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Stripe Experiments

A class of layered oxide materials similar to the high-Tc cuprates are known to form charge stripes.  They have also conclusively been shown to exist in extremely underdoped (non superconducting) cuprates.  Stripes are lattice-constant-wide lines on which all the charge carriers reside.  The stripes only form in directions parallel to the crystal axes and they are separated by anti-ferromagnetic insulating regions.   Stripes are known to be static in some materials, however in others they are believed to be dynamic.  The similarities between known stripe materials and the high-Tc cuprates have led to the creation of stripe models of high-Tc superconductivity.  In these models the stripes are believed to be fluctuating.  In such models the pseudogap is explained by the formation of charge stripes at T⁰.  At a lower temperature which corresponds to T*, each stripe becomes superconducting, but there’s no long range phase coherence.  The SC on each stripe can be explained by the nature of confining charge carriers to one dimension.  In one dimension spin-charge separation occurs and SC is established on each stripe due to a condensation of the chargons.   The stripes Josephson couple when T =Tc and long range phase coherence is established. The exact length of a stripe is unknown.  However, common sense and instinct leads on to believe they are 10-1000 lattice constants wide.  This would make their lengths somewhere between 4-400 nm.  We have two experiments designed to look for stripes.  One is simply measuring current-voltage characteristics of nanowires ranging in width from 50-300 nm.  It is possible stripes can be geometrically pinned due to the small sample size.  Large upward and downward resistance switches in a nanowire could indicate stripe domains, if phase slips can be ruled out.  The nanowires are fabricated at different angles with respect to the crystal lattice.  Any strong angular dependence in the IVC’s would also be a strong indicator for stripe phases.  The other stripe experiment involves 300-900 wide islands with 8 leads.  The 8 leads are arranged such that two orthogonal 4 point resistivity measurements can be made.  The idea here is to look for anti-correlations in resistivity fluctuations between orthogonal directions.