Normal State Resistivity Research Articles

Transport phase diagram and anomalous metallicity in superconducting infinite-layer nickelates.

Despite obvious similarities in their electronic and crystallographic structures, it remains unclear whether the interactions that shape the normal and superconducting (SC) state properties of high-Tc cuprates and infinite-layer nickelates (ILNs) have the same origin. This question has been brought into sharper focus with recent studies on ILNs of improved crystallinity that reveal a SC dome of comparable extent and similar transport properties above Tc as the hole-doped cuprates. The evolution of these properties in the magnetic-field-induced normal state, however, has yet to be determined. Here, we examine the magnetotransport properties of new-generation Nd1-xSrxNiO2 films in the T→0 limit across the phase diagram in fields up to 54 T. This extensive study reveals that the limiting low-T form of the normal-state resistivity in ILNs exhibits non-Fermi-liquid behaviour over an extended doping range inside the SC dome, rather than at a singular quantum critical point. While there are clear differences in the charge dynamics of ILNs and cuprates, most notably in the magnetoresistance, our findings reveal that both systems exhibit anomalous metallicity characteristic of a quantum critical phase.

Crystal growth and pressure effect on the transport properties in 122-type (La,Na,K)Fe2As2 superconductors

Abstract High-quality single crystals are essential for probing the intrinsic properties of unconventional superconductors. In this work, we report the successful growth of (La,Na,K)Fe2As2 single crystals, a novel 122-type iron-based superconductor, using the self-flux method. The crystal structure and chemical composition were characterized through x-ray diffraction and energy-dispersive x-ray spectroscopy. The (La,Na,K)Fe2As2 single crystals exhibit bulk superconductivity, with a critical transition temperature Tc of approximately 22 K. Magnetization measurements reveal a second peak effect and a critical current density Jc ~ 5×105 A/cm2 at 2 K in a self-field. The upper critical field anisotropy was systematically studied within the framework of the anisotropic Ginzburg–Landau theory, yielding an anisotropy value of approximately 2.6. Furthermore, we employ the diamond anvil cell technique to investigate the pressure effect on (La,Na,K)Fe2As2. Our results demonstrate that superconductivity is gradually suppressed with increasing pressure, while the normal state resistivity at low temperatures evolves from non-Fermi liquid to Fermi liquid behavior. This observation suggests that (La,Na,K)Fe2As2 may be situated on the right of the quantum critical point or, at the very least, within the over-doped region. These findings provide a critical sample platform and experimental insights for advancing the understanding of the physical properties of the newly discovered (La,Na,K)Fe2As2 superconductors.

Discovery of superconductivity and electron-phonon drag in the non-centrosymmetric Weyl semimetal LaRhGe3

We present an exploration of the effect of electron-phonon coupling and broken inversion symmetry on the electronic and thermal properties of the semimetal LaRhGe3. Our transport measurements reveal evidence for electron-hole compensation at low temperatures, resulting in a large magnetoresistance of 3000% at 1.8 K and 14 T. The carrier concentration is on the order of 1021/cm3 with high carrier mobilities of 2000 cm2/Vs. When coupled to our theoretical demonstration of symmetry-protected almost movable Weyl nodal lines, we conclude that LaRhGe3 supports a Weyl semimetallic state. We discover superconductivity in this compound with a Tc of 0.39(1) K and Bc(0) of 2.2(1) mT, with evidence from specific heat and transverse-field muon spin relaxation. We find an exponential dependence in the normal state electrical resistivity below ~50 K, while Seebeck coefficient and thermal conductivity measurements each reveal a prominent peak at low temperatures, indicative of strong electron-phonon interactions. To this end, we examine the temperature-dependent Raman spectra of LaRhGe3 and find that the lifetime of the lowest energy A1 phonon is dominated by phonon-electron scattering instead of anharmonic decay. We conclude that LaRhGe3 has strong electron-phonon coupling in the normal state, while the superconductivity emerges from weak electron-phonon coupling. These results open up the investigation of electron-phonon interactions in the normal state of superconducting non-centrosymmetric Weyl semimetals.

