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Scanning tunnelling spectroscopy of electron resonators  [PDF]
Richard Berndt,Joerg Kliewer,S. Crampin
Physics , 2001, DOI: 10.1088/1367-2630/3/1/322
Abstract: The electronic structure of artificial Mn atom arrays on Ag(111) is characterized in detail with scanning tunnelling spectroscopy and spectroscopic imaging at low temperature. We demonstrate the degree to which variations in geometry may be used to control spatial and spectral distributions of surface state electrons confined within the arrays, how these are influenced by atoms placed within the structure and how the ability to induce spectral features at specific energies may be exploited through lineshape analyses to deduce quasiparticle lifetimes near the Fermi level. Through extensive comparison of $dI/dV$ maps and spectra we demonstrate the utility of a model based upon two-dimensional s-wave scatterers for describing and predicting the characteristics of specific resonators.
Quantum Interference of Impurity Bound States in Bi$_{2}$Sr$_{2}$Ca(Cu$_{1-x}$Zn$_{x}$)$_{2}$O$_{8+δ}$ Probed by Scanning Tunneling Spectroscopy  [PDF]
Tadashi Machida,Takuya Kato,Hiroshi Nakamura,Masaki Fujimoto,Takashi Mochiku,Shuuichi Ooi,Ajay D. Thakur,Hideaki Sakata,Kazuto Hirata
Physics , 2011, DOI: 10.1103/PhysRevB.84.064501
Abstract: In conventional superconductors, magnetic impurities form an impurity band due to quantum interference of the impurity bound states, leading to suppression of the superconducting transition temperature. Such quantum interference effects can also be expected in d-wave superconductors. Here, we use scanning tunneling microscopy to investigate the effect of multiple non-magnetic impurities on the local electronic structure of the high-temperature superconductor Bi$_{2}$Sr$_{2}$Ca(Cu$_{1-x}$Zn$_{x}$)$_{2}$O$_{8+\delta}$. We find several fingerprints of quantum interference of the impurity bound states including: (i) a two-dimensional modulation of local density-of-states with a period of approximately 5.4 \AA\ along the $a$- and $b$-axes, which is indicative of the d-wave superconducting nature of the cuprates; (ii) abrupt spatial variations of the impurity bound state energy; (iii)an appearance of positive energy states; (iv) a split of the impurity bound state. All of these findings provide important insight into how the impurity band in d-wave superconductors is formed.
Charge trapping in polymer transistors probed by terahertz spectroscopy and scanning probe potentiometry  [PDF]
J. Lloyd-Hughes,T. Richards,H. Sirringhaus,E. Castro-Camus,L. M. Herz,M. B. Johnston
Physics , 2006, DOI: 10.1063/1.2340057
Abstract: Terahertz time-domain spectroscopy and scanning probe potentiometry were used to investigate charge trapping in polymer field-effect transistors fabricated on a silicon gate. The hole density in the transistor channel was determined from the reduction in the transmitted terahertz radiation under an applied gate voltage. Prolonged device operation creates an exponential decay in the differential terahertz transmission, compatible with an increase in the density of trapped holes in the polymer channel. Taken in combination with scanning probe potentionmetry measurements, these results indicate that device degradation is largely a consequence of hole trapping, rather than of changes to the mobility of free holes in the polymer.
Direct Observation of Spectroscopic Inhomogeneities on La0.7Sr0.3MnO3 Thin Films by Scanning Tunnelling Spectroscopy  [PDF]
R. Di Capua,C. A. Perroni,V. Cataudella,F. Miletto Granozio,P. Perna,M. Salluzzo,U. Scotti Di Uccio,R. Vaglio
Physics , 2006, DOI: 10.1088/0953-8984/18/35/007
Abstract: Scanning tunnelling spectroscopy measurements were performed on La0.7Sr0.3MnO3 thin films both at room temperature and liquid nitrogen temperature. While no inhomogeneities were recorded at liquid nitrogen temperature on any sample, a clear evidence of spectroscopic inhomogeneities was evident in tunnelling conductance maps collected at room temperature. The investigated films exhibit a transition from a ferromagnetic-metallic to a paramagnetic-insulating state around room temperature, so that the observed spectroscopic features can be interpreted within a phase separation scenario. A quantitative analysis of the observed spectroscopic features is reported pointing out the occurrence of phase modulation and its possible correlation with the properties of the system.
First Scanning Tunnelling Spectroscopy on Bi2Sr2Ca2Cu3O10 (Bi2223) single crystals  [PDF]
Martin Kugler,Giorgio Levy,Enrico Giannini,Alex Piriou,Alfred A. Manuel,Christian Hess,Oystein Fischer
Physics , 2005, DOI: 10.1016/j.jpcs.2005.10.155
Abstract: We report the first low temperature scanning tunnelling microscopy and spectroscopy study of high quality Bi2223 crystals. We present atomic resolution and show spectroscopic data acquired on two different samples. In one case, for Tc= 109K and a transition width of only 1K, we obtained an extremely homogeneous sample with a gap value of 60 meV over at least 50 nm. In the other case, the respective parameters were Tc= 111K with a transition width of 1.7K and yielded a slightly less homogeneous sample with a gap of 45 meV. We evidence strong similarities with Bi2Sr2CaCu2O8 (Bi2212) and discuss the doping level of our samples.
