Showing 1–41 of 41 results for author: Rosen, J

Data-driven discovery and rapid, direct synthesis of MXenes

Authors: Ali Saffar Shamshirgar, Guilherme Ribeiro Portugal, Soheil Ershadrad, Roman Ivanov, Martin Dahlqvist, Florian Chabanais, Sanjay Chakraborty, Rainer Traksmaa, Irina Hussainova, Fredrik Heintz, Per O. Å. Persson, Johanna Rosen

Abstract: MXenes, two-dimensional transition-metal carbides and nitrides, are typically obtained from MAX phases, yet historical reports suggest a broader, largely unexplored chemical space. Here we combine machine-learning-assisted database mining with experiments to uncover overlooked multilayer (ml) MXenes. Screening of repositories reveals a "Treasure Chest" of 38 previously synthesized but unrecognized… ▽ More MXenes, two-dimensional transition-metal carbides and nitrides, are typically obtained from MAX phases, yet historical reports suggest a broader, largely unexplored chemical space. Here we combine machine-learning-assisted database mining with experiments to uncover overlooked multilayer (ml) MXenes. Screening of repositories reveals a "Treasure Chest" of 38 previously synthesized but unrecognized ml-MXene candidates. Guided by these findings, we rediscover five MXenes using a rapid, scalable self-propagating high-temperature synthesis that requires no sustained external heating and completes within minutes. Inspired by the identified chemistries, we further realize 11 previously unexplored rare-earth-based M2CT2 MXenes (M= Pr, Nd, Sm, Gd, Tb, Ho, and Tm). Experiments and theory reveal semiconducting behavior and diverse magnetic states across this family. Together, these results expand the MXene family and demonstrate a data-driven strategy for accelerating materials discovery through sustainable methods. △ Less

Submitted 17 August, 2026; originally announced August 2026.

General and scalable vapor etching and transformation platform for two-dimensional materials

Authors: Zhiguo Du, Jikai Zhang, Jonas Björk, Zongju Cheng, Ningjun Chen, Qi Zhao, Hao Chen, Yuxuan Ye, Guang Yang, Haiyang Wang, Bin Li, Johanna Rosen, Shubin Yang

Abstract: Two-dimensional (2D) nanomaterials derived from non-van der Waals (non-vdW) solids offer exceptional physicochemical properties, yet their synthesis is impeded by intrinsic covalent/metallic bonding and high surface reactivity of the precursors. Here, we report a general vapor-phase etching and transformation platform for producing a library of 36 2D carbides, nitrides, and carbonitrides, exhibiti… ▽ More Two-dimensional (2D) nanomaterials derived from non-van der Waals (non-vdW) solids offer exceptional physicochemical properties, yet their synthesis is impeded by intrinsic covalent/metallic bonding and high surface reactivity of the precursors. Here, we report a general vapor-phase etching and transformation platform for producing a library of 36 2D carbides, nitrides, and carbonitrides, exhibiting electrical conductivities spanning six orders of magnitude. Using reactive vapors like hydrogen chloride, we selectively remove A-layers from MAX phases to yield well-defined layers (MXenes), including previously inaccessible semiconducting Hf2CTx. By varying the reactive vapor environment, MXenes can be engineered at X-site and surface-termination site and even be transformed into non-vdW layers such as 2D MAX phases. This general and scalable vapor-phase platform reframes 2D material synthesis, opening new avenues for various applications. △ Less

Submitted 16 July, 2026; originally announced July 2026.

Synthesis of Ti2B2Clx MBenes in molten salts from theoretical and experimental perspectives

Authors: Rodrigo M. Ronchi, Emile Defoy, Andrejs Petruhins, Justinas Palisaitis, Lianghao Yu, Lan Tang, Solenn Reguer, Dominique Thiaudière, Ningjun Chen, Durga Sankar Vavilapalli, David Portehault, Jonas Björk, Per O. Å. Persson, Johanna Rosen

Abstract: The unique properties and application possibilities of two-dimensional (2D) materials motivates the exploration of different nanolaminated compounds. Here, by using a molten salt approach, we selectively etch Ti2InB2 with ZnCl2 to produce a multilayer (ml) Ti2B2Clx MBene. Scanning transmission electron microscopy, in combination with energy dispersive X-ray, and electron energy loss spectroscopies… ▽ More The unique properties and application possibilities of two-dimensional (2D) materials motivates the exploration of different nanolaminated compounds. Here, by using a molten salt approach, we selectively etch Ti2InB2 with ZnCl2 to produce a multilayer (ml) Ti2B2Clx MBene. Scanning transmission electron microscopy, in combination with energy dispersive X-ray, and electron energy loss spectroscopies show that In atoms are completely removed from the precursor upon etching, being replaced by chlorine surface terminations with a coverage 1.1 < x < 1.4. Further, in situ X-ray diffraction indicates a direct biphasic transformation from Ti2InB2 to ml-MBene, with no signs of intermediate phase formation. A computational framework based on density functional theory further corroborates these experimental observations by showing a negative reaction free energy for the formation of ml-MBene, favourable over all competing processes. In addition, A-element substitution into to the 3D Ti2ZnB2 phase is predicted to be endergonic, consistent with the absence of experimental evidence for its formation. Initial Li-ion battery performance evaluation showed a stable discharge capacity similar or better than MAX phases and other borides. Altogether, the theoretical framework combined with materials synthesis and characterization provides a general approach for 2D materials development, for further expansion of the family of 2D materials. △ Less

Submitted 13 July, 2026; originally announced July 2026.

Comments: 4 figures, 27 pages

Benchmark Dataset for Catalysis on 2D MXenes

Authors: Pavlo Melnyk, Anmar Karmush, Mårten Wadenbäck, Ania Beatriz Rodríguez-Barrera, Johanna Rosen, Michael Felsberg, Jonas Björk

Abstract: Merging first-principles calculations with machine learning (ML), we aim to accelerate the exploration of catalytic behaviour in novel materials. We focus on two-dimensional (2D) Ti$_2$CT$_y$ MXenes, whose versatile surface chemistry makes them particularly compelling candidates for catalysis. Resolving their composition and structure under realistic conditions exceeds the reach of standard densit… ▽ More Merging first-principles calculations with machine learning (ML), we aim to accelerate the exploration of catalytic behaviour in novel materials. We focus on two-dimensional (2D) Ti$_2$CT$_y$ MXenes, whose versatile surface chemistry makes them particularly compelling candidates for catalysis. Resolving their composition and structure under realistic conditions exceeds the reach of standard density functional theory (DFT) due to computational cost. To address this challenge, we generate a comprehensive dataset of 50,000 DFT calculations for training and 10,000 for testing, encompassing both Ti$_2$CT$_y$ MXene configurations and molecular systems, along with an additional test dataset with 1000 genuinely new, larger systems to investigate how well models generalise. We train and validate widely used and competitive machine learning interatomic potential (MLIP) models, including EquiformerV2, MACE, MatRIS, and UPET, that accurately predict atomic forces and formation energies -- quantities that DFT must repeatedly compute for structural and catalytic investigations -- for these 2D materials. This combined DFT-ML framework achieves computational acceleration on the order of approximately $1-4 \cdot 10^3$ (on a CPU) while maintaining desired-level accuracy (approximately +/- $10$ meV/A for forces and approximately +/- $1$ meV for per-atom energies), paving the way for more efficient investigations of MXene catalytic behaviour. Moreover, we perform an extensive qualitative evaluation of the trained models, showcasing the importance of comprehensive simulation-based comparison beyond benchmark metrics. The dataset and the trained models with the code are available at https://huggingface.co/datasets/CatalystAnonymous/catalyst_mxenes. △ Less

Submitted 30 May, 2026; originally announced June 2026.

Generating Symmetric Materials using Latent Flow Matching

Authors: Anmar Karmush, Cedric Mathieu Brandenburg, Soheil Ershadrad, Johanna Rosén, Michael Felsberg, Filip Ekström Kelvinius

Abstract: Tackling the task of materials generation, we aim to enhance the previously proposed All-atom Diffusion Transformer (ADiT) by introducing SymADiT, a symmetry-aware variant. To do so, we use a representation of materials based on Wyckoff positions. We follow ADiT and perform generative modelling in latent space, adapted to our symmetry-aware representation. By forcing the output of the generative m… ▽ More Tackling the task of materials generation, we aim to enhance the previously proposed All-atom Diffusion Transformer (ADiT) by introducing SymADiT, a symmetry-aware variant. To do so, we use a representation of materials based on Wyckoff positions. We follow ADiT and perform generative modelling in latent space, adapted to our symmetry-aware representation. By forcing the output of the generative model to adhere to the symmetry restrictions imposed by the generated crystal's space group and each atom's Wyckoff-position, the generated materials exhibit more realistic symmetry properties. We benchmark our method against both symmetry-aware and symmetry-agnostic models for materials generation and show competitive performance, generating stable, symmetric materials with a simple Transformer architecture. △ Less

Submitted 11 May, 2026; originally announced May 2026.

