47,878 papers in this slice of arXiv.
Werner M. J. van Weerdenburg, Margarete Huisinga, Constantin Flommersfeld +2
The interplay between multiple quantum phases in layered materials may lead to incipient quantum behavior, where the material's ground state is close to a phase transition and sensitive to local disorder. The transition metal dichalcogenide material
Wen-Bo Dai, Ming Gong, Xianxin Wu +2
Identifying the pairing symmetry of Cooper pairs is a fundamental step toward understanding the microscopic mechanisms of unconventional superconductors. However, experimental identification remains a formidable challenge, particularly when unconventional pairing is obscured by a dominant s-wave component that masks its spectroscopic signatures. Here, we develop a symmetry-resolved framework to identify superconducting pairing symmetry through nonreciprocal conductance upon exchanging source and detector terminals in multiterminal devices. We show that nonreciprocal transport arises from symmetry-breaking components of the superconducting order parameter and exhibits a characteristic angular dependence that encodes the momentum-space structure of the pairing gap. In particular, time-reversal-breaking singlet pairing induces nonreciprocal charge transport, while spin-triplet pairing generates nonreciprocal spin responses, providing distinct transport fingerprints of the underlying order. We demonstrate this mechanism using representative models of iron-based and noncentrosymmetric superconductors and outline experimental protocols for multiterminal measurements. Our results advance the theoretical understanding of nonreciprocal transport in superconductors, and establish it as a symmetry-selective probe for identifying hidden unconventional pairing in a wide range of superconducting materials.
Karyn Le Hur, Kabir Narayanan, Óscar Mañas Chambert
We present an analysis on the geometrical and physical nature of the px+ipy superconductor on the square lattice, with an emphasis on the topological phase transition at half-filling. We develop a local topological marker from specific Dirac points within the Brillouin zone, which is introduced via the addition of two one-dimensional (1D) Z (Z2
Dongfei Wang, Wenbin Li, Eric Mascot +1
Engineered magnet-superconductor hybrids have recently been identified as promising platforms for the investigation of topological superconductivity. Beyond ferro- and antiferromagnetic structures, coupling non-collinear spin textures, such as skyrmion lattices, to superconductors offers an exciting route for creating and manipulating unconventional superconducting states. In this work, by preparing monolayer Fe on Ir(111) thin films grown epitaxially on a Nb(110) surface, we realize a hybrid system of a nano-skyrmion lattice proximitized to a superconducting substrate. Scanning tunneling spectroscopy shows that superconductivity becomes suppressed by the Fe nano-skyrmion lattice, with both the superconducting gap and coherence peaks disappearing. Tight-binding calculations reveal that with increasing exchange coupling, the gap is progressively filled up and eventually superconductivity gets quenched. These results reveal microscopic constraints for designing topologically non-trivial states based on magnet-superconducting heterostructures.
Zhihong Yuan, Rui Liu, Pengyu Zheng +1
Using first-principles calculations, we predict a new perovskite compound SrAsO3 . The undoped cubic phase has pronounced soft-phonon instabilities, which are gradually suppressed upon K doping the Sr site. The cubic phase becomes dynamically stable for K-doping levels above approximately 60%, and the stabilized K-doped phases are metallic with predicted conventional phonon mediated superconductivity. Moreover, the inclusion of nonlocal exchange interactions broadens the electronic bandwidth, enhances the electron-phonon coupling (EPC) strength, and increases the superconducting transition temperature (Tc) of these doped compounds. In particular, the HSE06 hybrid exchange-correlation functional corrected EPC constant λ
Yijie Mo, Zhongbo Yan
We uncover a universal mechanism for realizing layer-locked topological phases. Guided by it, we investigate the realization of layer-locked chiral topological superconductivity-the superconducting analogue of the quantum anomalous layer Hall effect-in a nonsymmorphic bilayer antiferromagnetic system with s-wave pairing. We identify three distinct gate-tunable topological phases and establish a direct correspondence between the nearly quantized layer-resolved Chern numbers and the layer-locking behavior of chiral Majorana edge states, vortex-core Majorana zero modes, and nearly quantized thermal Hall responses.
