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A material called LK-99, a modified-lead apatite crystal structure with the composition Pb10 – xCux(PO4)6O (0.9 < x < 1.1) has been reported to be an above-room-temperature superconductor at ambient pressure. It is hard to expect that it will be straightforward for other groups to reproduce the original results. We provide here some remarks which may be helpful for a success. [ABSTRACT FROM AUTHOR]

Harnessing the fascinating properties of correlated oxides requires precise control of their carrier density. Compared to other methods, oxygen doping provides an effective and more direct way to tune the electronic properties of correlated oxides. Although several approaches, such as thermal annealing and oxygen migration, have been introduced to change the oxygen content, a continuous and reversible solution that can be integrated with modern electronic technology is much in demand. Here, we report a novel ionic field-effect transistor using solid Gd-doped CeO2 as the gate dielectric, which shows a remarkable carrier-density-tuning ability via electric-field-controlled oxygen concentration at room temperature. In Bi2Sr2CaCu2O8+δ (Bi-2212) thin flakes, we achieve a reversible superconductor–insulator transition by driving oxygen ions in and out of the samples with electric fields, and map out the phase diagram all the way from the insulating regime to the over-doped superconducting regime by continuously changing the oxygen doping level. Scaling analysis indicates that the reversible superconductor–insulator transition for the Bi-2212 thin flakes follows the theoretical description of a two-dimensional quantum phase transition. Our work provides a route for realizing electric-field control of phase transition in correlated oxides. Moreover, the configuration of this type of transistor makes heterostructure/interface engineering possible, thus having the potential to serve as the next-generation all-solid-state field-effect transistor. [ABSTRACT FROM AUTHOR]

The conductivity of single-crystal nanoplates of the Sb2Te3 topological insulator has been investigated. A sharp drop in resistance occurs in ultrathin Sb2Te3 nanoplates at a temperature of about 4 K, which is a manifestation of superconductivity. The results show that the presence of an optimal degree of disorder is a necessary condition for the onset of superconductivity. A superconductor-insulator transition, tunable by a magnetic field, is observed in these nanoplates. The temperature dependence of the magnetoresistance in fields below the critical value (B < BC) shows a successive transformation of a weak antilocalization anomaly into a superconducting transition. The value of the correlation length exponent ν = 0.75 ± 0.05 was obtained using the scaling theory. [ABSTRACT FROM AUTHOR]

Spatial disorder has been shown to drive two-dimensional (2D) superconductors to an insulating phase through a superconductor- insulator transition (SIT). Numerical calculations predict that with increasing disorder, emergent electronic granularity is expected in these materials--a phenomenon where superconducting (SC) domains on the scale of the material's coherence length are embedded in an insulating matrix and coherently coupled by Josephson tunneling. Here, we present spatially resolved scanning tunneling spectroscopy (STS) measurements of the three-dimensional (3D) superconductor BaPb1-xBixO3 (BPBO), which surprisingly demonstrate three key signatures of emergent electronic granularity, having only been previously conjectured and observed in 2D thin-film systems. These signatures include the observation of emergent SC domains on the scale of the coherence length, finite energy gap over all space, and strong enhancement of spatial anticorrelation between pairing amplitude and gap magnitude as the SIT is approached. These observations are suggestive of 2D SC behavior embedded within a conventional 3D s-wave host, an intriguing but still unexplained interdimensional phenomenon, which has been hinted at by previous experiments in which critical scaling exponents in the vicinity of a putative 3D quantum phase transition are consistent only with dimensionality d = 2. [ABSTRACT FROM AUTHOR]

We study the effects of disorder on the zero-temperature quantum phase transition of a honeycomb array of Josephson junctions in a magnetic field with an average of f o flux quantum per plaquette. Bond disorder due to spatial variations in the Josephson couplings and magnetic flux disorder due to variations in the plaquette areas are considered. The model can describe the superconductor-insulator transition in ultra-thin films with a triangular pattern of nanoholes. Path integral Monte Carlo simulations of the equivalent (2 + 1)-dimensional classical model are used to study the critical behavior and estimate the universal resistivity at the transition. The results show that bond disorder leads to a rounding of the first-order phase transition for f o = 1 / 3 to a continuous transition. For integer f o , the decrease of the critical coupling parameter with flux disorder is significantly different from that of the same model defined on a square lattice. The results are compared with recent experimental observations on nanohole thin films with geometrical disorder and external magnetic field. [ABSTRACT FROM AUTHOR]