Comments: Preprint

Exploring the Structure and Chemistry of 1D and 2D Lepidocrocite TiO2 at Atomic Resolution

Authors: Eric Nestor Tseng, Jonas Björk, Risha Achaiah Iythichanda, Wei Zheng, Hatim Alnoor, Wei Hsiang Huang, Ming-Hsien Lin, Johanna Rosén, Per O. Å. Persson

Abstract: Low dimensional materials are critical for enabling next generation applications that are central to addressing critical global challenges. Titanium dioxide nanostructures stand out due to their structural versatility and relevance to catalysis, energy conversion, and environmental remediation. Here, we employ a combination of advanced electron microscopy, spectroscopy, and first principles theore… ▽ More Low dimensional materials are critical for enabling next generation applications that are central to addressing critical global challenges. Titanium dioxide nanostructures stand out due to their structural versatility and relevance to catalysis, energy conversion, and environmental remediation. Here, we employ a combination of advanced electron microscopy, spectroscopy, and first principles theoretical calculations to investigate the structural and chemical properties of one and two dimensional lepidocrocite type titania. Special emphasis is placed on the one dimensional material, which exhibits anisotropic growth, extending exclusively along a single crystallographic direction. Our analysis suggests that this unusual growth behavior can be attributed to light element impurities, such as carbon, that are incorporated during the bottom up synthesis. The results extend the understanding for these unexplored low dimensional titania materials and offer fundamental insights into their structure and chemistry. △ Less

Submitted 25 March, 2026; originally announced March 2026.

Unveiling the Thermal and Aqueous Stability of 1D Lepidocrocite Titania

Authors: Risha A. Iythichanda, Sukanya Maity, Mustafa M. Aboulsaad, Tomas Edvinsson, Johanna Rosen, Per O. Å. Persson

Abstract: One dimensional lepidocrocite titanium dioxide filaments are investigated with respect to their thermal and aqueous stability. Structural and phase evolution are examined using in situ heating in vacuum within transmission electron microscopy combined with electron energy loss spectroscopy, and at ambient conditions using Raman spectroscopy. The filaments retain their lepidocrocite structure up to… ▽ More One dimensional lepidocrocite titanium dioxide filaments are investigated with respect to their thermal and aqueous stability. Structural and phase evolution are examined using in situ heating in vacuum within transmission electron microscopy combined with electron energy loss spectroscopy, and at ambient conditions using Raman spectroscopy. The filaments retain their lepidocrocite structure up to 300 degree and above which localized sintering and amorphization occur at filament overlap junctions. With further heating, the amorphous regions crystallize into anatase, with Raman spectroscopy corroborating the onset of structural disorder. Long term aqueous storage up to 100 days at ambient conditions induces transformation into flake like anatase nanoparticles. This process is strongly suppressed under refrigerated storage, where no structural changes are observed over the same period. These results establish critical thermal and environmental stability thresholds that define operational advantages and limits for emerging applications of 1D lepidocrocite filaments. △ Less

Submitted 9 March, 2026; originally announced March 2026.

Superconducting qubit decoherence correlated with detected radiation events

Authors: A. R. Castelli, K. M. Beck, L. D. H. Alegria, L. A. Martinez, K. R. Chaves, S. R. O'Kelley, N. Materise, J. L DuBois, Y. J. Rosen

Abstract: Most quantum error correction (QEC) protocols for superconducting qubits assume spatially and temporally uncorrelated decoherence events; however, recent evidence suggests that cosmic radiation induces spatially correlated errors. We present a platform that sandwiches a superconducting transmon qubit between two microwave kinetic inductance detector (MKID) arrays, enabling real-time detection of r… ▽ More Most quantum error correction (QEC) protocols for superconducting qubits assume spatially and temporally uncorrelated decoherence events; however, recent evidence suggests that cosmic radiation induces spatially correlated errors. We present a platform that sandwiches a superconducting transmon qubit between two microwave kinetic inductance detector (MKID) arrays, enabling real-time detection of radiation-induced phonon bursts. By synchronizing MKID event detection with single-shot measurements of qubit energy relaxation ($T_1$) and phase coherence ($T_2$), we observe statistically significant reductions in both $T_1$ and $T_2$-up to 30.5%-immediately following dual MKID events attributed to penetrating muons. Our findings directly link radiating events to correlated qubit decoherence. Furthermore, our experimental platform provides a foundation for systematic studies of radiation effects, the development of shielding and mitigation techniques, and the refinement of error-correction algorithms tailored to correlated noise sources. △ Less

Submitted 19 December, 2025; originally announced December 2025.

Comments: 10 pages, 9 figures

Report number: LLNL-JRNL-2008718

Non-equilibrium Dynamics of Two-level Systems directly after Cryogenic Alternating Bias

Authors: V. Iaia, E. S. Joseph, S. Im, N. Hagopian, S. O'Kelley, C. Kim, N. Materise, S. Patra, V. Lordi, M. A. Eriksson, P. M. Voyles, K. G. Ray, Y. J. Rosen

Abstract: Two-level systems (TLSs) are tunneling states commonly found in amorphous materials that electrically couple to qubits, resonators, and vibrational modes in materials, leading to energy loss in those systems. Recent studies suggest that applying a large alternating electric field changes the oxide structure, potentially improving the performance of qubits and resonators. In this study, we probe th… ▽ More Two-level systems (TLSs) are tunneling states commonly found in amorphous materials that electrically couple to qubits, resonators, and vibrational modes in materials, leading to energy loss in those systems. Recent studies suggest that applying a large alternating electric field changes the oxide structure, potentially improving the performance of qubits and resonators. In this study, we probe the effect of alternating bias at cryogenic temperatures on TLS dynamics within amorphous oxide parallel-plate capacitors operating in the strongly coupled regime. We bias the TLSs in the capacitors using an electric field. This allows us to spectroscopically image TLSs and extract their densities and dipole moments. When an in-situ alternating bias is applied, the steady-state spectra from the standard TLS model disappear. Post-alternating bias TLS spectroscopy reveals transient behavior, in which the TLS frequency fluctuates on the order of minutes. Thermal cycling above 10 K reverses these effects, restoring the TLS spectrum to its original state, indicating a reversible mechanism. Importantly, the intrinsic loss tangent of the LC oscillator remains unchanged before and after the application of the alternating bias. We propose that the disappearance of the steady-state spectrum are caused by non-equilibrium energy build up from strain in the oxide film introduced by the pulsed voltage bias sequence. Understanding this non-equilibrium energy could inform future models of time-dependent TLS dynamics. △ Less

Submitted 30 September, 2025; v1 submitted 23 September, 2025; originally announced September 2025.

Comments: 13 pages, 9 figures

Report number: LLNL-JRNL-2011522

Charge sensitivity in the transmon regime

Authors: Rocio Gonzalez-Meza, Vito Iaia, Anika Zaman, Hiu-Yung Wong, Yujin Cho, Kristin Beck, Yaniv J. Rosen

Abstract: Transmons are widely adopted in quantum computing architectures for their engineered insensitivity to charge noise and correspondingly long relaxation times. Despite this advantage, transmons often exhibit large fluctuations in dephasing times across different devices and also within qubits on the same device. Existing transmon qubits are assumed to be insensitive to charge noise. However, very li… ▽ More Transmons are widely adopted in quantum computing architectures for their engineered insensitivity to charge noise and correspondingly long relaxation times. Despite this advantage, transmons often exhibit large fluctuations in dephasing times across different devices and also within qubits on the same device. Existing transmon qubits are assumed to be insensitive to charge noise. However, very little recent attention has been paid to the dependence of dephasing on the local charge environment. In this study, we see fluctuations in the dephasing time, $T_φ$, which correlate to charge offset. While charge offset fluctuations are slow, parity switches are fast processes tied to the charge offset and can affect $T_φ$ in Ramsey experiments. We implement a protocol to detect parity switching events using single-shot methods, which are interleaved within a Ramsey measurement. We find that events that remain in the same parity state have a higher $T_2$ than measurements averaged over both parities. Our results show that transmons can be limited by charge-noise, even with $E_\text{J}/E_\text{C} \approx 50$. Consequently, parity flip rates must be considered as a device characterization metric. △ Less

Submitted 11 August, 2025; v1 submitted 5 August, 2025; originally announced August 2025.

