27 research outputs found
Long range coherent magnetic bound states in superconductors
The quantum coherent coupling of completely different degrees of freedom is a
challenging path towards creating new functionalities for quantum electronics.
Usually the antagonistic coupling between spins of magnetic impurities and
superconductivity leads to the destruction of the superconducting order. Here
we show that a localized classical spin of an iron atom immersed in a
superconducting condensate can give rise to new kind of long range coherent
magnetic quantum state. In addition to the well-known Shiba bound state present
on top of an impurity we reveal the existence of a star shaped pattern which
extends as far as 12 nm from the impurity location. This large spatial
dispersion turns out to be related, in a non-trivial way, to the
superconducting coherence length. Inside star branches we observed short scale
interference fringes with a particle-hole asymmetry. Our theoretical approach
captures these features and relates them to the electronic band structure and
the Fermi wave length of the superconductor. The discovery of a directional
long range effect implies that distant magnetic atoms could coherently interact
leading to new topological superconducting phases with fascinating properties
Magnetic gap of fe-doped BiSbTe<sub>2</sub>Se bulk single crystals detected by tunneling spectroscopy and gate-controlled transports
Topological insulators with broken time-reversal symmetry and the Fermi level within the magnetic gap at the Dirac cone provides exotic topological magneto-electronic phenomena. Here, we introduce an improved magnetically doped topological insulator, Fe-doped BiSbTe2Se (Fe-BSTS) bulk single crystal, with an ideal Fermi level. Scanning tunneling microscopy and spectroscopy (STM/STS) measurements revealed that the surface state possesses a Dirac cone with the Dirac point just below the Fermi level by 12 meV. The normalized dI/dV spectra suggest a gap opening with Îmag ~55 meV, resulting in the Fermi level within the opened gap. Ionic-liquid gated-transport measurements also support the Dirac point just below the Fermi level and the presence of the magnetic gap. The chemical potential of the surface state can be fully tuned by ionic-liquid gating, and thus the Fe-doped BSTS provides an ideal platform to investigate exotic quantum topological phenomena.</p
Ferromagnetic Josephson switching device with high characteristic voltage
We develop a fast Magnetic Josephson Junction (MJJ) - a superconducting
ferromagnetic device for a scalable high-density cryogenic memory compatible in
speed and fabrication with energy-efficient Single Flux Quantum (SFQ) circuits.
We present experimental results for
Superconductor-Insulator-Ferromagnet-Superconductor (SIFS) MJJs with high
characteristic voltage IcRn of >700 uV proving their applicability for
superconducting circuits. By applying magnetic field pulses, the device can be
switched between MJJ logic states. The MJJ IcRn product is only ~30% lower than
that of conventional junction co-produced in the same process, allowing for
integration of MJJ-based and SIS-based ultra-fast digital SFQ circuits
operating at tens of gigahertz.Comment: 10 pages, 4 figure
Microwave analysis of the interplay between magnetism and superconductivity in EuFe 2 (As 1 -x P x ) 2 single crystals
This paper presents a microwave analysis of the interplay between magnetism and superconductivity in an iron-based ferromagnetic superconductor. By comparing the complex rf susceptibility with magnetic force images, the authors discuss the nature of the observed phase transitions and the possible presence of a quantum critical point
Revealing Josephson vortex dynamics in proximity junctions below critical current
Made of a thin non-superconducting metal (N) sandwiched by two
superconductors (S), SNS Josephson junctions enable novel quantum
functionalities by mixing up the intrinsic electronic properties of N with the
superconducting correlations induced from S by proximity. Electronic properties
of these devices are governed by Andreev quasiparticles [1] which are absent in
conventional SIS junctions whose insulating barrier (I) between the two S
electrodes owns no electronic states. Here we focus on the Josephson vortex
(JV) motion inside Nb-Cu-Nb proximity junctions subject to electric currents
and magnetic fields. The results of local (Magnetic Force Microscopy) and
global (transport) experiments provided simultaneously are compared with our
numerical model, revealing the existence of several distinct dynamic regimes of
the JV motion. One of them, identified as a fast hysteretic entry/escape below
the critical value of Josephson current, is analyzed and suggested for
low-dissipative logic and memory elements.Comment: 11 pages, 3 figures, 1 table, 43 reference
Ultrastrong photon-to-magnon coupling in multilayered heterostructures involving superconducting coherence via ferromagnetic layers