Superconducting nanowires undergoing quantum phase-slips have potential for impact in electronic devices, with a high-accuracy quantum current standard among a possible toolbox of novel components. A key element of developing such technologies is to understand the requirements for, and control the production of, superconducting nanowires that undergo coherent quantum phase-slips. We present three fabrication technologies, based on using electron-beam lithography or neon focussed ion-beam lithography, for defining narrow superconducting nanowires, and have used these to create nanowires in niobium nitride with widths in the range of 20–250 nm. We present characterisation of the nanowires using DC electrical transport at temperatures down to 300 mK. We demonstrate that a range of different behaviours may be obtained in different nanowires, including bulk-like superconducting properties with critical-current features, the observation of phase-slip centres and the observation of zero conductance below a critical voltage, characteristic of coherent quantum phase-slips. We observe critical voltages up to 5 mV, an order of magnitude larger than other reports to date. The different prominence of quantum phase-slip effects in the various nanowires may be understood as arising from the differing importance of quantum fluctuations. Control of the nanowire properties will pave the way for routine fabrication of coherent quantum phase-slip nanowire devices for technology applications.

Field-effect experiments on cuprates using ionic liquids have enabled the exploration of their rich phase diagrams [Leng X, et al. (2011) Phys Rev Lett 107(2):027001]. Conventional understanding of the electrostatic doping is in terms of modifications of the charge density to screen the electric field generated at the double layer. However, it has been recently reported that the suppression of the metal to insulator transition induced in VO2 by ionic liquid gating is due to oxygen vacancy formation rather than to electrostatic doping [Jeong J, et al. (2013) Science 339(6126):1402–1405]. These results underscore the debate on the true nature, electrostatic vs. electrochemical, of the doping of cuprates with ionic liquids. Here, we address the doping mechanism of the high-temperature superconductor YBa2Cu3O7-X (YBCO) by simultaneous ionic liquid gating and X-ray absorption experiments. Pronounced spectral changes are observed at the Cu K-edge concomitant with the superconductor-to-insulator transition, evidencing modification of the Cu coordination resulting from the deoxygenation of the CuO chains, as confirmed by first-principles density functional theory (DFT) simulations. Beyond providing evidence of the importance of chemical doping in electric double-layer (EDL) gating experiments with superconducting cuprates, our work shows that interfacing correlated oxides with ionic liquids enables a delicate control of oxygen content, paving the way to novel electrochemical concepts in future oxide electronics. [ABSTRACT FROM AUTHOR]

Field-effect experiments on cuprates using ionic liquids have enabled the exploration of their rich phase diagrams [Leng X, et al. (2011) Phys Rev Lett 107(2):027001]. Conventional understanding of the electrostatic doping is in terms of modifications of the charge density to screen the electric field generated at the double layer. However, it has been recently reported that the suppression of the metal to insulator transition induced in VO2 by ionic liquid gating is due to oxygen vacancy formation rather than to electrostatic doping [Jeong J, et al. (2013) Science 339(6126):1402–1405]. These results underscore the debate on the true nature, electrostatic vs. electrochemical, of the doping of cuprates with ionic liquids. Here, we address the doping mechanism of the high-temperature superconductor YBa2Cu3O7-X (YBCO) by simultaneous ionic liquid gating and X-ray absorption experiments. Pronounced spectral changes are observed at the Cu K-edge concomitant with the superconductor-to-insulator transition, evidencing modification of the Cu coordination resulting from the deoxygenation of the CuO chains, as confirmed by first-principles density functional theory (DFT) simulations. Beyond providing evidence of the importance of chemical doping in electric double-layer (EDL) gating experiments with superconducting cuprates, our work shows that interfacing correlated oxides with ionic liquids enables a delicate control of oxygen content, paving the way to novel electrochemical concepts in future oxide electronics. [ABSTRACT FROM AUTHOR]

