Origin and consequences of the ‘gap’ in the cuprate normal state

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Abstract We present an alternative to the spin gap as an explanation for the origin of the gap feature observed in the normal state of the high-Tc cuprates. We consider a model that has a non-degenerate as well as a degenerate component of charge carriers. The properties are governed by the location of the chemical potential relative to the top of the non-degenerate band. In the underdoped regime this translates into an energy gap for the non-degenerate carriers; this decreases with doping, vanishing at optimal doping. In the overdoped regime there emerges a small Fermi energy that governs the temperature dependence of properties. As illustrations we consider several spin and charge properties, namely spin susceptibility, entropy, in-plane resistivity, Hall effect and Hall angle.