Report number: LLNL-JRNL-2003358

Defect engineering and effect of vacancy concentration on the electrochemical performance of V-based MXenes

Authors: Leiqiang Qin, Rutuparna Samal, Jianxia Jiang, Joseph Halim, Ningjun Chen, Florian Chabanais, Per O. A. Persson, Johanna Rosen

Abstract: Vacancies play a pivotal role in determining the physical and chemical properties of materials. Introducing vacancies into two-dimensional (2D) materials offers a promising strategy for developing high-performance electrode materials for electrochemical energy storage. Herein, a facile top-down strategy is employed to create V-based MXenes with tunable vacancy concentrations, achieved by designing… ▽ More Vacancies play a pivotal role in determining the physical and chemical properties of materials. Introducing vacancies into two-dimensional (2D) materials offers a promising strategy for developing high-performance electrode materials for electrochemical energy storage. Herein, a facile top-down strategy is employed to create V-based MXenes with tunable vacancy concentrations, achieved by designing the precursor (V1-xCrx)2AlC (x=0.05, 0.1, 0.3) MAX phase and precisely controlling the etching process. Systematic investigations reveal that introducing a moderate concentration of Cr-induced vacancies significantly enhances both the capacitance and rate performance of V-based MXenes. Specifically, V1.9CTz achieves a capacitance of 760 F g-1, far exceeding the 420 F g-1 of vacancy-free V2CTz MXene. In contrast, an excessively high vacancy concentration lead to deteriorated electrochemical performance and compromised structural stability. This work illustrates that defect engineering is a powerful approach to tailor the electrochemical properties of MXenes, offering a framework for designing next-generation MXene-based energy storage systems. △ Less

Submitted 7 May, 2025; originally announced May 2025.

The 2D Materials Roadmap

Authors: Wencai Ren, Peter Bøggild, Joan Redwing, Kostya Novoselov, Luzhao Sun, Yue Qi, Kaicheng Jia, Zhongfan Liu, Oliver Burton, Jack Alexander-Webber, Stephan Hofmann, Yang Cao, Yu Long, Quan-Hong Yang, Dan Li, Soo Ho Choi, Ki Kang Kim, Young Hee Lee, Mian Li, Qing Huang, Yury Gogotsi, Nicholas Clark, Amy Carl, Roman Gorbachev, Thomas Olsen , et al. (48 additional authors not shown)

Abstract: Over the past two decades, 2D materials have rapidly evolved into a diverse and expanding family of material platforms. Many members of this materials class have demonstrated their potential to deliver transformative impact on fundamental research and technological applications across different fields. In this roadmap, we provide an overview of the key aspects of 2D material research and developme… ▽ More Over the past two decades, 2D materials have rapidly evolved into a diverse and expanding family of material platforms. Many members of this materials class have demonstrated their potential to deliver transformative impact on fundamental research and technological applications across different fields. In this roadmap, we provide an overview of the key aspects of 2D material research and development, spanning synthesis, properties and commercial applications. We specifically present roadmaps for high impact 2D materials, including graphene and its derivatives, transition metal dichalcogenides, MXenes as well as their heterostructures and moiré systems. The discussions are organized into thematic sections covering emerging research areas (e.g., twisted electronics, moiré nano-optoelectronics, polaritronics, quantum photonics, and neuromorphic computing), breakthrough applications in key technologies (e.g., 2D transistors, energy storage, electrocatalysis, filtration and separation, thermal management, flexible electronics, sensing, electromagnetic interference shielding, and composites) and other important topics (computational discovery of novel materials, commercialization and standardization). This roadmap focuses on the current research landscape, future challenges and scientific and technological advances required to address, with the intent to provide useful references for promoting the development of 2D materials. △ Less

Submitted 28 April, 2025; v1 submitted 28 March, 2025; originally announced March 2025.

Comments: 97 pages, to be published in 2D Materials

Hidden magnetic phases in i-MAX compounds

Authors: Dror Yahav, Ariel Maniv, Daniel Potashnikov, Asaf Pesach, El'ad N. Caspi, Arneil P. Reyes, Quanzheng Tao, Johanna Rosen, Eran Maniv

Abstract: We uncover a high-field magnetic phase in i-MAX compounds exhibiting a canted antiferromagnetic (AFM) order with unprecedented properties, revealed through NMR and AC susceptibility. Intriguingly, as the atomic number of Rare Earth increases, the transition field of this canted AFM phase grows at the expense of the lower-field AFM state. Our findings point to the complexity of the magnetic structu… ▽ More We uncover a high-field magnetic phase in i-MAX compounds exhibiting a canted antiferromagnetic (AFM) order with unprecedented properties, revealed through NMR and AC susceptibility. Intriguingly, as the atomic number of Rare Earth increases, the transition field of this canted AFM phase grows at the expense of the lower-field AFM state. Our findings point to the complexity of the magnetic structure in i-MAX compounds, demonstrating a non-trivial evolution of their phase diagram while increasing both the atomic number of the Rare Earth element and the external field. △ Less

Submitted 3 December, 2024; originally announced December 2024.

Comments: 8 pages, 5 figures

Crystallization of Binary Nanocrystal Superlattices and the Relevance of Short-Range Attraction

Authors: Emanuele Marino, R. Allen LaCour, Timothy C. Moore, Sjoerd W. van Dongen, Austin W. Keller, Di An, Shengsong Yang, Daniel J. Rosen, Guillaume Gouget, Esther H. R. Tsai, Cherie R. Kagan, Thomas E. Kodger, Sharon C. Glotzer, Christopher B. Murray

Abstract: The synthesis of binary nanocrystal superlattices (BNSLs) enables the targeted integration of orthogonal physical properties, like photoluminescence and magnetism, into a single superstructure, unlocking a vast design space for multifunctional materials. Yet, the formation mechanism of BNSLs remains poorly understood, restricting the use of simulation to predict the structure and properties of the… ▽ More The synthesis of binary nanocrystal superlattices (BNSLs) enables the targeted integration of orthogonal physical properties, like photoluminescence and magnetism, into a single superstructure, unlocking a vast design space for multifunctional materials. Yet, the formation mechanism of BNSLs remains poorly understood, restricting the use of simulation to predict the structure and properties of the superlattices. Here, we use a combination of in situ scattering and molecular simulation to elucidate the self-assembly of two common BNSLs through emulsion templating. Our self-assembly experiments reveal that no intermediate structures precede the formation of the final binary phases, indicating that their formation proceeds through classical nucleation. Using simulations, we find that, despite the formation of AlB2 and NaZn13 typically being attributed to entropy, their self-assembly is most consistent with the nanocrystals possessing short-range interparticle attraction, which we find can dramatically accelerate nucleation kinetics in BNSLs. We also find homogenous, classical nucleation in simulation, corroborating our experiments. These results establish a robust correspondence between experiment and theory, paving the way towards a priori prediction of BNSLs. △ Less

Submitted 22 October, 2024; originally announced October 2024.

Journal ref: Nature Synthesis 3, 111-122, 2024

Growth and Structure of alpha-Ta films for Quantum Circuit Integration

Authors: Loren D. Alegria, Alex Abelson, Eunjeong Kim, Soohyun Im, Paul M. Voyles, Vincenzo Lordi, Jonathan L Dubois, Yaniv J. Rosen

Abstract: Tantalum films incorporated into superconducting circuits have exhibited low surface losses, resulting in long-lived qubit states. Remaining loss pathways originate in microscopic defects which manifest as two level systems (TLS) at low temperature. These defects limit performance, so careful attention to tantalum film structures is critical for optimal use in quantum devices. In this work, we inv… ▽ More Tantalum films incorporated into superconducting circuits have exhibited low surface losses, resulting in long-lived qubit states. Remaining loss pathways originate in microscopic defects which manifest as two level systems (TLS) at low temperature. These defects limit performance, so careful attention to tantalum film structures is critical for optimal use in quantum devices. In this work, we investigate the growth of tantalum using magnetron sputtering on sapphire, Si, and photoresist substrates. In the case of sapphire, we present procedures for growth of fully-oriented films with alpha-Ta [1 1 1] // Al2O3 [0 0 0 1] and alpha-Ta [1 -1 0] // Al2O3 [1 0 -1 0] orientational relationships, and having residual resistivity ratios (RRR) ~ 60 for 220 nm thick films. On Si, we find a complex grain texturing with Ta [1 1 0] normal to the substrate and RRR ~ 30. We further demonstrate airbridge fabrication using Nb to nucleate alpha-Ta on photoresist surfaces. For the films on sapphire, resonators show TLS-limited quality factors of 1.3 +/- 0.3 x 10^6 at 10 mK (for waveguide gap and conductor widths of 3 microns and 6 microns, respectively). Structural characterization using scanning electron microscopy, X-ray diffraction, low temperature transport, secondary ion mass spectrometry, and transmission electron microscopy reveal the dependence of residual impurities and screw dislocation density on processing conditions. The results provide practical insights for fabrication of advanced superconducting devices including qubit arrays, and guide future work on crystallographically deterministic qubit fabrication. △ Less

Submitted 9 January, 2025; v1 submitted 12 May, 2024; originally announced May 2024.

