Enhanced charge density wave coherence in a light-quenched, high-temperature superconductor
S. Wandel, F. Boschini, E. H. da Silva Neto, L. Shen, M. X. Na, S. Zohar, Y. Wang, S. B. Welch, M. H. Seaberg, J. D. Koralek, G. L. Dakovski, W. Hettel, M-F. Li… 展开作者
S. Wandel, F. Boschini, E. H. da Silva Neto, L. Shen, M. X. Na, S. Zohar, Y. Wang, S. B. Welch, M. H. Seaberg, J. D. Koralek, G. L. Dakovski, W. Hettel, M-F. Lin, S. P. Moeller, W. F. Schlotter, A. H. Reid, M. P. Minitti, T. Boyle, F. He, R. Sutarto, R. Liang, D. Bonn, W. Hardy, R. A. Kaindl, D. G. Hawthorn, J. -S. Lee, A. F. Kemper, A. Damascelli, C. Giannetti, J. J. Turner, G. Coslovich
备注：
Accepted version. 34 pages, 11 figures, Main text and Supplementary Materials
Superconductivity and charge density waves (CDW) are competitive, yet coexisting orders in cuprate superconductors. To understand their microscopic interdependence, a probe capable of discerning their interaction on its natural length and time scales is necessary. We use ultrafast resonant soft x-ray scattering to track the transient evolution of CDW correlations in YBa$_{2}$Cu$_{3}$O$_{6+x}$ following the quench of superconductivity by an infrared laser pulse. We observe a non-thermal response of the CDW order characterized by a near doubling of the correlation length within $\approx$ 1 picosecond of the superconducting quench. Our results are consistent with a model in which the interaction between superconductivity and CDW manifests inhomogeneously through disruption of spatial coherence, with superconductivity playing the dominant role in stabilizing CDW topological defects, such as discommensurations.
We study the Loschmidt echo in the quenched two-dimensional $p$-wave topological superconductor. We find that if this superconductor is quenched out of the critical point separating its topological and non-topological phases into either of the two gapful phases, its Loschmidt echo features singularities occurring periodically in time where the second derivative of the Loschmidt echo over time diverges logarithmically. Conversely, we give arguments towards $s$-wave superconductors not having singularities in their Loschmidt echo regardless of the quench. We also demonstrate that the conventiona…
Within the kinetic energy driven superconducting mechanism, we study the interplay between superconductivity and the nodal and antinodal superconducting quasiparticle coherences in cuprate superconductors, and find the s-wave superconducting transition temperature is heavily suppressed by the antinodal superconducting quasiparticle coherence, while the d-wave superconducting transition temperature is enhanced, therefore the antinodal superconducting quasiparticle coherence plays a more crucial role in superconductivity of cuprate superconductors.
We scrutinize the enhanced superconducting performance of melt quench Bismuth based Bi2Sr2CaCu2O8 (Bi-2212) superconductor. The superconducting properties of melt quenched Bi-2212 (Bi2212-MQ) sample are compared with non-melted Bi2212-NM and Bi1.4Pb0.6Sr2Ca2Cu3O10 (Bi-2223). Crystal structure and morphology of the samples are studied using X-ray diffraction and Scanning Electron Microscopy (SEM) techniques. The high field (14T) magneto-transport and DC/AC magnetic susceptibility techniques are extensively used to study the superconducting properties of the investigated samples. The superconduc…
The suppressed NMR coherence peak in the fullerene superconductors is explained in terms of the dampings in the superconducting state induced by the Coulomb interaction between conduction electrons. The Coulomb interaction, modelled in terms of the onsite Hubbard repulsion, is incorporated into the Eliashberg theory of superconductivity with its frequency dependence considered self-consistently at all temperatures. The vertex correction is also included via the method of Nambu. The frequency dependent Coulomb interaction induces the substantial dampings in the superconducting state and, conseq…
Using small-angle neutron scattering, we have studied the flux-line lattice (FLL) in superconducting CeCoIn5. The FLL is found to undergo a first-order symmetry and reorientation transition at ~0.55 T at 50 mK. The FLL form factor in this material is found to be independent of the applied magnetic field, in striking contrast to the exponential decrease usually observed in superconductors. This result is consistent with a strongly field-dependent coherence length in CeCoIn5, in agreement with recent theoretical predictions for superclean, high-kappa superconductors.
