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| Open AccessTopologically protected surface states in a centrosymmetric superconductor β-PdBi2
Materials possessing topologically non-trivial electronic surface states are predicted to host exotic Majorana fermion excitations in the superconducting state. Here, the authors demonstrate the existence of topologically-protected surface states in the centrosymmetric layered superconductor β-PdBi2.
- M. Sakano
- , K. Okawa
- & K Ishizaka
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| Open AccessSingle Abrikosov vortices as quantized information bits
Superconductors can be used in future supercomputers because they can greatly reduce power consumption and facilitate nonvolatile quantized states that are ideal for Boolean logics. Here, the authors provide a proof-of-concept RAM memory based on a single Abrikosov vortex as bit.
- T. Golod
- , A. Iovan
- & V. M. Krasnov
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| Open AccessStripe-like nanoscale structural phase separation in superconducting BaPb1−xBixO3
In BaPb1−xBixO3a superconducting dome emerges in the proximity to a charge density wave phase. Here, the authors show with transmission electron microscopy measurements that for superconducting compositions of this allow, the structural dimorphism is accommodated in partially disordered nanoscale stripes.
- P. Giraldo-Gallo
- , Y. Zhang
- & I.R. Fisher
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| Open AccessStrong correlations elucidate the electronic structure and phase diagram of LaAlO3/SrTiO3 interface
The interface between SrTiO3 and LaAlO3has the properties of a superconducting two-dimensional electron gas. Here, the authors study the band structure of the interface and found that the population of the mobile band and its density of states are non-monotonic functions of the chemical potential.
- E. Maniv
- , M. Ben Shalom
- & Y. Dagan
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Emergent surface superconductivity in the topological insulator Sb2Te3
Combining the electronic properties of topological materials and superconductivity is predicted to yield exotic new transport phenomena. Here, the authors evidence surface superconductivity in the topological insulator Sb2Te3below 9 K induced by Te vapour over-pressuring during crystal growth.
- Lukas Zhao
- , Haiming Deng
- & Lia Krusin-Elbaum
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Accessing topological superconductivity via a combined STM and renormalization group analysis
A topological superconductor is an exotic state of matter that is gapped in the bulk but possesses gapless surface states, but its identification has been so far elusive. Here, the authors develop a theory for scanning tunnelling microscopy which would allow to resolve topological superconductor states.
- Lars Elster
- , Christian Platt
- & Ewelina M. Hankiewicz
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| Open AccessSignature of magnetic-dependent gapless odd frequency states at superconductor/ferromagnet interfaces
In the proximity of noncollinear magnetization, the Cooper-paired electrons of a superconductor may exist in a spin-triplet state. Here, the authors use scanning tunnel methods to directly observe this effect in Niobium as an adjacent film of Holmium is driven between helical and ferromagnetic order.
- A. Di Bernardo
- , S. Diesch
- & J.W.A. Robinson
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| Open AccessCalorimetric determination of the magnetic phase diagram of underdoped ortho II YBa2Cu3O6.54 single crystals
The presence of a charge order state in underdoped YBCO raises the question of the interplay between this phase and the superconducting one. Here, the authors characterize this material’s phase diagram through specific heat and magnetic measurements, providing strong constrains to theoretical models.
- C. Marcenat
- , A. Demuer
- & T. Klein
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| Open AccessBoundaries for martensitic transition of 7Li under pressure
Lithium metal under extreme pressures shows a sequence of structural phase transitions. Here, the authors use neutron scattering and X-ray diffraction techniques under high pressure to expand the experimental phase diagram of lithium, showing an unexpected deviation from existing boundaries.
- Anne Marie Schaeffer
- , Weizhao Cai
- & Shanti Deemyad
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| Open AccessUniversal self-field critical current for thin-film superconductors
In type-I superconductors the London penetration depth relates the self-field critical current density to the critical field. Here, the authors show that this relation extends to thin films of type-II superconductors, providing the chance to compute the penetration depth from critical current measurements.
