Semiconductor devices based on $15R$ silicon carbide (SiC) show improved properties compared to other polytypes. Here, we report the investigation of nitrogen-doped $15R$ SiC monocrystals with $\left(N_{\mathrm{D}}–N_{\mathrm{A}}\right)\sim 5\times {10}^{18}\mathrm{c}{\mathrm{m}}^{-3}$ using multifrequency electron paramagnetic resonance (EPR) and electrically detected magnetic resonance (EDMR) spectroscopic methods in the microwave (MW) frequency range from 9.4 to 328.84 GHz and in the temperature range from 4.2 to 300 K. A single intensive $S$ line with $S=1/2$, at $g_{\perp }=2.0026\left(2\right)$, and $g_{\parallel }=2.0043\left(2\right)$ dominates the EPR spectrum in $15R$ SiC at $T<160$ K and was attributed to the exchange-coupled nitrogen (N) donors substituting quasicubic “$k1$” site having the deeper energy level in $15R$ SiC lattice. From the analysis of the temperature behavior of the integral intensity, magnetic field position, intensity, shape, and width of the $S$ line, it was concluded that at $T<90$ K, the exchange coupling occurs between localized donor electrons, while at $T=90-150$ K the interaction between exchange-coupled N donors and conduction electrons takes place. In the temperature interval from 20 to 160 K, the $S$-line EPR width was characterized by a two-phonon Orbach relaxation process with the activation energy of $\sim 6.5$ meV corresponding to the valley-orbit splitting values for N donors in $15R$ SiC. The variable-range hopping regime obeying the $T^{1/4}$ law was found to take place at $T<20$ K leading to the appearance of the $S$ line in the EDMR spectrum at low temperatures. The appearance of the EDMR signal from exchange-coupled N donors is caused by the EPR-induced temperature-increase mechanism and the spin-flip hops process. The results obtained from MW conductivity measurements agree with EPR and EDMR data. The temperature variation of MW conductivity was described by several processes, including the electron-hopping process between N donor impurity atoms at $T<50$ K with activation energy ${\varepsilon }_3=1.5$ meV, electron transitions between Hubbard bands at $T=50–100$ K; the transition of the electrons from the donor energy levels to conduction band with ionization energy ${\varepsilon }_1=32$ meV at $T=100–200$ K and scattering of the conduction electrons by ionized donors occurred at the temperature higher than 200 K.

We have studied the insulator-to-metal transition and crystal structure evolution under high pressure in the van der Waals compound ${\mathrm{CoPS}}_3$ through in situ electrical resistance, Hall resistance, magnetoresistance, x-ray diffraction, and Raman scattering measurements. ${\mathrm{CoPS}}_3$ exhibits a $C2/m\to P\overline{3}$ structural transformation at 7 GPa accompanied by a $2.9\%$ reduction in the volume per formula unit. Concomitantly, the electrical resistance decreases significantly and ${\mathrm{CoPS}}_3$ becomes metallic. This metallic ${\mathrm{CoPS}}_3$ is a hole-dominant conductor with multiple conduction bands. The linear magnetoresistance and the small volume collapse at the metallization suggest the incomplete high-spin $\to$ low-spin transition in the metallic phase. Thus, the metallic ${\mathrm{CoPS}}_3$ possibly possesses an inhomogeneous magnetic moment distribution and short-range magnetic ordering. This paper summarizes the comprehensive phase diagram of $M{\mathrm{PS}}_3$ ($M=\mathrm{V}$, Mn, Fe, Co, Ni, and Cd) that metalize under pressures.