The main purpose of the paper is to discuss a possibility of the determination of the values of the coherence length and the Cooper-pair size in unconventional superconductors by using tunnelling spectroscopy. In the mixed state of type-II superconductors, an applied magnetic field penetrates the superconductor in the form of vortices which form a regular lattice. In unconventional superconductors, the inner structure of a vortex core has a complex structure which is determined by the order parameter of the superconducting state and by the pairing wavefunction of the Cooper pairs. In clean sup…
By performing experiments with thin-film resonators of NbSi, we elucidate a decoherence mechanism at work in disordered superconductors. This decoherence is caused by charged Two Level Systems (TLS) which couple to the conduction electrons in the BCS ground state; it does not involve any out-of-equilibrium quasiparticles, vortices, etc. Standard theories of mesoscopic disordered conductors enable making predictions regarding this mechanism, notably that decoherence should increase as the superconductor cross section decreases. Given the omnipresence of charged TLS in solid-state systems, this …
Recent ARPES experiments show a narrow quasiparticle peak at the gap edge along the antinodal [1,0]-direction for the overdoped cuprate superconductors. We show that within weak coupling BCS theory for a d-wave superconductor the s-wave single-impurity scattering cross section vanishes for energies of the gap edge. This coherence effect occurs through multiple scattering off the impurity. For small impurity concentrations the spectral function has a pronounced increase of the (scattering) lifetime for antinodal quasiparticles but shows a very broad peak in the nodal direction, in qualitative a…
We study macroscopic quantum tunneling of the magnetic moment in a single-domain particle placed above the surface of a superconductor. Such a setup allows one to manipulate the height of the energy barrier, preserving the degeneracy of the ground state. The tunneling amplitude and the effect of the dissipation in the superconductor are computed.
Angle resolved photoemission spectroscopy study is reported on a high quality optimally doped Bi2Sr1.6La0.4CuO6+delta high Tc superconductor. In the antinodal region with maximal d-wave gap, the symbolic superconducting coherence peak, which has been widely observed in multi-CuO2-layer cuprate superconductors, is unambiguously observed in a single layer system. The associated peak-dip separation is just about 19 meV, which is much smaller than its counterparts in multi-layered compounds, but correlates with the energy scales of spin excitations in single layer cuprates.
We study the peculiarities of coherency in a two-gap superconductor. The both intraband couplings, inducing superconductivity in the independent bands, and interband pair-transfer interaction have been taken into account. On the basis of the Ginzburg-Landau equations derived from the Bogoliubov-de Gennes equations and the relevant self-consistency conditions for a two-gap system, we find critical and non-critical coherence lengths in the spatial behaviour of the fluctuations of order parameters. The character of the temperature dependencies of these length scales is determined by the relative …
In this paper we present predictions for thermodynamic and transport properties of a BCS Bose-Einstein crossover theory, below Tc, which theory satisfies the reasonable constraints that it yield (i) the Leggett ground state and (ii) BCS theory at weak coupling and all temperatures. The nature of the strong coupling limit is inferred, along with the behavior of the Knight shift, superfluid density, and specific heat. Comparisons with existing data on short coherence length superconductors, such as organic and high Tc systems, are presented, which provide some support for the present picture.