Tuning the IcRn value of YBCO step edge Josephson junction through Ar+ ion irradiation

YBCO Step edge Josephson junctions are fabricated on single crystal MgO (100) substrates, and the effect of Ar+ ion irradiation on the critical current (Ic) and normal state resistance (Rn) is studied. It is shown that on the appropriate exposure of the YBCO step edge junction to Ar+ ion irradiation, the IcRn product of the junction can be enhanced up to 0.66 mV at 77 K, which is sufficiently good for many applications. With the increase in the exposure time of Ar+ ion irradiation, the value of Ic decreases, and the Rn value increases. After irradiating for 4 min, Ic as low as 70 μA and Rn as high as ∼9.4 Ω have been obtained at 77 K. It is found that for higher exposure time, the junction behavior tends to SIS-type junctions. The mechanism responsible for the decrease in Ic and increase in Rn seems to be associated with the vacancies as well as displacement of oxygen atoms caused by the ion irradiation, which causes the suppression of superconducting parameters as the superconducting properties critically depend on the concentration of the oxygen atoms in the Cu-O planes.

Effect of Proton Irradiation on Thin-Film YBa2Cu3O7-δ Superconductor.

We investigated the effect of 0.6 MeV proton irradiation on the superconducting and normal-state properties of thin-film YBa2Cu3O7-δ superconductors. A thin-film YBCO superconductor (≈567 nm thick) was subject to a series of proton irradiations with a total fluence of 7.6×1016 p/cm2. Upon irradiation, Tc was drastically decreased from 89.3 K towards zero with a corresponding increase in the normal-state resistivity above Tc. This increase in resistivity, which indicates an increase in defects inside the thin-film sample, can be converted to the dimensionless scattering rate. We found that the relation between Tc and the dimensionless scattering rate obtained during proton irradiation approximates the generalized d-wave Abrikosov-Gor'kov theory better than the previous results obtained from electron irradiations. This is an unexpected result, since the electron irradiation is known to be most effective to suppress superconductivity over other heavier ion irradiations such as proton irradiation. In comparison with the previous irradiation studies, we found that the result can be explained by two facts. First, the dominant defects created by 0.6 MeV protons can be point-like when the implantation depth is much longer than the sample thickness. Second, the presence of defects on all element sites is important to effectively suppress Tc.

Crystal growth and characterization of Fe1+δSe1-xTex (0.5 ≤ x ≤ 1) from LiCl/KCl flux

An eutectic LiCl/KCl flux method in a horizontal configuration has been used to grow a series of homogeneous Fe1+δSe1-xTex single crystals of high quality with 0.5 ≤ x ≤ 1. Compared with previously used melt-growth method, the stable crystallization process in LiCl/KCl flux below their peritectic temperatures results in better homogeneity and crystalline perfection identified by energy dispersive spectrometer and x-ray diffraction. The interstitial Fe value δ remains small within 0.5 ≤ x ≤ 0.85 where the superconducting temperature TC is not sensitive to the Te content with sharp superconducting transition widths ΔTC < 1 K and a maximum of TC = 14.3 K at x = 0.61. The value δ starts to increase quickly accompanied by a deviation of linear behavior of crystal lattice parameters as well as the broadening of ΔTC = 2.1 K at x = 0.91, then suddenly rises up to δ > 0.1 followed by the disappearance of superconductivity and emergence of antiferromagnetic order at x ≥ 0.96. We also observed a metallic to semiconducting transition in the normal state resistivity of Fe1+δSe1-xTex with increasing Te content which is related to a localized electronic state induced by the interstitial Fe. The interstitial Fe value δ might be a key physical parameter to understand various properties of Fe1+δSe1-xTex system.