We combine measurements of the longitudinal (ρxx) and Hall (ρxy) resistivities of disordered 2D amorphous indium-oxide films to study the magnetic-field tuned superconductor-to-insulator transition (H-SIT) in the T→0T→0 limit. At the critical field, Hc, the full resistivity tensor is T independent with ρxx(Hc)=h/4e ² ρxx(Hc)=h/4e² and ρxy(Hc)=0ρxy(Hc)=0 within experimental uncertainty in all films (i.e., these appear to be "universal" values); this is strongly suggestive that there is a particle--vortex self-duality at H=HcH=Hc. The transition separates the (presumably) superconducting state at HHcHc*>Hc, at which the Hall resistance is T independent and roughly equal to its classical value, ρxy≈H/necρxy≈H/nec, marks an additional crossover to a high-field regime (probably to a Fermi insulator) in which ρxy>H/necρxy>H/nec and possibly diverges as T→0T→0. We also highlight a profound analogy between the H-SIT and quantum-Hall liquid-to-insulator transitions (QHIT). [ABSTRACT FROM AUTHOR]

We study the effect of disorder on the superconductor-insulator transition in an inhomogeneous d-wave superconductor using the kernel polynomial method. As the Bogoliubov-de Gennes equations of the two-dimensional square lattice are solved self-consistently for the cases with more than 100000 unit cells, it is possible to observe the spatial fluctuations of the super-conducting order parameters at the nanoscale. We find that strong spatial fluctuation of the superconducting order parameters can be introduced by disorder, and some superconducting specific order parameters are even enhanced. Moreover, we find that some isolated superconducting 'islands' can survive the strong disorder, giving a boson insulator with some localized Cooper pairs. Our numerical calculations predict the existence of two sequential transitions with the increasing disorder strength: a d-wave to s-wave superconductor transition, and then an s-wave superconductor to insulator transition. The possibility of the appearance of a metallic phase between the superconducting and insulating phases is excluded by performing the lattice-size scaling of the generalized inverse participation ratio. In addition, we also discuss the effect of disorder on the optical conductivity of the d-wave superconductors. [ABSTRACT FROM AUTHOR]

The article discusses the study of the simple hydrothermal growth method and electronic transport property which is applied to synthesis bismuth oxychloride (BiOCl) single-crystalline microplates. Topics discussed include the observed nonlinear resistivity in the resistivity versus excitation, way to fabricate size-controllable BiOCl samples and the synthesis of BiOCl.

Highlights: [•] We model an S–I–S junction, whose insulating layer is actually a superconductor below its S–I transition. [•] We demonstrate that such a structure indeed behaves like a single Josephson junction. [•] The coherence length diverges as the insulating layer approaches its S–I transition [•] The model may describe so-called Cooper pair insulators studied in some experiments. [ABSTRACT FROM AUTHOR]