Red shift of the superconductivity cavity resonance in Josephson junction qubits as a direct signature of TLS population inversion

Authors: Alexander L. Burin, Moshe Schechter, Daniel Tennant, Keith G. Ray, Yaniv J. Rosen

Abstract: Quantum two-level systems (TLSs) limit the performance of superconducting qubits and superconducting and optomechanical resonators breaking down the coherence and absorbing the energy of oscillations. TLS absorption can be suppressed or even switched to the gain regime by inverting TLS populations. Here we theoretically explore the regime where the full inversion of TLS populations is attained at… ▽ More Quantum two-level systems (TLSs) limit the performance of superconducting qubits and superconducting and optomechanical resonators breaking down the coherence and absorbing the energy of oscillations. TLS absorption can be suppressed or even switched to the gain regime by inverting TLS populations. Here we theoretically explore the regime where the full inversion of TLS populations is attained at energies below a pump field quantization energy by simultaneously applying the pump field and the time varying bias. This regime is attained changing the bias sufficiently slowly to fully invert TLS populations when their energies cross resonance with the pump field and sufficiently fast to avoid TLS relaxation between two resonance crossing events. This population inversion is accompanied by a significant red shift of cavity resonance due to quantum level repulsion. The red-shift in frequency serves as a signature of the population inversion, as its re-entrant behavior as function of bias sweep rate and of the magnitude of the pump field allows the determination of the TLSs dipole moment and relaxation time. The predicted behavior is qualitatively consistent with the recent experimental observations in Al superconducting resonators. △ Less

Submitted 7 February, 2024; v1 submitted 28 January, 2024; originally announced January 2024.

Comments: 9 pages, 6 figures, to be submitted, comments are welcome!

Two-Level Systems in Nucleated and Non-Nucleated Epitaxial alpha-Tantalum films

Authors: L. D. Alegria, D. M. Tennant, K. R. Chaves, J. R. I. Lee, S. R. O'Kelley, Y. J. Rosen, J L DuBois

Abstract: Building usefully coherent superconducting quantum processors depends on reducing losses in their constituent materials. Tantalum, like niobium, has proven utility as the primary superconducting layer within highly coherent qubits. But, unlike Nb, high temperatures are typically used to stabilize the desirable body-centered-cubic phase, alpha-Ta, during thin film deposition. It has long been known… ▽ More Building usefully coherent superconducting quantum processors depends on reducing losses in their constituent materials. Tantalum, like niobium, has proven utility as the primary superconducting layer within highly coherent qubits. But, unlike Nb, high temperatures are typically used to stabilize the desirable body-centered-cubic phase, alpha-Ta, during thin film deposition. It has long been known that a thin Nb layer permits the room-temperature nucleation of alpha-Ta, although neither an epitaxial process nor few-photon microwave loss measurements have been reported for Nb-nucleated Ta films prior to this study. We compare resonators patterned from Ta films grown at high temperature (500 °C) and films nucleated at room temperature, in order to understand the impact of crystalline order on quantum coherence. In both cases, films grew with Al2O3 (001) || Ta (110) indicating that the epitaxial orientation is independent of temperature and is preserved across the Nb/Ta interface. We use conventional low-power spectroscopy to measure two level system (TLS) loss, as well as an electric-field bias technique to measure the effective dipole moments of TLS in the surfaces of resonators. In our measurements, Nb-nucleated Ta resonators had greater loss tangent (1.5 +/- 0.1 x 10^-5) than non-nucleated (5 +/- 1 x 10^-6) in approximate proportion to defect densities as characterized by X-ray diffraction (0.27 ° vs 0.18 ° [110] reflection width) and electron microscopy (30 nm vs 70 nm domain size). The dependence of the loss tangent on domain size indicates that the development of more ordered Ta films is likely to lead to improvements in qubit coherence times. Moreover, low-temperature alpha-Ta epitaxy may enable the growth of new, microstate-free heterostructures which would not withstand high temperature processing. △ Less

Submitted 18 September, 2023; v1 submitted 24 January, 2023; originally announced January 2023.

Journal ref: Appl. Phys. Lett. 123, 062601 (2023)

Tunable Localized Charge Transfer Excitons in a Mixed Dimensional van der Waals Heterostructure

Authors: Mahfujur Rahaman, Emanuele Marino, Alan G. Joly, Seunguk Song, Zhiqiao Jiang, Brian T. OCallahan, Daniel J. Rosen, Kiyoung Jo, Gwangwoo Kim, Patrick Z. El-Khoury, Christopher B. Murray, Deep Jariwala

Abstract: Observation of interlayer, charge-transfer (CT) excitons in van der Waals heterostructures (vdWHs) based on 2D-2D systems has been well investigated. While conceptually interesting, these charge transfer excitons are highly delocalized and spatially localizing them requires twisting layers at very specific angles. This issue of localizing the CT excitons can be overcome via making mixed dimensiona… ▽ More Observation of interlayer, charge-transfer (CT) excitons in van der Waals heterostructures (vdWHs) based on 2D-2D systems has been well investigated. While conceptually interesting, these charge transfer excitons are highly delocalized and spatially localizing them requires twisting layers at very specific angles. This issue of localizing the CT excitons can be overcome via making mixed dimensional vdWHs (MDHs) where one of the components is a spatially quantum confined medium. Here, we demonstrate the formation of CT excitons in a 2D/quasi-2D system comprising MoSe2 and WSe2 monolayers and CdSe/CdS based core/shell nanoplates (NPLs). Spectral signatures of CT excitons in our MDHs were resolved locally at the 2D/single-NPL heterointerface using tip-enhanced photoluminescence (TEPL) at room temperature. By varying both the 2D material, the shell thickness of the NPLs, and applying out-of-plane electric field, the exciton resonance energy was tuned by up to 120 meV. Our finding is a significant step towards the realization of highly tunable MDH-based next generation photonic devices. △ Less

Submitted 22 October, 2022; originally announced October 2022.

Comments: 4 figures, 20 pages

Yttrium incorporation in Cr2AlC: On the metastable phase formation and decomposition of (Cr,Y)2AlC MAX phase thin films

Authors: Clio Azina, Tim Bartsch, Damian M. Holzapfel, Martin Dahlqvist, Johanna Rosen, Lukas Löfler, Alba San Jose Mendez, Marcus Hans, Daniel Primetzhofer, Jochen M. Schneider

Abstract: Herein we report on the synthesis of a metastable (Cr,Y)2AlC MAX phase solid solution by co-sputtering from a composite Cr-Al-C and elemental Y target, at room temperature, followed by annealing. While direct high-temperature synthesis resulted in multiphase films, as evidenced by X-ray diffraction analyses, room temperature depositions, followed by annealing to 760 °C led to the formation of phas… ▽ More Herein we report on the synthesis of a metastable (Cr,Y)2AlC MAX phase solid solution by co-sputtering from a composite Cr-Al-C and elemental Y target, at room temperature, followed by annealing. While direct high-temperature synthesis resulted in multiphase films, as evidenced by X-ray diffraction analyses, room temperature depositions, followed by annealing to 760 °C led to the formation of phase pure (Cr,Y)2AlC by diffusion. Higher annealing temperatures caused decomposition of the metastable phase into Cr2AlC, Y5Al3 , and Cr-carbides. In contrast to pure Cr2AlC, the Y-containing phase crystallizes directly in the MAX phase structure instead of first forming a disordered solid solution. Furthermore, the crystallization temperature was shown to be Y-content dependent and was increased by ~200 °C for 5 at.% Y compared to Cr2AlC. Calculations predicting the metastable phase formation of (Cr,Y)2AlC and its decomposition are in excellent agreement with the experimental findings. △ Less

Submitted 15 September, 2022; originally announced September 2022.

Comments: submitted to Journal of the American Ceramic Society, 9 Figures, 30 pages total

Correlation strength, orbital-selective incoherence, and local moments formation in the magnetic MAX-phase Mn$_2$GaC

Authors: H. J. M. Jönsson, M. Ekholm, I. Leonov, M. Dahlqvist, J. Rosen, I. A. Abrikosov

Abstract: We perform a theoretical study of the electronic structure and magnetic properties of the prototypical magnetic MAX-phase Mn$_2$GaC with the main focus given to the origin of magnetic interactions in this system. Using the density functional theory+dynamical mean-field theory (DFT+DMFT) method we explore the effects of electron-electron interactions and magnetic correlations on the electronic prop… ▽ More We perform a theoretical study of the electronic structure and magnetic properties of the prototypical magnetic MAX-phase Mn$_2$GaC with the main focus given to the origin of magnetic interactions in this system. Using the density functional theory+dynamical mean-field theory (DFT+DMFT) method we explore the effects of electron-electron interactions and magnetic correlations on the electronic properties, magnetic state, and spectral weight coherence of paramagnetic and magnetically-ordered phases of Mn$_2$GaC. We also benchmark the DFT-based disordered local moment approach for this system by comparing the obtained electronic and magnetic properties with that of the DFT+DMFT method. Our results reveal a complex magnetic behavior characterized by a near degeneracy of the ferro- and antiferromagnetic configurations of Mn$_2$GaC, implying a high sensitivity of its magnetic state to fine details of the crystal structure and unit-cell volume, consistent with experimental observations. We observe robust local-moment behavior and orbital-selective incoherence of the spectral properties of Mn$_2$GaC, implying the importance of orbital-dependent localization of the Mn $3d$ states. We find that Mn$_2$GaC can be described in terms of local magnetic moments, which may be modeled by DFT with disordered local moments. However, the magnetic properties are dictated by the proximity to the regime of formation of local magnetic moments, in which the localization is in fact driven by the Hund's exchange interaction, and not the Coulomb interaction. △ Less

Submitted 19 January, 2022; originally announced January 2022.

