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Anisotropic magnon transport in an antiferromagnetic trilayer heterostructure: is BiFeO$_3$ an altermagnet?
Authors:
Sajid Husain,
Maya Ramesh,
Qian Song,
Sergei Prokhorenko,
Shashank Kumar Ojha,
Surya Narayan Panda,
Xinyan Li,
Yousra Nahas,
Yogesh Kumar,
Pushpendra Gupta,
Tenzin Chang,
Alan Ji-in Jung,
Rogério de Sousa,
James G. Analytis,
Lane W. Martin,
Zhi Yao,
Sang-Wook Cheong,
Laurent Bellaiche,
Manuel Bibes,
Darrell G. Schlom,
Ramamoorthy Ramesh
Abstract:
Magnons provide a route to ultra-fast transport and non-destructive readout of spin-based information transfer. Here, we report magnon transport and its emergent anisotropic nature in BiFeO$_3$ layers confined between ultrathin layers of the antiferromagnet LaFeO$_3$. Due to the confined state, BiFeO$_3$ serves as an efficient magnon transmission channel as well as a magnetoelectric knob by which…
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Magnons provide a route to ultra-fast transport and non-destructive readout of spin-based information transfer. Here, we report magnon transport and its emergent anisotropic nature in BiFeO$_3$ layers confined between ultrathin layers of the antiferromagnet LaFeO$_3$. Due to the confined state, BiFeO$_3$ serves as an efficient magnon transmission channel as well as a magnetoelectric knob by which to control the stack by means of an electric field. We discuss the mechanism of the anisotropic spin transport based on the interaction between the antiferromagnetic order and the electric field. This allows us to manipulate and amplify the spin transport in such a confined geometry. Furthermore, lower crystal symmetric and suppression of the spin cycloid in ultrathin BiFeO$_3$ stabilizes a non-trivial antiferromagnetic state exhibiting symmetry-protected spin-split bands that provide the non-trivial sign inversion of the spin current, which is a characteristic of an altermagnet. This work provides an understanding of the anisotropic spin transport in complex antiferromagnetic heterostructures where ferroelectricity and altermagnetism coexist, paving the way for a new route to realize electric-field control of a novel state of magnetism.
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Submitted 7 January, 2026;
originally announced January 2026.
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Membrane phononic crystals for high-Qm mechanical defect modes in piezoelectric aluminum nitride
Authors:
Anastasiia Ciers,
Laurentius Radit Nindito,
Alexander Jung,
Hannes Pfeifer,
Armin Dadgar,
Andre Strittmatter,
Witlef Wieczorek
Abstract:
Nanomechanical resonators with exceptionally low dissipation are advancing mechanics-based sensors and quantum technologies. The key for these advances is the engineering of localized phononic modes that are well-isolated from the environment, i.e., that exhibit a high mechanical quality factor, Qm. Membrane phononic crystals fabricated from strained thin films can realize high-Qm single or multip…
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Nanomechanical resonators with exceptionally low dissipation are advancing mechanics-based sensors and quantum technologies. The key for these advances is the engineering of localized phononic modes that are well-isolated from the environment, i.e., that exhibit a high mechanical quality factor, Qm. Membrane phononic crystals fabricated from strained thin films can realize high-Qm single or multiple localized phononic defect modes at MHz frequencies. These defect modes can be efficiently interfaced with out-of-plane light or coupled to a microwave quantum circuit, enabling readout and control of their motion. When membrane phononic crystals are fabricated from a crystalline film, they could offer built-in functionality. We demonstrate a membrane phononic crystal realized in a strained 90 nm-thin film of aluminum nitride (AlN), which is a crystalline piezoelectric material. We engineer a high-Qm localized phononic defect mode at 1.8 MHz with a Qxf-product of 1.5x10^13 Hz at room temperature. In future devices, the built-in piezoelectricity of AlN can be utilized for direct coupling to qubits or in-situ tuning of mechanical mode frequencies, defect mode couplings, or acoustic bandgaps, which can be used as building blocks of tunable phononic circuits or low-noise sensors.
