Scanning tunneling microscopy in the superconductor LaSb2 (original) (raw)
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Scanning tunneling microscopy and spectroscopy of thin film superconductor Pb
Journal of Vacuum Science & Technology B, 1991
A variable‐temperature scanning tunneling microscope system, which operates in the temperature range of 4<T<400 K, was employed to perform topographic and spectroscopic studies of conventional superconductors at low temperatures. Images of Pb thin films were obtained and local tunneling spectroscopy was performed. The N–I–S tunneling characteristic revealing superconducting gap structure was observed. In mapping the electronic density of states over the Pb surface, abrupt changes in the measured N–I–S tunneling characteristics were found, showing the existence of apparent normal surface regions. The implications of the tunneling spectroscopy results are discussed.
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.
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
Tunneling Spectroscopy in Small Grains of SuperconductingMgB2
Physical Review Letters, 2001
We report on tunneling spectroscopy experiments in small grains of the new binary intermetallic superconductor MgB2. Experiments have been performed at 2.5 K using a low temperature scanning tunneling microscope. Good fit to the BCS model is obtained, with a gap value of 2 meV. In the framework of this model, this value should correspond to a surface critical temperature of 13.2 K. No evidence of gap anisotropy has been found.
Tunneling spectroscopy: A probe for high-Tc superconductivity
Microelectronics Journal, 2008
After the pioneering work of Giaever [Phys. Rev. Lett. 5 (1960) 147. ] and Shapiro in the 1960s, tunneling spectroscopy has become an important method for studying different properties of superconductors, such as the superconducting gap and the density of states. At the interface with a superconductor there is a variety of tunneling processes depending on barrier properties and the type of materials in both sides of the junction. Among other phenomena, we have single electron tunneling, cooper pairs (Josephson) tunneling [B.D. Josephson, Phys. Rev. Lett. 1 (1962) 251. [17]] and mixed (Andreev-Saint-James reflections [A.F. Andreev, Zh. Eksp. Teor. Fiz. 46 (1964) 1823, Saint-James D., J. Phys 25 (1964) 899]) tunneling.
We report scanning tunneling spectroscopy measurements at 150 mK in single layer crystals of 2H-TaSe2. We find a singular spatial dependence of the tunneling conductance, changing from a zero bias peak on top of Se atoms to a gap in between Se atoms. The zero bias peak is additionally modulated by the commensurate 3a0 × 3a0 charge density wave of 2H-TaSe2. Multilayers of 2H-TaSe2 show, by contrast, a homogeneous superconducting gap with a critical temperature of about 1 K. The zero bias peak in single layers of 2H-TaSe2 evidences a zero energy bound state. We discuss possible origins for such a peculiar electronic spectrum, which seems to be characteristic of small superconducting single layers of 2H-TaSe2. Single layer crystals of dichalchogenide materials can be obtained through repeated exfoliation[1-3]. In spite of extensive searches, no clear experimental evidence of superconductivity has been found in them. On the other hand, in-situ grown single layer surfaces, mostly of Pb, are creating a rich playground, demonstrating that superconductivity can form in atomically thin crystals. However, the superconducting critical temperature T c decreases when achieving ultimate thickness[4-6], and the superconducting tunneling conductance shows s-wave BCS like gap features[7]. Signs of unconventional superconductivity, as proposed in doped graphene layers[8, 9], are until now absent.
2012
The discovery of novel high-T c superconductivity in MgB 2 (T c = 39.5 K) and Li0.48(THF)yHfNCl (Tc = 25.5 K) initiated substantial progress in the field of superconductivity physics and its applications despite the fact that competing high-Tc cuprates remain the world leaders in almost all practically important superconducting parameters. This article describes electron tunneling and point-contact experimental studies of the indicated two materials and related substances, being crucial to elucidate the character of the quasiparticle energy spectrum both in superconducting and normal state. The account is based mostly on our own experiments, although works carried out in other laboratories are taken into account as well.
Nova Science Monograph “Superconductivity: Theory, Materials and Applications”, Ed. Vladimir R. Romanovskii, Chapter 1, pp. 1-110, 2012
The discovery of novel high-T c superconductivity in MgB 2 (T c = 39.5 K) and Li0.48(THF)yHfNCl (Tc = 25.5 K) initiated substantial progress in the field of superconductivity physics and its applications despite the fact that competing high-Tc cuprates remain the world leaders in almost all practically important superconducting parameters. This article describes electron tunneling and point-contact experimental studies of the indicated two materials and related substances, being crucial to elucidate the character of the quasiparticle energy spectrum both in superconducting and normal state. The account is based mostly on our own experiments, although works carried out in other laboratories are taken into account as well.
Scanning tunneling spectroscopy in MgB2
Physica C: Superconductivity, 2003
We present scanning tunneling microscopy measurements of the surface of superconducting MgB2 with a critical temperature of 39K. In zero magnetic field the conductance spectra can be analyzed in terms of the standard BCS theory with a smearing parameter Γ. The value of the superconducting gap is 5.2 meV at 4.2 K, with no experimentally significant variation across the surface of the sample. The temperature dependence of the gap follows the BCS form, fully consistent with phonon-mediated superconductivity in this novel superconductor. The application of a magnetic field induces strong pair-breaking as seen in the conductance spectra in fields up to 6 T.