We investigate the role of disorder on the superconducting (SC) fluctuation in short coherence length d-wave superconductors. The particular intetest is focused on the disorder-induced microscopic inhomogeneity of SC fluctuation and its effect on the pseudogap phenomena. We formulate the self-consistent 1-loop order theory for the SC fluctuation in inhomogeneous systems and analyze the disordered $t$-$t'$-$V$ model. The SC correlation function, electronic DOS and the critical temperature are estimated. The SC fluctuation is localized like a nanoscale granular structure when the coherence lengt…
\begin{abstract} We have studied magnetic properties of water-quenched 5 wt.% (Fe, Ti) particle-doped MgB$_2$ comparing with that of air-cooled one. Generally, grain refinement is achieved by increasing cooling rate, which implies an increase of grainboundaries in the superconductor. Here we show that increased grainboundaries influence what kinds of effects on the field dependence of magnetization and what is the mechanism. As a result, they are served as a pinning center at a high field whereas they are served as a pathway to facilitate the movement of fluxes pinned on volume defects at a lo…
The nematic electronic state and its associated nematic critical fluctuations have emerged as potential candidates for superconducting pairing in various unconventional superconductors. However, in most materials their coexistence with other magnetically-ordered phases poses significant challenges in establishing their importance. Here, by combining chemical and hydrostatic physical pressure in FeSe$_{0.89}$S$_{0.11}$, we provide a unique access to a clean nematic quantum phase transition in the absence of a long-range magnetic order. We find that in the proximity of the nematic phase transiti…
Emergent quantum phenomena via phase-coherence engineering in infinite-layer nickelate superconductors
Peking University（北京大学）；University of Electronic Science and Technology of China（电子科技大学）；Renmin University of China（中国人民大学）；ShanghaiTech University（上海科技大学）；Tsinghua University（清华大学）；Institute of Physics Chinese Academy of Sciences（中国科学院物理研究所）；University of Chinese Academy of Sciences（中国科学院大学）；Songshan Lake Materials Laboratory（松山湖材料实验室）；Beijing Normal University（北京师范大学）；Fudan University（复旦大学）；Hefei National Laboratory（合肥国家实验室）
We study the superconducting transition in the attractive Hubbard model in two dimensions using the self-consistent $T$-matrix approximation. We demonstrate that for large system sizes, this approximate method produces XY critical scaling in the correlation length and pair susceptibility. For the parameters we investigate, the critical regime is quite large, extending beyond 5 times $\TKTB$. We discuss the role of vortex-pair unbinding in the normal state in the context of pseudogap behaviour and the relevance to the physics of underdoped cuprates.
Assuming the exchange of antiferromagnetic spin fluctuations as the Cooper pairing mechanism we calculate the doping dependence of the resonance peak seen in inelastic neutron scattering and the magnetic coherence effect. Most importantly, we find that the resonance peak in the magnetic susceptibility, ${Im}χ({\bf q},ω)$, appears {\it only} in the superconducting state, that it scales with $T_c$, and that magnetic coherence is a result of a d-wave order parameter. We further analyze the structure of ${Im}χ$ below $T_c$, the position of the peak at $ω_{res}$ and the consequences for photoemissi…
Higgs oscillations in nonequilibrium superconductors provide an unique tool to obtain information about the underlying order parameter. Several properties like the absolute value, existence of multiple gaps and the symmetry of the order parameter can be encoded in the Higgs oscillation spectrum. Studying Higgs oscillations with time-resolved angle-resolved photoemission spectroscopy (ARPES) has the advantage over optical measurements that a momentum-resolved analysis of the condensate dynamic is possible. In this paper, we investigate the time-resolved spectral function measured in ARPES for d…
We derive an appropriate Landau-Ginzburg-Wilson effective action to describe the nearest neighbour attractive Hubbard model. This allows us to discuss both the small V (BCS) limit and the large V (Bose-Einstein) limit within the same framework. The model is particularly interesting as it exhibits both extended s-wave and d-wave solutions as well as an intermediate s+id phase and an unstable p-wave phase. We note that in the large V limit, as pairs become localised on bonds, the s- and d-wave solutions become degenerate.
It has recently been established that the high temperature (high-Tc) superconducting state coexists with short-range charge-density-wave order and quenched disorder arising from dopants and strain. This complex, multiscale phase separation invites the development of theories of high temperature superconductivity that include complexity. The nature of the spatial interplay between charge and dopant order that provides a basis for nanoscale phase separation remains a key open question, because experiments have yet to probe the unknown spatial distribution at both the nanoscale and mescoscale (be…
Peaks in the magnetoresistivity of the layered superconductor $κ$-(BEDT-TTF)$_2$Cu(NCS)$_2$, measured in fields $\leq 45$ T applied within the layers, show that the Fermi surface is extended in the interlayer direction and enable the interlayer transfer integral ($t_{\perp} \approx 0.04$ meV) to be deduced. However, the quasiparticle scattering rate $τ^{-1}$ is such that $\hbar/τ\sim 6t_{\perp}$, implying that $κ$-(BEDT-TTF)$_2$Cu(NCS)$_2$ meets the criterion used to identify interlayer incoherence. The applicability of this criterion to anisotropic materials is thus shown to be questionable.