Journal ref: Phys. Rev. B 105, 035125 - Published 18 January 2022

Experimentally revealing anomalously large dipoles in a quantum-circuit dielectric

Authors: Liuqi Yu, Shlomi Matityahu, Yaniv J. Rosen, Chih-Chiao Hung, Andrii Maksymov, Alexander L. Burin, Moshe Schechter, Kevin D. Osborn

Abstract: Quantum two-level systems (TLSs) intrinsic to glasses induce decoherence in many modern quantum devices, such as superconducting qubits. Although the low-temperature physics of these TLSs is usually well-explained by a phenomenological standard tunneling model of independent TLSs, the nature of these TLSs, as well as their behavior out of equilibrium and at high energies above 1 K, remain inconclu… ▽ More Quantum two-level systems (TLSs) intrinsic to glasses induce decoherence in many modern quantum devices, such as superconducting qubits. Although the low-temperature physics of these TLSs is usually well-explained by a phenomenological standard tunneling model of independent TLSs, the nature of these TLSs, as well as their behavior out of equilibrium and at high energies above 1 K, remain inconclusive. Here we measure the non-equilibrium dielectric loss of TLSs in amorphous silicon using a superconducting resonator, where energies of TLSs are varied in time using a swept electric field. Our results show the existence of two distinct ensembles of TLSs, interacting weakly and strongly with phonons, where the latter also possesses anomalously large electric dipole moment. These results may shed new light on the low temperature characteristics of amorphous solids, and hold implications to experiments and applications in quantum devices using time-varying electric fields. △ Less

Submitted 28 July, 2022; v1 submitted 20 October, 2021; originally announced October 2021.

Journal ref: Sci Rep 12, 16960 (2022)

Low frequency correlated charge noise measurements across multiple energy transitions in a tantalum transmon

Authors: Daniel M. Tennant, Luis A. Martinez, Kristin M. Beck, Sean R. O'Kelley, Christopher D. Wilen, R. McDermott, Jonathan L DuBois, Yaniv J. Rosen

Abstract: Transmon qubits fabricated with tantalum metal have been shown to possess energy relaxation times greater than 300 $μ$s and, as such, present an attractive platform for high precision, correlated noise studies across multiple higher energy transitions. Tracking the multi-level fluctuating qudit frequencies with a precision enabled by the high coherence of the device allows us to extract the charge… ▽ More Transmon qubits fabricated with tantalum metal have been shown to possess energy relaxation times greater than 300 $μ$s and, as such, present an attractive platform for high precision, correlated noise studies across multiple higher energy transitions. Tracking the multi-level fluctuating qudit frequencies with a precision enabled by the high coherence of the device allows us to extract the charge offset and quasi-particle dynamics. We observe qualitatively different charge offset behavior in the tantalum device than those measured in previous low frequency charge noise studies. In particular, we find the charge offset dynamics are dominated by rare, discrete jumps between a finite number of quasi-stationary charge configurations, a previously unobserved charge noise process in superconducting qubits. △ Less

Submitted 29 November, 2021; v1 submitted 15 June, 2021; originally announced June 2021.

Comments: 19 pages, 11 figures

Magnetic structure determination of rare-earth based, high moment, atomic laminates; potential parent materials for 2D magnets

Authors: Daniel Potashnikov, Elad Nisan Caspi, Asaf Pesach, Quanzheng Tao, Johanna Rosen, Denis Sheptyakov, Hayden A. Evans, Clemens Ritter, Zaher Salman, Pietro Bonfa, Thierry Ouisse, Maxime Barbier, Oleg Rivin, Amit Keren

Abstract: We report muon spin rotation ($μ$SR) and neutron diffraction on the rare-earth based magnets (Mo$_{2/3}$RE$_{1/3}$)$_2$AlC, also predicted as parent materials for 2D derivatives, where RE = Nd, Gd (only ($μ$SR), Tb, Dy, Ho and Er. By crossing information between the two techniques, we determine the magnetic moment ($m$), structure, and dynamic properties of all compounds. We find that only for RE… ▽ More We report muon spin rotation ($μ$SR) and neutron diffraction on the rare-earth based magnets (Mo$_{2/3}$RE$_{1/3}$)$_2$AlC, also predicted as parent materials for 2D derivatives, where RE = Nd, Gd (only ($μ$SR), Tb, Dy, Ho and Er. By crossing information between the two techniques, we determine the magnetic moment ($m$), structure, and dynamic properties of all compounds. We find that only for RE = Nd and Gd the moments are frozen on a microsecond time scale. Out of these two, the most promising compound for a potential 2D high ($m$) magnet is the Gd variant, since the parent crystals are pristine with $m = 6.5 \pm 0.5 μ_B$, Néel temperature of $29 \pm 1$ K, and the magnetic anisotropy between in and out of plane coupling is smaller than $10^{-8}$. This result suggests that magnetic ordering in the Gd variant is dominated by in-plane magnetic interactions and should therefore remain stable if exfoliated into 2D sheets. △ Less

Submitted 21 September, 2021; v1 submitted 30 May, 2021; originally announced May 2021.

Comments: Includes Supplementary Information

Origin of Mechanical and Dielectric Losses from Two-Level Systems in Amorphous Silicon

Authors: M. Molina-Ruiz, Y. J. Rosen, H. C. Jacks, M. R. Abernathy, T. H. Metcalf, X. Liu, J. L Dubois, F. Hellman

Abstract: Amorphous silicon contains tunneling two-level systems, which are the dominant energy loss mechanisms for amorphous solids at low temperatures. These two-level systems affect both mechanical and electromagnetic oscillators and are believed to produce thermal and electromagnetic noise and energy loss. However, it is unclear whether the two-level systems that dominate mechanical and dielectric losse… ▽ More Amorphous silicon contains tunneling two-level systems, which are the dominant energy loss mechanisms for amorphous solids at low temperatures. These two-level systems affect both mechanical and electromagnetic oscillators and are believed to produce thermal and electromagnetic noise and energy loss. However, it is unclear whether the two-level systems that dominate mechanical and dielectric losses are the same; the former relies on phonon-TLS coupling, with an elastic field coupling constant, $γ$, while the latter depends on a TLS dipole moment, $p_0$, which couples to the electromagnetic field. Mechanical and dielectric loss measurements as well as structural characterization were performed on amorphous silicon thin films grown by electron beam deposition with a range of growth parameters. Samples grown at 425 $^{\circ}$C show a large reduction of mechanical loss (34 times) and a far smaller reduction of dielectric loss (2.3 times) compared to those grown at room temperature. Additionally, mechanical loss shows lower loss per unit volume for thicker films, while dielectric loss shows lower loss per unit volume for thinner films. Analysis of these results indicate that mechanical loss correlates with atomic density, while dielectric loss correlates with dangling bond density, suggesting a different origin for these two energy dissipation processes in amorphous silicon. △ Less

Submitted 17 August, 2020; originally announced August 2020.

Comments: 17 pages, 4 figures, 1 table

Journal ref: Phys. Rev. Materials 5, 035601 (2021)

Compatibility of $Zr_{2}AlC$ MAX phase-based ceramics with oxygen-poor, static liquid lead-bismuth eutectic

Authors: Bensu Tunca, Thomas Lapauw, Carolien Callaert, Joke Hadermann, Remi Delville, El'ad N. Caspi, Martin Dahlqvist, Johanna Rosén, Amalraj Marshal, Konda G. Pradeep, Jochen M. Schneider, Jozef Vleugels, Konstantina Lambrinou

Abstract: This work investigates the compatibility of $Zr_{2}AlC$ MAX phase-based ceramics with liquid LBE, and proposes a mechanism to explain the observed local $Zr_{2}AlC$/LBE interaction. The ceramics were exposed to oxygen-poor ($C_{O}\le2.2 \cdot10^{-10}$ mass%), static liquid LBE at 500°C for 1000 h. A new $Zr_{2}(Al,Bi,Pb)C$ MAX phase solid solution formed in-situ in the LBE-affected $Zr_{2}AlC$ gra… ▽ More This work investigates the compatibility of $Zr_{2}AlC$ MAX phase-based ceramics with liquid LBE, and proposes a mechanism to explain the observed local $Zr_{2}AlC$/LBE interaction. The ceramics were exposed to oxygen-poor ($C_{O}\le2.2 \cdot10^{-10}$ mass%), static liquid LBE at 500°C for 1000 h. A new $Zr_{2}(Al,Bi,Pb)C$ MAX phase solid solution formed in-situ in the LBE-affected $Zr_{2}AlC$ grains. Out-of-plane ordering was favorable in the new solid solution, whereby $\textit{A}$-layers with high and low-Bi/Pb contents alternated in the crystal structure, in agreement with first-principles calculations. Bulk $Zr_{2}(Al,Bi,Pb)C$ was synthesized by reactive hot pressing to study the crystal structure of the solid solution by neutron diffraction. △ Less

Submitted 4 May, 2020; originally announced May 2020.

