Selected Papers from the International Conference on Quantum Materials and Technologies (ICQMT2022)

A special issue of Condensed Matter (ISSN 2410-3896). This special issue belongs to the section "Quantum Materials".

Deadline for manuscript submissions: closed (31 December 2022) | Viewed by 31899

Special Issue Editors

Physics Department, Science Faculty, Ankara University, Ankara 06100, Turkey
Interests: superconducting materials; MgB2; Josephson junction devices; various qubit systems; quantum computing
Special Issues, Collections and Topics in MDPI journals
Instituto de Nanociencia y Materiales de Aragón, C/Pedro Cerbuna 12, 50009 Zaragoza, Spain
Interests: multifunctional magnetic molecular materials; carbon-based magnetism; graphene; 2D materials; low dimensional magnetism; molecular spintronics; skyrmions in quantum materials; molecular refrigeration; chiral magnetism; organic magnets; magneto-calorics and quantum computation
Special Issues, Collections and Topics in MDPI journals
Terra Quantum AG, Kornhausstrasse 25, 9000 St. Gallen, Switzerland
Interests: topological quantum matter; superconductivity; the new state of matter; superinsulator; superconductor–insulator transition; large-scale adoption of quantum technologies
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

In recent decades, there have been significant developments in the field of quantum materials and technologies, led by dedicated world-wide scientific and technological efforts. Advancements in quantum materials and technologies have already found their applications in industry and research; the USA, Germany, the UK, China and Japan being at the forefront of these efforts. We proudly open this Special Issue of the proceedings for the International Conference on Quantum Materials and Technologies (ICQMT-2022) where leading scientists and technologists will be sharing knowledge under seven main subgroups of this wide subject area. The goal of this Special Issue is to collect state-of-the-art results (from experiments, theories and simulations) centered on quantum phenomena, and to provide a perspective on how the achievements of quantum materials and technologies can be practically applied for fundamental developments, new technological applications and achievements in quantum devices.

  • Superconductivity and superconducting materials;
  • Correlated electronic physics and materials;
  • Various types of qubits;
  • Topological quantum physics and materials;
  • Other correlated systems;
  • Quantum phenomena in advanced energy materials;
  • Advanced quantum technologies and applications.

Prof. Dr. Ali Gencer
Prof. Dr. Annette Bussmann-Holder
Dr. J. Javier Campo Ruiz
Prof. Dr. Valerii Vinokur
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Condensed Matter is an international peer-reviewed open access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • quantum computing
  • energy efficiency
  • metrology
  • quantum annealing
  • quantum and correlated materials
  • quantum communication
  • quantum dots
  • quantum error correction and fault tolerance
  • quantum hall effect
  • quantum materials
  • quantum sensing
  • quantum spin hall
  • quantum spin liquids
  • spin–orbit coupling
  • superconductivity
  • thin films
  • topological hall effect

Published Papers (20 papers)

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Research

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8 pages, 2349 KiB  
Article
On the Optical Properties of Cr2Ge2Te6 and Its Heterostructure
by Hiroshi Idzuchi, Andres E. Llacsahuanga Allcca, Amanda Victo Haglund, Xing-Chen Pan, Takuya Matsuda, Katsumi Tanigaki, David Mandrus and Yong P. Chen
Condens. Matter 2023, 8(3), 59; https://doi.org/10.3390/condmat8030059 - 14 Jul 2023
Viewed by 1083
Abstract
Recently, there has been a growing interest in two-dimensional van der Waals (vdW) magnets owing to their unique two-dimensional magnetic phenomena and potential applications. Most vdW ferromagnets have the Curie temperature below room temperature, highlighting the need to explore how to enhance their [...] Read more.