The critical step for future quantum industry demands realization of efficient information exchange between different-platform hybrid systems that can harvest advantages of distinct platforms. The major restraining factor for the progress in certain hybrids is weak coupling strength between the elemental particles. In particular, this restriction impedes a promising field of hybrid magnonics. In this work, we propose an approach for realization of on-chip hybrid magnonic systems with unprecedentedly strong coupling parameters. The approach is based on multilayered microstructures containing superconducting, insulating, and ferromagnetic layers with modified photon phase velocities and magnon eigenfrequencies. The enhanced coupling strength is provided by the radically reduced photon mode volume. Study of the microscopic mechanism of the photon-to-magnon coupling evidences formation of the long-range superconducting coherence via thick strong ferromagnetic layers in superconductor/ferromagnet/superconductor trilayer in the presence of magnetization precession. This discovery offers new opportunities in microwave superconducting spintronics for quantum technologies
Magnetic Dirac semimetal state of (Mn,Ge)BiTe
For quantum electronics, the possibility to finely tune the properties of
magnetic topological insulators (TIs) is a key issue. We studied solid
solutions between two isostructural Z TIs, magnetic MnBiTe and
nonmagnetic GeBiTe, with Z invariants of 1;000 and 1;001,
respectively. For high-quality, large mixed crystals of
GeMnBiTe, we observed linear x-dependent magnetic
properties, composition-independent pairwise exchange interactions along with
an easy magnetization axis. The bulk band gap gradually decreases to zero for
from 0 to 0.4, before reopening for , evidencing topological phase
transitions (TPTs) between topologically nontrivial phases and the semimetal
state. The TPTs are driven purely by the variation of orbital contributions. By
tracing the x-dependent contribution to the states near the fundamental
gap, the effective spin-orbit coupling variation is extracted. As varies,
the maximum of this contribution switches from the valence to the conduction
band, thereby driving two TPTs. The gapless state observed at closely
resembles a Dirac semimetal above the Neel temperature and shows a magnetic gap
below, which is clearly visible in raw photoemission data. The observed
behavior of the GeMnBiTe system thereby demonstrates an
ability to precisely control topological and magnetic properties of TIs
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High-Quality Graphene Using Boudouard Reaction
Following the game-changing high-pressure CO (HiPco) process that established the first facile route toward large-scale production of single-walled carbon nanotubes, CO synthesis of cm-sized graphene crystals of ultra-high purity grown during tens of minutes is proposed. The Boudouard reaction serves for the first time to produce individual monolayer structures on the surface of a metal catalyst, thereby providing a chemical vapor deposition technique free from molecular and atomic hydrogen as well as vacuum conditions. This approach facilitates inhibition of the graphene nucleation from the CO/CO2 mixture and maintains a high growth rate of graphene seeds reaching large-scale monocrystals. Unique features of the Boudouard reaction coupled with CO-driven catalyst engineering ensure not only suppression of the second layer growth but also provide a simple and reliable technique for surface cleaning. Aside from being a novel carbon source, carbon monoxide ensures peculiar modification of catalyst and in general opens avenues for breakthrough graphene-catalyst composite production
Size-Dependent Superconducting Properties of In Nanowire Arrays
Arrays of superconducting nanowires may be useful as elements of novel nanoelectronic devices. The superconducting properties of nanowires differ significantly from the properties of bulk structures. For instance, different vortex configurations of the magnetic field have previously been predicted for nanowires with different diameters. In the present study, arrays of parallel superconducting In nanowires with the diameters of 45 nm, 200 nm, and 550 nmâthe same order of magnitude as coherence length Οâwere fabricated by templated electrodeposition. Values of magnetic moment M of the samples were measured as a function of magnetic field H and temperature T in axial and transverse fields. M(H) curves for the arrays of nanowires with 45 nm and 200 nm diameters are reversible, whereas magnetization curves for the array of nanowires with 550 nm diameter have several feature points and show a significant difference between increasing and decreasing field branches. Critical fields increase with a decrease in diameter, and the thinnest nanowires exceed bulk critical fields by 20 times. The qualitative change indicates that magnetic field configurations are different in the nanowires with different diameters. Variation of M(H) slope in small fields, heat capacity, and the magnetic field penetration depth with the temperature were measured. Superconductivity in In nanowires is proven to exist above the bulk critical temperature