25 research outputs found
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Surface of underdoped YBa2Cu3O7- δ as revealed by STM/STS
We performed scanning tunneling microscopy and spectroscopy on untwinned crystals of underdoped YBa2Cu3O7- δ at δ = 0.4. A comprehensive statistical analysis of our topographic data indicates a doping dependent cleaving behavior of this material. We find in particular that at δ = 0.4 the material primarily cleaves in multiples of one unit cell along the c-axis with a high corrugation of the topmost layer. Our data suggest that the low temperature cleaving mainly results in a disruption of the CuO chain layers involving a redistribution of the layer atoms onto the two cleaving planes. In a few instances, fractional step heights (in terms of the c-axis lattice constant) are observed as well. Scanning tunneling spectroscopy reveals that such fractional steps connect surfaces which differ significantly in their tunneling conductance
Bridging charge-orbital ordering and Fermi surface instabilities in half-doped single-layered manganite La_0.5Sr_1.5MnO_4
Density waves are inherent to the phase diagrams of materials that exhibit
unusual, and sometimes extraordinarily useful properties, such as
superconductivity and colossal magnetoresistance. While the pure charge density
waves (CDW) are well described by an itinerant approach, where electrons are
treated as waves propagating through the crystal, the charge-orbital ordering
(COO) is usually explained by a local approach, where the electrons are treated
as localized on the atomic sites. Here we show that in the half-doped manganite
La0.5Sr1.5MnO4 (LSMO) the electronic susceptibility, calculated from the
angle-resolved photoemission spectra (ARPES), exhibits a prominent
nesting-driven peak at one quarter of the Brillouin zone diagonal, that is
equal to the reciprocal lattice vector of the charge-orbital pattern. Our
results demonstrate that the Fermi surface geometry determines the propensity
of the system to form a COO state which, in turn, implies the applicability of
the itinerant approach also to the COO
Surface of underdoped YBa
We performed scanning tunneling microscopy and spectroscopy on untwinned crystals of underdoped YBa2Cu3O7-δ at δ = 0.4. A comprehensive statistical analysis of our topographic data indicates a doping dependent cleaving behavior of this material. We find in particular that at δ = 0.4 the material primarily cleaves in multiples of one unit cell along the c-axis with a high corrugation of the topmost layer. Our data suggest that the low temperature cleaving mainly results in a disruption of the CuO chain layers involving a redistribution of the layer atoms onto the two cleaving planes. In a few instances, fractional step heights (in terms of the c-axis lattice constant) are observed as well. Scanning tunneling spectroscopy reveals that such fractional steps connect surfaces which differ significantly in their tunneling conductance
Consequences of line defects on the magnetic structure of high anisotropy films: Pinning centers on
The narrow domain wall width w of high-anisotropy materials induces significant pinning of magnetic domains
at line defects which —due to spatial resolution limitations— could not be studied directly in the past.
By means of spin-polarized scanning tunneling microscopy we have directly correlated
the morphology and domain structure of ferromagnetic Dy/W(110) on the nanometer scale.
Indeed, the images reveal an effective pinning of the domain walls by two types of line defects.
They are identified by growth studies and atomic resolution STM as screw and edge dislocations,
two fundamental lattice distortions in solid-state physics
Surface of underdoped YBa2Cu3O7- δ as revealed by STM/STS
We performed scanning tunneling microscopy and spectroscopy on untwinned crystals of underdoped YBa2Cu3O7-δ at δ = 0.4. A comprehensive statistical analysis of our topographic data indicates a doping dependent cleaving behavior of this material. We find in particular that at δ = 0.4 the material primarily cleaves in multiples of one unit cell along the c-axis with a high corrugation of the topmost layer. Our data suggest that the low temperature cleaving mainly results in a disruption of the CuO chain layers involving a redistribution of the layer atoms onto the two cleaving planes. In a few instances, fractional step heights (in terms of the c-axis lattice constant) are observed as well. Scanning tunneling spectroscopy reveals that such fractional steps connect surfaces which differ significantly in their tunneling conductance
Un microscopio de tĂşnel de barrido de vacĂo ultra alto que opera a temperaturas sub-Kelvin y campos magnĂ©ticos altos para mediciones resueltas por espĂn
We present the construction and performance of an ultra-low-temperature scanning tunneling microscope (STM), working in ultra-high vacuum (UHV) conditions and in high magnetic fields up to 9 T. The cryogenic environment of the STM is generated by a single-shot 3He magnet cryostat in combination with a 4He dewar system. At a base temperature (300 mK), the cryostat has an operation time of approximately 80 h. The special design of the microscope allows the transfer of the STM head from the cryostat to a UHV chamber system, where samples and STM tips can be easily exchanged. The UHV chambers are equipped with specific surface science treatment tools for the functionalization of samples and tips, including high-temperature treatments and thin film deposition. This, in particular, enables spin-resolved tunneling measurements. We present test measurements using well-known samples and tips based on superconductors and metallic materials such as LiFeAs, Nb, Fe, and W. The measurements demonstrate the outstanding performance of the STM with high spatial and energy resolution as well as the spin-resolved capability
Atomically resolved magnetic structure of a Gd-Au surface alloy
The magnetic structure of a monolayer-thick GdAu2 surface alloy on Au(111) has been investigated down to the atomic level by spin-polarized scanning tunneling microscopy. Spin-resolved tunneling spectroscopy combined with density-functional theory calculations reveal the local spin polarization of both Gd and Au atomic sites within the surface alloy. Moreover, the impact of dislocation lines on the atomic-scale magnetic structure as well as on the local coercive field strength is demonstrated.We gratefully acknowledge financial support from the Office of Naval Research via Grant No. N00014-16-1-2900. Moreover, M.A. and J.B. acknowledge funding from the Spanish MINECO under Contracts No. MAT2013-46593-C6-
4-P and No. MAT2016-78293-C6-5-R as well as the Basque Government Grants No. IT621-13 and No. IT-756-13. T.H. acknowledges support by the DFG under Grant No. HA 6037/2-1. E.S. acknowledges financing from Polish budget
funds for science in 2014–2017 as a research project in the program “Diamond Grant” No. 0084/DIA/2014/43. M.H. acknowledges the support from the Ministry of Science and Higher Education in Poland within Project realized at Faculty
of Technical Physics, Poznan University of Technology, and Poznan Supercomputing and Networking Center (PSNC