Superconducting Phase Transition Temperature Research Articles

Optically Probing Unconventional Superconductivity in Atomically Thin Bi2Sr2Ca0.92Y0.08Cu2O8+δ.

Atomically thin cuprates exhibiting a superconducting phase transition temperature similar to that of the bulk have recently been realized, although the device fabrication remains a challenge and limits the potential for many novel studies and applications. Here, we use an optical pump-probe approach to noninvasively study the unconventional superconductivity in atomically thin Bi2Sr2Ca0.92Y0.08Cu2O8+δ (Y-Bi2212). Apart from finding an optical response due to the superconducting phase transition that is similar to that of bulk Y-Bi2212, we observe that the sign and amplitude of the pump-probe signal in atomically thin flakes vary significantly in different dielectric environments depending on the nature of the optical excitation. By exploiting the spatial resolution of the optical probe, we uncover the exceptional sensitivity of monolayer Y-Bi2212 to the environment. Our results provide the first optical evidence for the intralayer nature of the superconducting condensate in Bi2212 and highlight the role of double-sided encapsulation in preserving superconductivity in atomically thin cuprates.

Design and fabrication of the superconducting single-photon detector operating at the 5 - 10 micrometer wavelength band

High-performance mid-wave and long-wave infrared single-photon detectors not only have significant research value in the fields of infrared astronomy and defense technology, but are also challenging to be realized in the field of single-photon detection technology. Superconducting nanowire single-photon detectors (SNSPDs) have shown excellent performance in the near-infrared band. However, how to further improve the cutoff wavelength <i>λ</i><sub>c</sub> is a topic of widespread concern. In this paper, the method for improving <i>λ</i><sub>c</sub> by applying the regulation of the superconducting disorder is discussed, and a detector with an operating wavelength band of 5 - 10 μm is designed and fabricated. <br>Studies have shown that the multiplication and diffusion behaviors of the quasiparticles always occur during the photon detection events, although the microscopic photodetection mechanism of SNSPD still lacks a perfect theoretical explanation. Therefore, the theoretical analysis mainly considers the influence of the quasiparticles in this paper, and the mathematical formula of the detection cutoff wavelength <i>λ</i><sub>c</sub> can be obtained based on the phenomenological quasiparticle diffusion model. Furthermore, the disorder-dependent superconducting phase transition temperature <i>T</i><sub>c</sub>, superconducting energy gap <i><teshuzifu>D</i>, and electron thermalization time <i>τ</i><sub>th</sub> are also considered, in order to get more precise results.<br>Theoretical analysis suggests that the increase in the sheet resistance <i>R</i><sub>s</sub>, which evaluates the disorder strength, will help to increase <i>λ</i><sub>c</sub>. For example, when the nanowire width is kept at 30 nm and <i>R</i><sub>s</sub> > 380 Ω/□, it can be deduced that <i>λ</i><sub>c</sub> is larger than 10 μm.<br>Experimentally, the active area of the device consists of a straight superconducting nanowire with a length of 10 μm and a width of 30 nm, so that it can effectively reduce the probability of the defects on the nanowire and avoid the current crowding effect. We have fabricated a 30 nm-wide Mo<sub>0.8</sub>Si<sub>0.2</sub> mid infrared SNSPD, which has a cutoff wavelength <i>λ</i><sub>c</sub> no more than 5 μm, the effective strength of the disorder - the film sheet resistance <i>R</i><sub>s</sub> = 248.6 Ω/□. As a comparison, the sheet resistance, which is controlled by the film thickness, is increased to about 320 Ω/□ in this experiment.<br>It is demonstrated that the Mo<sub>0.8</sub>Si<sub>0.2</sub> detector with <i>R</i><sub>s</sub> ~320 Ω/□ can achieve saturated quantum efficiency at a wavelength of 6 μm. Furthermore, 53% quantum efficiency at the wavelength of 10.2 μm can be obtained when the detector works at a bias current of 0.9 <i>I</i><sub>SW</sub> (<i>I</i><sub>SW</sub> is the superconducting transition current), and it can theoretically reach a maximum value of 92% if the compression of switching current is excluded. Therefore, it can be predicted that the disorder regulation may become another efficient approach for designing high-performance mid-wave and long-wave infrared SNSPDs, in addition to the optimization of the superconducting energy gap and the cross section of superconducting nanowire.<br>However, the continuous increase in the disorder will cause a decrease in both the superconducting phase transition temperature <i>T</i><sub>c</sub> and <i>I</i><sub>SW</sub> of the detector from the point of detector fabrication and application. This downward trend is especially pronounced when the nanowire width is ultranarrow, which is not conducive to the signal readout of the detector. Thus, exploring the optimal disorder regulation technology and balancing the relationship between the operating temperature, the signal-to-noise ratio, and the cutoff wavelength will have key scientific and application value for the development of high-performance mid-wave and long-wave infrared SNSPDs.