• Resistivity of (Pb z Sn 1-z) 0.8 In 0.2 Te solid solutions with various z was studied. • Metallic conductivity observed for z ≤ 0.4, activation conductivity for z ≥ 0.5. • Conductivity type change induced by the shift of indium impurity band. • Superconductivity was observed in samples with metallic conductivity. • Superconductivity persists if activation energy is lower than superconducting gap We have studied temperature (1.5 K < T < 300 K) and magnetic field H < 5 T dependences of the electrical resistivity in bulk polycrystalline samples of semiconductor solid solutions (Pb z Sn 1-z) 0.8 In 0.2 Te with various Pb content 0.1 ≤ z ≤ 0.9. The transition to the superconducting (SC) state was observed in samples with z ≤ 0.5 at helium temperatures with the critical transition temperature increasing up to T c = 4.1 K with an increase of the Pb content up to z = 0.5. The bulk superconductivity in solid solutions with z ≥ 0.6 was not detected at temperatures T > 1.5 K. An exponential increase of the resistivity was observed in samples (Pb z Sn 1-z) 0.8 In 0.2 Te with z ≥ 0.5 in the temperature range 40 K < T < 120 K. Experimental data was interpreted considering a shift of the energy position of the indium impurity band E In in the complex valence band spectrum of (Pb z Sn 1-z) 0.8 In 0.2 Te with changing lead content z. The exponential increase of the resistivity with decreasing temperature in studied solid solutions is observed when an energy barrier E a appears between valence band states and quasilocal impurity states of In. The energy barrier increases with an increase of the Pb content in compounds with 0.5 ≤ z ≤ 0.8 and reaches maximum value E a = 9.7 meV in the solid solution with z = 0.8. The SC state at helium temperatures was observed in (Pb z Sn 1-z) 0.8 In 0.2 Te at z ≤ 0.4 when there is no energy barrier between zone and impurity states (i.e. the indium impurity band is located within the valence Σ-band), or at z = 0.5 when the activation energy Е а = 0.7 meV is less than the superconducting gap Δ S. Possible reasons for a decrease in the resistivity at T < 4.2 K in non-SC samples (Pb z Sn 1-z) 0.8 In 0.2 Te with z ≥ 0.6 are also discussed. [ABSTRACT FROM AUTHOR]

Transport and magnetization measurements of single crystas of BaPbBiO, for Bi compositions spanning the superconducting phase diagram, show signatures of granular and inhomogeneous superconductivity, possibly associated with the nanoscale structural phase separation found for compositions around optimal doping. The material exhibits a field-tuned superconductor-to-insulator transition for Bi compositions 0.24≤ x≤0.28. For optimally doped samples ( x≈0.25), the magnetoresistance curves show scaling, suggesting some kind of critical behavior. [ABSTRACT FROM AUTHOR]

The mean field theory due to Bardeen, Cooper, and Schrieffer (BCS) provides the conceptual foundation of our understanding of superconductivity, but many examples over the last few decades have forced condensed matter physicists to extend the BCS framework. In particular, the extension to strong coupling, the BCS to Bose-Einstein condensation (BEC) crossover, requires the treatment of amplitude and phase fluctuations above the mean field state. Similarly, the presence of disorder can lead to strong inhomogeneity in the pairing amplitude, enhance phase fluctuations, and suppress the transition temperature. Finally, magnetic scattering quickly leads to a gapless superconducting state and then the loss of order. All of these involve physics beyond the BCS scenario. We employ a real space method that reduces to inhomogeneous mean field theory in the ground state, but fully retains the amplitude and phase fluctuations of the pairing field at finite temperature. This paper reviews some of our work in the weak to strong coupling (BCS-BEC) crossover, the disorder driven superconductor-insulator transition, and the role of magnetic impurities. [ABSTRACT FROM AUTHOR]

Abstract: For nearly a half century the dominant orthodoxy has been that the only effect of the Cooper pairing is the state with zero resistivity at finite temperatures, superconductivity. In this work we demonstrate that by the symmetry of the Heisenberg uncertainty principle relating the amplitude and phase of the superconducting order parameter, Cooper pairing can generate the dual state with zero conductivity in the finite temperature range, superinsulation. We show that this duality realizes in the planar Josephson junction arrays (JJA) via the duality between the Berezinskii–Kosterlitz–Thouless (BKT) transition in the vortex–antivortex plasma, resulting in phase-coherent superconductivity below the transition temperature, and the charge-BKT transition occurring in the insulating state of JJA and marking formation of the low-temperature charge-BKT state, superinsulation. We find that in disordered superconducting films that are on the brink of superconductor–insulator transition the Coulomb forces between the charges acquire two-dimensional character, i.e. the corresponding interaction energy depends logarithmically upon charge separation, bringing the same vortex-charge-BKT transition duality, and realization of superinsulation in disordered films as the low-temperature charge-BKT state. Finally, we discuss possible applications and utilizations of superconductivity–superinsulation duality. [Copyright &y& Elsevier]

