Hall effect and resistivity of oxygen-deficient YBa2Cu3O7- delta thin films

Charge Order and Superconductivity in Underdoped YBa_{2}Cu_{3}O_{7-δ} under Pressure

In underdoped cuprates, an incommensurate charge density wave (CDW) order is known to coexist with superconductivity. A dip in T_{c} at the hole doping level where the CDW is strongest (n_{p}≃0.12) suggests that CDW order may suppress superconductivity. We investigate the interplay of charge order with superconductivity in underdoped YBa_{2}Cu_{3}O_{7-δ} by measuring the temperature dependence of the Hall coefficient R_{H}(T) at high magnetic field and at high hydrostatic pressure. We find that, although pressure increases T_{c} by up to 10 K at 2.6 GPa, it has very little effect on R_{H}(T). This suggests that pressure, at these levels, only weakly affects the CDW and that the increase in T_{c} with pressure cannot be attributed to a suppression of the CDW. We argue, therefore, that the dip in T_{c} at n_{p}≃0.12 at ambient pressure is probably not caused by the CDW formation.

Comprehensive phase diagram of two-dimensional space charge doped Bi2Sr2CaCu2O8+x

The phase diagram of hole-doped high critical temperature superconductors as a function of doping and temperature has been intensively studied with chemical variation of doping. Chemical doping can provoke structural changes and disorder, masking intrinsic effects. Alternatively, a field-effect transistor geometry with an electrostatically doped, ultra-thin sample can be used. However, to probe the phase diagram, carrier density modulation beyond 10¹⁴ cm⁻² and transport measurements performed over a large temperature range are needed. Here we use the space charge doping method to measure transport characteristics from 330 K to low temperature. We extract parameters and characteristic temperatures over a large doping range and establish a comprehensive phase diagram for one-unit-cell-thick BSCCO-2212 as a function of doping, temperature and disorder.

The determination of the phase diagram of cuprate superconductors involves chemical doping which introduces disorder and could mask intrinsic effects. Sterpetti et al. establish this phase diagram with transport measurements in ultra-thin samples by modulating the carrier density with an alternative electrostatic method.

Conductivity of underdoped YBa(2)Cu(3)O(7-delta): evidence for incoherent pair correlations in the pseudogap regime

A two-channel scenario for the conductivity of underdoped YBa 2Cu 3O (7-delta) is proposed. One is the single-particle excitations channel, which dominates in the optimally doped material, whose resistivity is linear as a function of temperature. The other one gives a contribution which merges the 3D Aslamazov-Larkin fluctuation conductivity at low temperature and obeys a power law at high temperature, depending on two superconductive parameters (T(c) and the zero temperature coherence length xi(c0)) and an energy scale Delta(*). This allows one to address the nature of the pseudogap in favor of incoherent pairing.