- E. F. Talantsev
- & J. L. Tallon
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| Open AccessSuperconductivity-induced re-entrance of the orthorhombic distortion in Ba1−xKxFe2As2
The interplay between magnetic and superconducting phases is important to understand the physics of iron-based superconductivity. Here, the authors use thermodynamic measurements on Ba1−xKxFe2As2 single crystals to provide details of its phase diagram and the re-entrance of a C2spin-density-wave phase.
- A. E. Böhmer
- , F. Hardy
- & C. Meingast
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| Open AccessSuperconductivity emerging from a suppressed large magnetoresistant state in tungsten ditelluride
Tungsten ditelluride has been recently discovered to possess very large and unsaturated magnetoresistance, which opens interesting perspectives for potential applications. Here the authors show suppression of the magnetoresistance and emergence of superconductivity at high pressure.
- Defen Kang
- , Yazhou Zhou
- & Zhongxian Zhao
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| Open AccessPressure-driven dome-shaped superconductivity and electronic structural evolution in tungsten ditelluride
Tungsten ditelluride has been recently discovered to possess very large and unsaturated magnetoresistance, up to 60 T. Here the authors apply high pressure on this material and observe a dome-shaped superconducting phase transition.
- Xing-Chen Pan
- , Xuliang Chen
- & Yuheng Zhang
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| Open AccessObservation of universal strong orbital-dependent correlation effects in iron chalcogenides
A proper theoretical description for unconventional superconductivity in iron-based compounds remains elusive. Here, the authors, to capture the electron correlation strength and the role of Fermi surfaces, report ARPES measurements of three iron chalcogenide superconductors to establish universal features.
- M. Yi
- , Z-K Liu
- & D.H. Lu
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| Open AccessPoint nodes persisting far beyond Tc in Bi2212
The pairing gap of the high-Tc cuprates has been expected to close at the transition temperature, similarly to the case of conventional superconductors. Here the authors perform ARPES measurements on Bi2212, and reveal a point nodal gap formation beyond Tc, characterized in terms of three parameters.
- Takeshi Kondo
- , W. Malaeb
- & S. Shin
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| Open AccessDigital quantum simulation of fermionic models with a superconducting circuit
Quantum simulation offers an unparalleled computational resource, but realizing it for fermionic systems is challenging due to their particle statistics. Here the authors report on the time evolutions of fermionic interactions implemented with digital techniques on a nine-qubit superconducting circuit.
- R. Barends
- , L. Lamata
- & John M. Martinis
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| Open AccessElectronic polymers and soft-matter-like broken symmetries in underdoped cuprates
High-Tc superconductivity is thought to be associated with spatial electronic ordering, which for cuprates is not well understood yet. Here the authors use Monte Carlo simulations to show the emergence of a soft-matter-like electronic phase between the antiferromagnetic and the superconducting states.
- M. Capati
- , S. Caprara
- & J. Lorenzana
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| Open AccessIntra-unit-cell magnetic correlations near optimal doping in YBa2Cu3O6.85
The pseudo-gap phenomenon is central to the description of high-Tcsuperconductivity in copper oxides. Here, the authors investigate nearly optimally doped YBCO using polarized neutron scattering to characterize intra-unit-cell magnetic correlations in relation with the pseudo-gap temperature.
- L. Mangin-Thro
- , Y. Sidis
- & P. Bourges
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| Open AccessLocal destruction of superconductivity by non-magnetic impurities in mesoscopic iron-based superconductors
The pairing symmetry of the wavefunction in high-Tciron-based superconductors remains not completely understood. To shed light on this problem, here the authors investigate the local destruction of superconductivity by introducing Zn impurities in the BKZn iron arsenide compound.
- Jun Li
- , Min Ji
- & Victor V. Moshchalkov
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| Open AccessCooper pair splitting in parallel quantum dot Josephson junctions
Spin-entangled electron pairs are one possible resource for future solid-state quantum information processing systems. Here, the authors directly prove spin entanglement between two electrons that had previously been a Cooper pair in a superconducting lead but were split using two quantum dots.