Yasutami Takada
Understanding how superconductivity can emerge in dilute electronic systems remains a central challenge in condensed matter physics. By performing first-principles calculations of the electron self-energy Σ(k,iw_n) in the low-density three-dimensional electron gas, we identify a sharp divergence at r_s ~ 8 and T ~ 10^{-4}E_ F, signaling a second-order phase transition. This critical behavior originates from one-dimensional superconducting fluctuations mediated by virtual excitations of an excitron---a quasi-1D electronic composite formed by an electron and longitudinal electron-hole pairs. Although the superconducting mechanism itself is plasmon-mediated, the excitron channel provides a unique window into its fluctuation dynamics. Near the transition, we observe a pseudogap and a linear-in-T inverse electron lifetime, reminiscent of phenomena in high-T_c materials. These results reveal an unexpected route by which plasmon-driven superconductivity manifests in the dilute 3D electron gas through quasi-1D excitron dynamics.
Zhong C. F. Li, Yuxuan Deng, Dmitri K. Efetov +1
In well-established theories of Josephson junctions, the superconducting critical current Ic increases as the normal state conductance G increases. However, in a recent experiment in twisted bilayer graphene (TBG) based Josephson junctions, unexpectedly, it was observed that the increase of the critical current is accompanied by a decrease of the normal state conductance. We call this phenomenon the critical current anomaly. In this work, we point out that in the TBG-based Josephson junction, due to the suppression of the conventional Josephson current by the flatness of the band and the quantum metric enabled Josephson current (QMJC), the critical current anomaly can occur. The QMJC appears if the quantum metric length is comparable or longer than the junction length. We show that both G and Ic have the conventional and the quantum metric contributions, and there are parameter regimes in which Ic increases even when G decreases. We first demonstrate the critical current anomaly by a simple modified Lieb-lattice model both analytically and numerically. The incredible consistency with the experimental results is demonstrated using a realistic six-band model of twisted bilayer graphene. Therefore, we suggest that the critical current anomaly observed in the experiment provide strong evidence of QMJC which were ignored in well-established theories of Josephson junctions.
Priya Singh, Konrad Kwatek, Tatiana Zajarniuk +3
Motivated by recent reports of enhanced superconducting performance in several families of iron-based superconductors (IBS) processed by high-pressure (HP) synthesis, we investigate the influence of high gas pressure and high-temperature synthesis (HP-HTS) process on the structural, microstructural, electrical transport, and magnetic properties of Pr-based oxypnictide PrFeAsO1-xFx (Pr1111) using the processing conditions of 0.5 GPa for 1 h previously optimized for other IBS families. Representative underdoped (x = 0.2), optimal doped (x = 0.3), and overdoped (x = 0.5) compositions from the ambient-pressure electronic phase diagram of Pr1111 are selected to evaluate its composition-dependent effects of HP-HTS. The results demonstrate that HP-HTS enhances fluorine incorporation, improves phase formation, and produces a denser microstructure with improved grain connectivity in the underdoped and optimal doped compositions. Magnetic measurements reveal increased in the superconducting transition temperature (Tc) of ~1 K for x = 0.2 and ~6 K for x = 0.3, whereas only a marginal improvement in the critical current density is observed. Electrical resistivity measurements of the underdoped composition show a slight increase in Tc accompanied by a broader resistive transition, indicating residual structural inhomogeneity. In contrast, the overdoped composition exhibits increased impurity phase segregation, accompanied by suppression of superconductivity. These results demonstrate that the effectiveness of HP-HTS in Pr1111 is strongly composition dependent and governed by the interplay among fluorine incorporation, phase stability, and microstructural evolution, highlighting the need for further optimization of the HP-HTS processing conditions.