We report the evolution of superconducting properties with disorder, in 3-dimensional homogeneously disordered epitaxial NbN thin films. The effective disorder in NbN is controlled from moderately clean limit down to Anderson metal-insulator transition by changing the deposition conditions. We propose a phase diagram for NbN in temperature-disorder plane. With increasing disorder, we observe that as k l→1 the superconducting transition temperature ( T) and normal state conductivity in the limit T→0 ( σ) go to zero. The phase diagram shows that in homogeneously disordered 3-D NbN films, the metal-insulator transition and the superconductor-insulator transition occur at a single quantum critical point, k l∼1. [ABSTRACT FROM AUTHOR]

Abstract: When charge carriers are introduced in diamond, e.g. by chemical doping with Boron (B), the diamond:B can exhibit an insulator-to-metal transition . Under even heavier boron doping , diamond becomes superconducting. Using microwave plasma-assisted chemical vapor deposition (MPCVD) we have prepared diamond:B thin films with critical offset temperatures below 3K. We have investigated the transport properties of these diamond:B thin films, which show pronounced granular effects. It turns out, that this granularity is both intrinsic as well as extrinsic. The extrinsic granularity is the effect of the growth method which needs to start from a seeding of the substrate with detonation nanodiamond, which acts as nucleation centers for further MPCVD growth of the film. In using SPM/STM techniques, we also observed intrinsic granularity, meaning that within physical grains, we observe also a strong intragrain modulation of the order parameter. As a consequence of these granularities, the transport properties show evidence of (i) strong superconducting fluctuations and (ii) Cooper pair tunneling and/or quasiparticle tunneling. The latter effects explain the observed negative magnetoresistance. [ABSTRACT FROM AUTHOR]

Abstract: A quantum pseudo-spin model with random spin sizes is introduced to study the effects of charging-energy disorder on the superconducting transition in granular superconducting materials. Charging-energy effects result from the small electrical capacitance of the grains when the Coulomb charging energy is comparable to the Josephson-coupling energy. In the pseudo-spin model, randomness in the spin size is argued to arise from the inhomogeneous grain-size distribution. For a particular bimodal spin-size distribution, the model describes percolating granular superconductors. A mean-field theory is developed to obtain the phase diagram as a function of temperature, average charging energy and disorder. [Copyright &y& Elsevier]

Abstract: We have measured the thickness dependence of the superconducting critical temperature, , in amorphous Bi/Sb films patterned with a regular array of holes as well as nanoscale thickness variations. We find that the mean field is suppressed relative to simultaneously produced unstructured films of the same thickness. Surprisingly, however, the functional form for , remains unaffected. The role of the thickness variations in suppressing is compared to the role of the holes, through parameterization of the surface, as measured through AFM/SEM and a proximity effect calculation. These results suggest that these two nanoscale modifications suppress about equally and are consistent with being determined on a microscopic length scale. [Copyright &y& Elsevier]

Abstract: We study the disorder-driven superconductor-to-insulator transition in amorphous films of high carrier-concentration indium-oxide. Using thin films with various sizes and aspect ratios we show that the ‘critical’ sheet-resistance R □ depends systematically on sample geometry; superconductivity disappears when R □ exceeds ≈6kΩ in large samples. On the other hand, wide and sufficiently short samples of the same batch exhibit superconductivity (judged by conductivity vs. temperature) up to R □ which is considerably larger. These results support the inhomogeneous scenario for the superconductor–insulator transition. [Copyright &y& Elsevier]

Abstract: We report on thickness-tuned superconductor–insulator transitions in amorphous Bi films quench-condensed onto underlayers of Ge, Sb, and SiO. Bi films on Ge and SiO have almost the same values, of the critical resistance per square at temperatures down to 0.9K, whereas those on Sb have a larger value of . On the insulating side, the conductance of Bi films on Sb depends logarithmically on temperature in contrast to the thermally activated form of those on SiO and Ge. The results suggest that the peculiar temperature dependence of the resistance per square of Bi films on Sb is the behavior characteristic of an Sb underlayer which becomes insulating from semimetal by quench-condensation. [Copyright &y& Elsevier]