Possible quantum phase transition in partially Cu-doped ZrNi2-xCuxGa Heusler alloys

We have studied the magneto-transport properties of a series of ZrNi2-xCuxGa compounds. For all Cu concentration (x ≤ 0.5) the samples exhibited the L21 cubic structure at room temperature and demonstrated superconductivity below 2 K. A superconducting phase transition temperature of as low as ∼1 K and a critical magnetic field of 1.78 T was observed in the system. A linear extrapolation of TC to T = 0 highly indicated that a stoichiometry-dependent superconducting quantum phase transition may occur in ZrNi2-xCuxGa at xc = 0.90.

Design and fabrication of superconducting single-photon detector operating in 5–10 μm wavelength band

<sec>High-performance mid-wave and long-wave infrared single-photon detectors not only have significant research value in the fields of infrared astronomy and defense technology, but also are the challenges in the field of single-photon detection technology. Superconducting nanowire single-photon detectors (SNSPDs) have shown excellent performances in the near-infrared band. However, how to further improve the cutoff wavelength <i>λ</i><sub>c</sub> is a topic of widespread concern. In this paper, the method of improving <i>λ</i><sub>c</sub> by regulating the superconducting disorder is discussed, and a detector with an operating wavelength band of 5–10 μm is designed and fabricated.</sec><sec>The studies show that the multiplication and diffusion behaviors of the quasiparticles always occur during the photon detection events, although the microscopic photodetection mechanism of SNSPD still lacks a perfect theoretical explanation. Therefore, the theoretical analysis mainly considers the influence of the quasiparticles in this paper, and the mathematical formula of the detection cutoff wavelength <i>λ</i><sub>c</sub> can be obtained based on the phenomenological quasiparticle diffusion model. Furthermore, the disorder-dependent superconducting phase transition temperature <i>T</i><sub>c</sub>, superconducting energy gap <i>Δ</i>, and electron thermalization time <i>τ</i><sub>th</sub> are also considered, in order to obtain more precise results.</sec><sec>Theoretical analysis suggests that the increase in the sheet resistance <i>R</i><sub>s</sub>, which evaluates the disorder strength, will help to increase <i>λ</i><sub>c</sub>. For example, when the nanowire width is kept at 30 nm and <i>R</i><sub>s</sub> > 380 Ω/square, it can be deduced that <i>λ</i><sub>c</sub> is larger than 10 μm.</sec><sec>Experimentally, the active area of the device consists of a straight superconducting nanowire with a length of 10 μm and a width of 30 nm, so that it can effectively reduce the probability of the defects on the nanowire and avoid the current crowding effect. We fabricate a 30 nm-wide Mo<sub>0.8</sub>Si<sub>0.2</sub> mid infrared SNSPD, which has a cutoff wavelength <i>λ</i><sub>c</sub> no more than 5 μm, the effective strength of the disorder－the film sheet resistance <i>R</i><sub>s</sub> = 248.6 Ω/square. For comparison, the sheet resistance, which is controlled by the film thickness, increases to about 320 Ω/square in this experiment.</sec><sec>It is demonstrated that the Mo<sub>0.8</sub>Si<sub>0.2</sub> detector with <i>R</i><sub>s <inline-formula><tex-math id="Z-20221216014812-1">\begin{document}$ \sim $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20221594_Z-20221216014812-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20221594_Z-20221216014812-1.png"/></alternatives></inline-formula></sub>320 Ω/square can achieve saturated quantum efficiency at a wavelength of 6 μm. Furthermore, 53% quantum efficiency at a wavelength of 10.2 μm can be obtained when the detector works at a bias current of 0.9<i>I</i><sub>SW</sub> (<i>I</i><sub>SW</sub> is the superconducting transition current), and it can theoretically reach a maximum value of 92% if the compression of switching current is excluded. Therefore, it can be predicted that the disorder regulation may become another efficient approach to designing high-performance mid-wave and long-wave infrared SNSPDs, in addition to the optimization of the superconducting energy gap and the cross section of superconducting nanowire.</sec><sec>However, the continuous increase in the disorder will cause both the superconducting phase transition temperature <i>T</i><sub>c</sub> and <i>I</i><sub>SW</sub> of the detector to decrease from the viewpoint of detector fabrication and application. This downward trend is especially pronounced when the nanowire width is ultranarrow, which is not conducive to the signal readout of the detector. Thus, exploring the optimal disorder regulation technology and balancing the relationship among the operating temperature, the signal-to-noise ratio, and the cutoff wavelength will have key scientific and application value for the development of high-performance mid-wave and long-wave infrared SNSPDs.</sec>

