Scanning SQUID Susceptometry of a paramagnetic superconductor

Abstract

Scanning SQUID susceptometry images the local magnetization and susceptibility of a sample. By accurately modeling the SQUID signal we can determine the physical properties such as the penetration depth and permeability of superconducting samples. We calculate the scanning SQUID susceptometry signal for a superconducting slab of arbitrary thickness with isotropic London penetration depth, on a non-superconducting substrate, where both slab and substrate can have a paramagnetic response that is linear in the applied field. We derive analytical approximations to our general expression in a number of limits. Using our results, we fit experimental susceptibility data as a function of the sample-sensor spacing for three samples: 1) delta-doped SrTiO3, which has a predominantly diamagnetic response, 2) a thin film of LaNiO3, which has a predominantly paramagnetic response, and 3) a two-dimensional electron layer (2-DEL) at a SrTiO3/AlAlO3 interface, which exhibits both types of response. These formulas will allow the determination of the concentrations of paramagnetic spins and superconducting carriers from fits to scanning SQUID susceptibility measurements.

11 pages, 13 figures

References in corpus (13)

• Direct imaging of the coexistence of ferromagnetism and superconductivity at the LaAlO3/SrTiO3 interface
• Magnetic Penetration Depth in Unconventional Superconductors
• Dominant mobility modulation by the electric field effect at the LaAlO_3 / SrTiO_3 interface
• Two-dimensional quantum oscillations of the conductance at LaAlO3/SrTiO3 interfaces
• Fundamental studies of superconductors using scanning magnetic imaging
• Evidence for nodal quasiparticles in electron-doped cuprates from penetration depth measurements
• Evidence for Nodal Superconductivity in LaFePO from Scanning SQUID Susceptometry
• Local measurement of the superfluid density in the pnictide superconductor Ba(Fe${}_{1-x}$Co${}_x$)${}_2$As${}_2$ across the superconducting dome
• Enhanced superfluid density on twin boundaries in Ba(Fe1-xCox)2As2
• Superconducting thin rings with finite penetration depth
• Spin-like susceptibility of metallic and insulating thin films at low temperature
• Meissner response of anisotropic superconductors
• Magnetic fields above the surface of a superconductor with internal magnetism

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• Magnetic Quantum Criticality inside the Superconducting State Revealed by Penetration Depth Scaling with Local $T_{\mathrm{c}}$