Superconductivity investigation of (Bi, Pb)-2223 added with different nanoferrites and their composites

In this study, the impact of different types of nanoferrites additions of Zn0.5Ni0.5Fe2O4 and Ba0.4Sr0.4Ca0.2Fe12O19 nanoparticles and their nanocomposite of (Zn0.5Ni0.5Fe2O4)0.5 (Ba0.4Sr0.4Ca0.2Fe12O19)0.5 on the structural and normal state resistivity of Bi1.6Pb0.4Sr2Ca2Cu3O10, ((Bi,Pb)-2223) superconducting phase were systematically investigated. The samples were synthesised using high purity oxide powders via a solid-state reaction approach. Based on the Rietveld analysis of x-ray diffraction (XRD) data, the tetragonal structure of (Bi,Pb)-2223 was established to be the predominant phase for all composite samples of the three nano-additions’ contents. However, a little change to the lattice parameters ( a and c ) was obtained. Furthermore, the small amounts (0.04 wt%) of Ba0.4Sr0.4Ca0.2Fe12O19 and (Zn0.5Ni0.5Fe2O4)0.5(Ba0.4Sr0.4Ca0.2Fe12O19)0.5 improved the development of the (Bi,Pb)-2223 phase. The volume fraction of the (Bi,Pb)-2223 phase increased from 86.47% to 88.73% and 88.69%, respectively. Then, it declined to 74.25% and 71.48% upon rising x to 0.40 wt%, respectively, as well as for Zn0.5Ni0.5Fe2O4 nanoparticles up to 0.40 wt%. SEM images verify the host superconducting matrix’s granular structure for all three nanoadditions up to 0.40 wt%. The existence of three nano additions in the host superconductor matrix is verified by employing energy dispersive x-ray (EDX) and x-ray photoelectron spectroscopy (XPS) analysis. The measurements for the resistivity dependency of temperature presented that, as compared to the pure sample (Tc = 108.67 K), the nano-(Zn0.5Ni0.5Fe2O4) x added in the (Bi,Pb)-2223 phase exhibits more negative impact than it is with the other two additions. In contrast, the nano-(Ba0.4Sr0.4Ca0.2Fe12O19) x has the highest value of Tc with a value of 110.95 K at x = 0.04 wt%. Furthermore, the superconducting transition width (∆Tc) improved for all composite samples except for the sample at x = 0.04 wt%, for Ba0.4Sr0.4Ca0.2Fe12O19 and (Zn0.5Ni0.5Fe2O4)0.5 (Ba0.4Sr0.4 Ca0.2Fe12O19)0.5 which showed the sharpest transition width. This suggests that their addition is anticipated to act as artificial pinning centers and strengthen the coupling between the grains in the (Bi,Pb)-2223 ceramic.

Emergence of quantum Griffiths singularity in disordered TiN thin films

The association of quantum Griffiths singularity (QGS) to the magnetic-field-induced superconductor-metal transition predicts the unconventional diverging behaviour of dynamical critical exponent in low disorder crystalline two-dimensional superconductors. But whether this state exists in the superconducting systems exhibiting superconductor-insulator transition remains elusive. Here, we report the emergence of quantum Griffiths singularity in ultrathin disordered TiN thin films with more than two orders of magnitude variation in their normal state resistance. For both superconductor-metal transition and superconductor-insulator transition types, a diverging critical exponent is observed while approaching the quantum phase transition. Further, the magnetoresistance isotherms obey a direct activated scaling governed by an infinite-randomness fixed critical point. Finally, this work establishes the robustness of the QGS phenomenon towards a wide range of temperature and also towards a wide range of disorder strength as correlated with the normal state resistance.

Effect of ion irradiation on superconducting thin films

We demonstrate ion irradiation by argon or gallium as a wafer-scale post-processing method to increase disorder in superconducting thin films. We study several widely used superconductors, both single-elements and compounds. We show that ion irradiation increases normal-state resistivity in all our films, which is expected to enable tuning their superconducting properties, for example, toward a higher kinetic inductance. We observe an increase in superconducting transition temperature for Al and MoSi and a decrease for Nb, NbN, and TiN. In MoSi, ion irradiation also improves the mixing of the two materials. We demonstrate the fabrication of an amorphous and homogeneous film of MoSi with uniform thickness, which is promising, for example, for superconducting nanowire single-photon detectors.

