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Thupakula U, Perrin V, Palacio-Morales A, Cario L, Aprili M, Simon P, Massee F. Coherent and Incoherent Tunneling into Yu-Shiba-Rusinov States Revealed by Atomic Scale Shot-Noise Spectroscopy. Phys Rev Lett 2022; 128:247001. [PMID: 35776485 DOI: 10.1103/physrevlett.128.247001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2021] [Revised: 12/27/2021] [Accepted: 05/18/2022] [Indexed: 06/15/2023]
Abstract
The pair breaking potential of individual magnetic impurities in s-wave superconductors generates localized states inside the superconducting gap commonly referred to as Yu-Shiba-Rusinov (YSR) states whose isolated nature makes them promising building blocks for artificial structures that may host Majorana fermions. One of the challenges in this endeavor is to understand their intrinsic lifetime, ℏ/Λ, which is expected to be limited by the inelastic coupling with the continuum thus leading to decoherence. Here we use shot-noise scanning tunneling microscopy to reveal that electron tunneling into superconducting 2H-NbSe_{2} mediated by YSR states is not Poissonian, but ordered as a function of time, as evidenced by a reduction of the noise. Moreover, our data show the concomitant transfer of charges e and 2e, indicating that incoherent single particle and coherent Andreev processes operate simultaneously. From the quantitative agreement between experiment and theory we obtain Λ=1 μeV≪k_{B}T demonstrating that shot noise can probe energy scales and timescales inaccessible by conventional spectroscopy whose resolution is thermally limited.
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Affiliation(s)
- U Thupakula
- Laboratoire de Physique des Solides (CNRS UMR 8502), Bâtiment 510, Université Paris-Sud/Université Paris-Saclay, 91405 Orsay, France
| | - V Perrin
- Laboratoire de Physique des Solides (CNRS UMR 8502), Bâtiment 510, Université Paris-Sud/Université Paris-Saclay, 91405 Orsay, France
| | - A Palacio-Morales
- Laboratoire de Physique des Solides (CNRS UMR 8502), Bâtiment 510, Université Paris-Sud/Université Paris-Saclay, 91405 Orsay, France
| | - L Cario
- Université de Nantes, CNRS, Institut des Matériaux Jean Rouxel, IMN, F-44000 Nantes, France
| | - M Aprili
- Laboratoire de Physique des Solides (CNRS UMR 8502), Bâtiment 510, Université Paris-Sud/Université Paris-Saclay, 91405 Orsay, France
| | - P Simon
- Laboratoire de Physique des Solides (CNRS UMR 8502), Bâtiment 510, Université Paris-Sud/Université Paris-Saclay, 91405 Orsay, France
| | - F Massee
- Laboratoire de Physique des Solides (CNRS UMR 8502), Bâtiment 510, Université Paris-Sud/Université Paris-Saclay, 91405 Orsay, France
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Kuzmanović M, Wu BY, Weideneder M, Quay CHL, Aprili M. Evidence for spin-dependent energy transport in a superconductor. Nat Commun 2020; 11:4336. [PMID: 32859913 PMCID: PMC7455713 DOI: 10.1038/s41467-020-18161-w] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2020] [Accepted: 07/31/2020] [Indexed: 11/20/2022] Open
Abstract
In ferromagnetic materials, spin up and down electrons can carry different heat currents. This spin-dependent energy excitation mode ('spin energy mode') occurs only when spin up and down energy distribution functions are different. In superconductors, heat is carried by quasiparticle excitations and the spin energy mode can be excited by spin-polarised current injection. In the presence of a finite Zeeman magnetic field, the spin energy mode surprisingly leads to a charge imbalance (different numbers of hole- and electron-like quasiparticles) at the superconducting gap edge. By performing spin-resolved spectroscopy of the out-of-equilibrium quasiparticle populations in a mescoscopic superconductor, we reveal that their distribution functions are non-Fermi-Dirac. In addition, our spectroscopic technique allows us to observe a charge imbalance, localised in energy to the gap edge and thus unambiguously identify the spin energy mode. Our results agree well with theory and shed light on energy transport in superconducting spintronics.