In (1+1)-dimensional topological phases, unpaired Majorana zero modes (MZMs) can arise only if the internal symmetry group $G_f$ of the ground state splits as $G_f=G_b\times {\mathbb{Z}}_2^f$, where ${\mathbb{Z}}_2^f$ is generated by fermion parity ${(-1)}^F$. In contrast, (2+1)-dimensional [(2+1)D] topological superconductors (TSC) can host unpaired MZMs at defects even when $G_f$ is not of the form $G_b\times {\mathbb{Z}}_2^f$. In this paper we study how $G_f$ together with the chiral central charge $c_{-}$ strongly constrain the existence of unpaired MZMs and the quantum numbers of symmetry defects. Our results utilize a recent algebraic characterization of (2+1)D invertible fermionic topological states, which provides a nonperturbative approach based on topological quantum field theory, beyond free fermions. We study physically relevant groups such as $\mathrm{U}{\left(1\right)}^f⋊H,\mathrm{SU}{\left(2\right)}^f\times H,\mathrm{U}{\left(2\right)}^f⋊H$, generic Abelian groups, as well as more general compact Lie groups, antiunitary symmetries, and crystalline symmetries. We present an algebraic formula for the fermionic crystalline equivalence principle, which gives an equivalence between states with crystalline and internal symmetries. In light of our theory, we discuss several previously proposed realizations of unpaired MZMs in TSC materials such as ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$, transition metal dichalcogenides, and iron superconductors, in which crystalline symmetries are often important; in some cases we present additional predictions for the properties of these models.

We have proposed an efficient algorithm to calculate physical quantities in the translational invariant three-dimensional tensor networks, which is particularly relevant to the study of the three-dimensional classical statistical models and the ($2+1$)-dimensional quantum lattice models. In the context of a classical model, we determine the partition function by solving the dominant eigenvalue problem of the transfer matrix, whose left and right dominant eigenvectors are represented by two projected entangled simplex states. These two projected entangled simplex states are not Hermitian conjugate to each other but are appropriately arranged so that their inner product can be computed much more efficiently than in the usual prescription. For the three-dimensional Ising model, the calculated internal energy and spontaneous magnetization agree with the published results in the literature. The possible improvement and extension to other models are also discussed.

Entanglement phase transitions in hybrid quantum circuits describe individual quantum trajectories rather than the measurement-averaged ensemble, despite the fact that results of measurements are not conventionally used for feedback. Here, we numerically demonstrate that a class of generalized measurements with identical measurement-averaged dynamics give different phases and phase transitions. We show that measurement-averaged destruction of Bell state entanglement is a useful proxy for determining which hybrid circuit yields the lowest-entanglement dynamics. We use this to argue that no unfolding of our model can avoid a volume law phase, which has implications for simulation of open quantum systems.

In a class of non-Hermitian quantum walk in lossy lattices with open boundary conditions, an unexpected peak in the distribution of the decay probabilities appears at the edge, referred to as an edge burst. It is proposed that the edge burst originates jointly from the non-Hermitian skin effect (NHSE) and the imaginary gaplessness of the spectrum [W.-T. Xue et al., Phys. Rev. Lett. 128, 120401 (2022)]. Using a particular one-dimensional lossy lattice with a nonuniform loss rate, we show that the edge burst can occur even in the absence of skin localizations. Furthermore, we discuss that the edge burst may not appear if the spectrum satisfies the imaginary gapless condition. Aside from its fundamental importance, by removing the restrictions on observing the edge burst effect, our results open the door to broader design space for future applications of the edge burst effect.

Recent theoretical investigations of quantum spin liquids have described phenomenology amenable to experimental observation using scanning tunneling microscopy. This includes characteristic resonances found at the edge of the upper Hubbard band of the host Mott insulator, that under certain conditions shift into the Mott gap under external magnetic field [W.-Y. He and P. A. Lee, arXiv:2212.08767]. In light of this we report scanning tunneling microscopy observations, in samples of the quantum spin liquid candidate $1T\text{−}{\mathrm{TaS}}_2$, of a conductance peak at the upper Hubbard band edge and its magnetic field dependent behavior. These observations potentially represent evidence for the existence of a quantum spin liquid in $1T\text{−}{\mathrm{TaS}}_2$. We also observe samples in which such field dependence is absent, but with no observed correlate for the presence or absence of field dependence. This suggests one or more material properties controlling electronic behavior that are yet to be understood, and should help to motivate renewed investigation of the microscopic degrees of freedom in play in $1T\text{−}{\mathrm{TaS}}_2$, as well as the possible realization of a quantum spin liquid phase.

