Journal of Physics: Condensed Matter

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ISSN / EISSN : 0953-8984 / 1361-648X
Published by: IOP Publishing (10.1088)
Total articles ≅ 37,190
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, Luis A. Jauregui, Chris Wilen, , David B Newell, , Yong P Chen
Published: 14 September 2021
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac268f

Abstract:
Decoherence in quantum bits (qubits) is a major challenge for realizing scalable quantum computing. One of the primary causes of decoherence in qubits and quantum circuits based on superconducting Josephson junctions is the critical current fluctuation. Many efforts have been devoted to suppressing the critical current fluctuation in Josephson junctions. Nonetheless, the efforts have been hindered by the defect-induced trapping states in oxide-based tunnel barriers and the interfaces with superconductors in the traditional Josephson junctions. Motivated by this, along with the recent demonstration of 2D insulator h-BN with exceptional crystallinity and low defect density, we fabricated a vertical NbSe2/h-BN/Nb Josephson junction consisting of a bottom NbSe2 superconductor thin layer and a top Nb superconductor spaced by an atomically thin h-BN layer. We further characterized the superconducting current and voltage (I-V) relationships and Fraunhofer pattern of the NbSe2/h-BN/Nb junction. Notably, we demonstrated the critical current noise (1/f noise power) in the h-BN-based Josephson device is at least a factor of four lower than that of the previously studied aluminum oxide-based Josephson junctions. Our work offers a strong promise of h-BN as a novel tunnel barrier for high-quality Josephson junctions and qubit applications.
Bo Zhang, Zheyong Fan, ,
Published: 14 September 2021
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac268d

Abstract:
Lattice thermal conductivity (LTC) is a key parameter for many technological applications. Based on the Peierls-Boltzmann transport equation (PBTE), many unique phonon transport properties of various materials were revealed. Accurate calculation of LTC with PBTE, however, is a time-consuming task, especially for compounds with a complex crystal structure or taking high-order phonon scattering into consideration. Graphical processing units (GPUs) have been extensively used to accelerate scientific simulations, making it possible to use a single desktop workstation for calculations that used to require supercomputers. Due to its fundamental differences from traditional processors, GPUs are especially suited for executing a large group of similar tasks with minimal communication, but require completely different algorithm design. In this paper, we provide a new algorithm optimized for GPUs, where a two-kernel method is used to avoid divergent branching. A new open-source code, GPU_PBTE, is developed based on the proposed algorithm. As demonstrations, we investigate the thermal transport properties of silicon and silicon carbide, and find that accurate and reliable LTC can be obtained by our software. GPU_PBTE performed on NVIDIA Tesla V100 can extensively improve double precision performance, making it two to three orders of magnitude faster than our CPU version performed on Intel Xeon CPU Gold 6248 @ 2.5 GHz. Our work also provides an idea of accelerating calculations with other novel hardware that may come out in the future.
Snehashish Chatterjee, , Saurav Giri,
Published: 14 September 2021
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac268c

Abstract:
Heusler compounds are a large group of intermetallic compositions with versatile material properties. In the recent times, they are found to be important for their practical applications in the fields of spintronics and shape memory effect. Interestingly, their physical properties can be easily tuned by varying the valence electron concentration through proper doping and substitution. Empirical laws concerning the valence electron concentration, such as Slater-Pauling or Hume-Rothery rules are found to be useful in predicting their electronic, magnetic and structural properties quite accurately. Electrical transport measurements are simple laboratorybased techniques to gather a handful of information on the electronic properties of metals and semiconductors. The present review aimed to provide a comprehensive view of the transport in 3d and 4d transition metal based bulk Heusler compositions. The main emphasis is given on resistivity, magnetoresistance, Hall effect, thermopower as well as spin-dependent transport in spintronics devices. The review primarily focuses on magnetic Heusler compounds and alloys, albeit it also addresses several non-magnetic materials showing superconductivity or large thermopower.
, Dennis Wong, Chrisitan Schulz, F. Rodrı́guez,
Published: 13 September 2021
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2648

Abstract:
We investigate the electronic structure of Cs$_2$CuCl$_4$, a material discussed in the framework of a frustrated quantum antiferromagnet, by means of resonant inelastic x-ray scattering (RIXS) and Density Functional Theory (DFT). From the non-dispersive highly localized \textit{dd} excitations, we resolve the crystal field splitting of the Cu$^{2+}$ ions in a strongly distorted tetrahedral coordination. This allows us to model the RIXS spectrum within the Crystal Field Theory (CFT), assign the \textit{dd} orbital excitations and retrieve experimentally the values of the crystal field splitting parameters \textit{D}$_q$, \textit{D}$_s$ and \textit{D}$_{\tau}$. The electronic structure obtained \textit{ab-initio} agrees with the RIXS spectrum and modelled by CFT, highlighting the potential of combined spectroscopic, cluster and DFT calculations to determine the electronic ground state of complex materials.
Jia Bao, Yanhong Liu,
Published: 13 September 2021
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac2647