Recently, there has been a growing interest in two-dimensional van der Waals (vdW) magnets owing to their unique two-dimensional magnetic phenomena and potential applications. Most vdW ferromagnets have the Curie temperature below room temperature, highlighting the need to explore how to enhance their magnetism. In our previous report, we successfully increased the Curie temperature of the prototypical vdW magnet Cr2Ge2Te6 using a NiO overlayer. In layered materials, the presence of wrinkles is often observed and evaluating them using optical microscopy proves to be useful; however, there have been limited investigations into the optical constants of vdW magnets, hampering progress in understanding their optical properties. In this study, we present the optical constants of Cr2Ge2Te6 obtained through ellipsometry measurements. To account for the presence of wrinkles, we model a vacuum region between the substrate and the vdW magnet, and we calculate the reflectivity as a function of wavelength and vacuum thickness to visualize the optical image. Furthermore, we discuss the relationship between the optical constants and the electronic structure of the material. Full article
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21 pages, 2747 KiB  
Article
Thermodynamics in Stochastic Conway’s Game of Life
by Krzysztof Pomorski and Dariusz Kotula
Condens. Matter 2023, 8(2), 47; https://doi.org/10.3390/condmat8020047 - 19 May 2023
Cited by 1 | Viewed by 1441
Abstract
Cellular automata can simulate many complex physical phenomena using the power of simple rules. The presented methodological platform expresses the concept of programmable matter, of which Newton’s laws of motion are an example. Energy is introduced as the equivalent of the “Game of [...] Read more.
Cellular automata can simulate many complex physical phenomena using the power of simple rules. The presented methodological platform expresses the concept of programmable matter, of which Newton’s laws of motion are an example. Energy is introduced as the equivalent of the “Game of Life” mass, which can be treated as the first level of approximation. The temperature presence and propagation was calculated for various lattice topologies and boundary conditions, using the Shannon entropy measure. This study provides strong evidence that, despite the principle of mass and energy conservation not being fulfilled, the entropy, mass distribution, and temperature approach thermodynamic equilibrium. In addition, the described cellular automaton system transitions from a positive to a negative temperature, which stabilizes and can be treated as a signature of a system in equilibrium. The system dynamics is presented for a few species of cellular automata competing for maximum presence on a given lattice with different boundary conditions. Full article
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17 pages, 6567 KiB  
Article
Superconducting Stiffness and Coherence Length of FeSe0.5Te0.5 Measured in a Zero-Applied Field
by Amotz Peri, Itay Mangel and Amit Keren
Condens. Matter 2023, 8(2), 39; https://doi.org/10.3390/condmat8020039 - 23 Apr 2023
Cited by 1 | Viewed by 1721
Abstract
Superconducting stiffness ρs and coherence length ξ are usually determined by measuring the penetration depth λ of a magnetic field and the upper critical field Hc2 of a superconductor (SC), respectively. However, in magnetic SC, which is iron-based, this could [...] Read more.
Superconducting stiffness ρs and coherence length ξ are usually determined by measuring the penetration depth λ of a magnetic field and the upper critical field Hc2 of a superconductor (SC), respectively. However, in magnetic SC, which is iron-based, this could lead to erroneous results, since the internal field could be very different from the applied one. To overcome this problem in Fe1+ySexTe1x with x0.5 and y0 (FST), we measured both quantities with the Stiffnessometer technique. In this technique, one applies a rotor-free vector potential A to a superconducting ring and measures the current density j via the ring’s magnetic moment m. ρs and ξ are determined from London’s equation, j=ρsA, and its range of validity. This method is particularly accurate at temperatures close to the critical temperature Tc. We find weaker ρs and longer ξ than existing literature reports, and critical exponents which agree better with expectations based on the Ginzburg–Landau theory. Full article
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12 pages, 754 KiB  
Article
Superconducting Diode Effect in Topological Hybrid Structures
by Tairzhan Karabassov, Emir S. Amirov, Irina V. Bobkova, Alexander A. Golubov, Elena A. Kazakova and Andrey S. Vasenko
Condens. Matter 2023, 8(2), 36; https://doi.org/10.3390/condmat8020036 - 14 Apr 2023
Cited by 6 | Viewed by 1854
Abstract
Currently, the superconducting diode effect (SDE) is being actively discussed, due to its large application potential in superconducting electronics. In particular, superconducting hybrid structures, based on three-dimensional (3D) topological insulators, are among the best candidates, due to their having the strongest spin–orbit coupling [...] Read more.