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Submitted 25 June, 2025; v1 submitted 31 January, 2025;
originally announced January 2025.
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Thickness dependence of the mechanical properties of piezoelectric high-$Q_m$ nanomechanical resonators made from aluminium nitride
Authors:
Anastasiia Ciers,
Alexander Jung,
Joachim Ciers,
Laurentius Radit Nindito,
Hannes Pfeifer,
Armin Dadgar,
Jürgen Bläsing,
André Strittmatter,
Witlef Wieczorek
Abstract:
Nanomechanical resonators with high quality factors (\Qm{}) enable mechanics-based quantum technologies, in particular quantum sensing and quantum transduction. High-\Qm{} nanomechanical resonators in the kHz to MHz frequency range can be realized in tensile-strained thin films that allow the use of dissipation dilution techniques to drastically increase \Qm{}. In our work, we study the material p…
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Nanomechanical resonators with high quality factors (\Qm{}) enable mechanics-based quantum technologies, in particular quantum sensing and quantum transduction. High-\Qm{} nanomechanical resonators in the kHz to MHz frequency range can be realized in tensile-strained thin films that allow the use of dissipation dilution techniques to drastically increase \Qm{}. In our work, we study the material properties of tensile-strained piezoelectric films made from aluminium nitride (AlN). We characterize crystalline AlN films with a thickness ranging from \SI{45}{\nano\meter} to \SI{295}{\nano\meter}, which are directly grown on Si(111) by metal-organic vapour-phase epitaxy. We report on the crystal quality and surface roughness, the piezoelectric response, and the residual and released stress of the AlN thin films. Importantly, we determine the intrinsic quality factor of the films at room temperature in high vacuum. We fabricate and characterize AlN nanomechanical resonators that exploit dissipation dilution to enhance the intrinsic quality factor by utilizing the tensile strain in the film. We find that AlN nanomechanical resonators below \SI{200}{\nano\meter} thickness exhibit the highest \Qf{}-product, on the order of $10^{12}$\,Hz. We discuss possible strategies to optimize the material growth that should lead to devices that reach even higher \Qf{}-products. This will pave the way for future advancements of optoelectromechanical quantum devices made from tensile-strained piezoelectric AlN.
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Submitted 13 January, 2025; v1 submitted 4 October, 2024;
originally announced October 2024.
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Coherent Dipolar Coupling between Magnetoelastic Waves and Nitrogen Vacancy Centers
Authors:
Adi Jung,
Samuel Margueron,
Ausrine Bartasyte,
Sayeef Salahuddin
Abstract:
We experimentally demonstrate coherent Rabi oscillations of Nitrogen Vacancy (NV) centers by magnetoelastic waves. The coupling is consistent with dipolar stray field drive from spin-wave modes in a ferromagnetic film, and displays a significant improvement in Radio Frequency power efficiency relative to other methods of microwave excitation. Further, it demonstrates coherent coupling with NV cent…
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We experimentally demonstrate coherent Rabi oscillations of Nitrogen Vacancy (NV) centers by magnetoelastic waves. The coupling is consistent with dipolar stray field drive from spin-wave modes in a ferromagnetic film, and displays a significant improvement in Radio Frequency power efficiency relative to other methods of microwave excitation. Further, it demonstrates coherent coupling with NV centers over mm-scale distances from the microwave excitation source. By utilizing a piezoelectric-magnetostrictive heterostucture, where magnetoelastic waves can be launched by an applied voltage, a pure voltage driven coherent drive of the NV centers is achieved. This voltage driven, magnetoelastic excitation enables a new approach to couple with two level quantum states that is not reliant on long spin-wave coherence lengths.
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Submitted 18 September, 2024; v1 submitted 16 September, 2024;
originally announced September 2024.