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Affiliation(s)
- M Kuzmanović
- Laboratoire de Physique des Solides (CNRS UMR 8502), Université Paris-Saclay, 91405, Orsay, France
| | - B Y Wu
- Laboratoire de Physique des Solides (CNRS UMR 8502), Université Paris-Saclay, 91405, Orsay, France
- Graduate Institute of Applied Physics, National Taiwan University, Taipei, 10617, Taiwan
| | - M Weideneder
- Laboratoire de Physique des Solides (CNRS UMR 8502), Université Paris-Saclay, 91405, Orsay, France
- Institute for Experimental and Applied Physics, University of Regensburg, 93053, Regensburg, Germany
| | - C H L Quay
- Laboratoire de Physique des Solides (CNRS UMR 8502), Université Paris-Saclay, 91405, Orsay, France.
| | - M Aprili
- Laboratoire de Physique des Solides (CNRS UMR 8502), Université Paris-Saclay, 91405, Orsay, France
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3
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Abstract
Single-atom manipulation within doped correlated electron systems could help disentangle the influence of dopants, structural defects, and crystallographic characteristics on local electronic states. Unfortunately, the high diffusion barrier in these materials prevents conventional manipulation techniques. Here, we demonstrate the possibility to reversibly manipulate select sites in the optimally doped high-temperature superconductor Bi2Sr2CaCu2O8+x using the local electric field of the tip of a scanning tunneling microscope. We show that upon shifting individual Bi atoms at the surface, the spectral gap associated with superconductivity is seen to reversibly change by as much as 15 milli-electron volts (on average ~5% of the total gap size). Our toy model, which captures all observed characteristics, suggests that the electric field induces lateral movement of local pairing potentials in the CuO2 plane.
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Affiliation(s)
- F Massee
- Laboratoire de Physique des Solides, CNRS UMR 8502, Bâtiment 510, Université Paris-Sud, Université Paris-Saclay, 91405 Orsay, France.
| | - Y K Huang
- Institute of Physics, University of Amsterdam, 1098XH Amsterdam, Netherlands
| | - M Aprili
- Laboratoire de Physique des Solides, CNRS UMR 8502, Bâtiment 510, Université Paris-Sud, Université Paris-Saclay, 91405 Orsay, France
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4
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Abstract
Dopants and impurities are crucial in shaping the ground state of host materials: semiconducting technology is based on their ability to donate or trap electrons, and they can even be used to transform insulators into high temperature superconductors. Due to limited time resolution, most atomic-scale studies of the latter materials focussed on the effect of dopants on the electronic properties averaged over time. Here, by using atomic-scale current-noise measurements in optimally doped Bi2Sr2CaCu2O8+x, we visualize sub-nanometre sized objects where the tunnelling current-noise is enhanced by at least an order of magnitude. We show that these objects are previously undetected oxygen dopants whose ionization and local environment leads to unconventional charge dynamics resulting in correlated tunnelling events. The ionization of these dopants opens up new routes to dynamically control doping at the atomic scale, enabling the direct visualization of local charging on e.g. high-Tc superconductivity. The effects of dopants in high-temperature superconductors on the surrounding electronic structure give insights into their unconventional microscopic behaviour. Here the authors find a new class of defects that they identify as oxygen dopants whose ionization and local environment induce unusual atomic-scale charge dynamics.
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Affiliation(s)
- F Massee
- Laboratoire de Physique des Solides (CNRS UMR 8502), Bâtiment 510, Université Paris-Sud/Université Paris-Saclay, 91405, Orsay, France.
| | - Y K Huang
- Institute of Physics, University of Amsterdam, 1098 XH, Amsterdam, The Netherlands
| | - M S Golden
- Institute of Physics, University of Amsterdam, 1098 XH, Amsterdam, The Netherlands
| | - M Aprili
- Laboratoire de Physique des Solides (CNRS UMR 8502), Bâtiment 510, Université Paris-Sud/Université Paris-Saclay, 91405, Orsay, France
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5
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Massee F, Dong Q, Cavanna A, Jin Y, Aprili M. Atomic scale shot-noise using cryogenic MHz circuitry. Rev Sci Instrum 2018; 89:093708. [PMID: 30278734 DOI: 10.1063/1.5043261] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/07/2018] [Accepted: 08/12/2018] [Indexed: 06/08/2023]
Abstract
By implementing dedicated cryogenic circuitry operating in the MHz regime, we have developed a scanning tunneling microscope (STM) capable of conventional, low frequency (<10 kHz), microscopy as well spectroscopy and shot-noise detection at 1 MHz. After calibrating our AC circuit on a gold surface, we illustrate our capability to detect shot-noise at the atomic scale and at low currents (<1 nA) by simultaneously measuring the atomically resolved differential conductance and shot-noise on the high temperature superconductor Bi2Sr2CaCu2O8+x . We further show our direct sensitivity to the temperature of the tunneling electrons at low voltages. Our MHz circuitry opens up the possibility to study charge and correlation effects at the atomic scale in all materials accessible to STM.