Currently, the superconducting diode effect (SDE) is being actively discussed, due to its large application potential in superconducting electronics. In particular, superconducting hybrid structures, based on three-dimensional (3D) topological insulators, are among the best candidates, due to their having the strongest spin–orbit coupling (SOC). Most theoretical studies on the SDE focus either on a full numerical calculation, which is often rather complicated, or on the phenomenological approach. In the present paper, we compare the linearized and nonlinear microscopic approaches in the superconductor/ferromagnet/3D topological insulator (S/F/TI) hybrid structure. Employing the quasiclassical Green’s function formalism we solve the problem self-consistently. We show that the results obtained by the linearized approximation are not qualitatively different from the nonlinear solution. The main distinction in the results between the two methods was quantitative, i.e., they yielded different supercurrent amplitudes. However, when calculating the so-called diode quality factor the quantitative difference is eliminated and both approaches result in good agreement. Full article
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11 pages, 1357 KiB  
Article
Angle-dependent Magnetoresistance of an Ordered Bose Glass of Vortices in YBa2Cu3O7-δ Thin Films with a Periodic Pinning Lattice
by Bernd Aichner, Lucas Backmeister, Max Karrer, Katja Wurster, Reinhold Kleiner, Edward Goldobin, Dieter Koelle and Wolfgang Lang
Condens. Matter 2023, 8(2), 32; https://doi.org/10.3390/condmat8020032 - 27 Mar 2023
Cited by 1 | Viewed by 1747
Abstract
The competition between intrinsic disorder in superconducting YBa2Cu3O7δ (YBCO) thin films and an ultradense triangular lattice of cylindrical pinning centers spaced at 30 nm intervals results in an ordered Bose glass phase of vortices. The samples [...] Read more.
The competition between intrinsic disorder in superconducting YBa2Cu3O7δ (YBCO) thin films and an ultradense triangular lattice of cylindrical pinning centers spaced at 30 nm intervals results in an ordered Bose glass phase of vortices. The samples were created by scanning the focused beam of a helium-ion microscope over the surface of the YBCO thin film to form columns of point defects where superconductivity was locally suppressed. The voltage–current isotherms reveal critical behavior and scale in the vicinity of the second-order glass transition. The latter exhibits a distinct peak in melting temperature (Tg) vs. applied magnetic field (Ba) at the magnetic commensurability field, along with a sharp rise in the lifetimes of glassy fluctuations. Angle-dependent magnetoresistance measurements in constant-Lorentz-force geometry unveil a strong increase in anisotropy compared to a pristine reference film where the density of vortices matches that of the columnar defects. The pinning is therefore, dominated by the magnetic-field component parallel to the columnar defects, exposing its one-dimensional character. These results support the idea of an ordered Bose glass phase. Full article
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19 pages, 3452 KiB  
Article
Investigating the Individual Performances of Coupled Superconducting Transmon Qubits
by Halima Giovanna Ahmad, Caleb Jordan, Roald van den Boogaart, Daan Waardenburg, Christos Zachariadis, Pasquale Mastrovito, Asen Lyubenov Georgiev, Domenico Montemurro, Giovanni Piero Pepe, Marten Arthers, Alessandro Bruno, Francesco Tafuri, Oleg Mukhanov, Marco Arzeo and Davide Massarotti
Condens. Matter 2023, 8(1), 29; https://doi.org/10.3390/condmat8010029 - 21 Mar 2023
Cited by 2 | Viewed by 2072
Abstract
The strong requirement for high-performing quantum computing led to intensive research on novel quantum platforms in the last decades. The circuital nature of Josephson-based quantum superconducting systems powerfully supports massive circuital freedom, which allowed for the implementation of a wide range of qubit [...] Read more.
