Scanning tunneling microscopy and spectroscopy of thin film superconductor Pb (original) (raw)
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Review of Scientific Instruments, 2013
We report the construction and performance of a low temperature, high field scanning tunneling microscope (STM) operating down to 350mK and in magnetic fields up to 9T, with thin film deposition and in-situ single crystal cleaving capabilities. The main focus lies on the simple design of STM head and a sample holder design that allows us to get spectroscopic data on superconducting thin films grown in-situ on insulating substrates. Other design details on sample transport, sample preparation chamber and vibration isolation schemes are also described. We demonstrate the capability of our instrument through the atomic resolution imaging and spectroscopy on NbSe 2 single crystal and spectroscopic maps obtained on homogeneously disordered NbN thin film.
2013
We report the construction and performance of a low temperature, high field scanning tunneling microscope (STM) operating down to 350mK and in magnetic fields up to 9T, with thin film deposition and in-situ cleaving capabilities. The main focus lies on the simple design of STM head allowing top loading of the sample and innovative sample holder design that allows us to get spectroscopic data on superconducting thin films grown in-situ on insulating substrates. Other design details on sample transport, chamber and vibration isolation scheme are also described. We demonstrate the capability of our instrument through the atomic resolution imaging and spectroscopy on NbSe2 single crystal and spectroscopic maps obtained on homogeneously disordered NbN thin film.
Scanning tunneling microscopy in the superconductor LaSb2
Physical Review B, 2013
We present very low temperature (0.15 K) scanning tunneling microscopy and spectroscopy experiments in the layered superconductor LaSb2. We obtain topographic microscopy images with surfaces showing hexagonal and square atomic size patterns, and observe in the tunneling conductance a superconducting gap. We find well defined quasiparticle peaks located at a bias voltage comparable to the weak coupling s-wave BCS expected gap value (0.17 meV). The amount of states at the Fermi level is however large and the curves are significantly broadened. We find Tc of 1.2 K by following the tunneling conductance with temperature.
Tunneling spectroscopy of superconducting MoN and NbTiN grown by atomic layer deposition
Applied Physics Letters, 2014
A tunneling spectroscopy study is presented of superconducting MoN and Nb 0.8 Ti 0.2 N thin films grown by atomic layer deposition (ALD). The films exhibited a superconducting gap of 2 meV and 2.4 meV, respectively, with a corresponding critical temperature of 11.5 K and 13.4 K, among the highest reported T c values achieved by the ALD technique. Tunnel junctions were obtained using a mechanical contact method with a Au tip. While the native oxides of these films provided poor tunnel barriers, high quality tunnel junctions with low zero bias conductance (below $10%) were obtained using an artificial tunnel barrier of Al 2 O 3 on the film's surface grown ex situ by ALD. We find a large critical current density on the order of 4 Â 10 6 A/cm 2 at T ¼ 0.8T c for a 60 nm MoN film and demonstrate conformal coating capabilities of ALD onto high aspect ratio geometries. These results suggest that the ALD technique offers significant promise for thin film superconducting device applications. V C 2014 AIP Publishing LLC. [http://dx.
Atomic site tunneling spectroscopy on high-Tc superconductors
Physica B: Condensed Matter, 1994
Superconducting gap structures of BizSr2CaCu2Oy (BSCCO) and YBa2Cu3Oy (YBCO) have been probed by scanning tunneling microscopy (STM) at cryogenic temperatures. The tunneling conductance curves observed on bulk single crystals of BSCCO and epitaxial thin films of YBCO revealed clear overshooting peaks and flat bottom regions around V= 0 with quite low zero-bias conductances of -1%. Since the electron tunneling process in STM is essentially incoherent, the present observation is favored by the s-wave pairing mechanism. However, the conductance curves were found to be substantially smeared in comparison with the conventional excitation spectra predicted in the BCS (isotropic s-wave) superconductors, suggesting gap anisotropy. 0921-4526/94/$07.00 ~ 1994 Elsevier Science B.V. All rights reserved SSDI: 0921-4526(93)E0192-J
Low temperature physics, 2019
The systematic study of the nanoscale local electronic states on the MgB 2 surface was performed using the low-temperature scanning tunnel microscopy/spectroscopy (STM/STS). The STM topography shows the atomic image of the hexagonal lattice with the constant parameter a′ = 0.31 nm, which is identified as mainly the Mg site occupancy. The temperature-dependent STS measurements were analyzed assuming the existence of two energy gaps. As a result, the fitting gap amplitudes ∆ fit 10.2 meV and 4.8 meV were found at T = 4.9 K. The scanned conductance (dI / dV) maps in the area of 4×2 nm 2 show homogenous distributions of the gaps associated with the π-band. In addition, the conductance peaks at zero-bias voltage were observed through defined lines with lengths about ∼0.8 nm, which is much smaller than the superconducting coherence length ξ ab ~ 40 nm of MgB 2. The form of the zero-bias peaks looks like that in the case of the Andreev-Saint-James reflection at the tip-sample contact.