Tuning of superconducting phase transition and magnetic properties of ferroelectric-superconducting PbZr0.48Ti0.52O3/YBa2Cu3O7-δ heterostructure

Tuning of superconducting phase transition temperature (Ts) and interfacial magnetism is of great technological importance for micro and nanoelectronics. To achieve the cherished goal, an ultra-thin layer (4 nm, 6 nm, 8 nm 10 nm) of ferroelectrics PbZr0.48Ti0.52O3 (PZT) on high-temperature superconductor YBa2Cu3O7-δ (YBCO) has deposited to tailor the magnetic and superconducting properties. The existence of Meissner effect confirmed the superconducting nature of YBCO in the heterostructures. However, its Ts significantly shifted to the lower temperature side with an increase in PZT capping layers' thickness. Nearly 10 K reduction in Ts was observed with an increase in the capping layer from 4 to 10 nm. A significant amount of magnetic moment was found in the heterostructures, which increases almost three times compared to the YBCO/LAO magnetic moment above Ts. We believe novel weak magnetic phases above the Ts may be due to the re-arrangement of oxygen anion near the ferroelectric-superconducting interface.

A terahertz Brewster switch based on superconductor hyperbolic metamaterial

Active polarization switching devices are important to control the polarization state of light including terahertz (THz) waves that are technologically challenging to manipulate. Here, we propose and numerically demonstrate a hyperbolic metamaterial-based (HMM-based) active Brewster polarization switch for the intensity and phase modulation of THz light. The proposed multilayered HMM consists of alternating thin layers of high temperature superconductors such as yttrium barium copper oxide and dielectric materials such as lanthanum aluminate. The HMM shows elliptical dispersion above the superconducting phase transition temperature and type II hyperbolic dispersion in the superconducting state. By varying the temperature from the dielectric to the superconducting phase of the HMM, we demonstrate above 98% THz intensity modulation and 100% phase tunability (180°) at Brewster’s angle. The proposed HMM can work as an efficient reflective THz modulator by properly selecting the angle of incidence.

Coexistence of magnetism and superconductivity in thin films of the Fe-based superconductor Ba1−xLaxFe2As2

Magnetization measurements have been performed to understand the role of the magnetic structure on the superconducting properties of epitaxial thin films of Ba1−xLaxFe2As2 (x = 0.08, 0.13, and 0.18) deposited on single crystal (001)-oriented MgO substrates by pulsed laser deposition. All samples exhibit a reentrant-spinglass like behavior at normal state. At lower temperatures, we observe the same magnetic state coexisting with superconductivity and it is also observed a prominent non-linear giant diamagnetism in an intermediate temperature range just above the superconducting phase transition temperature. Furthermore, no significant change in the magnetic domain structure was detected by the onset of superconductivity. Based on their magnetic states, we claim that each domain (as a disconnected superconducting island) has its own bulk superconducting properties. Finally, we discussed the dual character played by the La atoms in the superconducting properties. That duality character has been also confirmed by analyzing resistivity data.

Enhanced ferroelectric polarization in epitaxial superconducting–ferroelectric heterostructure for non-volatile memory cell

We report the growth and polarization switching properties of epitaxial ferroelectric–superconducting heterostructure PbZr0.52Ti0.48O3 (PZT) (100 nm)/YBa2Cu3O7−δ (YBCO) (100 nm) thin films for non-volatile ferroelectric random access memory elements. The epitaxial nature of the heterostructure is verified using the reciprocal space mapping data with the superconducting phase transition temperature (Tc) of nearly 25 K far below the Tc of as-grown YBCO under the same condition. The significant remanent polarization (Pr) ∼ 45 µC/cm2 at 1 kHz can switch from one state to another using 1 μs pulse. The devices meet the basic criteria of memory elements, such as high resistance ∼10 GΩ at 8 V, a butterfly-like capacitance–voltage (C/V) loop, significant polarization, a sharp change in the displacement current, long-time charge retention, and small fatigue at room temperature.