The strong requirement for high-performing quantum computing led to intensive research on novel quantum platforms in the last decades. The circuital nature of Josephson-based quantum superconducting systems powerfully supports massive circuital freedom, which allowed for the implementation of a wide range of qubit designs, and an easy interface with the quantum processing unit. However, this unavoidably introduces a coupling with the environment, and thus to extra decoherence sources. Moreover, at the time of writing, control and readout protocols mainly use analogue microwave electronics, which limit the otherwise reasonable scalability in superconducting quantum circuits. Within the future perspective to improve scalability by integrating novel control energy-efficient superconducting electronics at the quantum stage in a multi-chip module, we report on an all-microwave characterization of a planar two-transmon qubits device, which involves state-of-the-art control pulses optimization. We demonstrate that the single-qubit average gate fidelity is mainly limited by the gate pulse duration and the quality of the optimization, and thus does not preclude the integration in novel hybrid quantum-classical superconducting devices. Full article
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9 pages, 443 KiB  
Article
Using Quantum Nodes Connected via the Quantum Cloud to Perform IoT Quantum Network
by Doaa Subhi and Laszlo Bacsardi
Condens. Matter 2023, 8(1), 24; https://doi.org/10.3390/condmat8010024 - 23 Feb 2023
Viewed by 1561
Abstract
Computer networks consist of millions of nodes that need constant protection because of their continued vulnerability to attacks. Classical security methods for protecting such networks will not be effective enough if quantum computers become widespread. On the other hand, we can exploit the [...] Read more.
Computer networks consist of millions of nodes that need constant protection because of their continued vulnerability to attacks. Classical security methods for protecting such networks will not be effective enough if quantum computers become widespread. On the other hand, we can exploit the capabilities of quantum computing and communications to build a new quantum communication network. In this paper, we focused on enhancing the performance of the classical client–server Internet application. For this sake, we introduced a novel Internet of Things (IoT) quantum network that provides high security and Quality of Service (QoS) compared with the traditional IoT network. This can be achieved by adding quantum components to the traditional IoT network. Quantum counterpart nodes, channels, and servers are used. In order to establish a secure communication between the quantum nodes and the quantum server, we defined a new Communication Procedure (CP) for the suggested IoT quantum network. The currently available quantum computer has a small qubit size (from 50 to 433 qubits). The proposed IoT quantum network allows us to overcome this problem by concatenating the computation efforts of multiple quantum nodes (quantum processors). Full article
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10 pages, 1382 KiB  
Article
The Origin of the Magnetic and Electric Dipole Moments of Ni2+ in NiCr2O4
by Mikhail Eremin and Kirill Vasin
Condens. Matter 2023, 8(1), 23; https://doi.org/10.3390/condmat8010023 - 18 Feb 2023
Viewed by 1119
Abstract
The energy level schema of the ground term of the nickel ion in NiCr2O4 was calculated. The parameters of the interaction with the electric field were determined, and the distribution pattern of the electric dipole moments over different positions of [...] Read more.
The energy level schema of the ground term of the nickel ion in NiCr2O4 was calculated. The parameters of the interaction with the electric field were determined, and the distribution pattern of the electric dipole moments over different positions of nickel in the unit cell was calculated. The model of the NiCr2O4 magnetoelectric structure at T < Tc was constructed taking into account the data on neutron scattering and the results of the electric polarization measurements. The origin of the magnetodielectric effect was attributed to the peculiarities of the ground state of the nickel ion. Full article
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12 pages, 3461 KiB  
Article
A Method to Probe the Interfaces in La2−xSrxCuO4-LaSrAlO4-La2−xSrxCuO4 Trilayer Junctions
by Xiaotao Xu, Xi He, Anthony T. Bollinger, Myung-Geun Han, Yimei Zhu, Xiaoyan Shi and Ivan Božović
Condens. Matter 2023, 8(1), 21; https://doi.org/10.3390/condmat8010021 - 10 Feb 2023
Cited by 2 | Viewed by 1171
Abstract
C-axis trilayer cuprate Josephson junctions are essential for basic science and digital circuit applications of high-temperature superconductors. We present a method for probing the interface perfection in La2−xSrxCuO4 (LSCO)-LaSrAlO4 (LSAO)-La2−xSrxCuO [...] Read more.