Irina Abaloszewa, Victor V. Chabanenko, Aleksander Abaloszew
Thermomagnetic avalanches in type-II superconductors occur in two qualitatively different regimes, electromagnetically controlled in thin films and thermally limited in bulk samples, distinguished by the sign of the temperature derivative of the threshold field Hth(T). The two regimes are separated by a critical thermal boundary conductance hc, and a non-monotonic Hth(T) has been predicted in the transitional region where the interface conductance h approaches hc. We approach this region in a bulk NbTi disk by raising the interface coupling above the pure-nonadecane baseline with a silver-filled interface layer. Whereas the pure interface gives a monotonically decreasing Hth(T), the silver-filled interface produces a non-monotonic dependence not previously realized in a bulk superconductor: a temperature interval of positive slope, dHth/dT>0, terminating in a maximum at T∗≈6.1--6.4 K. The effect is reproduced for two independent silver-filled compositions; in a third, with the highest loading, the low-temperature decrease is absent altogether and Hth(T) is flat up to the same T∗, the evolution expected for stronger coupling. The position of the maximum is set by the intrinsic properties of NbTi, independent of the silver content. The onset of the positive-slope interval coincides in temperature with a change of the avalanche morphology from narrow channeled fingers to broad fronts. The reversal of the sign of dHth/dT is a direct experimental signature of the onset of the transitional regime, in which heat removal during the instability becomes dynamically relevant.
Xu-Cheng Wang, Yang Qi
Preformed pairs and phase fluctuations are believed to play a vital role in predicting the charge pseudogap in the normal state of two-dimensional superconductors. In this work, we extend this idea and further identify the emergent magnetic pseudogap from pure phase fluctuations without invoking any competing order. We examine the NMR relaxation rate 1/T1T by evaluating the bubble contribution and leading-order vertex correction within perturbation theory. It is found that the magnetic pseudogap, manifesting as a smooth suppression of 1/T1T in the normal state, is characterized by a temperature scale TmPG distinct from the superconducting gap ΔSC and transition temperature Tc. The onset scales of both charge and magnetic pseudogap are dominated by the competition of BKT correlation length ξ(T) and BCS coherence length ξBCS. Moreover, the vertex correction is shown to be irrelevant for d-wave pairing, while it becomes prominent in s-wave systems and drives a coherent enhancement of 1/T1T at lower temperatures just above Tc. We attribute this normal-state enhancement of 1/T1T to the diverging coherence peak at the s-wave superconducting gap edge, which shares the same spirit as the celebrated Hebel-Slichter peak in the BCS theory. Analogous to the coherent Hebel-Slichter peak, regularization by Fermi-liquid-like scatterings is important and is characterized by a scattering length ℓ. The normal-state coherent enhancement of 1/T1T is hence described by the competition of ξ(T) and ℓ, through which the coherence scale Tcoh is determined. As a result, the complete evolution of 1/T1T is understood quantitatively in a unified picture as the interplay among hierarchy of scales ξ(T), ξBCS and ℓ.
Luis Filsinger, Roland Willa
In numerous physical, chemical, and biological systems the dynamics can be reduced to the motion of state variables in a complex potential landscape. In case the manifold is known, the motion and response of the embedded object can be described deterministically up to stochastic effects usually associated with a noise. In contrast, if the manifold is unknown, the static and dynamic response of the state variable may be used as a spectroscopic tool to characterize the potential landscape. Inspired by a seminal work of L.\ Embon and co-workers, [Sci.\ Rep.\ 5, 7598 (2015)] we investigate the statistical properties of potential minima, in particular, their stability to thermal and quantum activation. For Gaussian random manifolds, we derive an algebraic expression to evaluate the statistical probability of the potential character (value, slope, curvature, ...). With this tool, we compute the expectation value for the rate of thermal and quantum activation and link these findings to the principal characteristics of the Gaussian potential, i.e., its Green's function. This link provides the opportunity to access information on the potential's Green's function by studying the activation behavior of an object in this manifold.