${\mathrm{K}}_{0.5}{\mathrm{Na}}_{0.5}\mathrm{Nb}{\mathrm{O}}_3$ (KNN)-modified morphotropic phase boundary (MPB) compositions of the two ${\mathrm{Na}}_{0.5}{\mathrm{Bi}}_{0.5}\mathrm{Ti}{\mathrm{O}}_3$-based lead-free piezoelectrics, namely, $0.94{\mathrm{Na}}_{0.5}{\mathrm{Bi}}_{0.5}\mathrm{Ti}{\mathrm{O}}_3\text{−}0.06\mathrm{BaTi}{\mathrm{O}}_3$ (NBT-6BT) and $0.80{\mathrm{Na}}_{0.5}{\mathrm{Bi}}_{0.5}\mathrm{Ti}{\mathrm{O}}_3\text{−}0.20{\mathrm{K}}_{0.5}{\mathrm{Bi}}_{0.5}\mathrm{Ti}{\mathrm{O}}_3$ (NBT-20KBT) are model systems exhibiting large $(>0.4\%)$ electric-field-driven strain. There is a general perception that (i) increasing KNN concentration monotonically weakens the direct piezoelectric response $\left(d_{33}\right)$, and (ii) maximum electrostrain occurs when KNN pushes the system in the fully ergodic relaxor state. We have examined these issues using various complementary techniques involving electrostrain, piezoelectric coefficient $\left(d_{33}\right)$, ferroelectric switching-current measurements, and field-driven structural studies on the global and local scales using laboratory and synchrotron x-ray diffraction, neutron powder diffraction, and ${\mathrm{Eu}}^{+3}$ photoluminescence techniques. Our investigations revealed the following important features: (i) In the low-concentration regime, KNN induces a tetragonal ferroelectric distortion, which improves the weak signal piezoresponse. (ii) Beyond a threshold concentration, in-phase octahedral tilt sets in and weakens the long-range ferroelectric order to partially stabilize an ergodic state. (iii) The maximum electrostrain (∼0.6%) is achieved in the mixed (nonergodic + ergodic) state. (iv) The mixed state invariably exhibits a less-known phenomenon of field-driven ferroelectric-to-relaxor transformation during bipolar field cycling. (v) The enhanced electrostrain in the mixed state is associated with the electric field increasing the correlation lengths of the short-ranged tetragonal and rhombohedral ferroelectric regions without overall transformation of one phase to the other. We summarize the findings of this work in a comprehensive electric field composition (E-x) phase diagram. The findings reported here are likely to be true for other NBT-based MPB systems.

Raman scattering is commonly used to quantify defects in $s{p}^2$ carbons, mostly based on the values of the double-resonant D-band intensity. It is well known that this peculiar band undergoes changes when the $s{p}^2$ carbon is polished. However, the physical process behind this phenomenon is unclear so far. In this paper, we provide a deep understanding of the fundamental optical properties of the polishing-induced defects by combining angle-resolved polarized Raman scattering and theoretical calculations. We address the question regarding the types of these additional defects that participate in the intervalley double-resonance Raman process and contribute to the spatially inhomogeneous increase of the relative D-band intensity. The study was performed on anthracene-based coke pyrolyzed at $2000{}^{\circ }\mathrm{C}$ and uses highly oriented pyrolytic graphite with known crystallographic orientations as a model material. The results shed light on the types of defects as well as the D-band peculiar behavior as a function of the spatial orientation of graphene layers dictated by polishing with respect to the fixed direction of the incident and scattered light. Moreover, the insignificant change in $I_{2\mathrm{D}}/I_{\mathrm{G}}$, the width and the position of the G band after polishing, and the insensitivity of less ordered carbons to this process are also discussed.