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Energy efficient coherent quantum control of nitrogen vacancy (NV) spin with nanoscale magnets
Authors:
Md Fahim F Chowdhury,
Adi Jung,
Lea La Spina,
Ausrine Bartasyte,
Samuel Margueron,
Jayasimha Atulasimha
Abstract:
We investigate coherent quantum control of a nitrogen vacancy (NV) center in diamond with microwave fields generated from a nanoscale magnet that is proximal to the NV center. Our results show remarkable coherent control with high contrast Rabi oscillations using nearfield microwaves from shape anisotropic nanomagnets of lateral dimensions down to 200 nm x 180 nm, driven remotely by surface acoust…
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We investigate coherent quantum control of a nitrogen vacancy (NV) center in diamond with microwave fields generated from a nanoscale magnet that is proximal to the NV center. Our results show remarkable coherent control with high contrast Rabi oscillations using nearfield microwaves from shape anisotropic nanomagnets of lateral dimensions down to 200 nm x 180 nm, driven remotely by surface acoustic wave (SAW) excitation that is at least 400 times and potentially 4 orders of magnitude more energy efficient than generating microwaves with an antenna. Furthermore, we show that varying the acoustic power driving such nanomagnets can achieve control over Rabi frequency. We also report spin-lattice relaxation time T1 is 103 +/-0.5 micro-seconds, the spin-spin relaxation time T2 is 1.23+/-0.29 micro-seconds, and the Ramsey coherence time T2* is 218+/-27 nanoseconds measured using microwave pulses generated by such nanomagnets. The use of the nanoscale magnets to implement highly localized and energy efficient coherent quantum control can replace thermally noisy microwave circuits and demonstrate a path to scalable quantum computing and sensing with NV-defects in diamond and other spin qubits.
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Submitted 19 July, 2024;
originally announced July 2024.
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Nanomechanical crystalline AlN resonators with high quality factors for quantum optoelectromechanics
Authors:
Anastasiia Ciers,
Alexander Jung,
Joachim Ciers,
Laurentius Radit Nindito,
Hannes Pfeifer,
Armin Dadgar,
Andre Strittmatter,
Witlef Wieczorek
Abstract:
High-\Qm{} mechanical resonators are crucial for applications where low noise and long coherence time are required, as mirror suspensions, quantum cavity optomechanical devices, or nanomechanical sensors. Tensile strain in the material enables the use of dissipation dilution and strain engineering techniques, which increase the mechanical quality factor. These techniques have been employed for hig…
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High-\Qm{} mechanical resonators are crucial for applications where low noise and long coherence time are required, as mirror suspensions, quantum cavity optomechanical devices, or nanomechanical sensors. Tensile strain in the material enables the use of dissipation dilution and strain engineering techniques, which increase the mechanical quality factor. These techniques have been employed for high-\Qm{} mechanical resonators made from amorphous materials and, recently, from crystalline materials such as InGaP, SiC, and Si. A strained crystalline film exhibiting substantial piezoelectricity expands the capability of high-\Qm{} nanomechanical resonators to directly utilize electronic degrees of freedom. In this work we realize nanomechanical resonators with \Qm{} up to $2.9\times 10^{7}$ made from tensile-strained \SI{290}{\nano\meter}-thick AlN, which is an epitaxially-grown crystalline material offering strong piezoelectricity. We demonstrate nanomechanical resonators that exploit dissipation dilution and strain engineering to reach a \Qf-product approaching $10^{13}$\,\SI{}{\hertz} at room temperature. We realize a novel resonator geometry, triangline, whose shape follows the Al-N bonds and offers a central pad that we pattern with a photonic crystal. This allows us to reach an optical reflectivity above 80\% for efficient coupling to out-of-plane light. The presented results pave the way for quantum optoelectromechanical devices at room temperature based on tensile-strained AlN.
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Submitted 19 September, 2024; v1 submitted 19 February, 2024;
originally announced February 2024.