- R. S. Deacon
- , A. Oiwa
- & S. Tarucha
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| Open AccessInduced superconductivity in high-mobility two-dimensional electron gas in gallium arsenide heterostructures
Superconductivity has been induced in 2D electron gases, but high-field interplay between it and quantum Hall edge states remains elusive. Here the authors reach this regime by growing transparent superconducting contacts in GaAs, reporting modification of resistance in the quantum Hall regime.
- Zhong Wan
- , Aleksandr Kazakov
- & Leonid P. Rokhinson
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Charge-ordering cascade with spin–orbit Mott dimer states in metallic iridium ditelluride
The influence of spin–orbit coupling on itinerant electrons underlies the formation of spin–orbit Mott states. Here, the authors demonstrate a temperature-hysteretic cascade between charge-ordered phases stabilized by localized 5dspin–orbit Mott dimer states in metallic iridium ditelluride.
- K.-T. Ko
- , H.-H. Lee
- & J.-H. Park
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| Open AccessMacroscopic quantum tunnelling in spin filter ferromagnetic Josephson junctions
Spin triplet superconductivity may benefit spintronics, providing dissipation-free spin-polarized currents. Here, the authors demonstrate macroscopic quantum tunnelling in spin filter Josephson junctions containing a ferromagnetic insulator barrier of GdN, evidencing unconventional superconductivity below 100 mK.
- D. Massarotti
- , A. Pal
- & F. Tafuri
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Evidence for an anomalous current–phase relation in topological insulator Josephson junctions
A topological insulator-based Josephson junction is expected to host low-energy Andreev-bound states. Here, Kurter et al. study Josephson interferometry and SQUID oscillations in Bi2Se3junctions to evidence anomalous non-sinusoidal supercurrent contributions as possible signatures of these states.
- C. Kurter
- , A.D.K. Finck
- & D. J. Van Harlingen
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Charge order from orbital-dependent coupling evidenced by NbSe2
Two-dimensional charge ordering cannot be fully described by Peierls-like weak coupling mechanisms appropriate for one-dimensional materials. Here, the authors show how strong orbital-dependent electron–phonon coupling drives two-dimensional charge ordering in archetypal niobium diselenide.
- Felix Flicker
- & Jasper van Wezel
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| Open AccessDetecting bit-flip errors in a logical qubit using stabilizer measurements
Future quantum computers will employ error correction to protect quantum data from decoherence and faulty hardware. Here, using a quantum processor with five superconducting qubits, the authors demonstrate how to protect one logical qubit from bitflip errors using multi-qubit, stabilizer measurements.
- D. Ristè
- , S. Poletto
- & L. DiCarlo
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| Open AccessDemonstration of a quantum error detection code using a square lattice of four superconducting qubits
The physical realization of a quantum computer requires built-in error-correcting codes that compensate the disruption of quantum information arising from noise. Here, the authors demonstrate a quantum error detection scheme for arbitrary single-qubit errors on a four superconducting qubit lattice.
- A.D. Córcoles
- , Easwar Magesan
- & Jerry M. Chow
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| Open AccessEvidence for carrier localization in the pseudogap state of cuprate superconductors from coherent quench experiments
Understanding the nature of the pseudogap phase is an important challenge for high-temperature superconductivity. Madan et al. present a series of ultrafast spectroscopy experiments on the pseudogap phase of Bi2Sr2CaCu2O8+δand find evidence of carrier localization into a textured polaronic state.
- I. Madan
- , T. Kurosawa
- & D. Mihailovic
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| Open AccessDirac surface states and nature of superconductivity in Noncentrosymmetric BiPd
The alloy bismuth-palladium is a candidate material for observing topological superconductivity. Here, the authors study the interplay of spin–orbit interactions and superconductivity in this noncentrosymmetric compound using scanning tunnelling spectroscopy and relativistic first-principles calculations.
- Zhixiang Sun
- , Mostafa Enayat
- & Peter Wahl
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Field-induced density wave in the heavy-fermion compound CeRhIn5
Strong electron correlations often lead to unusual electronic ground states. Here, the authors present evidence for a density wave in the compound CeRhIn5, the first for a so-called heavy-fermion metal where electrons have a very high effective mass.
