepault,
C Proust,
D Vignolles,
N Bittner,
W Biberacher,
A Erb,
J Wosnitza, R Gross
New Journal of Physics. 01/2011; 13.
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T Helm,
M V Kartsovnik,
I Sheikin,
M Bartkowiak,
F Wolff-Fabris,
N Bittner,
W Biberacher,
M Lambacher,
A Erb,
J Wosnitza, R Gross
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ABSTRACT: We report on semiclassical angle-dependent magnetoresistance oscillations and the Shubnikov-de Haas effect in the electron-overdoped cuprate superconductor Nd(2-x)CexCuO4. Our data provide convincing evidence for magnetic breakdown in the system. This shows that a reconstructed multiply connected Fermi surface persists, at least at strong magnetic fields, up to the highest doping level of the superconducting regime.
Physical Review Letters 12/2010; 105(24):247002. · 7.37 Impact Factor
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T. Helm,
M. V. Kartsovnik,
I. Sheikin,
M. Bartkowiak,
F. Wolff-Fabris,
N. Bittner,
W. Biberacher,
M. Lambacher,
A. Erb,
J. Wosnitza, R Gross
[show abstract]
[hide abstract]
ABSTRACT: We report on semiclassical angle-dependent magnetoresistance oscillations (AMRO) and the Shubnikov-de Haas effect in the electron-overdoped cuprate superconductor Nd$_{2-x}$Ce$_x$CuO$_4$. Our data provide convincing evidence for magnetic breakdown in the system. This shows that a reconstructed multiply-connected Fermi surface persists, at least at strong magnetic fields, up to the highest doping level of the superconducting regime. Our results suggest an intimate relation between translational symmetry breaking and the superconducting pairing in the electron-doped cuprate superconductors. Comment: 5 pages, 4 figures, submitted to PRL
08/2010;
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ABSTRACT: We report on the direct probing of the Fermi surface in the bulk of the electron-doped superconductor Nd(2-x)Ce(x)CuO(4) at different doping levels by means of magnetoresistance quantum oscillations. Our data reveal a sharp qualitative change in the Fermi surface topology, due to translational symmetry breaking in the electronic system which occurs at a critical doping level significantly exceeding the optimal doping. This result implies that the (pi/a, pi/a) ordering, known to exist at low doping levels, survives up to the overdoped superconducting regime.
Physical Review Letters 10/2009; 103(15):157002. · 7.37 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We report on the direct probing of the Fermi surface in the bulk of the electron-doped superconductor Nd$_{2-x}$Ce$_x$CuO$_4$ at different doping levels by means of magnetoresistance quantum oscillations. Our data reveal a sharp qualitative change in the Fermi surface topology, due to translational symmetry breaking in the electronic system which occurs at a critical doping level significantly exceeding the optimal doping. This result implies that the $(\pi/a,\pi/a)$ ordering, known to exist at low doping levels, survives up to the overdoped superconducting regime. Comment: 12 pages, 4 figures; submitted to PRL
06/2009;