Deposition of MAX phase containing thin films from a (Ti,Zr)2AlC compound target

Authors: Clio Azina, Bensu Tunca, Andrejs Petruhins, Binbin Xin, Melike Yildizhan, Per O. Å. Persson, Jozef Vleugels, Konstantina Lambrinou, Johanna Rosén, Per Eklund

Abstract: This work reports on sputter depositions carried out from a compound (Ti,Zr)2AlC target, whereupon Al-containing (Ti,Zr)C thin films (30-40 nm in thickness) were deposited on MgO(111) and Al2O3(0001) substrates at temperatures ranging between 500 and 900 °C. The presence of Al within the carbide structure was evidenced by lattice parameter variations. Furthermore, chemical analyses showed that the… ▽ More This work reports on sputter depositions carried out from a compound (Ti,Zr)2AlC target, whereupon Al-containing (Ti,Zr)C thin films (30-40 nm in thickness) were deposited on MgO(111) and Al2O3(0001) substrates at temperatures ranging between 500 and 900 °C. The presence of Al within the carbide structure was evidenced by lattice parameter variations. Furthermore, chemical analyses showed that the Al distribution throughout the film thickness was fairly homogeneous. Thicker films (80-90 nm) deposited from the same compound target consisted of the pseudo-binary (Ti,Zr)C and intermetallic compounds in the Ti-Zr-Al system up to 800 °C, as well as solid solution MAX phases with different Ti:Zr ratios at 900 °C. X-ray diffraction and transmission electron microscopy showed that both (Ti,Zr)2AlC and (Ti,Zr)3AlC2 solid solution MAX phases were formed. Moreover, this work discusses the growth mechanism of the thicker films, which started with the formation of the mixed (Ti,Zr)C carbide, followed by the nucleation and growth of aluminides, eventually leading to the formation of the MAX phases, which was the primary objective of the sputter depositions. △ Less

Submitted 12 August, 2020; v1 submitted 9 September, 2019; originally announced September 2019.

Anomalous Charge Noise in Superconducting Qubits

Authors: B. G. Christensen, C. D. Wilen, A. Opremcak, J. Nelson, F. Schlenker, C. H. Zimonick, L. Faoro, L. B. Ioffe, Y. J. Rosen, J. L. DuBois, B. L. T. Plourde, R. McDermott

Abstract: We have used Ramsey tomography to characterize charge noise in a weakly charge-sensitive superconducting qubit. We find a charge noise that scales with frequency as $1/f^α$ over 5 decades with $α= 1.93$ and a magnitude $S_q(\text{1Hz})= 2.9\times10^{-4}~e^2/\text{Hz}$. The noise exponent and magnitude of the low-frequency noise are much larger than those seen in prior work on single electron trans… ▽ More We have used Ramsey tomography to characterize charge noise in a weakly charge-sensitive superconducting qubit. We find a charge noise that scales with frequency as $1/f^α$ over 5 decades with $α= 1.93$ and a magnitude $S_q(\text{1Hz})= 2.9\times10^{-4}~e^2/\text{Hz}$. The noise exponent and magnitude of the low-frequency noise are much larger than those seen in prior work on single electron transistors, yet are consistent with reports of frequency noise in other superconducting qubits. Moreover, we observe frequent large-amplitude jumps in offset charge exceeding 0.1$e$; these large discrete charge jumps are incompatible with a picture of localized dipole-like two-level fluctuators. The data reveal an unexpected dependence of charge noise on device scale and suggest models involving either charge drift or fluctuating patch potentials. △ Less

Submitted 31 May, 2019; originally announced May 2019.

Comments: 10 pages, 7 figures

Journal ref: Phys. Rev. B 100, 140503 (2019)

Protecting superconducting qubits from phonon mediated decay

Authors: Yaniv J. Rosen, Matthew Horsley, Sara E. Harrison, Eric T. Holland, Allan S. Chang, Tiziana Bond, Jonathan L DuBois

Abstract: For quantum computing to become fault tolerant, the underlying quantum bits must be effectively isolated from the noisy environment. It is well known that including an electromagnetic bandgap around the qubit operating frequency improves coherence for superconducting circuits. However, investigations of bandgaps to other environmental coupling mechanisms remain largely unexplored. Here we present… ▽ More For quantum computing to become fault tolerant, the underlying quantum bits must be effectively isolated from the noisy environment. It is well known that including an electromagnetic bandgap around the qubit operating frequency improves coherence for superconducting circuits. However, investigations of bandgaps to other environmental coupling mechanisms remain largely unexplored. Here we present a method to enhance the coherence of superconducting circuits by introducing a phononic bandgap around the device operating frequency. The phononic bandgaps block resonant decay of defect states within the gapped frequency range, removing the electromagnetic coupling to phonons at the gap frequencies. We construct a multi-scale model that derives the decrease in the density of states due to the bandgap and the resulting increase in defect state $T_1$ times. We demonstrate that emission rates from in-plane defect states can be suppressed by up to two orders of magnitude. We combine these simulations with theory for resonators operated in the continuous-wave regime and show that improvements in quality factors are expected by up to the enhancement in defect $T_1$ times. Furthermore, we use full master equation simulation to demonstrate the suppression of qubit energy relaxation even when interacting with 200 defects states. We conclude with an exploration of device implementation including tradeoffs between fabrication complexity and qubit performance. △ Less

Submitted 1 May, 2019; v1 submitted 14 March, 2019; originally announced March 2019.

Comments: The following article has been submitted to Applied Physics Letters

Journal ref: Applied Physics Letters 114, 202601 (2019)

Tin+1Cn MXene with fully saturated and thermally stable Cl terminations

Authors: J. Lu, I. Persson, H. Lind, M. Li, Y. Li, K. Chen, J. Zhou, S. Du, Z. Chai, Z. Huang, L. Hultman, J. Rosen, P. Eklund, Q. Huang, P. O. Å. Persson

Abstract: MXenes are a rapidly growing family of 2D materials that exhibit a highly versatile structure and composition, allowing for significant tuning of the material properties. These properties are, however, ultimately limited by the surface terminations, which are typically a mixture of species, including F and O that are inherent to the MXene processing. Other and robust terminations are lacking. Here… ▽ More MXenes are a rapidly growing family of 2D materials that exhibit a highly versatile structure and composition, allowing for significant tuning of the material properties. These properties are, however, ultimately limited by the surface terminations, which are typically a mixture of species, including F and O that are inherent to the MXene processing. Other and robust terminations are lacking. Here, we apply high-resolution scanning transmission electron microscopy (STEM), corresponding image simulations and first-principles calculations to investigate the surface terminations on MXenes synthesized from MAX phases through Lewis acidic melts. The results show that atomic Cl terminates the synthesized MXenes, with mere residual presence of other termination species. Furthermore, in situ STEM-electron energy loss spectroscopy (EELS) heating experiments show that the Cl terminations are stable up to 750 °C. Thus, we present an attractive new termination that widely expands the MXenes functionalization space and enable new applications. △ Less

Submitted 16 January, 2019; originally announced January 2019.

Comments: 14 pages, 4 figures, 5 pages supplemental info

Element Replacement Approach by Reaction with Lewis Acidic Molten Salts to Synthesize Nanolaminated MAX Phases and MXenes

Authors: Mian Li, Jun Lu, Kan Luo, Youbing Li, Keke Chang, Ke Chen, Jie Zhou, Johanna Rosen, Lars Hultman, Per Eklund, Per O. Å. Persson, Shiyu Du, Zhifang Chai, Zhengren Huang, Qing Huang

Abstract: Nanolaminated materials are important because of their exceptional properties and wide range of applications. Here, we demonstrate a general approach to synthesize a series of Zn-based MAX phases and Cl-terminated MXenes originating from the replacement reaction between the MAX phase and the late transition metal halides. The approach is a top-down route that enables the late transitional element… ▽ More Nanolaminated materials are important because of their exceptional properties and wide range of applications. Here, we demonstrate a general approach to synthesize a series of Zn-based MAX phases and Cl-terminated MXenes originating from the replacement reaction between the MAX phase and the late transition metal halides. The approach is a top-down route that enables the late transitional element atom (Zn in the present case) to occupy the A site in the pre-existing MAX phase structure. Using this replacement reaction between Zn element from molten ZnCl2 and Al element in MAX phase precursors (Ti3AlC2, Ti2AlC, Ti2AlN, and V2AlC), novel MAX phases Ti3ZnC2, Ti2ZnC, Ti2ZnN, and V2ZnC were synthesized. When employing excess ZnCl2, Cl terminated MXenes (such as Ti3C2Cl2 and Ti2CCl2) were derived by a subsequent exfoliation of Ti3ZnC2 and Ti2ZnC due to the strong Lewis acidity of molten ZnCl2. These results indicate that A-site element replacement in traditional MAX phases by late transition metal halides opens the door to explore MAX phases that are not thermodynamically stable at high temperature and would be difficult to synthesize through the commonly employed powder metallurgy approach. In addition, this is the first time that exclusively Cl-terminated MXenes were obtained, and the etching effect of Lewis acid in molten salts provides a green and viable route to prepare MXenes through an HF-free chemical approach. △ Less

Submitted 15 March, 2019; v1 submitted 15 January, 2019; originally announced January 2019.