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Quantum Carnot thermal machines re-examined: Definition of efficiency and the effects of strong coupling
Authors:
Junjie Liu,
Kenneth A. Jung
Abstract:
Whether the strong coupling to thermal baths can improve the performance of quantum thermal machines remains an open issue under active debate. Here, we revisit quantum thermal machines operating with the quasi-static Carnot cycle and aim to unveil the role of strong coupling in maximum efficiency. Our analysis builds upon definitions of excess work and heat derived from an exact formulation of th…
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Whether the strong coupling to thermal baths can improve the performance of quantum thermal machines remains an open issue under active debate. Here, we revisit quantum thermal machines operating with the quasi-static Carnot cycle and aim to unveil the role of strong coupling in maximum efficiency. Our analysis builds upon definitions of excess work and heat derived from an exact formulation of the first law of thermodynamics for the working substance, which captures the non-Gibbsian thermal equilibrium state that emerges at strong couplings during quasi-static isothermal processes. These excess definitions differ from conventional ones by an energetic cost for maintaining the non-Gibbsian characteristics. With this distinction, we point out that one can introduce two different yet thermodynamically allowed definitions for efficiency of both the heat engine and refrigerator modes. We dub them excess and hybrid definitions which differ in the way of defining the gain for the thermal machines at strong couplings by either just analyzing the energetics of the working substance or instead evaluating the performance from an external system upon which the thermal machine acts, respectively. We analytically demonstrate that the excess definition predicts that the Carnot limit remains the upper bound for both operation modes at strong couplings, whereas the hybrid one reveals that strong coupling can suppress the maximum efficiency rendering the Carnot limit unattainable. These seemingly incompatible predictions thus indicate that it is imperative to first gauge the definition for efficiency before elucidating the exact role of strong coupling, thereby shedding light on the on-going investigation on strong-coupling quantum thermal machines.
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Submitted 2 February, 2024; v1 submitted 26 November, 2023;
originally announced November 2023.
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Surface acoustic wave resonators on thin film piezoelectric substrates in the quantum regime
Authors:
Thomas Luschmann,
Alexander Jung,
Stephan Geprägs,
Franz X. Haslbeck,
Achim Marx,
Stefan Filipp,
Simon Gröblacher,
Rudolf Gross,
Hans Huebl
Abstract:
Lithium niobate (LNO) is a well established material for surface acoustic wave (SAW) devices including resonators, delay lines and filters. Recently, multi-layer substrates based on LNO thin films have become commercially available. Here, we present a systematic low-temperature study of the performance of SAW devices fabricated on LNO-on-insulator and LNO-on-Silicon substrates and compare them to…
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Lithium niobate (LNO) is a well established material for surface acoustic wave (SAW) devices including resonators, delay lines and filters. Recently, multi-layer substrates based on LNO thin films have become commercially available. Here, we present a systematic low-temperature study of the performance of SAW devices fabricated on LNO-on-insulator and LNO-on-Silicon substrates and compare them to bulk LNO devices. Our study aims at assessing the performance of these substrates for quantum acoustics, i.e. the integration with superconducting circuits operating in the quantum regime. To this end, we design SAW resonators with a target frequency of 5 GHz and perform experiments at millikelvin temperatures and microwave power levels corresponding to single photons or phonons. The devices are investigated regarding their internal quality factors as a function of the excitation power and temperature, which allows us to characterize and quantify losses and identify the dominating loss mechanism. For the measured devices, fitting the experimental data shows that the quality factors are limited by the coupling of the resonator to a bath of two-level-systems. Our results suggest that SAW devices on thin film LNO on silicon have comparable performance to devices on bulk LNO and are viable for use in SAW-based quantum acoustic devices.
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Submitted 13 April, 2023; v1 submitted 26 January, 2023;
originally announced January 2023.