- Philip J. W. Moll
- , Bin Zeng
- & Filip Ronning
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Bound vortex dipoles generated at pinning centres by Meissner current
A Meissner current is the resistance-free flow of charge induced by magnetic field in a superconductor. Here, the authors observe that Meissner currents flowing through an area containing a pinning centre generate two opposite-sense current half-loops that produce a bound vortex–antivortex pair.
- Jun-Yi Ge
- , Joffre Gutierrez
- & Victor V. Moshchalkov
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| Open AccessThe a.c. Josephson effect without superconductivity
Most of the peculiar effects resulting from superconductivity have counterparts in nonsuperconducting nanoelectronic devices, but not yet in the a.c. Josephson effect. Here, the authors propose how to generate a transient version of this phenomenon in a normal conductor by abruptly changing the bias voltage.
- Benoit Gaury
- , Joseph Weston
- & Xavier Waintal
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| Open AccessIncipient charge order observed by NMR in the normal state of YBa2Cu3Oy
The nature and universality of the ordering phenomena observed in the normal state of high-temperature superconductors remain unclear. Here, Wu et al. observe several aspects of incipient charge ordering in YBCO via NMR measurements, clarifying the role of quenched disorder in their emergence.
- Tao Wu
- , Hadrien Mayaffre
- & Marc-Henri Julien
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Controlling superconductivity by tunable quantum critical points
The heavy fermion system CeRhIn5has a local quantum critical point, but its role in the onset of superconductivity is unclear. Here, the authors tune the quantum critical point by tin doping and verify that fluctuations from the antiferromagnetic criticality promote this unconventional superconductivity.
- S. Seo
- , E. Park
- & Tuson Park
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| Open AccessObservation of directly interacting coherent two-level systems in an amorphous material
Material defects create spurious two-level systems that are a source of noise in nanostructured devices. Lisenfeld et al.use a superconducting qubit to perform high-resolution defect spectroscopy, providing direct evidence of quantum coherent interaction between two defects.
- Jürgen Lisenfeld
- , Grigorij J. Grabovskij
- & Alexey V. Ustinov
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Topological superconductivity and unconventional pairing in oxide interfaces
When the insulators SrTiO3 and LaAlO3 are brought together, a two-dimensional electron gas forms that exhibits both superconductivity and magnetic behaviour. Mathias Scheurer and Jörg Schmalian propose a link between the topological nature of the superconducting state and its microscopic mechanism.
- Mathias S Scheurer
- & Jörg Schmalian
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Atomistic origin of an ordered superstructure induced superconductivity in layered chalcogenides
The interplay between superconductivity, electron correlation and atomic ordering is at the heart of condensed-matter physics. Here, the authors demonstrate a link between superconductivity in the layered chalcogenide TaS2−xSexand the ordering of the sulphur and selenium atoms
- R. Ang
- , Z. C. Wang
- & Y. Ikuhara
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The phase diagram of electron-doped La2−xCexCuO4−δ
The relationship between superconductivity and antiferromagnetism is an unresolved question in electron-doped high-Tc superconductors. Saadaoui et al. perform low-energy muon spin relaxation measurements to study the phase diagram of La2−xCexCuO4−δat the magnetic-superconducting transition region.
- H. Saadaoui
- , Z. Salman
- & R. F. Kiefl
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Observation of strong electron pairing on bands without Fermi surfaces in LiFe1−xCoxAs
It remains to be seen if high-Tc superconductors rely on similar Fermi-surface instabilities as their BCS counterparts. Miao et al. study the high-Tc compound LiFe1−xCoxAs with high-resolution ARPES and find a robust gap with Co doping that suggests the order parameter is not tied to such instabilities.
- H. Miao
- , T. Qian
- & H. Ding
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| Open AccessHour-glass magnetic excitations induced by nanoscopic phase separation in cobalt oxides
High-temperature superconducting cuprates exhibit hour-glass shaped magnetic excitation spectra which are not well understood. Here, the authors show that the hour-glass shaped magnetic excitation spectra in an isostructural cobaltate arise from nanoscopic phase separation.