Alexander Weitzel, Lea Pfaffinger, Animesh Panda +8
Theory predicts the superconductor-to-insulator transition (SIT) to emerge from the competition between Anderson localization, which tends to localize single-particle wavefunctions, and superconductivity, which establishes long-range correlations in the superconducting order parameter. In two-dimensional (2D) superconducting films, the transition temperature Tc at which resistance vanishes, R□(TBKT)=0, is set by the Berezinskii-Kosterlitz-Thouless (BKT) mechanism and satisfies TBKT<Tc0, where Tc0 is the mean-field transition temperature. In weakly disordered samples TBKT≲Tc0, whereas increasing disorder drives TBKT≪Tc0 near the SIT. Whether the finite-temperature transition retains its BKT character throughout this crossover remains an open question. Here, we investigate the evolution of both sheet resistance R□(T) and superfluid stiffness Js(T) over a wide range of disorder strength W. We establish that even near the SIT, the finite-temperature transition from the superconducting to the resistive state remains of BKT type. However, as disorder approaches the critical value, the zero temperature superfluid phase stiffness, Js(0), is found to vanish rapidly while Tc0 remains finite, which we attribute to quantum phase fluctuations as the drive for the zero-temperature transition. Three decades after its experimental discovery by Haviland, Liu, and Goldman, our measurements clarify the origin of the SIT in 2D films.
Kenjiro Okawa, Takao Sasagawa
We systematically investigated the magnetoresistance ratio (MR) of single-crystalline, nonmagnetic layered Pd-based metals, including centrosymmetric PdTe2, PdPb2, and beta-PdBi2 and noncentrosymmetric alpha-PdBi. Our study identifies a distinct class of large MR in multiband, high-carrier-density systems. Unlike well-studied extremely large MR materials, such as Dirac and Weyl semimetals described by simple compensated-carrier models, these compounds possess complex Fermi surfaces, as validated by our first-principles calculations. Nevertheless, they exhibit a remarkably simple MR scaling governed by carrier mobility, manifested in systematic dependencies on magnetic field, temperature, and the residual resistivity ratio (RRR). The validity of Kohler's rule in high-RRR crystals indicates that MR is governed by a single effective scattering time, even in these multiband systems. The field and RRR dependences of MR follow an intermediate power-law behavior between linear and quadratic, attributable to imperfect carrier compensation and a distribution of carrier mobilities. Among the studied compounds, alpha-PdBi exhibits the largest MR, reaching 1500% (2 K, 7 T), owing to its exceptionally high RRR (approximately 660). However, when compared on an equal-RRR basis, its MR is smaller than that of its centrosymmetric counterparts. This trend suggests that additional scattering channels arising from spin-orbit-induced band splitting in noncentrosymmetric systems reduce the effective carrier mobility. Our results establish a new class of large MR in clean multiband metals where complex electronic structures give rise to emergent single-parameter scaling, highlighting the interplay between disorder, mobility, and symmetry.
S. I. Bondarenko, A. A. Prokhorov, N. N. Galtsov +3
Using an EPR spectrometer, the properties of single-crystal FeSe were studied in a magnetic field up to 6000 Oe at temperatures from 3.5 K to 8 K in the superconducting state and at temperatures above 8K and up to 25K in the normal state. It was shown that by measuring non-resonant spectrometer signals in zero and weak magnetic fields up to 30 Oe, it is possible to determine critical temperature Tc, the superconducting transition width, and the value of the first critical magnetic field Hc1 in FeSe single-crystal. Resonant EPR signals are observed in fields at 1400 Oe and 3400 Oe, which corresponds to the paramagnetism of doubly ionized iron atoms (Fe2+) in the FeSe crystal. Non-resonant EPR signals in a magnetic field up to 6000 Oe at temperatures from 3.5K to 8K are a nonlinear function of the field, and correspond to the superconducting mixed state of the FeSe, but at temperatures above 8K (up to 25K) they are field independent.
Pim H. Vree, Merel A. Bouma, Michael Borst +3
Spin waves are promising signal carriers for microwave control at the micrometer scale. However, realizing low-damping, tunable control of spin-wave propagation remains a central challenge. Here we use magnetic shielding by superconducting control elements to tune the local spin-wave dispersion and realize temperature-controlled refraction of spin waves in a thin-film magnetic insulator. Using magnetic imaging based on spins in diamond, we characterize the refractive index and demonstrate both positive and negative refraction as well as wavefront shaping by the superconductors. The observed refraction is explained by a geometrical analysis of the superconductivity-induced modification of the hyperbolic spin-wave dispersion. Our results demonstrate that superconductors enable tunable spin-wave optical elements, opening new opportunities for microwave control in classical or quantum information devices.