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Optimal linear cyclic quantum heat engines cannot benefit from strong coupling
Authors:
Junjie Liu,
Kenneth A. Jung
Abstract:
Uncovering whether strong system-bath coupling can be an advantageous operation resource for energy conversion can facilitate the development of efficient quantum heat engines (QHEs). Yet, a consensus on this ongoing debate is still lacking owing to challenges arising from treating strong couplings. Here we conclude the debate for optimal linear cyclic QHEs operated under a small temperature diffe…
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Uncovering whether strong system-bath coupling can be an advantageous operation resource for energy conversion can facilitate the development of efficient quantum heat engines (QHEs). Yet, a consensus on this ongoing debate is still lacking owing to challenges arising from treating strong couplings. Here we conclude the debate for optimal linear cyclic QHEs operated under a small temperature difference by revealing the detrimental role of strong system-bath coupling in their optimal operations. We analytically demonstrate that both the efficiency at maximum power and maximum efficiency of strong-coupling linear cyclic QHEs are upper bounded by their weak-coupling counterparts and, particularly, experience a quadratic suppression relative to the Carnot limit under strong time-reversal symmetry breaking.
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Submitted 4 July, 2022; v1 submitted 22 June, 2022;
originally announced June 2022.
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Optically induced anisotropy in time-resolved scattering: Imaging molecular scale structure and dynamics in disordered media with experiment and theory
Authors:
Andrés Montoya-Castillo,
Michael S. Chen,
Sumana L. Raj,
Kenneth A. Jung,
Kasper S. Kjaer,
Tobias Morawietz,
Kelly J. Gaffney,
Tim B. van Driel,
Thomas E. Markland
Abstract:
Time-resolved scattering experiments enable imaging of materials at the molecular scale with femtosecond time resolution. However, in disordered media they provide access to just one radial dimension thus limiting the study of orientational structure and dynamics. Here we introduce a rigorous and practical theoretical framework for predicting and interpreting experiments combining optically induce…
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Time-resolved scattering experiments enable imaging of materials at the molecular scale with femtosecond time resolution. However, in disordered media they provide access to just one radial dimension thus limiting the study of orientational structure and dynamics. Here we introduce a rigorous and practical theoretical framework for predicting and interpreting experiments combining optically induced anisotropy and time-resolved scattering. Using impulsive nuclear Raman and ultrafast X-ray scattering experiments of chloroform and simulations, we demonstrate that this framework can accurately predict and elucidate both the spatial and temporal features of these experiments.
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Submitted 7 February, 2022;
originally announced February 2022.
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Periodically-driven quantum thermal machines from warming up to limit cycle
Authors:
Junjie Liu,
Kenneth A. Jung,
Dvira Segal
Abstract:
Theoretical treatments of periodically-driven quantum thermal machines (PD-QTMs) are largely focused on the limit-cycle stage of operation characterized by a periodic state of the system. Yet, this regime is not immediately accessible for experimental verification. Here, we present a general thermodynamic framework that can handle the performance of PD-QTMs both before and during the limit-cycle s…
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Theoretical treatments of periodically-driven quantum thermal machines (PD-QTMs) are largely focused on the limit-cycle stage of operation characterized by a periodic state of the system. Yet, this regime is not immediately accessible for experimental verification. Here, we present a general thermodynamic framework that can handle the performance of PD-QTMs both before and during the limit-cycle stage of operation. It is achieved by observing that periodicity may break down at the ensemble average level, even in the limit-cycle phase. With this observation, and using conventional thermodynamic expressions for work and heat, we find that a complete description of the first law of thermodynamics for PD-QTMs requires a new contribution, which vanishes only in the limit-cycle phase under rather weak system-bath couplings. Significantly, this contribution is substantial at strong couplings even at limit cycle, thus largely affecting the behavior of the thermodynamic efficiency. We demonstrate our framework by simulating a quantum Otto engine building upon a driven resonant level model. Our results provide new insights towards a complete description of PD-QTMs, from turn-on to the limit-cycle stage and, particularly, shed light on the development of quantum thermodynamics at strong coupling.
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Submitted 21 June, 2021; v1 submitted 19 June, 2021;
originally announced June 2021.