2009
In this talk we give an update on the next generation of ultra low temperature, high magnetic field (15T) scanning tunneling microscope (STM). With this system, we plan to extend the capability of STM to include higher energy resolution (∼1µeV) for scanning tunneling spectroscopy (STS) with operation at 20 mK. To realize this energy resolution in STS, we constructed an ultra high vacuum dilution refrigerator (DR) for STM applications. It operates with two independent modes of He3-He4 mixture gas condensation: a traditional 1K pot condenser, or a Joule-Thomson condenser for possible lower noise operation. This eliminates potential vibration problems during operation of the DR. To match the very low limit of thermal noise in this system, our new system includes extensive vibration isolation and RF shielding. Our STM sample holder has five isolated electrical contacts. This allows four-probe macroscopic electrical measurements to be performed simultaneously with microscopic STM measurements. The current progress and performance of this new system will be discussed. 8:12AM A27.00002 Design and construction of a millikelvin scanning tunneling microscopy system , MARK GUBRUD
Tunneling spectroscopy in thin films YBCO/Pb tunnel structures
IEEE Transactions on Magnetics, 1989
Experimental r e s u l t s on electron tunneling i n t o t h i n superconducting f i l m s YBa2Cu30x i n YBCO/Pb tunnel junct i o n s are reported. Thin superconducting f i l m s YBCO (thickness 0.7(um) were prepared by codeposition of Y, BaO, and Cu onto single c r y s t a l substratessaphire, MgO, SrTi03. Maximum c r i t i c a l temperature a t zero resis-
Journal of Materials Science, 1992
The surface morphology of laser-deposited superconducting YBa2Cu307_ x thin films has been studied using scanning tunnelling microscopy (STM). Very high resolution of the surface morphology has been obtained showing well-textured surfaces with very distinct growth patterns. The thin films produced by in situ laser deposition are highly oriented with typical Jc values >1 x 106A cm -2 at 77 K. The morphology of these surfaces as revealed by STM is a terraced, layer-like structure with a discrete rise of each terrace level approximately equal to the c-axis lattice spacing. These terraces are stacked upon each other in an ordered fashion. These terraces can also be viewed as a series of chip-like morphologies which increase in size at the lower levels. The surface structure (amount of texturing and size of terraces near the surface) shows a small but observable dependence upon the deposition conditions, with lower deposition rates producing larger grain sizes. We have also studied the chemical etching of these surfaces and the resultant morphologies have been followed using atomic force microscopy. Upon chemical etching the individual grains are revealed and due to the epitaxial growth of these films, most likely represent mutually aligned but separate grains. These etching studies provide valuable information about substructures. A model for film growth based upon nucleation and growth will be described.
Physical Review B, 2011
Evidence of a non-thermal magnetic relaxation in the intermediate state of a type-I superconducor is presented. It is attributed to quantum tunneling of interfaces separating normal and superconducting regions. Tunneling barriers are estimated and temperature of the crossover from thermal to quantum regime is obtained from Caldeira-Leggett theory. Comparison between theory and experiment points to tunneling of interface segments of size comparable to the coherence length, by steps of order one nanometer. PACS numbers: 74.25.Ha, 74.50.+r, 75.45.+j Quantum tunneling of relatively macroscopic solidstate objects like flux lines in type-II superconductors and domain walls in magnets have been subject of intensive research in the past. Pinning by defects and impurities creates complex potential landscape that traps flux lines and domain walls inside metastable energy minima. Their interaction with environment makes this problem the one of macroscopic quantum tunneling with dissipation [4]. The latter is especially important for the tunneling of flux lines because of their predominantly dissipative dynamics . If individual pinning centers are small compared to the dimensions of the vortex or the width of the domain wall, the pinning is collective. In this case the energy barriers and spatial scales of thermal and quantum diffusion of flux lines and domain walls are non-trivially determined by statistical mechanics of the pinning potential [1, 2, 10, 11].