- Y. Drees
- , Z. W. Li
- & A. C. Komarek
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Superconductivity and its mechanism in an ab initio model for electron-doped LaFeAsO
Understanding unconventional superconductivity is a challenge in condensed matter physics. Ab initiocalculations by Takahiro Misawa and Masatoshi Imada reproduce many experimental features of the iron-based superconductor LaFeAsO, and suggest the mechanism is mediated by electron density fluctuations.
- Takahiro Misawa
- & Masatoshi Imada
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Measurement and control of quasiparticle dynamics in a superconducting qubit
Superconducting circuits are one possible way of realizing qubits, but the time for which they can maintain their quantum state is limited by single-electron-like excitations. Wang et al. now demonstrate a technique for controlling these so-called quasiparticles and improving qubit lifetime.
- C. Wang
- , Y. Y. Gao
- & R. J. Schoelkopf
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Anisotropic softening of magnetic excitations along the nodal direction in superconducting cuprates
The nature of the relationship between the spin-ordered and superconducting states of the cuprates is a longstanding puzzle. X-ray measurements conducted by Guarise et al. suggest that a continuum model rather than overdamped magnon model provides a more complete picture of the spin spectrum of Bi2Sr2CaCu2O8+δ.
- M. Guarise
- , B. Dalla Piazza
- & M. Grioni
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Connecting high-field quantum oscillations to zero-field electron spectral functions in the underdoped cuprates
The nature of the so-called pseudogap phase exhibited by many cuprate superconductors is one of the most puzzling questions in the field of unconventional superconductivity. Allais et al. present a model that can reconcile some of the experimental observations at high and low fields.
- Andrea Allais
- , Debanjan Chowdhury
- & Subir Sachdev
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Intra-unit-cell nematic charge order in the titanium-oxypnictide family of superconductors
Nematic charge order has been observed in both cuprate and iron-based superconductors, but whether this is peculiar to these materials or a universal feature of unconventional superconductivity is unclear. Frandsen et al.have now found it in a third family of superconductors—the titanium-oxypnictides.
- Benjamin A. Frandsen
- , Emil S. Bozin
- & Simon J. L. Billinge
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High-Tc superconductivity in ultrathin Bi2Sr2CaCu2O8+x down to half-unit-cell thickness by protection with graphene
So-called two-dimensional superconductivity has been reported in several material systems but just how thin a system can be and maintain a superconducting state has been difficult to determine. Da Jiang and colleagues demonstrate that Bi2Sr2CaCu2O8+xcontinues to be superconducting even when it is just half a unit cell thick.
- Da Jiang
- , Tao Hu
- & Mianheng Jiang
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Disorder-induced topological change of the superconducting gap structure in iron pnictides
The superconducting gap of most unconventional superconductors has nodes that support low-energy excitations. Mizukami et al. report that disorder introduced by electron irradiation in BaFe2(As1−xPx)2induces a sequence of transitions from a nodal to a nodeless gap and then to another gapless state.
- Y. Mizukami
- , M. Konczykowski
- & T. Shibauchi
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Hidden two-qubit dynamics of a four-level Josephson circuit
Qudits, multiple-level quantum systems, enable more efficient scaling of physical resources in quantum computing than qubits, but they are more difficult to control. Svetitsky et al.now experimentally demonstrate a simplifying technique that converts a four-level qudit into a pair of qubits.
- Elisha Svetitsky
- , Haim Suchowski
- & Nadav Katz
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Ubiquitous long-range antiferromagnetic coupling across the interface between superconducting and ferromagnetic oxides
When tightly coupled, a metallic magnet and a conventional superconductor are known to disturb each-other's order also at some distance from the interface. Here, the authors observe how this proximity effect between a ferromagnetic oxide and a high-Tcsuperconductor develops at microscopic scale.
- G. M. De Luca
- , G. Ghiringhelli
- & M. Salluzzo