A Detailed Numerical Analysis for High-Tc Superconductivity and Physical Analysis of the High-Tc Phase Diagram Based on the U(1) Slave-Boson Approach to the t − J Hamiltonian

One of the major theoretical challenges in high-Tc superconductivity is to first reproduce the observed phase diagrams that display the monotonously decreasing pseudogap temperature T* and the dome-shaped superconducting phase transition temperature Tc in the plane of temperature vs. hole concentration. Earlier Lee and Salk [J. Korean Phys. Soc. 37, 545 (2000); Phys. Rev. B 64, 052501 (2001)] reported a successful reproduction of the phase diagram by providing a realistic gauge theoretic [SU(2)/U(1)] slave-boson approach to the t - J Hamiltonian. Most recently, we [S.-H. S. Salk, Quantum Studies: Mathematics and Foundations 5, 149 (2018)] presented a comprehensive discussion on both the SU(2) and the U(1) approaches from which one can readily understand the intimate relationship between the two formalisms and discussed that both approaches can lead to room-temperature superconductivity with suitably high values of the antiferromagnetic coupling constant J, owing to the demonstration of identical physical propensities, i.e., the higher the J is, the higher the superconducting phase transition temperature Tc is. Here, we discuss hither-to-unreported detailed numerical computations of the phase diagrams by varying the values of J by using the U(1) gauge slave-boson approach to the t − J Hamiltonian. For the sake of testing convergence, we vary the unit-cell lattice sizes from 10 × 10 to a sufficiently large size of 50 × 50. We find that even a small square lattice size of 20 × 20 is seen to show reliable agreement with the results for higher lattice sizes while the 50 × 50 lattice size displays complete convergence in both T*and Tc. In addition, we present a physical analysis of the structure of the high-Tc phase diagram, focusing on the role of the spin pairing order in association with the interplay between the pseudo-gap (spin gap) temperature and the bose-condensation temperature/dome-shaped superconducting phase transition temperature.

Magnetism and electronic properties of LiFeAs superconducting thin filma under two-dimensional strains effect

The magnetism, band properties and electronic density of states of LiFeAs superconducting thin film with two-dimensional strain are investigated by using the first principles calculations based on density functional theory, and the influences of different strains on the characteristics of superconducting films are analyzed in detail. The results show that the magnetic ground configuration is the striped antiferromagnetic state of nostrained LiFeAs thin film, and the ground structure of this system is unchanged in the range of applied 1%−6% compressive and tensile strain. The density of states near the Fermi level is mainly from the contribution of Fe-3d orbital and a few As-4p electrons. The electron spin exchange coupling between Fe ions is realized by As ions. Furthermore, unlike the case of the nostrain and the tensile strain, with increasing the compressive strain, the localized antiparallel electron spin magnetic moments of Fe ion decrease, the density of states at the Fermi surface improves, and the itinerant electron magnetism of Fe ions increases, which all greatly suppress the antiferromagnetic properties of thin film and enhance the superconducting phase transition temperature. The superconductivity of LiFeAs thin film originates from the Cooper pairs of electrons between the hole-type and electronic-type bands near the Fermi surface through the antiferromagnetic superexchange coupling effect. Instead, the LiFeAs thin film with the tensile strain presents completely opposite properties, that is to say, the decrease of the electronic density of states in the Fermi level brings about the weakening of the metal properties and the increasing of the antiferromagnetic exchange coupling. Particularly, the band structure of hole-type near the Fermi surface disappears, and the occurrence of Cooper pairs of electrons becomes significantly reduced, resulting in the suppressed superconducting phase transition when the LiFeAs thin film is subjected to tensile strain. In addition, the change of antiferromagnetic exchange coupling and magnetic moments of Fe ions are also explained according to the variation of electronic density of states of the Fe-3d energy levels during the distortion of FeAs tetrahedrons due to compressive strain. In brief, our researches provide an effective way to improve the superconducting properties of LiFeAs thin film and may promote the relevant practical applications of iron-based superconductors in the future.

