Superconductivity 1911- investigated low temperature resistance of mercury Superconductivity occurs in certain materials at very low temperatures. Kelvin At superconducting state the resistance of the material is zero electrons freeze and resistance increases no interior magnetic field (The Meissner effect). Heike Kamerlingh Onnes 1913 Nobel prize for Physics

(superconducting state) Conductors vs. Superconductors Normal conductors: r=r0 at T=0 Superconductors: r=0 at T<Tc (superconducting state) Tc = = critical temperature Superconductor: YBa2Cu3O7 Tc ~ 90 K Voltmeter: measure voltage across superconductor V = IR V = 0, R = 0 (at superconducting state)

Applications Superconducting magnets are some of the most powerful electromagnets known. They are used in MRI and NMR machines, mass spectrometers, and the beam-steering magnets used in particle accelerators RF and microwave filters for mobile phone base stations cryogenic micro-calorimeter photon detectors. JR-Maglev Magnetic pressure is used to counteract the effects of the gravitational force.

New trends in the field of super conductivity Manipulation of the electronic states of condensed matter by external stimuli is a key topic in the field of modern electronics Optical stimuli are of considerable importance because they present many possibilities for realizing optical memory or switching devices Photoinduced changes in superconducting properties have been reported in several systems Yttrium barium copper oxide (YBCO) films, YBCO-LCMO (lanthanum calcium manganese oxide) hetero films, Alkali-metal fullerides. All the reported photoinduced superconducting properties are irreversible

Experimental The Nb thin films were deposited on the glass or silicon substrate by RF sputtering The 10 nm-thick films deposited with sputtering time for 1 min, while 100 nm-thick films for 10 min. To deposit AZ-monolayers, the cleaned Nb film were submerged in 1 mM solution of AZ in toluene for 48 h at room temperature. After deposition, the substrates were thoroughly rinsed with toluene and ethanol and then dried in gently-flowing argon. indicating the adsorption of AZ layer on the surface of Nb film. Reflection-absorption spectrum (FTIR-RAS) of the AZ-SAM on Nb film in the C-H stretching modes The SAM formation was also characterized by XPS studies and contact angle measurements

The azobenzene monolayer was formed on the surface of the Nb film by immersing the bare Nb film into AZ solution for 48 h. GIXD patterns of a bare Nb film on a glass substrate. The five peaks that are observed for (110), (200), (211), (220), (310) are consistent with a face-centered cubic crystal structure of Nb with lattice constant a=3.29 , which is ca. 5% smaller than the corresponding value for bulk Nb (3.45 ).

Temperature dependence of the Nb film resistance before (filled blue circles) and after (open red circles) the surface passivation of the AZ monolayer. V–I measurements of the Nb film before and after the surface passivation of the AZ monolayer at 2 K. The Ic value of 53 mA for the bare Nb film (filled circles) decreased to 20 mA after surface passivation (open circles).

Temperature dependence of the resistance of the hybrid film for the initial state (dashed line), the UV photostationary state (filled blue circles) and the visible photostationary state (open red circles). Resistance values are normalized. V–I measurements of the hybrid film for the initial state (dashed line), the UV photostationary state (filled blue circles), and the visible photostationary state (open red circles) at 2 K.

Discussion Nb is a type II superconductor has a nonuniform electron density on the surface When a SAM is formed on a type II superconducting thin film, charge is transferred at the surface between the superconductor and the organic layer in order to reduce repulsion within the organic layer, thus resulting in a uniform distribution of the charge density along the surface. Variations in the electron density at the film surface that are induced by the absorbed organized molecular layer are responsible for the dramatic decrease in the Ic value. the presence of a more uniform distribution of charge density along the surface caused by the charge transfer process increases the Tc ZERO value.

-0.15D 1.53D Changes in the work function arising from the photoisomerization of AZ Metal work function, which is linearly related to the dipole moment density perpendicular to the surface. The trans- and cis-AZ monolayer have different dipoles, they can be used to change the work function of the substrate by photoirradiation.

Summary The work function of bare Nb substrates was reduced by the negative surface dipole of trans-AZ upon surface passivation, and charge transfer from the Nb substrate to the organic monolayer was induced. Charge-transfer processes decrease the inhomogeneities of the electron distribution along the surface. On UV illumination, the charge transfer could be reversed with trans to cis photoisomerization because of the positive surface dipole of cis-AZ. The values of Ic and Tc could be controlled by employing alternating photoillumination with UV and visible light, which caused changes in the electron density along the surface because of the photoisomerization of AZ.