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Interfilament Resistance at 77 K in Striated HTS Coated Conductors
Authors:
R. Gyuráki,
A. Godfrin,
A. Jung,
A. Kario,
R. Nast,
E. Demenčik,
W. Goldacker,
F. Grilli
Abstract:
Striating HTS coated conductor (CC) tapes into narrow filaments offers the possibility of reducing the tapes' magnetization losses without unreasonably decreasing their current-carrying capability. However, realizing well-separated striations presents technological challenges, especially if the number of filaments is large and/or if a thick layer of metallic stabilizer is present. In these situati…
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Striating HTS coated conductor (CC) tapes into narrow filaments offers the possibility of reducing the tapes' magnetization losses without unreasonably decreasing their current-carrying capability. However, realizing well-separated striations presents technological challenges, especially if the number of filaments is large and/or if a thick layer of metallic stabilizer is present. In these situations, the filaments can be easily coupled and their effectiveness to reduce magnetization losses is strongly diminished or eliminated. While the onset of coupling is well visible from magnetization loss measurements, the actual path of the coupling current is unknown. In this contribution we present a systematic study of the transverse resistance in HTS CC samples in order to get a deeper understanding of those paths. The measured samples differ in terms of manufacturer (SuperPower and SuperOx), and presence and thickness of stabilizer material. In addition, oxidation is used as a means to increase the resistance between the filaments in non-stabilized samples. The results are interpreted with a chain network model. This work provides useful insights on the factors determining the transverse resistance in striated HTS CCs, thus indicating ways to improve the effectiveness of the striation process for AC loss reduction.
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Submitted 16 January, 2017; v1 submitted 2 May, 2016;
originally announced May 2016.
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DC and AC Characterization of Pancake Coils Made from Roebel-Assembled Coated Conductor Cable
Authors:
Anna Kario,
Michal Vojenčiak,
Francesco Grilli,
Andrea Kling,
Alexandra Jung,
Jörg Brand,
Andrej Kudymow,
Johann Willms,
Uwe Walschburger,
Victor Zermeno,
Wilfried Goldacker
Abstract:
Roebel cables made of HTS coated conductors can carry high currents with a compact design and reduced AC losses. They are therefore good candidates for manufacturing coils for HTS applications such as motors and generators. In this paper we present the experimental DC and AC characterization of several coils assembled from a 5 meter long Roebel cable built at KIT, which differ in the number of tur…
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Roebel cables made of HTS coated conductors can carry high currents with a compact design and reduced AC losses. They are therefore good candidates for manufacturing coils for HTS applications such as motors and generators. In this paper we present the experimental DC and AC characterization of several coils assembled from a 5 meter long Roebel cable built at KIT, which differ in the number of turns and turn-to-turn spacing. Our experiments, supported by finite-element method (FEM) calculations, show that a more tightly wound Roebel coil, despite having a lower critical (and therefore operating) current, can produce a higher magnetic field than a loosely wound one. For a given magnetic field produced at the coil's center, all the coils have similar AC losses, with the exception of the most loosely wound one, which has much higher losses due to the relatively large current needed to produce the desired field. The experiments presented in this paper are carried out on the geometry of pancake coils made of Roebel cables, but they are exemplary of a more general strategy that, coupling experiments and numerical simulations, can be used to optimize the coil design with respect to different parameters, such as tape quantity, size, or AC loss, the relative importance of which is dictated by the specific application.
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Submitted 29 May, 2017; v1 submitted 4 August, 2014;
originally announced August 2014.