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Affiliation(s)
- F Massee
- Laboratoire de Physique des Solides (CNRS UMR 8502), Bâtiment 510, Université Paris-Sud/Université Paris-Saclay, 91405 Orsay, France
| | - Q Dong
- Centre de Nanosciences et de Nanotechnologies, CNRS, Université Paris-Sud, Université Paris-Saclay, C2N-Marcoussis, 91460 Marcoussis, France
| | - A Cavanna
- Centre de Nanosciences et de Nanotechnologies, CNRS, Université Paris-Sud, Université Paris-Saclay, C2N-Marcoussis, 91460 Marcoussis, France
| | - Y Jin
- Centre de Nanosciences et de Nanotechnologies, CNRS, Université Paris-Sud, Université Paris-Saclay, C2N-Marcoussis, 91460 Marcoussis, France
| | - M Aprili
- Laboratoire de Physique des Solides (CNRS UMR 8502), Bâtiment 510, Université Paris-Sud/Université Paris-Saclay, 91405 Orsay, France
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Quay CHL, Aprili M. Out-of-equilibrium spin transport in mesoscopic superconductors. Philos Trans A Math Phys Eng Sci 2018; 376:rsta.2015.0342. [PMID: 29941629 PMCID: PMC6030150 DOI: 10.1098/rsta.2015.0342] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 04/16/2016] [Indexed: 06/08/2023]
Abstract
The excitations in conventional superconductors, Bogoliubov quasi-particles, are spin-[Formula: see text] fermions but their charge is energy-dependent and, in fact, zero at the gap edge. Therefore, in superconductors (unlike normal metals) spin and charge degrees of freedom may be separated. In this article, we review spin injection into conventional superconductors and focus on recent experiments on mesoscopic superconductors. We show how quasi-particle spin transport and out-of-equilibrium spin-dependent superconductivity can be triggered using the Zeeman splitting of the quasi-particle density of states in thin-film superconductors with small spin-mixing scattering. Finally, we address the spin dynamics and the feedback of quasi-particle spin imbalances on the amplitude of the superconducting energy gap.This article is part of the theme issue 'Andreev bound states'.
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Affiliation(s)
- C H L Quay
- Laboratoire de Physique des Solides (CNRS UMR 8502), Bâtiment 510, Université Paris-Sud/Université, Paris-Saclay, 91405 Orsay, France
| | - M Aprili
- Laboratoire de Physique des Solides (CNRS UMR 8502), Bâtiment 510, Université Paris-Sud/Université, Paris-Saclay, 91405 Orsay, France
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7
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Dvir T, Massee F, Attias L, Khodas M, Aprili M, Quay CHL, Steinberg H. Spectroscopy of bulk and few-layer superconducting NbSe 2 with van der Waals tunnel junctions. Nat Commun 2018; 9:598. [PMID: 29426840 PMCID: PMC5807409 DOI: 10.1038/s41467-018-03000-w] [Citation(s) in RCA: 57] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2017] [Accepted: 01/12/2018] [Indexed: 11/28/2022] Open
Abstract
Tunnel junctions, an established platform for high resolution spectroscopy of superconductors, require defect-free insulating barriers; however, oxides, the most common barrier, can only grow on a limited selection of materials. We show that van der Waals tunnel barriers, fabricated by exfoliation and transfer of layered semiconductors, sustain stable currents with strong suppression of sub-gap tunneling. This allows us to measure the spectra of bulk (20 nm) and ultrathin (3- and 4-layer) NbSe2 devices at 70 mK. These exhibit two distinct superconducting gaps, the larger of which decreases monotonically with thickness and critical temperature. The spectra are analyzed using a two-band model incorporating depairing. In the bulk, the smaller gap exhibits strong depairing in in-plane magnetic fields, consistent with high out-of-plane Fermi velocity. In the few-layer devices, the large gap exhibits negligible depairing, consistent with out-of-plane spin locking due to Ising spin-orbit coupling. In the 3-layer device, the large gap persists beyond the Pauli limit.
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Affiliation(s)
- T Dvir
- The Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem, 91904, Israel
| | - F Massee
- Laboratoire de Physique des Solides (CNRS UMR 8502), Bâtiment 510, Université Paris-Sud/Université Paris-Saclay, 91405, Orsay, France
| | - L Attias
- The Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem, 91904, Israel
| | - M Khodas
- The Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem, 91904, Israel
| | - M Aprili
- Laboratoire de Physique des Solides (CNRS UMR 8502), Bâtiment 510, Université Paris-Sud/Université Paris-Saclay, 91405, Orsay, France
| | - C H L Quay
- Laboratoire de Physique des Solides (CNRS UMR 8502), Bâtiment 510, Université Paris-Sud/Université Paris-Saclay, 91405, Orsay, France
| | - H Steinberg
- The Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem, 91904, Israel.
