Effect of deposition pressure on the superconductivity of Ti ₄₀ V ₆₀ alloy thin films

Abstract The growth and characterization of superconducting thin films is essential for fundamental understanding and also for the use of these films in technological applications. In the present study, Ti 40 V 60 alloy thin films have been deposited using DC magnetron co-sputtering of Ti and V at ambient temperatures. The effect of deposition pressure on the film morphology, superconducting and normal state properties has been studied. Measurement of electrical resistance as a function of temperature indicates that up to a certain deposition pressure, the 20 nm thick Ti 40 V 60 films exhibit metallic behavior in the normal state and superconductivity at low temperatures. Beyond a threshold pressure, the films show a negative temperature coefficient of resistance with a residual resistance ratio less than one. Electrical transport measurements in the presence of magnetic field were performed to find the current–voltage ( I–V ) characteristics of the thin films. Analysis of the I–V curves indicates that the Ti 40 V 60 alloy thin films have a high transport critical current density ( J C ) e.g. <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>1.48</mml:mn> <mml:mo>×</mml:mo> <mml:mrow> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> <mml:mstyle scriptlevel="0"/> <mml:mrow> <mml:mtext>A</mml:mtext> </mml:mrow> <mml:mstyle scriptlevel="0"/> <mml:mrow> <mml:msup> <mml:mrow> <mml:mtext>m</mml:mtext> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:mrow> </mml:math> in zero magnetic field and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>2.66</mml:mn> <mml:mo>×</mml:mo> <mml:mrow> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>9</mml:mn> </mml:msup> </mml:mrow> <mml:mstyle scriptlevel="0"/> <mml:mrow> <mml:mtext>A</mml:mtext> </mml:mrow> <mml:mstyle scriptlevel="0"/> <mml:mrow> <mml:msup> <mml:mrow> <mml:mtext>m</mml:mtext> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:mrow> </mml:math> in 4 T (both at 4 K). Analysis of the field dependence of flux line pinning force density indicates a combined effect of core <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:mi>k</mml:mi> </mml:mrow> </mml:math> surface and core <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:mi>k</mml:mi> </mml:mrow> </mml:math> point pinning mechanisms (where k is the Ginzburg–Landau parameter). Additionally, spatial variations in the superconducting critical temperature <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mo>(</mml:mo> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mrow> <mml:mtext>C</mml:mtext> </mml:mrow> </mml:msub> </mml:mrow> </mml:mrow> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> across the sample contribute to δ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mrow> <mml:mtext>C</mml:mtext> </mml:mrow> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> pinning. In higher magnetic fields, a contribution from δl pinning (where l is the electron mean free path) also becomes significant. The findings indicate the potential of Ti 40 V 60 alloy thin film for superconducting device applications like cryogenic radiation detectors.