Abstract:
We study the global quantum discord (GQD) in the Lipkin-Meshkov-Glick (LMG) model at zero and finite temperatures, in which all spins are mutually interacted and introduced in an external magnetic field (denoted by $h$). We confirm that the high coordinate number is one of the most distinguishing features of the LMG model, which directly results in the nontrivial behaviors of quantum correlations. We compare the GQD with other quantum correlations measures (such as concurrence, quantum discord, and global entanglement) and find the remarkable difference between them. For instance, we find that GQD spreads in the entire system and captures more information on quantum correlations when comparing with concurrence and quantum (pairwise) discord. We discover that GQD can characterize multipartite correlations in the both broken phase ($h0$ in the anisotropic cases for any fixed magnetic field. We further show that GQD behaves as $\mathcal{G}|_{s_n} \sim k \cdot \frac{1}{N}+c$ with $k<0$ in the isotropic cases for any Dicke state $|s_n\rangle$. Herein $k$ and $c$ are the fitting parameters. We also find that the thermal stability of the GQD at low temperatures depends on the energy gap. We further reveal that the extraordinary behaviors of the thermal-state GQD in the isotropic LMG model are explained by the contribution theory of the energy levels.
Tomoya Taguchi, Mitsuki Ikeda, Huan Li, Ai Suzuki, Xiaofan Yang, Hirofumi Ishii, Yen-Fa Liao, Hiromi Ota, Hidenori Goto, Ritsuko Eguchi, et al.
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac244b

Abstract:
The crystal structures of Sb2Te3-ySey (y = 0.6 and y = 1.2) at 0 – 24 GPa were investigated by synchrotron X-ray diffraction (XRD). The stoichiometry of Sb2Te3-ySey used in this study was determined to be Sb2Te2.19(9)Se0.7(2) for y = 0.6 and Sb2Te1.7(1)Se1.3(3) for y = 1.2, on the basis of energy-dispersive X-ray spectroscopy. The sample of Sb2Te2.19(9)Se0.7(2) showed a structural phase transition from a rhombohedral structure (space group No. 166, Rm) (phase I) to a monoclinic structure (space group No. 12, C2/m) (phase II), with increasing pressure up to ~9 GPa. A new structural phase (phase II') emerged at 17.7 GPa, a monoclinic structure with the space group C2/c (No.15). Finally, a 9/10-fold monoclinic structure (space group No. 12, C2/m) (phase III) was observed at 21.8 GPa. In contrast, the sample of Sb2Te1.7(1)Se1.3(3) provided only phase I (space group No. 166, Rm) and phase II (space group No. 12, C2/m), showing one structural phase transition from 0 – 19.5 GPa. These samples were not superconductors at ambient pressure, but superconductivity suddenly appeared with increasing pressure. Superconductivity with superconducting transition temperatures (Tc's) of 2 and 4 K was observed above 6 GPa in phase I of Sb2Te2.19(9)Se0.7(2). In this sample, the Tc values of 6 and 9 K were observed in phase II and phase II' or III of Sb2Te2.19(9)Se0.7(2), respectively. Superconductivity with Tc's of 4 and 5 K suddenly emerged in Sb2Te1.7(1)Se1.3(3) at 13.6 GPa, which corresponds to phase II, and it evolved to 6.0 K under further increased pressure. A Tc value of 9 K was finally found above 15 GPa. The magnetic field dependence of Tc in phase II of Sb2Te2.19(9)Se0.7(2) and Sb2Te1.7(1)Se1.3(3) followed a p-wave polar model, suggesting topologically nontrivial superconductivity.
, Samuel Roy Baty,
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac23fb

Abstract:
Silver has been considered as one of the simple one-phase materials that do not exhibit high pressure or high temperature polymorphism. The solid phase of Ag at ambient conditions is face-centered cubic (fcc) one. However, very recently another solid phase of silver, body-centered cubic (bcc) one, was detected in shock-wave (SW) experiments, and a more sophisticated phase diagram of Ag with the two solid phases was published by Smirnov. In this work, using a suite of ab initio quantum molecular dynamics (QMD) simulations based on the Z methodology which combines both direct Z method for the simulation of melting curves and inverse Z method for the calculation of solid-solid phase boundaries, we refine the phase diagram of Smirnov. We calculate the melting curves of both fcc-Ag and bcc-Ag and obtain an equation for the fcc-bcc solid-solid phase transition boundary. We also obtain the thermal equation of state of Ag which is in agreement with experimental data and QMD simulations. We argue that, despite being a polymorphic rather than a simple one-phase material, silver can be considered as a SW standard.
Xiao-Yan Chen, Zhi-Bo Yin, Shuang Liu, ,
Journal of Physics: Condensed Matter; https://doi.org/10.1088/1361-648x/ac23fc

Abstract:
The van der Waals ferromagnetic material VI3 is a magnetic Mott insulator. In this work, we investigate the effects of isotropic and anisotropic pressure on the atomic structure and the electronic structure of VI3 using the first-principles method. The in-plane strain induces structural distortion and breaks the three-fold rotational symmetry of the lattice. Both the in-plane and out-of-plane strain widen the conduction and the valence bands, reduce the energy band gap and drive VI3 from a semiconductor to a three-dimensional metal. The structural distortion is not the cause of insulator-to-metal transition. Calculations of the magnetocrystalline anisotropy energy indicate an easy-axis to easy-plane transition when the pressure is higher than 2 GPa. The ferromagnetic Curie temperature falls from 63 K at 0 GPa to 25 K at 6 GPa.
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