Irradiation-induced confinement in a quasi-one-dimensional metal

A disorder-enhanced quasi-one-dimensional superconductor

A powerful approach to analysing quantum systems with dimensionality d>1 involves adding a weak coupling to an array of one-dimensional (1D) chains. The resultant quasi-1D (q1D) systems can exhibit long-range order at low temperature, but are heavily influenced by interactions and disorder due to their large anisotropies. Real q1D materials are therefore ideal candidates not only to provoke, test and refine theories of strongly correlated matter, but also to search for unusual emergent electronic phases. Here we report the unprecedented enhancement of a superconducting instability by disorder in single crystals of Na_2−δMo₆Se₆, a q1D superconductor comprising MoSe chains weakly coupled by Na atoms. We argue that disorder-enhanced Coulomb pair-breaking (which usually destroys superconductivity) may be averted due to a screened long-range Coulomb repulsion intrinsic to disordered q1D materials. Our results illustrate the capability of disorder to tune and induce new correlated electron physics in low-dimensional materials.

Disorder localizes electrons, which is usually detrimental to the onset of superconductivity. Here, Petrović et al. report a disorder-enhanced superconducting instability in quasi-one dimensional Na_2-dMo₆Se₆ and suggest that this effect may originate from an intrinsically screened Coulomb repulsion.

The Wiedemann-Franz law in the putative one-dimensional metallic phase of PrBa₂Cu₄O₈

The nature of the electronic state of a metal depends strongly on its dimensionality. In a system of isolated conducting chains, the Fermi-liquid (quasiparticle) description appropriate for higher dimensions is replaced by the so-called Tomonaga-Luttinger liquid picture characterized by collective excitations of spin and charge. Temperature is often regarded as a viable tuning parameter between states of different dimensionality, but what happens once thermal broadening becomes comparable to the interchain hopping energy remains an unresolved issue, one that is central to many organic and inorganic conductors. Here we use the ratio of the thermal to electrical conductivities to probe the nature of the electronic state in PrBa₂Cu₄O₈ as a function of temperature. We find that despite the interchain transport becoming non-metallic, the charge carriers within the CuO chains appear to retain their quasiparticle nature. This implies that temperature alone cannot induce a crossover from Fermi-liquid to Tomonaga-Luttinger-liquid behaviour in quasi-one-dimensional metals.

Directional field-induced metallization of quasi-one-dimensional Li0.9Mo6O17

We report a detailed magnetotransport study of the highly anisotropic quasi-one-dimensional oxide Li(0.9)Mo(6)O(17) whose in-chain electrical resistivity diverges below a temperature T_{min} approximately 25 K. For T < T_{min}, a magnetic field applied parallel to the conducting chain induces a large negative magnetoresistance and, ultimately, the recovery of a metallic state. We show evidence that this insulator-metal crossover is a consequence of field-induced suppression of a density-wave gap in a highly one-dimensional conductor. At the highest fields studied, there is evidence for the possible emergence of a novel superconducting state with an onset temperature T_{c} > 10 K.