MgB[formula omitted] Josephson Junctions fabricated by Focused Helium Ion Beam with different irradiation doses on SiC and MgO substrates

Recently, high quality MgB2 single junctions and junction arrays fabricated by Focused Helium Ion Beam irradiation (He-FIB) have been reported. However, the effects of irradiation doses and substrates on junction properties have not been analysed systematically. In this work, 30 nm MgB2 thin films were deposited on SiC (0001) and MgO (111) substrates using Hybrid Physical–Chemical Vapour Deposition (HPCVD) technique and then etched into 2–4 μm wide microbridges. 2000–6000 ions/nm doses of He-FIB were irradiated across these microbridges, creating narrow junction barriers. R–T curves exhibit a clear foot-like structure that enlarges as irradiation dose increases. Temperature dependence of junction properties (critical current Ic, junction normal state resistance Rn, characteristic voltage Vc) shows that all junctions in our experiment exhibit superconductor–normal–superconductor (SNS) like behaviour and higher irradiation doses create thicker junction barriers. Furthermore, we analyse junction properties dependence on irradiation doses which yields an exponential change law. Finally, Fraunhofer diffraction-like patterns and Shapiro steps of junctions are also measured. Our results show MgB2 Josephson Junctions with adjustable properties can be fabricated by He-FIB on SiC and MgO substrates, which provides a solid foundation for future application devices research.

Engineering underdoped CuO2 nanoribbons in nm-thick a -axis YBa2Cu3O7−δ films

In underdoped cuprate high-Tc superconductors, various local orders and symmetry-breaking states, in addition to superconductivity, reside in the CuO2 planes. The confinement of the CuO2 planes can therefore play a fundamental role in modifying the hierarchy between the various orders and their intertwining with superconductivity. Here we present the growth of a-axis oriented YBa2Cu3O7−δ films, spanning the whole underdoped side of the phase diagram. In these samples, the CuO2 planes are confined by the film thickness, effectively forming unit-cell-thick nanoribbons. The unidirectional confinement at the nanoscale enhances the in-plane anisotropy of the films. By x-ray diffraction and resistance vs temperature measurements, we have discovered the suppression of the orthorhombic-to-tetragonal transition at low dopings, and a very high anisotropy of the normal state resistance in the b−c plane, the latter being connected to a weak coupling between adjacent CuO2 nanoribbons. These findings show that the samples we have grown represent a novel system, different from the bulk, where future experiments can possibly shed light on the rich and mysterious physics occurring within the CuO2 planes. Published by the American Physical Society 2024

Demonstration of high-impedance superconducting NbRe Dayem bridges

Here, we demonstrate superconducting Dayem-bridge weak-links made of different stoichiometric compositions of NbRe. Our devices possess a relatively high critical temperature, normal-state resistance, and kinetic inductance. In particular, the high kinetic inductance makes this material a good alternative to more conventional niobium-based superconductors (e.g., NbN or NbTiN) for the realization of superinductors and high-quality factor resonators, whereas the high normal-state resistance yields a large output voltage in superconducting switches and logic elements realized upon this compound. Moreover, out-of-plane critical magnetic fields exceeding 2 T ensure that possible applications requiring high magnetic fields can also be envisaged. Altogether, these features make this material appealing for a number of applications in the framework of quantum technologies.

Indium Bump Bonding: Advanced Integration Techniques for Low-Temperature Detectors and Readout

We have examined the influence of bump shape and bonding pressure on low-temperature electrical properties of indium bump connections including superconducting transition temperature, normal state resistance, and superconducting critical current. We describe our test structures, bonding process, and methods of characterization. At temperatures below 1 K, we observe critical currents greater than 70 mA for indium bump connections with a nominal bump size of 17 µm × 17 µm.

Toward Reliable Synthesis of Superconducting Infinite Layer Nickelate Thin Films by Topochemical Reduction.