Linear-T resistivity at high temperature

The linear-T resistivity is one of the characteristic and universal properties of strange metals. There have been many progresses in understanding it from holographic perspective (gauge/gravity duality). In most holographic models, the linear-T resistivity is explained by the property of the infrared geometry and valid at low temperature limit. On the other hand, experimentally, the linear-T resistivity is observed in a large range of temperatures, up to room temperature. By using holographic models related to the Gubser-Rocha model, we investigate how much the linear-T resistivity is robust at higher temperature above the superconducting phase transition temperature. We find that strong momentum relaxation plays an important role to have a robust linear-T resistivity up to high temperature.

Strain-mediated electric-field manipulation of superconducting properties of FeSe0.5Te0.5 thin films grown on piezoelectric single crystals

Superconducting thin films of FeSe0.5Te0.5 are epitaxially grown on piezoelectric 0.71Pb(Mg1/3Nb1/2)O3-0.29PbTiO3 (PMN-PT) single-crystal substrates. Upon the application of an electric field to the PMN-PT along the thickness direction the superconducting properties of the FeSe0.5Te0.5 films, such as the normal-state resistance, superconducting phase transition temperature, upper critical field, critical current, and coherence length are in situ modified via the ferroelectric polarization rotation, converse piezoelectric effect, and structural phase transition of the PMN-PT. Our findings demonstrate that the combination of superconducting thin films with piezoelectrically active PMN-PT offers a promising approach for exploring the intrinsic lattice strain effects of iron-based superconducting systems.

Tunneling current in magnetic-ferroelectric-superconducting heterostructures

We report the tunneling current behavior of magnetic-ferroelectric-superconducting heterostructures for multistates non-volatile random access memory (NVRAM) elements. A heterostructure of La0.67Sr0.33MnO3 (LSMO) (50 nm)/PbZr0.52Ti0.48O3 (PZT) (5 nm)/Bi-Sr-Ca-Cu2-OX (BSCCO) (100 nm)/LaAlO3 (LAO) architecture was fabricated by pulsed laser deposition technique. The tunneling effects were investigated well above and below the superconducting phase transition temperature of the BSCCO bottom electrode. A divergent current and conductance paths were observed for polarization up and down direction above the coercive field of the ferroelectric tunnel barrier. This behaviour was significant below Ts where the moderate effect of the external magnetic field was also observed on the tunneling current. The dynamic conductance G(V) data fitted well with Brinkman's model for both polarizations up and polarization down states which suggest the presence of large tunnel electro-resistance.

Screening properties of multiply connected ferromagnet–superconductor hybrid structures

Superconducting phase transition temperature T c of a ferromagnet/superconductor (SF) hybrid structure consisting of a hollow superconducting (S) cylinder (shell) with the central part (core) filled with a ferromagnetic (F) metal has been analyzed on the basis of linearized Usadel equations. It has been shown that the proximity effect between the S and F metals, as well as the exchange interaction, may induce an inhomogeneous superconducting state with Δ ~ exp(iLθ + ipz), which is characterized by nonzero circulation of phase L and wavenumber p describing the Larkin–Ovchinnikov–Fulde–Ferrell (LOFF) instability along the cylinder axis. The transitions between the states with different values of L and p, which are accompanied by a nonmonotonic dependence of superconducting transition temperature T c and effective magnetic field penetration depth Λ into the SF structure on the characteristic size of the ferromagnetic region, have been investigated.

Thermally activated flux mechanism in Mg-doped InN epitaxial film

The superconducting behaviour of InN has been observed in many experiments where the origin of superconductivity is addressed to presence of (i) In–In chains in ab-plane, (ii) specific carrier density range limited Mott transition critical carrier density and (iii) presence of In2O3 impurities. Although the superconductivity can be observed when the above conditions are enough for epitaxial grown InN films, the superconductivity properties of InN, so far, have not worked comprehensively. Here, we report the magneto-resistance, upper critical field and thermally activated flux mechanism of superconductor Mg doped InN epitaxial film grown by Molecular Beam Epitaxy. The superconducting phase transition temperature was observed at ~3.9 K at zero magnetic field. The carrier density of the film is found in the range of Mott transition and superconductivity to metal transition. The effect of magnetic field on the superconductivity of Mg-doped InN film is studied by employing the magnetoresistance and Hall resistance measurement with a typical Hall-bar shape device. The magnetoresistance analysis has been carried out by flux-flow and flux-creep models. The activation energy is found as highly sensitive with field in a range of 0.0 to 1.0 T. The upper critical field at zero temperature and coherence length estimated by Ginzburg–Landau relation were found as around 0.8 T and 216.9 Å, respectively. The superconducting properties of the epitaxial growth Mg-doped InN film are discussed through the manuscript.