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AC loss and coupling currents in YBCO coated conductors with varying number of filaments
Authors:
Eduard Demencik,
Michal Vojenciak,
Anna Kario,
Rainer Nast,
Alexandra Jung,
Wilfried Goldacker,
Francesco Grilli
Abstract:
Striation of HTS coated conductors (CCs) as a way to reduce their magnetization AC losses has been the subject of intense research in the past years by several groups. While the principle of this approach is well understood, its practical application on commercial material to be used in power application is still far to be implemented due to manufacturing and technological constraints. Recent adva…
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Striation of HTS coated conductors (CCs) as a way to reduce their magnetization AC losses has been the subject of intense research in the past years by several groups. While the principle of this approach is well understood, its practical application on commercial material to be used in power application is still far to be implemented due to manufacturing and technological constraints. Recent advances in tape quality and striation technology are now enabling systematic investigations of the influence of the number of filaments on AC loss reduction with a consistency that was not available in the past. In this work we demonstrate the technological feasibility of reducing the magnetization losses of commercially available CC by striating them into a high number of filaments (up to 120). The loss reduction exceeds one order of magnitude and does not come at the expense of current-carrying capability: samples with 10 and 20 filaments are unaffected by the striation process, while samples with 80 and 120 filaments still retain 80 and 70% of the current-carrying potential, respectively. We also investigate the transverse resistivity in order to understand the paths followed by the coupling currents: we found that the coupling current prevalently flows in the metallic substrate, rather than in and out of the filaments. Finally, we use oxidation as a method to reduce the coupling currents and losses. The contribution of this work is three-fold: 1) It describes the know-how to produce a large number of high quality striations in commercially available CCs, greatly reducing their losses without extensively degrading their transport properties; 2) It provides a comprehensive characterization of said samples (e.g. measurements in a wide frequency range, transverse resistance profiles, influence of oxidation on DC and AC behavior); 3) It provides new insight on the patterns of the coupling currents.
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Submitted 29 May, 2017; v1 submitted 19 June, 2014;
originally announced June 2014.
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Kondo-like behaviors in magnetic and thermal properties of single crystal Tm5Si2Ge2
Authors:
J. H. Kim,
S. J. Kim,
C. I. Lee,
M. A. Jung,
H. J. Oh,
Jong-Soo Rhyee,
Younghun Jo,
Hiroyuki Mitani,
Hidetoshi Miyazaki,
Shin-ichi Kimura,
Y. S. Kwon
Abstract:
We grew the single crystal of stoichiometric Tm5Si2.0Ge2.0 using a Bridgeman method and performed XRD, EDS, magnetization, ac and dc magnetic susceptibilities, specific heat, electrical resistivity and XPS experiments. It crystallizes in orthorhombic Sm5Ge4-type structure. The mean valence of Tm ions in Tm5Si2.0Ge2.0 is almost trivalent. The 4f states is split by the crystalline electric field.…
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We grew the single crystal of stoichiometric Tm5Si2.0Ge2.0 using a Bridgeman method and performed XRD, EDS, magnetization, ac and dc magnetic susceptibilities, specific heat, electrical resistivity and XPS experiments. It crystallizes in orthorhombic Sm5Ge4-type structure. The mean valence of Tm ions in Tm5Si2.0Ge2.0 is almost trivalent. The 4f states is split by the crystalline electric field. The ground state exhibits the long range antiferromagnetic order with the ferromagnetically coupled magnetic moments in the ac plane below 8.01 K, while the exited states exhibit the reduction of magnetic moment and magnetic entropy and -log T-behaviors observed in Kondo materials.
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Submitted 30 November, 2009;
originally announced November 2009.