We study theoretically the coexistence of the spin-density-wave (SDW) and superconductivity in electron-doped iron-pnictide superconductors based on the two orbital model and Bogoliubov-de Gennes equations. The phase diagram is mapped out and the evolution of the Fermi surface as the doping varies is presented. The local density of states (LDOS) has also been calculated from low to high doping. We show that the strength of the superconducting coherent peak at the positive energy gets enhanced and the one at the negative energy is suppressed by the SDW order in the underdoped region. Several fe…
Based on the London equation, we use a rotor-free vector potential ${\bf A}$, and current measurements by a SQUID, to determine the superconducting Pearl length $Λ$, and coherence length $ξ$, of ultra-thin, ring shaped, MoSi films, as a function of thickness $d$ and temperature $T$. We find that $ξ$ is a function of $d$ with a jump at $ξ\sim d \sim 5$nm. At base temperature the superconducting stiffness, defined by $1/λ^2=1/(Λd)$, is an increasing function of $T_c$. Similar behavior, known as the Uemura plot, exist in bulk layered superconductors, but with doping as an implicit parameter. We a…
The interlayer magnetoresistance $ρ_{zz}$ of the organic metal \cuscn is studied in fields of up to 45 T and at temperatures $T$ from 0.5 K to 30 K. The peak in $ρ_{zz}$ seen in in-plane fields, a definitive signature of interlayer coherence, remains to $T$s exceeding the Anderson criterion for incoherent transport by a factor $\sim 30$. Angle-dependent magnetoresistance oscillations are modeled using an approach based on field-induced quasiparticle paths on a 3D Fermi surface, to yield the $T$ dependence of the scattering rate $τ^{-1}$. The results suggest that $τ^{-1}$ does not vary strongly…
For unconventional heavy Fermion superconductors, typified by UBe_13, the superconducting transition temperatures Tc are shown to correlate with a characteristic energy hbar^2 /(m* xi^2), m* being the effective mass and xi the coherence length. For four of the six materials for which Tc, m* and xi are available, kB Tc ~ 20 hbar^2 / (m* xi^2). One heavy Fermion material, UPd_2Al_3, reveals a tendency for the above linear behaviour to saturate at substantially larger hbar^2 / (m* xi^2) than for UBe_13. The sixth material considered, URu_2Si_2, falls between UBe_13 and UPd_2Al_3. To embrace d-wav…
It is usually believed that a coherence peak just below T$_{c}$ in the nuclear spin lattice relaxation rate T$_{1}^{-1}$ in superconducting materials is a signature of conventional s-wave pairing. In this paper we demonstrate that any unconventional superconductor obeying BCS pure-case weak-coupling theory should show a small T$_{1}^{-1}$ coherence peak near T$_{c}$, generally with a height between 3 and 15 percent greater than the normal state T$_{1}^{-1}$ at T$_{c}$. It is largely due to impurity effects that this peak has not commonly been observed.