S. Feyrer, V. Dimic, I. Lobato +15
We investigate the microwave electrodynamics of a proximitized two-dimensional electron gas in hybrid superconductor/semiconductor heterostructures. Using lumped-element resonators with inductor wires oriented relative to an in-plane magnetic field, we directly probe the superfluid stiffness via the kinetic inductance. As the field increases, the resonance frequency exhibits a non-monotonic and strongly anisotropic evolution that cannot be explained by orbital pair breaking alone. We show that this behavior is consistent with the emergence of Bogoliubov Fermi surfaces, which selectively suppress the supercurrent response depending on the direction of the magnetic field. Microscopic calculations of the stiffness tensor capture the observed anisotropy driven by the interplay of Zeeman and orbital Fulde-Ferrell effects. Our results establish microwave stiffness measurements as a sensitive probe of anisotropic gapless superconductivity in hybrid systems.
Tomas T. Osterholt, Thijs van der Meer, Pim H. Vree +4
We investigate spin-wave transport in ferromagnetic insulator-superconductor (FMI-SC) heterostructures and develop a general theoretical framework for spin-wave optics in these hybrid systems. We demonstrate that Meissner screening by the superconductor gives rise to a range of unconventional wave phenomena, including negative phase- and group-velocity refraction, and reflection and refraction laws that differ fundamentally from their optical counterparts. Within this framework, we derive the spin-wave Fresnel equations governing reflection and transmission at FMI-SC interfaces and show that the scattering properties exhibit a pronounced temperature dependence, enabling tunable spin-wave mirrors and refractive elements. Most strikingly, we find that superconducting screening can produce nearly straight isofrequency contours, far flatter than the kinked, intrinsically curved contours attainable in conventional dipolar spin-wave systems. We show that these straight contours enable functionalities such as perfect spin-wave imaging, efficient waveguiding, and interferometric elements, such as phase shifters and beam splitters, with unconventional properties. Our results establish FMI-SC heterostructures as a versatile platform for temperature-tunable spin-wave optics and interferometric magnonic devices.
Roberto Menta, Lindsay Bassman Oftelie, Ashkan Abedi +5
Reaching fault tolerance means scaling qubit counts by orders of magnitude, a jump that conventional superconducting architectures cannot sustain without solving the so-called `wiring problem'. Global control sidesteps this bottleneck, but implementing quantum error correction (QEC) on previously proposed global architectures incurs extremely steep overhead costs, due to the need for separate correction procedures for the computational and auxiliary qubits that comprise the global device. We resolve this by introducing the first globally-controlled architecture with zero qubit overhead. Every physical qubit is a computational qubit, and thus, every qubit is protected under a single error correcting scheme. We identify a class of cyclic stabilizer codes realizable through global iSWAP and single-qubit gates, yielding QEC thresholds nearly seven orders of magnitude larger than previous estimates for globally-controlled arrays. We further show these thresholds improve systematically as the global architecture is augmented with a limited amount of local measurement sites, demonstrating a trade-off between wiring simplicity and fault-tolerant performance.
Shengshan Qin, Chi Wu, Lun-hui Hu +2
When the surface states of a topological insulator becomes superconducting, topological superconductivity can be obtained, and each vortex on the surface can host one single Majorana zero-energy mode which is usually a wave packet decaying exponentially off the vortex core. Here, we predict stable Majorana zero-energy mode whose wave function is ring-shape, dubbed as annular Majorana mode, in the superconducting vortex in topological insulators respecting 3-fold or 6-fold rotational symmetry. Such topological insulators are featured with a single nonlinear Dirac cone located at Γˉ or three linear Dirac cones at Mˉ in the surface Brillouin zone. The annular Majorana mode originates from the effective chiral f-wave superconductivity on the nonlinear Dirac cone in the former case and the interference of the effective chiral p-wave superconductivity on the three linear Dirac cones in the latter. In both cases, the annular Majorana mode is stabilized by the rotational symmetry and the winding number 3 carried by the surface states. Candidate materials supporting the annular Majorana mode are predicted. Our work provides new insights into the topological superconductivity in superconducting topological insulators.