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Transformation of in-plane $ρ(T)$ in $YBa_{2}Cu_{3}O_{7-δ}$ at fixed oxygen content
Authors:
M. M. Abdelhadi,
J. A. Jung
Abstract:
This paper reveals the origin of variation in the magnitude and temperature dependence of the normal state resistivity frequently observed in different YBCO single crystal or thin film samples with the same $T_{c}$. We investigated temperature dependence of resistivity in $YBa_{2}Cu_{3}O_{7-δ}$ thin films with 7- $δ= 6.95$ and 6.90, which were subjected to annealing in argon at 400-420 K (…
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This paper reveals the origin of variation in the magnitude and temperature dependence of the normal state resistivity frequently observed in different YBCO single crystal or thin film samples with the same $T_{c}$. We investigated temperature dependence of resistivity in $YBa_{2}Cu_{3}O_{7-δ}$ thin films with 7- $δ= 6.95$ and 6.90, which were subjected to annealing in argon at 400-420 K ($120-140^{o}C$). Before annealing these films exhibited a non-linear $ρ_{ab}(T)$, with a flattening below 230 K, similar to $ρ_{b}(T)$ and $ρ_{ab}(T)$ observed in untwinned and twinned YBCO crystals, respectively. For all films the annealing causes an increase of resistivity and a transformation of $ρ_{ab}(T)$ from a non-linear dependence towards a more linear one (less flattening). In films with 7- $δ= 6.90$ the increase of resistivity is also associated with an increase in $T_{c}$. We proposed the model that provides an explanation of these phenomena in terms of thermally activated redistribution of residual O(5) oxygens in the chain-layer of YBCO. Good agreement between the experimental data for $ρ_{ab}(t,T)$, where t is the annealing time, and numerical calculations was obtained.
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Submitted 7 May, 2003;
originally announced May 2003.
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Ferrofluids as thermal ratchets
Authors:
Andreas Engel,
Hanns Walter Mueller,
Peter Reimann,
Achim Jung
Abstract:
Colloidal suspensions of ferromagnetic nano-particles, so-called ferrofluids, are shown to be suitable systems to demonstrate and investigate thermal ratchet behavior: By rectifying thermal fluctuations, angular momentum is transferred to a resting ferrofluid from an oscillating magnetic field without net rotating component. Via viscous coupling the noise driven rotation of the microscopic ferro…
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Colloidal suspensions of ferromagnetic nano-particles, so-called ferrofluids, are shown to be suitable systems to demonstrate and investigate thermal ratchet behavior: By rectifying thermal fluctuations, angular momentum is transferred to a resting ferrofluid from an oscillating magnetic field without net rotating component. Via viscous coupling the noise driven rotation of the microscopic ferromagnetic grains is transmitted to the carrier liquid to yield a macroscopic torque. For a simple setup we analyze the rotation of the ferrofluid theoretically and show that the results are compatible with the outcome of a simple demonstration experiment.
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Submitted 23 June, 2003; v1 submitted 5 September, 2002;
originally announced September 2002.
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Investigation of phase-slip-like resistivity in underdoped YBCO
Authors:
Maher M. Abdelhadi,
J. A. Jung
Abstract:
We investigated the anomalous peak resistivity below the onset $T_c$ in underdoped YBCO, reminiscent of that observed in 1D wires of conventional superconductors. We performed measurements of the angular dependence of resistivity $ρ(θ)$ in a magnetic field and the temperature dependence of resistivity $ρ(T)$, which exhibit a peak for $\textbf{B} \parallel$ ab-planes. This peak in $ρ(T)$ disappea…
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We investigated the anomalous peak resistivity below the onset $T_c$ in underdoped YBCO, reminiscent of that observed in 1D wires of conventional superconductors. We performed measurements of the angular dependence of resistivity $ρ(θ)$ in a magnetic field and the temperature dependence of resistivity $ρ(T)$, which exhibit a peak for $\textbf{B} \parallel$ ab-planes. This peak in $ρ(T)$ disappears for $\textbf{B} \parallel$ c-axis. The width of the corresponding maximum in $ρ(θ)$ at $θ=0^o$ ($\textbf{B} \parallel$ ab-planes) decreases with increasing c-axis component of the field ($B \sin θ$). The maximum in $ρ(θ)$ and $ρ(T)$ decreases with an increasing applied transport current. We analyzed the data using three different models of resistivity based on 2D resistor array, flux motion, and thermally activated phase-slips. Numerical calculations suggest that in a filamentary underdoped system, the phase-slip events could produce the anomalous resistivity close to $T_c$.
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Submitted 31 May, 2002;
originally announced June 2002.