Superfluid density in the underdoped YBa_2Cu_3O_{7-x}: Evidence for d-density wave order of pseudogap

TL;DR

This paper studies the superfluid density in underdoped YBa_2Cu_3O_{7-x} and finds evidence supporting the d-density wave order as an explanation for pseudogap phenomena.

Contribution

It provides experimental evidence for d-density wave order in underdoped cuprates through superfluid density measurements.

Findings

Superfluid density at zero temperature depends linearly on doping p.

The temperature derivative of superfluid density increases rapidly at low doping.

Low-temperature behavior shifts from linear to square root dependence on T.

Abstract

The investigation of the penetration depth \lambda_{ab}(T,p) in YBa_2Cu_3O_{7-x} crystals allowed to observe the following features of the superfluid density n_s(T,p)\propto \lambda_{ab}^{-2}(T,p) as a function of temperature T<Tc/2 and carrier concentration 0.078\le p\le 0.16 in CuO_2 planes: (i) n_s(0,p) depends linearly on p, (ii) the derivative |dn_s(T,p)/dT|_{T\to 0} depends on p slightly in the optimally and moderately doped regions (0.10<p\le 0.16); however, it rapidly increases with p further lowering and (iii) the latter finding is accompanied by the linear low-temperature dependence [-\Delta n_s(T)]\propto T changing to [-\Delta n_s(T)]\propto \sqrt{T}. All these peculiarities can be treated in the framework of d-density wave scenario of electronic processes in underdoped high-Tc materials.