Graphene quantum dots probed by scanning tunneling spectroscopy and transport spectroscopy after local anodic oxidation  [PDF]
Markus Morgenstern,Nils Freitag,Aviral Vaid,Marco Pratzer,Marcus Liebmann
Physics , 2015,
Abstract: Graphene quantum dots are considered as promising alternatives to quantum dots in III-V semiconductors, e.g., for the use as spin qubits due to their consistency made of light atoms including spin-free nuclei which both imply relatively long spin decoherene times. However, this potential has not been realized in experiments so far, most likely, due to a missing control of the edge configurations of the quantum dots. Thus, a more fundamental investigation of Graphene quantum dots appears to be necessary including a full control of the wave function properties most favorably during transport spectroscopy measurements. Here, we review the recent success in mapping wave functions of graphene quantum dots supported by metals, in particular Ir(111), and show how the goal of probing such wave functions on insulating supports during transport spectroscopy might be achieved.
Scanning tunnelling spectroscopy of the vortex state in NbSe2 using a superconducting tip  [PDF]
J. G. Rodrigo,V. Crespo,S. Vieira
Physics , 2007, DOI: 10.1016/j.physc.2007.11.019
Abstract: The vortex electronic structure in the multiband superconductor NbSe2 is studied by means of Scanning Tunneling Spectroscopy (STS) using a superconducting tip. The use of a superconducting tip (Pb) as a probe provides an enhancement of the different features related to the DOS of NbSe2 in the tunneling conductance curves. This use allows the observation of rich patterns of electronic states in the conductance images around the vortex cores in a wide range of temperature, as well as the simultaneous acquisition of Josephson current images in the vortex state.
Highly reproducible low temperature scanning tunnelling microscopy and spectroscopy with in situ prepared tips  [PDF]
Andres Castellanos-Gomez,Gabino Rubio-Bollinger,Manuela Garnica,Sara Barja,Amadeo L. Vázquez de Parga,Rodolfo Miranda,Nicolás Agra?t
Physics , 2012, DOI: 10.1016/j.ultramic.2012.07.021
Abstract: An in situ tip preparation procedure compatible with ultra-low temperature and high magnetic field scanning tunneling microscopes is presented. This procedure does not require additional preparation techniques such as thermal annealing or ion milling. It relies on the local electric-field-induced deposition of material from the tip onto the studied surface. Subsequently, repeated indentations are performed onto the sputtered cluster to mechanically anneal the tip apex and thus to ensure the stability of the tip. The efficiency of this method is confirmed by comparing the topography and spectroscopy data acquired with either unprepared or in situ prepared tips on epitaxial graphene grown on Ru (0001). We demonstrate that the use of in situ prepared tips increases the stability of the scanning tunneling images and the reproducibility of the spectroscopic measurements.
Reversible hydrogenation and band gap opening of graphene and graphite surfaces probed by scanning tunneling spectroscopy  [PDF]
Andres Castellanos-Gomez,Magdalena Wojtaszek,Arramel,Nikolaos Tombros,Bart J. van Wees
Physics , 2012, DOI: 10.1002/smll.201101908
Abstract: The effect of hydrogenation on the topography and the electronic properties of graphene and graphite surfaces are studied by scanning tunneling microscopy and spectroscopy. The surfaces are chemically modified using Ar/H2 plasma. Analyzing thousands of scanning tunneling spectroscopy measurements we determine that the hydrogen chemisorption on the surface of graphite/graphene opens on average an energy band gap of 0.4 eV around the Fermi level. We find that although the plasma treatment modifies the surface topography in a non-reversible way, the change in the electronic properties can be reversed by a moderate thermal annealing and the samples can be hydrogenated again yielding a similar, but slightly reduced, semiconducting behavior after the second hydrogenation.
Evidence for Induced Magnetization in Superconductor-Ferromagnet Hetero-structures: a Scanning Tunnelling Spectroscopy Study  [PDF]
Itay Asulin,Ofer Yuli,Gad Koren,Oded Millo
Physics , 2009, DOI: 10.1103/PhysRevB.79.174524
Abstract: We performed scanning tunneling spectroscopy of c-axis oriented YBCO films on top of which ferromagnetic SRO islands were grown epitaxially in-situ. When measured on the ferromagnetic islands, the density of states exhibits small gap-like features consistent with the expected short range penetration of the order parameter into the ferromagnet. However, anomalous split-gap structures are measured on the superconductor in the vicinity of ferromagnetic islands. This observation may provide evidence for the recently predicted induced magnetization in the superconductor side of a superconductor/ ferromagnet junction. The length scale of the effect inside the superconductor was found to be an order of magnitude larger than the superconducting coherence length. This is inconsistent with the theoretical prediction of a penetration depth of only a few superconducting coherence lengths. We discuss a possible origin for this discrepancy.
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