C-axis trilayer cuprate Josephson junctions are essential for basic science and digital circuit applications of high-temperature superconductors. We present a method for probing the interface perfection in La2−xSrxCuO4 (LSCO)-LaSrAlO4 (LSAO)-La2−xSrxCuO4 trilayer junctions. A series of LSCO-LSAO superlattices with atomically smooth surfaces and sharp interfaces were grown by the atomic-layer-by-layer molecular beam epitaxy (ALL-MBE) technique. We have systematically varied the thickness of LSCO and LSAO layers with monolayer precision. By studying the mutual inductance and electrical transport in these superlattices, we detect the non-superconducting (“dead”) layers at the interfaces and quantify their thicknesses. Our results indicate that two optimally doped LSCO monolayers just above and below the one monolayer LSAO barrier are no longer superconducting, rendering the actual barrier thickness of five monolayers. Next, we have shown that introducing a protective highly-overdoped LSCO layer reduces the thickness of dead layers by one or two monolayers. Full article
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7 pages, 1234 KiB  
Article
Influence of Anharmonic and Frustration Effects on Josephson Phase Qubit Characteristics
by Iman N. Askerzade
Condens. Matter 2023, 8(1), 20; https://doi.org/10.3390/condmat8010020 - 09 Feb 2023
Cited by 1 | Viewed by 1010
Abstract
This study is devoted to the investigation of the Josephson phase qubit spectrum considering the anharmonic current-phase relation of the junction. The change in energy difference in the spectrum of phase qubits based on single-band/multiband Josephson junctions is also analyzed. It was shown [...] Read more.
This study is devoted to the investigation of the Josephson phase qubit spectrum considering the anharmonic current-phase relation of the junction. The change in energy difference in the spectrum of phase qubits based on single-band/multiband Josephson junctions is also analyzed. It was shown that the presence of the anharmonic term in the current-phase relation and frustration effects in the junction electrodes leads to changing effective plasma frequencies in the different cases and results in an energy spectrum. Full article
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10 pages, 2312 KiB  
Article
Influence of f Electrons on the Electronic Band Structure of Rare-Earth Nickelates
by Andrzej Ptok, Surajit Basak, Przemysław Piekarz and Andrzej M. Oleś
Condens. Matter 2023, 8(1), 19; https://doi.org/10.3390/condmat8010019 - 08 Feb 2023
Cited by 3 | Viewed by 1774
Abstract
Recently, superconductivity was discovered in the infinite layer of hole-doped nickelates NdNiO2. Contrary to this, superconductivity in LaNiO2 is still under debate. This indicates the crucial role played by the f electrons on the electronic structure and the pairing mechanism [...] Read more.
Recently, superconductivity was discovered in the infinite layer of hole-doped nickelates NdNiO2. Contrary to this, superconductivity in LaNiO2 is still under debate. This indicates the crucial role played by the f electrons on the electronic structure and the pairing mechanism of infinite-layer nickelates. Here, we discuss the role of the electron correlations in the f electron states and their influence on the electronic structure. We show that the lattice parameters are in good agreement with the experimental values, independent of the chosen parameters within the DFT+U approach. Increasing Coulomb interaction U tends to shift the f states away from the Fermi level. Surprisingly, independently of the position of f states with respect to the Fermi energy, these states play an important role in the electronic band structure, which can be reflected in the modification of the NdNiO2 effective models. Full article
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12 pages, 7991 KiB  
Article
Detection of Surface States in Quantum Materials ZrTe2 and TmB4 by Scanning Tunneling Microscopy
by Maria Victoria Ale Crivillero, Jean C. Souza, Vicky Hasse, Marcus Schmidt, Natalya Shitsevalova, Slavomir Gabáni, Konrad Siemensmeyer, Karol Flachbart and Steffen Wirth
Condens. Matter 2023, 8(1), 9; https://doi.org/10.3390/condmat8010009 - 16 Jan 2023
Viewed by 1863
Abstract
Scanning Tunneling Microscopy and Spectroscopy (STM/S), with its exceptional surface sensitivity and exquisite energy resolution, is well suited for the investigation of surface states down to atomic length scales. As such, it became an essential tool to probe the surface states of materials, [...] Read more.