Abstract: We have observed the superconductor–insulator (S–I) transition induced by over-deposited Ge in the insulating ultrathin amorphous Nb (a-Nb) film. The experiments are performed by depositing Ge onto the insulating a-Nb film with a thickness of 1.04nm. For , where was a thickness for Ge film, the reduction of electrical sheet resistances was seen at low temperature region, suggesting superconductor. The normal sheet resistance at 8K decreased monotonically with increasing . The simplest explanation of this S–I transition is that the electron localization effect is weakened due to the addition of Ge film. [Copyright &y& Elsevier]

Abstract: We have shown so far that thin amorphous (a-)Mo x Si1−x films exhibit the field-driven superconductor–insulator transition (SIT) at zero temperature (T =0), while the existence of a metallic quantum–vortex–liquid at T =0 has been reported in several thin amorphous films. Here we reexamine the possibility of the metallic phase by measuring the T dependence of resistance R(T) for the thin a-Mo x Si1−x films with various transition temperatures T c0 in fields B below the critical field of the “SIT”. We find that the value of T c0 dominates R(T) at low T. For films with T c0 larger than 1.0K, the activation energy U derived from the slope of the Arrhenius plot of R is constant over the whole T region, while for films with T c0 <1.0K, U exhibits a discontinuous decrease below about 0.1K; however, U remains constant and positive down to the lowest T. All of the data are consistent with the picture of the field-driven SIT. [Copyright &y& Elsevier]

Abstract: We present measurements of the time(t)-dependent component of the flux-flow voltage δV(t) about the average voltage in the vortex-liquid phase of a thin amorphous Mo x Si1−x film. At low temperatures T, δV(t) due to the vortex motion is clearly visible and the distribution of δV(t) is asymmetric, indicative of large velocity and/or number fluctuations of driven vortices. This result is very similar to that which has been observed in the quantum-liquid phase of a thick film. The anomalous vortex motion for the thick and thin films is found to occur in nearly the same reduced-temperature regime. Also, we find that for the thin film the anomalous motion is visible only in the high-field regime. We suggest that vortex dynamics in the low-T liquid phase of thin and thick films is dominated by common physical mechanisms related to quantum effects. [Copyright &y& Elsevier]

We investigate superconductivity and magnetism in the organic conductor λ-(BETS)2FexGa1-xCl4. In this material, it is known that the d-electrons on Fe-ions are ordered antiferromagnetically (TN<8.5–9 K) for 0.4, while superconductivity (TSC<6 K) of π-electrons appears when 0⩽x<0.4. In this paper, including the detailed band structure of this material, we discuss the exchange interaction between the d- and π-electrons, focusing on its role in the antiferromagnetism and superconductivity. We show that the inclusion of only this π–d exchange interaction is difficult to explain both the observed x-dependence of TN and TSC. To understand the phase diagram of λ-(BETS)2FexGa1-xCl4, we point out that the Coulomb interaction between π-electrons is also important. [Copyright &y& Elsevier]

We measured the temperature dependence and Josephson-coupling-energy (EJ) dependence of the zero-bias resistance of one-dimensional Josephson junction chains. Each junction in the chains was shunted by an ohmic resistance of several kΩ, and the charging energy was more than an order of magnitude larger than EJ. The results for overdamped junction chains are in agreement with a theory considering phase fluctuation in the presence of dissipation. [Copyright &y& Elsevier]

Various experimental observations of the magnetic-field-induced superconductor–insulator transition are described and compared with different theoretical models: one based on boson–vortex duality, next exploring the properties of granular superconductors and the third analyzing effect of the superconducting fluctuations in the magnetic field at low temperature. All the models point to the existence of pairwise electron correlations at the Fermi-level of the insulator. These so-called localized pairs should vanish in high magnetic fields. The localized pairs apparently come from the parity effect in ultrasmall quasigrains––local minima of the random potential which can admit only small limited number of electrons. [Copyright &y& Elsevier]