Tetramer spin singlet instability in the fluorine-substituted pyrochlore superconducting system Cd2Re2O7−xFx

We synthesized polycrystalline samples of the fluorine-substituted pyrochlore rhenates Cd2Re2O7−xFx, and investigated their magnetic, transport and structural properties. The transition temperature Ts1, where each Re4 tetrahedron in the Re pyrochlore network alternately expands and contracts, decreases with increasing x from 200 K at x = 0 to 100 K at x = 0.5. The strong x dependence of the magnetic and transport properties at the low-temperature phase indicates that the driving force of structural phase transition is fluctuations of the tetramer spin singlet formation in order to release the spin frustration in the pyrochlore lattice. Furthermore, we found unconventional superconducting properties in Cd2Re2O7−xFx. It was found that the superconducting phase transition temperature Tc markedly decreases with increasing x, suggesting that the addition of imperfection suppresses a condensation of Cooper-pair. In addition, the estimated upper critical field at zero temperature exceeds the Pauli paramagnetic limit and increases with increasing x in spite of the reduction of Tc. Hence, Cd2Re2O7−xFx is suggested to be an exotic superconductor realized in the itinerant electron systems on a spin frustrated lattice.

Transport Characteristics of Charge Carriers in Normal State Superconductor YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-<i>δ</i></sub>

The general expressions based on the Fermi distribution of the free charge carriers are applied for estimation of the transport characteristics in superconductors at the temperature well above the superconducting phase transition temperature TC. The Hall-effect experimental results in the normal state of the superconductor YBa2Cu3O7-δ are not finally explained. On the ground of the randomly moving charge carriers, the transport characteristics of the randomly moving charge carriers for both single type and two types of the charge carriers are presented. The particular attention has been pointed to the Hall-effect measurement results of the high-TC superconductor YBa2Cu3O7-δ. It is at the first time derived the Hall coefficient expression for two type of highly degenerate charge carriers (electrons and holes) on the ground of the randomly moving charge carriers at the Fermi surface. It is shown that the Hall coefficient and other transport characteristics are determined by the ratio between the electron-like and hole-like densities of states at the Fermi surface.

On the Boson–Fermion resonant model on a lattice

We review briefly the properties of a mixture of mutually interacting bosons (bound electron pairs) and itinerant fermions on a lattice (the boson–fermion model). The calculations of the superconducting phase transition temperature () and the phase diagram are the main concern. The self-consistent -matrix method is applied to determine the superconducting critical temperature from a pseudogap phase. The method takes into account the pairing fluctuations effects. The -matrix results for are given for a three-dimensional (3-D) cubic lattice with tight-binding dispersion of electrons and standard bosons, and they are also compared with those of the BCS- mean-field approximation. Our results describe the BCS-Bose-Einstein condensation crossover in the boson–fermion mixture with resonant interaction. The energy scales involved in the pseudogap formation are also analysed.

Time-Reversal Symmetry in the Hidden Order and Superconducting States of URu2Si2

The presence of a time-reversal symmetry-breaking field in the hidden order and superconducting states of URu2Si2 has been studied by muon spin relaxation (μSR) spectroscopy. The development of an internal magnetic field has been observed in the hidden order state. Longitudinal-field μSR experiments have shown that the internal magnetic field is static on the time scale of μSR. The presence of both a- and c-axis components of the internal magnetic field at the muon sites was revealed by transverse-field μSR experiments. This is in contrast to the pressure-induced antiferromagnetic state, where the internal magnetic field is parallel to the c-axis. We also found that the muon spin relaxation rate is further enhanced below the superconducting phase transition temperature, indicating further development of the internal magnetic field.

Plasmon-induced transparency in metamaterials: Active near field coupling between bright superconducting and dark metallic mode resonators

Structured plasmonic metamaterial devices offer the design flexibility to be size scaled for operation across the electromagnetic spectrum and are extremely attractive for generating electromagnetically induced transparency and slow-light behaviors via coupling of bright and dark subwavelength resonators. Here, we experimentally demonstrate a thermally active superconductor-metal coupled resonator based hybrid terahertz metamaterial on a sapphire substrate that shows tunable transparency and slow light behavior as the metamaterial chip is cooled below the high-temperature superconducting phase transition temperature. This hybrid metamaterial opens up the avenues for designing micro-sized active circuitry with switching, modulation, and “slowing down terahertz light” capabilities.