Recent inelastic neutron scattering (INS) experiments on La$_{2-x}$Sr$_x$CuO$_4$ have established the existence of a {\it magnetic coherence effect}, i.e., strong frequency and momentum dependent changes of the spin susceptibility, $χ''$, in the superconducting phase. We show, using the spin-fermion model for incommensurate antiferromagnetic spin fluctuations, that the magnetic coherence effect establishes the ability of INS experiments to probe the electronic spectrum of the cuprates, in that the effect arises from the interplay of an incommensurate magnetic response, the form of the underlyi…
High-temperature superconductivity in iron-based layered compounds discovered by Hosono group (Kamihara et al 2006 J. Am. Chem. Soc. 128 10012) is fascinating physical phenomenon which still has many unanswered questions. One of these questions is the superconducting gap symmetry in iron-based superconductors (IBS), for which the most agreed concept is multiple-band $s$-wave symmetry. Recently, an alternative concept of single-band $p$-wave symmetry has been proposed. To disprove/reaffirm the latter concept, in this paper we analyse temperature dependent in-plane coherence length in FeSe, FeSe…
Recent inelastic neutron scattering (INS) experiments on La$_{2-x}$Sr$_x$CuO$_4$ observed a {\it magnetic coherence effect}, i.e., strong frequency and momentum dependent changes of the spin susceptibility, $χ''$, in the superconducting phase. We show that this effect is a direct consequence of changes in the damping of incommensurate antiferromagnetic spin fluctuations due to the appearance of a d-wave gap in the fermionic spectrum. Our theoretical results provide a quantitative explanation for the weak momentum dependence of the observed spin-gap. Moreover, we predict {\bf (a)} a Fermi surfa…
We study the effects of quenched disorder on the two-dimensional d-wave superconductors (SC's) at zero temperature by Monte-Carlo simulations. The model is defined on the three-dimesional (3D) lattice and the SC pair field is put on each spatial link as motivated in the resonating-valence-bond theory of the high-$T_{\rm c}$ SC's. For the nonrandom case, the model exhibits a second-order phase transition to a SC state as density of charge carriers is increased. It belongs to the universality class {\it different from} that of the 3D XY model. Quenched disorders (impurities) are introduced both …
We report on the measurement of atomic spin coherence near the surface of a superconducting niobium wire. As compared to normal conducting metal surfaces, the atomic spin coherence is maintained for time periods beyond the Johnson noise limit. The result provides experimental evidence that magnetic near field noise near the superconductor is strongly suppressed. Such long atomic spin coherence times near superconductors open the way towards the development of coherently coupled cold atom / solid state hybrid quantum systems with potential applications in quantum information processing and prec…
We show that an array of Josephson coupled Cooper paired planes can never have long range phase coherence at any finite temperature due to an infrared divergence of phase fluctuations. The phase correlations decay in a slow enough manner providing enough local phase coherence as to make possible the nucleation of vortices. The planes then acquire Kosterlitz-Thouless topological order with its intrinsic rigidity and concomitant superfluidity. We thus conclude that the high temperature superconducting cuprates are topologically ordered superconductors rather than phase ordered superconductors. F…
We investigate the impurity scattering rates for quasi-particles in vortex cores of sign-reversing s-wave superconductors as a probe to detect the internal phase difference of the order parameters among different Fermi surfaces. The impurity scattering rates and coherence factors are related to quasiparticle interference effect by the scanning tunneling microscopy and spectroscopy technique. With use of the Born and Kramer-Pesch approximations for the Andreev bound states, we show that the sign-reversed forward scatterings are dominant in vortex cores. Owing to the coherence factor in vortex c…
Field and temperature microwave measurements have been carried out on MgB2 thin film grown on Al2O3 substrate. The analysis reveals the mean field coherence length xi_{MF} in the mixed state and a temperature independent anisotropy ratio gamma_{MF} = xi_{MF}^{ab} / xi_{MF}^c approximately 2. At the superconducting transition, the scaling of the fluctuation conductivity yields the Ginzburg-Landau coherence length with a different anisotropy ratio gamma_{GL} = 2.8, also temperature independent.
We consider the real part of the conductivity, σ_1(ω), arising from classical phase fluctuations in a model for high-T_c superconductors. We show that the frequency integral of that conductivity, \int_0^\infty σ_1 dω, is non-zero below the superconducting transition temperature $T_c$, provided there is some quenched disorder in the system. Furthermore, for a fixed amount of quenched disorder, this integral at low temperatures is proportional to the zero-temperature superfluid density, in agreement with experiment. We calculate σ_1(ω) explicitly for a model of overdamped phase fluctuations.
The superfluid density is calculated theoretically for incompressible vortex lattices in two dimensions that have isolated dislocations quenched in by a random arrangement of pinned vortices. The latter are assumed to be sparse and to be fixed to material defects. It is shown that the pinned vortices act to confine a single dislocation of the vortex lattice along its glide plane. Plastic creep of the two-dimensional vortex lattice is thereby impeded, and macroscopic phase coherence results at low temperature in the limit of a dilute concentration of quenched-in dislocations.