Scanning Tunneling Microscopy and Spectroscopy (STM/S), with its exceptional surface sensitivity and exquisite energy resolution, is well suited for the investigation of surface states down to atomic length scales. As such, it became an essential tool to probe the surface states of materials, including those with non-trivial topology. One challenge, however, can be the preparation of clean surfaces which allow the study of preferably unchanged surface properties with respect to the bulk amount. Here, we report on the STM/S of two materials, ZrTe2 and TmB4. The former cleaves easily and defects can be examined in detail. However, our STS data can only qualitatively be compared to the results of band structure calculations. In the case of TmB4, the preparation of suitable surfaces is highly challenging, and atomically flat surfaces (likely of B-termination) were only encountered rarely. We found a large density of states (DOS) at the Fermi level EF and a mostly featureless differential conductance near EF. Further efforts are required to relate our results to the electronic structure predicted by ab initio calculations. Full article
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15 pages, 1613 KiB  
Article
Magnetic Monopoles, Dyons and Confinement in Quantum Matter
by Carlo A. Trugenberger
Condens. Matter 2023, 8(1), 2; https://doi.org/10.3390/condmat8010002 - 27 Dec 2022
Cited by 1 | Viewed by 1732
Abstract
We show that magnetic monopoles appear naturally in granular quantum matter. Their condensation leads to a new state of matter, superinsulation, in which Cooper pairs are bound into purely electric pions by strings of electric flux. These electric flux tubes, the dual of [...] Read more.
We show that magnetic monopoles appear naturally in granular quantum matter. Their condensation leads to a new state of matter, superinsulation, in which Cooper pairs are bound into purely electric pions by strings of electric flux. These electric flux tubes, the dual of Abrikosov vortices, prevent the separation of charge–hole pairs, thereby causing an infinite resistance, even at finite temperatures, the dual behaviour of superconductors. We will discuss the electric Meissner effect, asymptotic freedom and their measurements and describe the recent direct detection of a linear, confining potential by dynamic relaxation experiments. Finally, we consider dyons, excitations carrying both a magnetic and an electric charge, and show that a condensate of such dyons leads to a possible solution of the mysteries of the pseudogap state of high-Tc cuprates. Full article
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8 pages, 468 KiB  
Article
Conductivity Sum Rule in the Nearly Free Two-Dimensional Electron Gas in an Uniaxial Potential
by Zoran Rukelj and Danko Radić
Condens. Matter 2023, 8(1), 1; https://doi.org/10.3390/condmat8010001 - 23 Dec 2022
Cited by 1 | Viewed by 1471
Abstract
We report an investigation of the conductivity sum rule in the two-dimensional system of free electrons in a weak uniaxial potential. The sum rule is defined through the integration of a real part of a multiband conductivity tensor and separates between the intraband [...] Read more.
We report an investigation of the conductivity sum rule in the two-dimensional system of free electrons in a weak uniaxial potential. The sum rule is defined through the integration of a real part of a multiband conductivity tensor and separates between the intraband and interband charge transport concentrations. It is shown how the relative direction of the electric field and the uniaxial potential defines the transport concentrations of the nearly free electron system and why the sum rule is obeyed. Full article
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13 pages, 447 KiB  
Article
DC Transport and Magnetotransport Properties of the 2D Isotropic Metallic System with the Fermi Surface Reconstructed by the Charge Density Wave
by Barbara Keran, Petra Grozić, Anatoly M. Kadigrobov, Zoran Rukelj and Danko Radić
Condens. Matter 2022, 7(4), 73; https://doi.org/10.3390/condmat7040073 - 09 Dec 2022
Viewed by 1289
Abstract
We report the ground state stabilization and corresponding electrical transport and magnetotransport properties of a 2D metallic system with an isotropic Fermi surface reconstructed by a charge density wave. The onset of the charge density wave is a spontaneous process, stabilized by the [...] Read more.