Infinite layer (IL) nickelates provide a new route beyond copper oxides to address outstanding questions in the field of unconventional superconductivity. However, their synthesis poses considerable challenges, largely hindering experimental research on this new class of oxide superconductors. That synthesis is achieved in a two-step process that yields the most thermodynamically stable perovskite phase first, then the IL phase by topotactic reduction, the quality of the starting phase playing a crucial role. Here, a reliable synthesis of superconducting IL nickelate films is reported after successive topochemical reductions of a parent perovskite phase with nearly optimal stoichiometry. Careful analysis of the transport properties of the incompletely reduced films reveals an improvement in the strange metal behavior of their normal state resistivity over subsequent topochemical reductions, offering insight into the reduction process.

Global Room‐Temperature Superconductivity in Graphite

AbstractRoom temperature superconductivity under normal conditions has been a major challenge of physics and material science since its discovery. Here the global room‐temperature superconductivity observed in cleaved highly oriented pyrolytic graphite carrying dense arrays of nearly parallel surface line defects is reported. The multiterminal measurements performed at the ambient pressure in the temperature interval 4.5 K ≤ T ≤ 300 K and at magnetic fields 0 ≤ B ≤ 9 T applied perpendicular to the basal graphitic planes reveal that the superconducting critical current Ic(T, B) is governed by the normal state resistance RN(T, B) so that Ic(T, B) is proportional to 1/RN(T, B). Magnetization M(T, B) measurements of superconducting screening and hysteresis loops together with the critical current oscillations with temperature that are characteristic for superconductor‐ferromagnet‐superconductor Josephson chains, provide strong support for the occurrence of superconductivity at T &gt; 300 K. A theory of global superconductivity emerging in the array of linear structural defects is developed which well describes the experimental findings and demonstrate that global superconductivity arises as a global phase coherence of superconducting granules in linear defects promoted by the stabilizing effect of underlying Bernal graphite via tunneling coupling to the three dimensional (3D) material.

Investigation on Magnetotransport Properties and Specific Heat Capacity of FeTe0.58Se0.42 Single Crystals Grown by Self‐Flux Method

A comprehensive study of magnetotransport and field‐dependent specific heat of FeTe0.58Se0.42 single crystals synthesized using the self‐flux method is reported. The transport measurement reveals the presence of Fermi liquid behavior in the normal state resistivity of the single crystals. Furthermore, the grown single crystals exhibit anisotropy and demonstrate a high value of upper critical magnetic field (HC2). The magnetoresistance exhibits a linear behavior as the magnetic field increases, suggesting the possible presence of a Dirac‐cone state. Anisotropy is also observed in magnetoresistance near the superconducting transition temperature (TC). The sign reversal of the Hall coefficient and the violation of Kohler's rules are observed, which provide evidence of the presence of multiband effects in FeTe0.58Se0.42 single crystals. Specific heat measurements confirm the bulk superconductivity in the grown single crystals. Additionally, the specific heat jump is estimated, which is approximately equal to . The magnetic field‐dependent specific heat also suggests multiband superconductivity and offers insights into the upper critical field. Furthermore, the electronic specific heat is best fitted with a two‐band model. Moreover, the field‐dependent residual Sommerfeld coefficient gives information about the superconducting pairing symmetry.

Diffusion mediated growth of superconducting Nb-Ti composite films by high temperature annealing

The fabrication of superconducting Nb-Ti alloy by high temperature annealing of Nb/Ti bilayer thin films is reported here. During the annealing process, Nb and Ti diffuse into each other and Nb-Ti composite film formation occurs at the interface of the bilayer. Two types of substrates, namely, SiO2/Si and Si3N4/Si are used to grow the bilayers of Nb/Ti by using dc magnetron sputtering. Annealing at temperature about 820 °C leads the substrates to take part into the diffusion process. The alloying of Nb-Ti and the effect of substrates on the structural properties are studied by x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). Ti-rich Nb-Ti phases are present in the XRD while interface studies through XPS confirms the interdiffusion of the two elements Nb and Ti along with the presence of the decomposed elements from the substrates. Appearance of nitride phases in case of Si3N4/Si substrate confirms the substrate’s involvement in the diffusion process. Further low temperature transport measurements are carried out to study the superconducting properties of the Nb-Ti composite films grown on both oxide (SiO2/Si) and nitride (Si3N4/Si) substrates. Nb-Ti composite films offer higher transition temperature (T C ) compared to that of pure Nb with similar thickness used in Nb/Ti bilayer films. Higher normal state resistance (R N ) with wider transition width for Nb-Ti on nitride substrate in comparison with the oxide substrate indicates a possible role of N atoms in tuning the disorder and hence controlling the transport properties. Finally, the presented method can be used to fabricate superconducting stoichiometric NbTi and NbTiN thin films for future phase slip and superconducting single photon detector-based applications.