To study the vortex states below the critical field Bc of the superconductor–insulator transition in two dimensions (2D), we measure the magnetoresistance at low perpendicular fields B (<Bc) for a thin (4 nm) a-MoxSi1−x film. We find that the very small temperature-independent resistance remains at T→0 in finite B below Bc. Such resistance is not observed for a thick (100 nm) film as well as for the thin film in parallel fields. These results suggest quantum motion of a small number of vortices (dislocations) in the 2D vortex-glass phase in the presence of the current. [Copyright &y& Elsevier]

We investigate the roles of flux pinning on vortex motion at low temperatures (T) in two-dimensional (2D) superconductors using two thin (4 nm) amorphous Mo[sub x]Si[sub 1-x] films with different pinning strength. We measure the T dependence of resistance R at fields B below the critical field B[sub c] of the 2D superconductor-insulator (SI) transition. For both films we observe the very small T-independent R at T→0 in certain field regions below B[sub c], suggesting quantum motion of a small number of vortices (dislocations) in the 2D vortex-glass phase in the presence of current. For the film with weaker pinning, the activation energy decreases at T<0.1 K. [ABSTRACT FROM AUTHOR]

We present measurements of the magnetoresistance (MR) for insulating amorphous MoxSi1−x films. The field B is applied both perpendicular R⊥(B) and parallel R&par;(B) to the plane of the film. For the most resistive film the difference between R⊥ and R&par;, Ra (i.e., anisotropy component of MR), is positive and shows a monotonic increase with increasing B. On the other hand, for the less resistive film which lies closer to the zero-field superconductor–insulator transition, Ra(B) also shows an increase at low fields but it then takes a broad peak at higher B. The behavior is not explained only by the orbital effect for fermions, suggesting the contribution of superconductivity. [Copyright &y& Elsevier]

Abstract: A Cooper pair insulator (CPI) phase emerges near the superconductor–insulator transitions of a number of strongly-disordered thin film systems. Much recent study has focused on a mechanism driving the underlying Cooper pair localization. We present data showing that a CPI phase develops in amorphous Pb0.9Bi0.1 films deposited onto nano-porous anodized aluminum oxide surfaces just as it has been shown to develop for a-Bi films. This result confirms the assertion that this CPI phase emerges due to the structure of the substrate. It supports the picture that nanoscale film thickness variations induced by the substrate drive the localization. Moreover, it implies that the CPI phase can be induced in any superconducting material that can be deposited onto this surface. [Copyright &y& Elsevier]

• The intervening Bose metal (BM) state is the bosonic topological insulator. • In the bulk vortices and Cooper pairs are frozen by Aharonov-Bohm interactions. • Transport in the Bose metal is mediated by topologically protected edge modes. • Transitions BM–superinsulator and BM–superconductor are quantum BKT transitions. A low-temperature intervening metallic regime arising in the two-dimensional superconductor-insulator transition challenges our understanding of electronic fluids. Here we develop a gauge theory revealing that this emergent anomalous metal is a bosonic topological insulator where bulk transport is suppressed by mutual statistics interactions between out-of-condensate Cooper pairs and vortices and the longitudinal conductivity is mediated by symmetry-protected gapless edge modes. We explore the magnetic-field-driven superconductor-insulator transition in a niobium titanium nitride device and find marked signatures of a bosonic topological insulator behavior of the intervening regime with the saturating resistance. The observed superconductor-anomalous metal and insulator-anomalous metal dual phase transitions exhibit quantum Berezinskii-Kosterlitz-Thouless criticality in accord with the gauge theory. [ABSTRACT FROM AUTHOR]

Resistively shunted, single Josephson junctions are studied theoretically. The method complements the band picture and is aimed at the superconductor–insulator transition regime in the EJ/EC, Rq/R plane, where EJ and EC are the Josephson energy and the charging energy EC=e2/2C,C being the capacitance of the junction and Rq=h/4e2 and R are the quantum resistance and the shunt resistance. The I–V characteristic is formulated by a new theory and evaluated by the path-integral transfer matrix method. The obtained result is in accordance with the recent experiments. [Copyright &y& Elsevier]