Coherence effects by the impurity scattering of Caroli--de Gennes--Matricon (CdGM) modes in a vortex for nodal topological superconductors have been studied. The coherence effects reflect a topological number defined on a particular momentum space avoiding the superconducting gap nodes. First, we analytically derived the eigenvalue and eigenfunction of the CdGM modes, including the zero-energy modes, in a nodal topological superconducting state without impurities, where we focused on a possible superconducting state of UPt$_3$ as an example. Then, we studied impurity effects on the CdGM modes …
Miniature Hall-probe arrays were used to measure the critical current densities for the three main directions of vortex motion in the stoichiometric LiFeAs superconductor. These correspond to vortices oriented along the c-axis moving parallel to the ab-plane, and to vortices in the ab-plane moving perpendicular to, and within the plane, respectively. The measurements were carried out in the low-field regime of strong vortex pinning, in which the critical current anisotropy is solely determined by the coherence length anisotropy parameter, ε_ξ. This allows extraction of ε_ξ at magnetic fields f…
A classical SU(2) Einstein-Yang-Mills theory in 3+1 dimensional anti-de Sitter spacetime is believed to be dual to a p-wave superconductor in 2+1 dimensional flat spacetime. In order to calculate the superconductiong coherence length $ξ$ of the holographic superconductor near the superconducting phase transition point, we study the perturbation of the gravity theory analytically. The superconductiong coherence length $ξ$ is found to be proportional to $(1-T/T_c)^{-1/2}$ near the critical temperature $T_c$. We also obtain the magnetic penetration depth $λ\propto(T_c-T)^{1/2}$ by adding a small …
The loss of single-particle coherence going from the superconducting state to the normal state in underdoped cuprates is a dramatic effect that has yet to be understood. Here, we address this issue by performing angle resolved photoemission spectroscopy (ARPES) measurements in the presence of a transport current. We find that the loss of coherence is associated with the development of an onset in the resistance, in that well before the midpoint of the transition is reached, the sharp peaks in the ARPES spectra are completely suppressed. Since the resistance onset is a signature of phase fluctu…
A characteristic feature of the BCS theory of superconductivity is the quantum-mechanical coherence of particle and hole states. Direct observation of particle-hole coherence in unusual superconducting materials is a strong indication of traditional superconductivity. We use the Fermi liquid theory of superconductivity to study the implications of particle-hole coherence on properties of d-wave superconductors near surfaces. Typical surface phenomena are the suppression of the superconducting order parameter, surface bound states associated with Andreev reflection, anomalous screening currents…
High temperature superconductivity is a property of doped antiferromagnetic insulators. The electronic structure is inhomogeneous on short length and time scales, and, as the temperature decreases, it evolves via two crossovers, before long range superconducting order is achieved. Except for overdoped materials, pairing and phase coherence occur at different temperatures, and phase fluctuations determine both T$_c$ and the temperature dependence of the superfluid density for a wide range of doping. A mechanism for obtaining a high pairing scale in a short coherence length material with a stron…
Results of low-temperature upper critical field measurements for Nd$_{2-x}$Ce$_x$CuO$_{4+δ}$ single crystals with various $x$ and nonstoichiometric disorder ($δ$) are presented. The coherence length of pair correlation $ξ$ and the product $k_F$$ξ$, where $k_F$ is the Fermi wave vector, are estimated. It is shown that for investigated single crystals parameter $k_F$$ξ$ $\cong$ 100 and thus phenomenologically NdCeCuO - system is in a range of Cooper-pair-based (BCS) superconductivity.
The correlations of the electrons field-emitted from a superconductor are fully analyzed, both in space and time. It is proposed that a coincidence experiment would reveal a positive correlation between the electrons emitted in opposite directions. The electrons can be entangled and can even violate Bell's inequality. The crucial role played by Andreev's process is scrutinized, analytical formulas are derived for the correlations, and the physics behind the phenomenon is clarified.
