The anisotropic resistivity of PrBa2Cu4O8 has been measured as a function of electron irradiation fluence. Localization effects are observed for extremely small amounts of disorder corresponding to electron mean-free-paths of order 100 unit cells. Estimates of the localization corrections suggest that this anomalous localization threshold heralds a crossover to a ground state with pronounced one-dimensional character in which conduction electrons become confined to a small cluster of chains.Disorder-induced metal/insulator transitions (MIT) have been a dominant theme in solid state research for several decades yet many outstanding issues remain. In three-dimensional (3D) metals, metallic behavior is observed only for k F ℓ 0 (the product of the Fermi wave vector and the mean-free-path) > 1 [1]. The insulating state, characterized by a vanishing of σ 0 the dc conductivity at T = 0, occurs once the carrier concentration (∝ k F ), disorder potential (∝ 1/ℓ 0 ) or some other control parameter reach a critical value. Neither this nor the critical exponents at the transition however, are known precisely [2]. Scaling theory advocates no genuine metallic state in two dimensions [3] yet in 2D electron gases, a MIT is observed at the universal sheet resistance 2h/e 2 [4]. In strictly 1D systems, all electronic states are localized at T =0 in the presence of weak disorder [5]. In real materials with finite interchain coupling t ⊥ however, the situation is not so clear. Abrikosov and Ryzchkin claim that any finite t ⊥ stabilizes the metallic state [6] whilst Prigodin and Firsov (PF) argue that impurity scattering rates /τ 0 > t ⊥ render the system effectively 1D and therefore susceptible to localization at low T [7]. This controversy has never been resolved experimentally, due to the lack of quantitative studies of the MIT in quasi-1D conductors and the lack of systems of the appropriate dimensionality displaying low-T metallic behavior.Irradiation experiments are a reliable means of controllably changing the defect density in solids with the added advantage that transport properties can be measured insitu. In this Letter, we report a systematic study of the effects of electron irradiation on the anisotropic resistivity of the quasi-1D cuprate PrBa 2 Cu 4 O 8 (Pr124). Pr124 comprises a 1D network of zig-zag double chains (oriented along the b-axis) sandwiched between insulating CuO 2 bilayers (in the ab-plane). In clean Pr124, a highly anisotropic but nevertheless 3D metallic state develops at low T with ρ(T ) ∼ T 2 for (ρ a :ρ b :ρ c ∼ 1000:1:3000) [8,9]. With increasing irradiation, low-T upturns in ρ(T ) develop simultaneously for I a, b and c once k F ℓ 0 < 60. For I b (in-chain conductivity), these upturns are consistent with 1D inter-electron interference corrections of a magnitude that implies confinement of the charge carriers to a very small number of chains. A set of crystals (see Ref.[10] for growth details) of appropriate geometries were mounted in different contact configurations to ensure uniaxial current flow...

In this article we report on the experimental realization of dimensional crossover phenomena in the chain compound PrBa 2 Cu 4 O 8 using temperature, high magnetic fields and disorder as independent tuning parameters. In purer crystals of PrBa 2 Cu 4 O 8 , a highly anisotropic three-dimensional Fermi-liquid state develops at low temperatures. This metallic state is extremely susceptible to disorder however and localization rapidly sets in. We show, through quantitative comparison of the relevant energy scales, that this metal/insulator crossover occurs precisely when the scattering rate within the chain exceeds the interchain hopping rate(s), i.e. once carriers become confined to a single conducting element.PACS numbers: 71.27.+a, 71.30.+h, 72.15.Rn Fragile three-dimensionality in the quasi-one-dimensional cuprate PrBa 2 Cu 4 O 8

In the chain compound PrBa2Cu4O8 localization appears simultaneously with a dimensional crossover in the electronic ground state when the scattering rate in the chains exceeds the hopping rate between the chains. Here we report the discovery of a large, transverse magnetoresistance in PrBa2Cu4O8 in the localized regime. This result suggests a novel form of localization whereby electrons retain their metallic (quasi-one-dimensional) character over a microscopic length scale despite the fact that, macroscopically, they exhibit localized (one-dimensional) behavior.

In the quasi-one-dimensional cuprate PrBa2Cu4O8, the Pr cations order antiferromagnetically at 17 K in zero field. Through a combination of magnetic susceptibility, torque magnetometry, specific heat and interchain transport measurements, the anisotropic temperature-magnetic field phase diagram associated with this ordering has been mapped out. A low-temperature spin-flop transition in the Pr sub-lattice is found to occur at the same magnetic field strength and orientation as a dimensional crossover in the ground state of the metallic CuO chains. This coincidence suggests that the spin reorientation is driven by a change in the anisotropic Rudermann-Kittel-Kasuya-Yosida (RKKY) interaction induced by a corresponding change in effective dimensionality of the conduction electrons.