Automated superconducting qubit characterization platform based on a modified 3D printer

Josephson Junctions are important components in superconducting qubits. It introduces anharmonicity to the energy level spacings of the qubit which allow us to identify two unique quantum energy states for computing. It is difficult to fabricate multiple junctions within the same desired parameter range. Characterisation of the junctions is, therefore, a necessary step after fabrication. In particular, the critical current of the junctions is determined by measuring their normal state resistance. This is done via two-point or four-point resistance measurement at a manual probe station which is a time-consuming process, especially for wafer-scale fabrication. This bottleneck can be circumvented by automation with object detection. The base of the automated probe station is a 3D printer modified with multiple Arduino Uno microcontrollers and motorized linear stages. The automation process is achieved via auto-alignment of the probes and an automatic measurement procedure. As a result, the fully automated process will take about 27–29[Formula: see text]s to measure the resistance of one junction which saves 28%–51% of the time compared to the manual probe station and can be unsupervised. Due to the reuse of a commercial 3D printer, the cost of this system is 800 SGD which is much less than comparable commercial solutions.

Current–voltage characteristics of focused ion beam fabricated superconducting tungsten meanders

We report on the superconducting properties and intermediate resistive steps (IRS) observed in the current–voltage characteristics (IVC) of tungsten meander (MW) structures fabricated using focused ion beam (FIB) technique. Three number of MWs were studied with individual wire widths of 240 nm, 640 nm and 850 nm with superconducting transition temperatures () of 4.5 K, 4.55 K and 4.60 K respectively. The measured normal state resistance values at 8 K for these wires are of ∼182 kΩ, ∼49 kΩ and ∼32 kΩ, respectively as a function of increasing wire widths; are higher than the quantum of resistance ( is a Planck constant and is electronic charge) indicating extreme disorder nature of the fabricated samples. The variation of resistance with respect to temperature (for ) follows the theoretical simulation of weak-link induced thermally activated phase slip (WL-TAPS) for the MW wire of width ∼240 nm, while for other samples the convergence between WL-TAPS and the experimental data are not so satisfactory. Though the IRS features are present in all the samples with varying degree of prominence, an external magnetic field causes its evolution demarcating different boundary lines with respect to temperatures. Herein, we believe that the occurrence of IRS is due to phase slip (PS) mechanism which further proliferates through phase slip centers or phase slip lines in IVC either with respect to temperature or magnetic field. As per our knowledge, such IRS features are not being reported for W-meander wires fabricated using FIB technique. The observation of PS (IRS) features is promising for the use of FIB fabricated W nanowires for various quantum applications including single photon detector, bolometers.

Multi-source excited travelling-wave bowtie antenna based on a meander series of YBCO bicrystal Josephson junctions

Series superconducting Josephson junctions (JJs), as terahertz (THz) mixers, have attracted increasing attentions due to their advantages in solving the saturation problem of superconducting mixers, achieving higher mixing harmonics and higher sensitivity in THz band. However, the normal-state resistances of the series JJs are so low that there exists an impedance mismatch between the coupled antenna and the JJs. In this paper, a meander embedding travelling-wave bowtie antenna is proposed for a series of bicrystal JJs. With this antenna, not only the problem of impedance mismatch can be solved, but also more series JJs can be inserted into the antenna. Five and even seven series JJs in the meander match the proposed antenna well. Furthermore, combined current distribution, far-field radiation patterns and parameter study are investigated in the numerical simulation to analyze this antenna.