Comments: Title changed; experimental section and discussion revised

Journal ref: J. Am. Chem. Soc. 2019, 141, 11, 4730-4737

High-Kinetic Inductance Additive Manufactured Superconducting Microwave Cavity

Authors: Eric T. Holland, Yaniv J. Rosen, Nicholas Materise, Nathan Woollett, Thomas Voisin, Y. Morris Wang, Jorge Mireles, Gianpaolo Carosi, Jonathan L DuBois

Abstract: Investigations into the microwave surface impedance of superconducting resonators have led to the development of single photon counters that rely on kinetic inductance for their operation. While concurrent progress in additive manufacturing, `3D printing', opens up a previously inaccessible design space for waveguide resonators. In this manuscript, we present results from the first synthesis of th… ▽ More Investigations into the microwave surface impedance of superconducting resonators have led to the development of single photon counters that rely on kinetic inductance for their operation. While concurrent progress in additive manufacturing, `3D printing', opens up a previously inaccessible design space for waveguide resonators. In this manuscript, we present results from the first synthesis of these two technologies in a titanium, aluminum, vanadium (Ti-6Al-4V) superconducting radio frequency resonator which exploits a design unattainable through conventional fabrication means. We find that Ti-6Al-4V has two distinct superconducting transition temperatures observable in heat capacity measurements. The higher transition temperature is in agreement with DC resistance measurements. While the lower transition temperature, not previously known in literature, is consistent with the observed temperature dependence of the superconducting microwave surface impedance. From the surface reactance, we extract a London penetration depth of $8\pm3μ$m - roughly an order of magnitude larger than other titanium alloys and several orders of magnitude larger than other conventional elemental superconductors. This large London penetration depth suggests that Ti-6Al-4V may be a suitable material for high kinetic inductance applications such as single photon counting or parametric amplification used in quantum computing. △ Less

Submitted 14 August, 2017; originally announced August 2017.

Comments: 4 pages, 4 figures

Superconducting TiN Films Sputtered over a Large Range of Substrate DC Bias

Authors: H. M. Iftekhar Jaim, J. A. Aguilar, B. Sarabi, Y. J. Rosen, A. N. Ramanayaka, E. H. Lock, C. J. K. Richardson, K. D. Osborn

Abstract: We have investigated properties of superconducting titanium nitride (TiN) films that were sputtered over a large range of RF-induced DC bias voltage applied to the substrate. Films grown with the largest bias voltages contained cubic TiN phases with a large fraction of the (200) crystalline growth orientation. These films also contained the smallest concentrations of oxygen impurities, resulting i… ▽ More We have investigated properties of superconducting titanium nitride (TiN) films that were sputtered over a large range of RF-induced DC bias voltage applied to the substrate. Films grown with the largest bias voltages contained cubic TiN phases with a large fraction of the (200) crystalline growth orientation. These films also contained the smallest concentrations of oxygen impurities, resulting in stoichiometric TiN. Over the range of bias, variations of the stress from slightly tensile to highly compressive were measured and correlated to crystallinity of the (200) growth. The films exhibited highly uniform thickness and resistivity, and show the potential for yielding reproducible low-temperature devices. Finally, coplanar resonators fabricated with the films exhibited high kinetic inductance and quality factor, where the latter was obtained in part from temperature-dependent frequency shifts. △ Less

Submitted 24 October, 2014; v1 submitted 13 August, 2014; originally announced August 2014.

Journal ref: IEEE T. Appl. Supercon. 25 (2015) 1-5

Highly Effective Superconducting Vortex Pinning in Conformal Crystals

Authors: S. Guénon, Y. J. Rosen, Ali C. Basaran, Ivan K. Schuller

Abstract: We have investigated the vortex dynamics in superconducting thin film devices with non-uniform patterns of artificial pinning centers (APCs). The magneto-transport properties of a conformal crystal and a randomly diluted APC pattern are compared with that of a triangular reference lattice. We have found that in both cases the magneto-resistance below the first matching field of the triangular refe… ▽ More We have investigated the vortex dynamics in superconducting thin film devices with non-uniform patterns of artificial pinning centers (APCs). The magneto-transport properties of a conformal crystal and a randomly diluted APC pattern are compared with that of a triangular reference lattice. We have found that in both cases the magneto-resistance below the first matching field of the triangular reference lattice is significantly reduced. For the conformal crystal, the magneto-resistance is below the noise floor indicating highly effective vortex pinning over a wide magnetic field range. Further, we have discovered that for asymmetric patterns the R vs. H curves are mostly symmetric.This implies that the enhanced vortex pinning is due to the commensurability with a stripe in the non-uniform APC pattern and not due to a rearrangement and compression of the whole vortex lattice. △ Less

Submitted 24 May, 2013; originally announced May 2013.

Comments: submitted to APL on 29/04/13

Determining the Surface-To-Bulk Progression in the Normal-State Electronic Structure of Sr2RuO4 by Angle-Resolved Photoemission and Density Functional Theory

Authors: C. N. Veenstra, Z. -H. Zhu, B. Ludbrook, M. Capsoni, G. Levy, A. Nicolaou, J. A. Rosen, R. Comin, S. Kittaka, Y. Maeno, I. S. Elfimov, A. Damascelli

Abstract: In search of the potential realization of novel normal-state phases on the surface of Sr2RuO4 - those stemming from either topological bulk properties or the interplay between spin-orbit coupling (SO) and the broken symmetry of the surface - we revisit the electronic structure of the top-most layers by ARPES with improved data quality as well as ab-initio LDA slab calculations. We find that the cu… ▽ More In search of the potential realization of novel normal-state phases on the surface of Sr2RuO4 - those stemming from either topological bulk properties or the interplay between spin-orbit coupling (SO) and the broken symmetry of the surface - we revisit the electronic structure of the top-most layers by ARPES with improved data quality as well as ab-initio LDA slab calculations. We find that the current model of a single surface layer (\surd2x\surd2)R45° reconstruction does not explain all detected features. The observed depth-dependent signal degradation, together with the close quantitative agreement with LDA+SO slab calculations based on the LEED-determined surface crystal structure, reveal that (at a minimum) the sub-surface layer also undergoes a similar although weaker reconstruction. This points to a surface-to-bulk progression of the electronic states driven by structural instabilities, with no evidence for Dirac and Rashba-type states or surface magnetism. △ Less

Submitted 12 February, 2013; v1 submitted 18 May, 2012; originally announced May 2012.

Comments: 4 pages, 4 figures, 1 table. Further information and PDF available at: http://www.phas.ubc.ca/~quantmat/ARPES/PUBLICATIONS/articles.html

Journal ref: Phys. Rev. Lett. 110, 097004 (2013)

Na2IrO3 as a spin-orbit-assisted antiferromagnetic insulator with a 340 meV gap

Authors: R. Comin, G. Levy, B. Ludbrook, Z. -H. Zhu, C. N. Veenstra, J. A. Rosen, Yogesh Singh, P. Gegenwart, D. Stricker, J. N. Hancock, D. van der Marel, I. S. Elfimov, A. Damascelli

Abstract: We study Na2IrO3 by ARPES, optics, and band structure calculations in the local-density approximation (LDA). The weak dispersion of the Ir 5d-t2g manifold highlights the importance of structural distortions and spin-orbit coupling (SO) in driving the system closer to a Mott transition. We detect an insulating gap Δ_gap = 340 meV which, at variance with a Slater-type description, is already open at… ▽ More We study Na2IrO3 by ARPES, optics, and band structure calculations in the local-density approximation (LDA). The weak dispersion of the Ir 5d-t2g manifold highlights the importance of structural distortions and spin-orbit coupling (SO) in driving the system closer to a Mott transition. We detect an insulating gap Δ_gap = 340 meV which, at variance with a Slater-type description, is already open at 300 K and does not show significant temperature dependence even across T_N ~ 15 K. An LDA analysis with the inclusion of SO and Coulomb repulsion U reveals that, while the prodromes of an underlying insulating state are already found in LDA+SO, the correct gap magnitude can only be reproduced by LDA+SO+U, with U = 3 eV. This establishes Na2IrO3 as a novel type of Mott-like correlated insulator in which Coulomb and relativistic effects have to be treated on an equal footing. △ Less

Submitted 12 November, 2012; v1 submitted 19 April, 2012; originally announced April 2012.