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8
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Hammer J, Aprili M, Petković I. Microwave cooling of Josephson plasma oscillations. Phys Rev Lett 2011; 107:017001. [PMID: 21797564 DOI: 10.1103/physrevlett.107.017001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2010] [Indexed: 05/31/2023]
Abstract
An extended Josephson junction can be described as a microwave cavity coupled to a Josephson oscillator. This is formally equivalent to a Fabry-Perot cavity with a freely vibrating mirror, where it has been shown that radiation pressure from photons in the cavity can reduce (increase) the vibrations of the mirror, effectively cooling (heating) it. We demonstrate that, similarly, the superconducting phase difference across a Josephson junction-the Josephson phase-can be "cooled" or "heated" by microwave excitation of the junction and that both these effects increase with microwave power.
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Affiliation(s)
- J Hammer
- Institute for Experimental and Applied Physics, University of Regensburg, Germany
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9
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Abstract
We use microwave excitation to elucidate the dynamics of long superconductor-normal metal-superconductor Josephson junctions. By varying the excitation frequency in the range 10 MHz-40 GHz, we observe that the critical and retrapping currents, deduced from the dc voltage versus dc current characteristics of the junction, are set by two different time scales. The critical current increases when the ac frequency is larger than the inverse diffusion time in the normal metal, whereas the retrapping current is strongly modified when the excitation frequency is above the electron-phonon rate in the normal metal. Therefore the critical and retrapping currents are associated with elastic and inelastic scattering, respectively.
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Affiliation(s)
- F Chiodi
- Laboratoire de Physique des Solides, UMR8502, Bâtiment 510, Université Paris-Sud, 91405 ORSAY Cedex, France
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10
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Petković I, Aprili M. Phase dynamics of ferromagnetic Josephson junctions. Phys Rev Lett 2009; 102:157003. [PMID: 19518669 DOI: 10.1103/physrevlett.102.157003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2008] [Indexed: 05/27/2023]
Abstract
We have investigated the classical phase dynamics of underdamped ferromagnetic Josephson junctions by measuring the switching probability in both the stationary and nonstationary regimes down to 350 mK. We found the escape temperature to be the bath temperature, with no evidence of additional spin noise. In the nonstationary regime, we have performed a pump-probe experiment on the Josephson phase by increasing the frequency of the junction current bias. We show that an incomplete energy relaxation leads to dynamical phase bifurcation. Bifurcation manifests itself as premature switching, resulting in a bimodal switching distribution. We directly measure the phase relaxation time tau_{phi} by following the evolution of the bimodal switching distribution when varying the bias frequency. Numerical simulations account for the experimental values of tau_{phi}.
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Affiliation(s)
- I Petković
- Laboratoire de Physique des Solides, UMR 8502, Bâtiment 510, Université Paris-Sud, 91405 Orsay Cedex, France.
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11
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Della Rocca ML, Aprili M, Kontos T, Gomez A, Spathis P. Ferromagnetic 0-pi junctions as classical spins. Phys Rev Lett 2005; 94:197003. [PMID: 16090200 DOI: 10.1103/physrevlett.94.197003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2005] [Indexed: 05/03/2023]
Abstract
The ground state of highly damped PdNi based 0-pi ferromagnetic Josephson junctions shows a spontaneous half quantum vortex, sustained by a supercurrent of undetermined sign. This supercurrent flows in the electrode of a Josephson junction used as a detector and produces a phi(0)/4 shift in its magnetic diffraction pattern. We have measured the statistics of the positive or the negative sign shift occurring at the superconducting transition of such a junction. The randomness of the shift sign, the reproducibility of its magnitude, and the possibility of achieving exact flux compensation upon field cooling are the features which show that 0-pi junctions behave as classical spins, just as magnetic nanoparticles with uniaxial anisotropy.
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Affiliation(s)
- M L Della Rocca
- Ecole Supèrieure de Physique et Chimie Industrielles (ESPCI), Paris, France.