We present NMR measurements of the layered nitride superconductor Li_xZrNCl. The nuclear spin-lattice relaxation rate, 1/T_1, shows that the coherence peak is strongly suppressed in Li_xZrNCl in contrast to conventional BCS superconductors. In the lightly-doped region close to the insulating state, the system shows a gap-like behavior, i.e., pseudogap, that is characterized by a reduction in the magnitude of the Knight shift and 1/T_1T. A higher superconducting (SC) transition temperature, T_c, is achieved by coexisting with the pseudogap state. These unusual behaviors, which deviate from the …
Spin/magnetisation relaxation and coherence times, respectively T_1 and T_2, initially defined in the context of nuclear magnetic resonance (NMR), are general concepts applicable to a wide range of systems, including quantum bits [1-4]. At first glance, these ideas might seem to be irrelevant to conventional Bardeen-Cooper-Schrieffer (BCS) superconductors, as the BCS superconducting ground state is a condensate of Cooper pairs of electrons with opposite spins (in a singlet state) [5]. It has recently been demonstrated, however, that a non-equilibrium magnetisation can appear in the quasipartic…
A notable aspect of high-temperature superconductivity in the copper oxides is the unconventional nature of the underlying paired-electron state. A direct manifestation of the unconventional state is a pairing energy - that is, the energy required to remove one electron from the superconductor - that varies (between zero and a maximum value) as a function of momentum or wavevector: the pairing energy for conventional superconductors is wavevector-independent. The wavefunction describing the superconducting state will include not only the pairing of charges, but also of the spins of the paired …
We present synthesis and $^{75}$As-nuclear quadrupole resonance (NQR) measurements for the noncentrosymmetric superconductor CaPtAs with a superconducting transition temperature $T_c$ of $\sim 1.5$ K. We discovered two different forms of CaPtAs during synthesis; one is a high-temperature tetragonal form that was previously reported, and the other is a low-temperature form consistent with the orthorhombic structure of CaPtP. According to the $^{75}$As-NQR measurement for superconducting tetragonal CaPtAs, the nuclear spin-lattice relaxation rate $1/T_1$ has an obvious coherence peak below $T_c$…
We show that in superconductors that break time reversal symmetry and have anisotropy, such as p+ip materials, all order parameters and magnetic modes are mixed. Excitation of the gap fields produces an excitation of the magnetic field and vice versa. Correspondingly the long-range decay of the magnetic field and order parameter are in general given by the same exponent. Thus one cannot characterize p+ip superconductors by the usual coherence and magnetic field penetration lengths. Instead the system has normal modes that are associated with linear combinations of magnetic fields, moduli of an…
After decades of explorations, suffering from low critical temperature and subtle nature, whether a metallic ground state exists in a two-dimensional system beyond Anderson localization is still a mystery. Supremely, phase coherence could be the key that unlocks its intriguing nature. This work reveals how quantum phase coherence evolves across bosonic superconductor-metal-insulator transitions via magneto-conductance quantum oscillations in high-Tc superconducting films. A robust intervening anomalous metallic state characterized by both resistance and oscillation amplitude saturations in the…
We report measurements of the Nernst effect and of the magneto-resistance of granular aluminum films near the metal to insulator transition. These films show sharp transitions as a function of temperature and magnetic field. At low temperatures the Nernst signal displays a sharp peak at a field where more than 90% of the normal state resistance has been restored, suggesting a transition involving entropy transport after superconducting coherence has been destroyed. At temperatures higher than the critical temperature the fluctuation paraconductivity scales with the Nernst signal, in agreement …
Using resistivity, heat-capacity, thermal-expansion, and susceptibility measurements we study the normal-state behavior of KFe2As2. We find that both the Sommerfeld coefficient gamma = 103 mJ mol-1 K-2 and the Pauli susceptibility chi = 4x10-4 are strongly enhanced, which confirm the existence of heavy quasiparticles inferred from previous de Haas-van Alphen and ARPES experiments. We discuss this large enhancement using a Gutzwiller slave-boson mean-field calculation, which reveals the proximity of KFe2As2 to an orbital-selective Mott transition. The temperature dependence of the magnetic susc…