Comments: Accepted in Physical Review Letters. Auxiliary and related material can be found at: http://www.phas.ubc.ca/~quantmat/ARPES/PUBLICATIONS/articles.html

Journal ref: Phys. Rev. Lett. 109, 266406 (2012)

Surface-enhanced charge-density-wave instability in underdoped Bi2201

Authors: J. A. Rosen, R. Comin, G. Levy, D. Fournier, Z. -H. Zhu, B. Ludbrook, C. N. Veenstra, A. Nicolaou, D. Wong, P. Dosanjh, Y. Yoshida, H. Eisaki, G. R. Blake, F. White, T. T. M. Palstra, R. Sutarto, F. He, A. Frano, Y. Lu, B. Keimer, G. A. Sawatzky, L. Petaccia, A. Damascelli

Abstract: Neutron and x-ray scattering experiments have provided mounting evidence for spin and charge ordering phenomena in underdoped cuprates. These range from early work on stripe correlations in Nd-LSCO to the latest discovery of charge-density-waves in YBCO. Both phenomena are characterized by a pronounced dependence on doping, temperature, and an externally applied magnetic field. Here we show that t… ▽ More Neutron and x-ray scattering experiments have provided mounting evidence for spin and charge ordering phenomena in underdoped cuprates. These range from early work on stripe correlations in Nd-LSCO to the latest discovery of charge-density-waves in YBCO. Both phenomena are characterized by a pronounced dependence on doping, temperature, and an externally applied magnetic field. Here we show that these electron-lattice instabilities exhibit also a previously unrecognized bulk-surface dichotomy. Surface-sensitive electronic and structural probes uncover a temperature-dependent evolution of the CuO2 plane band dispersion and apparent Fermi pockets in underdoped Bi2201, which is directly associated with an hitherto-undetected strong temperature dependence of the incommensurate superstructure periodicity below 130K. In stark contrast, the structural modulation revealed by bulk-sensitive probes is temperature independent. These findings point to a surface-enhanced incipient charge-density-wave instability, driven by Fermi surface nesting. This discovery is of critical importance in the interpretation of single-particle spectroscopy data and establishes the surface of cuprates and other complex oxides as a rich playground for the study of electronically soft phases. △ Less

Submitted 9 May, 2013; v1 submitted 11 November, 2011; originally announced November 2011.

Comments: A high-resolution version with supplementary material can be found at http://www.physics.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Articles/Bi2201_PG_Q2.pdf

Journal ref: Nature Communications 4, 1977 (2013)

Rashba spin-splitting control at the surface of the topological insulator Bi2Se3

Authors: Z. -H. Zhu, G. Levy, B. Ludbrook, C. N. Veenstra, J. A. Rosen, R. Comin, D. Wong, P. Dosanjh, A. Ubaldini, P. Syers, N. P. Butch, J. Paglione, I. S. Elfimov, A. Damascelli

Abstract: The electronic structure of Bi2Se3 is studied by angle-resolved photoemission and density functional theory. We show that the instability of the surface electronic properties, observed even in ultra-high-vacuum conditions, can be overcome via in-situ potassium deposition. In addition to accurately setting the carrier concentration, new Rashba-like spin-polarized states are induced, with a tunable,… ▽ More The electronic structure of Bi2Se3 is studied by angle-resolved photoemission and density functional theory. We show that the instability of the surface electronic properties, observed even in ultra-high-vacuum conditions, can be overcome via in-situ potassium deposition. In addition to accurately setting the carrier concentration, new Rashba-like spin-polarized states are induced, with a tunable, reversible, and highly stable spin splitting. Ab-initio slab calculations reveal that these Rashba state are derived from the 5QL quantum-well states. While the K-induced potential gradient enhances the spin splitting, this might be already present for pristine surfaces due to the symmetry breaking of the vacuum-solid interface. △ Less

Submitted 2 June, 2011; originally announced June 2011.

Comments: A high-resolution version can be found at http://www.physics.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Articles/BiSe_K.pdf

Journal ref: Phys. Rev. Lett. 107, 186405 (2011)

Reply to "Comment on arXiv:1012.1484v1 Structural origin of apparent Fermi surface pockets in angle-resolved photoemission of Bi_2Sr_{2-x}La_xCuO_{6+δ} by King et al."

Authors: P. D. C. King, J. A. Rosen, W. Meevasana, A. Tamai, E. Rozbicki, R. Comin, G. Levy, D. Fournier, Y. Yoshida, H. Eisaki, K. M. Shen, N. J. C. Ingle, A. Damascelli, F. Baumberger

Abstract: Reply to comment by Zhou et al. (arXiv:1012.3602) on arXiv:1012.1484 / Phys. Rev. Lett. 106, 127005 (2011). Reply to comment by Zhou et al. (arXiv:1012.3602) on arXiv:1012.1484 / Phys. Rev. Lett. 106, 127005 (2011). △ Less

Submitted 10 May, 2011; originally announced May 2011.

Comments: 2 pages

Vortex ratchet reversal: The role of interstitial vortices

Authors: D. Perez de Lara, M. Erekhinsky, E. M. Gonzalez, Y. J. Rosen, Ivan K. Schuller, J. L. Vicent

Abstract: Triangular arrays of Ni nanotriangles embedded in superconducting Nb films exhibit unexpected dynamical vortex effects. Collective pinning with a vortex lattice configuration different from the expected fundamental triangular "Abrikosov state" is found. The vortex motion which prevails against the triangular periodic potential is produced by channelling effects between triangles. Interstitial vort… ▽ More Triangular arrays of Ni nanotriangles embedded in superconducting Nb films exhibit unexpected dynamical vortex effects. Collective pinning with a vortex lattice configuration different from the expected fundamental triangular "Abrikosov state" is found. The vortex motion which prevails against the triangular periodic potential is produced by channelling effects between triangles. Interstitial vortices coexisting with pinned vortices in this asymmetric potential, lead to ratchet reversal, i.e. a DC output voltage which changes sign with the amplitude of an applied alternating drive current. In this landscape, ratchet reversal is always observed at all magnetic fields (all numbers of vortices) and at different temperatures. The ratchet reversal is unambiguously connected to the presence of two locations for the vortices: interstitial and above the artificial pinning sites. △ Less

Submitted 7 May, 2011; originally announced May 2011.

Comments: 21 pages, 4 figures, 1 Table

Journal ref: Physical Review B 83 (2011)

Structural origin of apparent Fermi surface pockets in angle-resolved photoemission of Bi$_2$Sr$_{2-x}$La$_x$CuO$_{6+δ}$

Authors: P. D. C. King, J. A. Rosen, W. Meevasana, A. Tamai, E. Rozbicki, R. Comin, G. Levy, D. Fournier, Y. Yoshida, H. Eisaki, K. M. Shen, N. J. C. Ingle, A. Damascelli, F. Baumberger

Abstract: We observe apparent hole pockets in the Fermi surfaces of single-layer Bi-based cuprate superconductors from angle-resolved photoemission (ARPES). From detailed low-energy electron diffraction measurements and an analysis of the ARPES polarization-dependence, we show that these pockets are not intrinsic, but arise from multiple overlapping superstructure replicas of the main and shadow bands. We f… ▽ More We observe apparent hole pockets in the Fermi surfaces of single-layer Bi-based cuprate superconductors from angle-resolved photoemission (ARPES). From detailed low-energy electron diffraction measurements and an analysis of the ARPES polarization-dependence, we show that these pockets are not intrinsic, but arise from multiple overlapping superstructure replicas of the main and shadow bands. We further demonstrate that the hole pockets reported recently from ARPES [Meng et al, Nature 462, 335 (2009)] have a similar structural origin, and are inconsistent with an intrinsic hole pocket associated with the electronic structure of a doped CuO$_2$ plane. The nature of the Fermi surface topology in the enigmatic pseudogap phase therefore remains an open question. △ Less

Submitted 7 December, 2010; originally announced December 2010.

Comments: 5 pages, 4 figures

Journal ref: Phys. Rev. Lett. 106, 127005 (2011)

Soft Manifold Dynamics Behind Negative Thermal Expansion

Authors: Z. Schlesinger, J. A. Rosen, J. N. Hancock, A. P. Ramirez

Abstract: Minimal models are developed to examine the origin of large negative thermal expansion (NTE) in under-constrained systems. The dynamics of these models reveals how underconstraint can organize a thermodynamically extensive manifold of low-energy modes which not only drives NTE but extends across the Brillioun zone. Mixing of twist and translation in the eigenvectors of these modes, for which in… ▽ More Minimal models are developed to examine the origin of large negative thermal expansion (NTE) in under-constrained systems. The dynamics of these models reveals how underconstraint can organize a thermodynamically extensive manifold of low-energy modes which not only drives NTE but extends across the Brillioun zone. Mixing of twist and translation in the eigenvectors of these modes, for which in ZrW2O8 there is evidence from infrared and neutron scattering measurements, emerges naturally in our model as a signature of the dynamics of underconstraint. △ Less

Submitted 8 July, 2008; originally announced July 2008.

Comments: 5 pages, 3 figures

Journal ref: Phys. Rev. Lett. 101, 015501 (2008)