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12
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Kontos T, Aprili M, Lesueur J, Grison X, Dumoulin L. Superconducting proximity effect at the paramagnetic-ferromagnetic transition. Phys Rev Lett 2004; 93:137001. [PMID: 15524751 DOI: 10.1103/physrevlett.93.137001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2003] [Revised: 05/04/2004] [Indexed: 05/24/2023]
Abstract
The exchange-enhanced electron-electron interactions at the paramagnetic-ferromagnetic transition were studied experimentally via proximity effect tunneling spectroscopy. By solving the Usadel equations in both the paramagnetic and ferromagnetic states, the electron-spin fluctuation coupling constant and the exchange field are derived from the tunneling spectra.
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Affiliation(s)
- T Kontos
- CSNSM-CNRS, Bâtiment 108 Université Paris-Sud, 91405 Orsay, France
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13
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Bauer A, Bentner J, Aprili M, Della Rocca ML, Reinwald M, Wegscheider W, Strunk C. Spontaneous supercurrent induced by ferromagnetic pi junctions. Phys Rev Lett 2004; 92:217001. [PMID: 15245309 DOI: 10.1103/physrevlett.92.217001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2003] [Indexed: 05/24/2023]
Abstract
We present magnetization measurements of mesoscopic superconducting niobium loops containing a ferromagnetic (PdNi) pi junction. The loops are prepared on top of the active area of a micro-Hall sensor based on high mobility GaAs/AlGaAs heterostructures. We observe asymmetric switching of the loop between different magnetization states when reversing the sweep direction of the magnetic field. This provides evidence for a spontaneous current induced by the intrinsic phase shift of the pi junction. In addition, the presence of the spontaneous current near zero applied field is directly revealed by an increase of the magnetic moment with decreasing temperature, which results in half integer flux quantization in the loop at low temperatures.
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Affiliation(s)
- A Bauer
- Institut für Experimentelle und Angewandte Physik, Universität Regensburg, 93040 Regensburg, Germany
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14
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Guichard W, Aprili M, Bourgeois O, Kontos T, Lesueur J, Gandit P. Phase sensitive experiments in ferromagnetic-based Josephson junctions. Phys Rev Lett 2003; 90:167001. [PMID: 12731993 DOI: 10.1103/physrevlett.90.167001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/13/2002] [Indexed: 05/24/2023]
Abstract
We have measured the ground state of ferromagnetic Josephson junctions using a single dc SQUID (superconducting quantum interference device).We show that the Josephson coupling is either positive (0 coupling) or negative (pi coupling) depending on the ferromagnetic layer thickness. As expected, the sign change of the Josephson coupling is observed as a shift of half a quantum flux in the SQUID diffraction pattern when operating in the linear limit.
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Affiliation(s)
- W Guichard
- CRTBT-CNRS, 25 Avenue des Martyrs, 38042 Grenoble, France
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15
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Kontos T, Aprili M, Lesueur J, Genêt F, Stephanidis B, Boursier R. Josephson junction through a thin ferromagnetic layer: negative coupling. Phys Rev Lett 2002; 89:137007. [PMID: 12225057 DOI: 10.1103/physrevlett.89.137007] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2001] [Indexed: 05/23/2023]
Abstract
We investigate Josephson coupling through a ferromagnetic thin film using superconductor-insulator-ferromagnet-superconductor planar junctions. Damped oscillations of the critical current are observed as a function of the ferromagnetic layer thickness. We show that they result from the exchange energy gained or lost by a quasiparticle Andreev-reflected at the ferromagnet-superconductor interface. The critical current cancels out at the transition from positive ("0") to negative ("pi") coupling, in agreement with theoretical calculations.
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Affiliation(s)
- T Kontos
- CSNSM-CNRS, Université Paris-Sud, 91405 Orsay Cedex, France
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16
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Kontos T, Aprili M, Lesueur J, Grison X. Inhomogeneous superconductivity induced in a ferromagnet by proximity effect. Phys Rev Lett 2001; 86:304-307. [PMID: 11177817 DOI: 10.1103/physrevlett.86.304] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2000] [Indexed: 05/23/2023]
Abstract
Planar tunneling spectroscopy reveals damped oscillations of the superconducting order parameter induced into a ferromagnetic thin film by the proximity effect. The oscillations are due to the finite momentum transfer provided for Cooper pairs by the splitting of the spin-up and spin-down bands in the ferromagnet. As a consequence, for negative values of the superconducting order parameter the tunneling spectra are capsized ("pi state"). The oscillations' damping and period are set by the same length scale, which depends on the spin polarization.
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Affiliation(s)
- T Kontos
- CSNSM-CNRS, Bât. 108, Université Paris-Sud, 91405 Orsay Cedex, France
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