We report the ground state stabilization and corresponding electrical transport and magnetotransport properties of a 2D metallic system with an isotropic Fermi surface reconstructed by a charge density wave. The onset of the charge density wave is a spontaneous process, stabilized by the condensation energy gain due to the self-consistent mechanism of topological reconstruction of the Fermi surface and opening of the pseudo-gap around it. We address the signature of the uni-axial reconstruction in terms of the measurable quantities, such as the intra-band transport properties, including the one-particle density of states, the total and effective concentration of electrons, and the Hall coefficient. Additionally, we analyze the magnetotransport properties of the system reconstructed by the bi-axial, checkerboard-like charge density wave, under conditions of magnetic breakdown. It manifests huge quantum oscillations in diagonal components of magnetoconductivity, while the Hall conductivity changes sign, varying the external magnetic field with a finite region of vanishing Hall coefficient in between. Full article
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Review

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10 pages, 291 KiB  
Review
Superconductors with a Topological Gap
by Maria Cristina Diamantini
Condens. Matter 2023, 8(2), 46; https://doi.org/10.3390/condmat8020046 - 16 May 2023
Cited by 1 | Viewed by 946
Abstract
I review a new superconductivity mechanism in which the gap is opened through a topological mechanism and not through the Landau mechanism of spontaneous symmetry breaking. As a consequence, the low-energy effective theory which describes these new superconductors is not the Landau–Ginzburg theory, [...] Read more.
I review a new superconductivity mechanism in which the gap is opened through a topological mechanism and not through the Landau mechanism of spontaneous symmetry breaking. As a consequence, the low-energy effective theory which describes these new superconductors is not the Landau–Ginzburg theory, formulated in terms of a local-order parameter, but a topological-field theory formulated in terms of emerging gauge fields. This new mechanism is realized as global superconductivty in Josephson junction arrays and in thin superconducting films with thicknesses comparable to the superconducting coherence length, which exhibits emergent granularity. Full article
26 pages, 9897 KiB  
Review
Is Nematicity in Cuprates Real?
by Ivan Božović, Xi He, Anthony T. Bollinger and Roberta Caruso
Condens. Matter 2023, 8(1), 7; https://doi.org/10.3390/condmat8010007 - 10 Jan 2023
Cited by 3 | Viewed by 1784
Abstract
In La2-xSrxCuO4 (LSCO), a prototype high-temperature superconductor (HTS) cuprate, a nonzero transverse voltage is observed in zero magnetic fields. This is important since it points to the breaking of the rotational symmetry in the electron fluid, [...] Read more.
In La2-xSrxCuO4 (LSCO), a prototype high-temperature superconductor (HTS) cuprate, a nonzero transverse voltage is observed in zero magnetic fields. This is important since it points to the breaking of the rotational symmetry in the electron fluid, the so-called electronic nematicity, presumably intrinsic to LSCO (and other cuprates). An alternative explanation is that it arises from extrinsic factors such as the film’s inhomogeneity or some experimental artifacts. We confront this hypothesis with published and new experimental data, focusing on the most direct and sensitive probe—the angle-resolved measurements of transverse resistivity (ARTR). The aggregate experimental evidence overwhelmingly refutes the extrinsic scenarios and points to an exciting new effect—intrinsic electronic nematicity. Full article
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Other

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7 pages, 2421 KiB  
Project Report
Effects of Focused Ion Beam Lithography on La2−xSrxCuO4 Single Crystals
by Roberta Caruso, Fernando Camino, Genda Gu, John M. Tranquada, Myung-Geun Han, Yimei Zhu, Anthony T. Bollinger and Ivan Božović
Condens. Matter 2023, 8(2), 35; https://doi.org/10.3390/condmat8020035 - 13 Apr 2023
Cited by 1 | Viewed by 1323
Abstract
Focused ion beam (FIB) milling is a mask-free lithography technique that allows the precise shaping of 3D materials on the micron and sub-micron scale. The recent discovery of electronic nematicity in La2−xSrxCuO4 (LSCO) thin films triggered the [...] Read more.
Focused ion beam (FIB) milling is a mask-free lithography technique that allows the precise shaping of 3D materials on the micron and sub-micron scale. The recent discovery of electronic nematicity in La2−xSrxCuO4 (LSCO) thin films triggered the search for the same phenomenon in bulk LSCO crystals. With this motivation, we have systematically explored FIB patterning of bulk LSCO crystals into micro-devices suitable for longitudinal and transverse resistivity measurements. We found that several detrimental factors can affect the result, ultimately compromising the possibility of effectively using FIB milling to fabricate sub-micrometer LSCO devices, especially in the underdoped regime. Full article
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12 pages, 1834 KiB  
Technical Note
Methods to Create Novel La2−xSrxCuO4 Devices with Multiple Atomically Sharp Interfaces
by Anthony T. Bollinger, Xi He, Roberta Caruso, Xiaotao Xu, Xiaoyan Shi and Ivan Božović
Condens. Matter 2023, 8(1), 14; https://doi.org/10.3390/condmat8010014 - 20 Jan 2023
Cited by 1 | Viewed by 1373
Abstract
We present methods to create devices that utilize the high-temperature superconductor La2-xSrxCuO4 grown by atomic layer-by-layer molecular beam epitaxy (ALL-MBE). The ALL-MBE synthesis technique provides atomically precise interfaces necessary for the tunnel junctions, Josephson junctions, and dyon [...] Read more.
We present methods to create devices that utilize the high-temperature superconductor La2-xSrxCuO4 grown by atomic layer-by-layer molecular beam epitaxy (ALL-MBE). The ALL-MBE synthesis technique provides atomically precise interfaces necessary for the tunnel junctions, Josephson junctions, and dyon detection devices that will be considered. A series of microfabrication processing steps using established techniques are given for each device, and their details are discussed. These procedures are easily extended to generate more complex designs and could be suitable for a wider variety of materials. Full article
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14 pages, 2915 KiB  
Protocol
Optimization of La2−xSrxCuO4 Single Crystal Film Growth via Molecular Beam Epitaxy
by Xi He, Xiaotao Xu, Xiaoyan Shi and Ivan Božović
Condens. Matter 2023, 8(1), 13; https://doi.org/10.3390/condmat8010013 - 20 Jan 2023
Cited by 2 | Viewed by 1337
Abstract
Atomic layer-by-layer molecular beam epitaxy (ALL-MBE) combined with ozone is one of the best methods to fabricate single-crystal thin films of complex oxides. Cuprate such as La2−xSrxCuO4 (LSCO) is a representative complex-oxide high-temperature superconductor (HTS) material. Our group [...] Read more.
Atomic layer-by-layer molecular beam epitaxy (ALL-MBE) combined with ozone is one of the best methods to fabricate single-crystal thin films of complex oxides. Cuprate such as La2−xSrxCuO4 (LSCO) is a representative complex-oxide high-temperature superconductor (HTS) material. Our group utilizes this method to produce high-quality single-crystal HTS films with atomically smooth surfaces and interfaces. In addition, ALL-MBE enables us to engineer multilayer heterostructures with atomic precision. This allows the fabrication of tunnel junctions, various nanostructures, and other HTS devices of interest for superconducting electronics. We have synthesized over three thousand LSCO thin films in the past two decades. These films’ structural and electronic properties have been studied and characterized by various methods. Here, we distill the extensive experience we accumulated into a step-by-step protocol to fabricate atomically perfect LSCO films. The recipe includes substrate preparation, ozone generation and distillation, source calibration, the in situ monitoring of the film synthesis, post-growth annealing, and ex situ characterization. It discloses a reproducible way to fabricate single-crystal LSCO films for basic research and HTS electronic applications. Full article
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