We report the Griffiths phase (GP)-like state along with a cluster-glass-like state in geometrically frustrated antiferromagnetic Cr-substituted ${\text{Y}}_2{\text{Ir}}_2{\text{O}}_7$ pyrochlore iridates. The strength of the GP-like behavior increases with substitution. Interestingly, isothermal remanent magnetization suggests the Ising-like interaction of spins in the GP region. The GP-like state is not attributed to the structural disorder as substitution of Cr does not induce any structural change. Then the spin coupling between ${\text{Cr}}^{3+}\leftrightarrow {\text{Cr}}^{3+}$, ${\text{Ir}}^{4+}\leftrightarrow {\text{Ir}}^{4+}$, ${\text{Ir}}^{4+}\leftrightarrow {\text{Cr}}^{3+}$, and ${\text{Ir}}^{4+}\leftrightarrow {\text{Ir}}^{5+}$ leads to the competition between antiferromagnetic and ferromagnetic correlations. It gives rise to Ruderman-Kittel-Kasuya-Yosida (RKKY)-like interaction between ${\text{Cr}}^{3+}$ local magnetic moments mediated by itinerant Ir conduction electrons, hence, as a result, GP and cluster-glass-like states emerge.

We report the observation of cluster glasslike properties in a double perovskite ruthenate ${\mathrm{Ba}}_2{\mathrm{CoRuO}}_6$ through structural (neutron and synchrotron x-ray diffraction), magnetic, and transport measurements. The system exhibits classic glassy characteristics such as a frequency dependence in ac susceptibility, aging and memory effects, along with the persistence of short-range correlations up to room temperature. The significant ($\sim 30\%$) antisite disorder on the dimer sites, coupled with the inherent geometrical frustration, allows a variety of exchange (both antiferro- and ferromagnetic) interactions to be distributed randomly across the lattice. On cooling, locally dominant interactions cause spins to nucleate and form local, short-range ordered clusters which grow in size until a global freezing occurs at about $T_f\sim 43\text{K}$.

Through an antiferromagnetic proximity effect, we demonstrate the evidence for quenched magnetic impurity scattering in a spin-orbit-coupled semimetal ${\mathrm{SrIrO}}_3$ proximitized with an antiferromagnetic ${\mathrm{SrCuO}}_2$ layer from quantum interference originated magnetoconductance study. Two distinct observations, i.e., (i) enhanced effective phase coherence length ($l_{\varphi }$) and (ii) emergence of chiral-anomaly-induced topological response in longitudinal magnetoconductance ($\vec{B}\left|\right|\vec{E}$), signify that the magnetic impurity scattering is suppressed in the ${\mathrm{SrCuO}}_2/{\mathrm{SrIrO}}_3$ bilayer. The quenching of magnetic impurity scattering is discussed in the framework of the antiferromagnetic proximity effect, which is originated from spin Andreev reflection at the ${\mathrm{SrCuO}}_2/{\mathrm{SrIrO}}_3$ interface. This work unfolds a practical means to circumvent the detrimental effect of unintended magnetic impurity scattering and preserve quantum phenomena in complex materials.

The relationship between waves and static pattern formation is an intriguing effect and remains unexplained in many areas of physics, including magnetism. We study the spin-wave-mediated spin reorientation transition (SRT) in magnetic films with uniaxial magnetic anisotropy and Dzyaloshinskii-Moriya interaction (DMI). In particular, we show that propagating spin waves can freeze in the SRT, causing periodic magnetic domains to arise, which is reminiscent of the wave amplitude distribution. This process can take place under the influence of a change in the magnetic field, but also of other parameters. Interestingly, at the SRT, DMI nonreciprocity leads to the emergence of flowing magnetization patterns, which suggests a spontaneous breaking of translational symmetry, and the formation of magnonic space-time crystals. The described phenomena are general and should take place in a large family of magnetic materials. Therefore, the results should be of great importance for the further development of spintronics and magnonics.

The negative differential thermal conductance (NDTC) provides the key mechanism for realizing thermal transistors. This exotic effect has been the object of an extensive theoretical investigation, but the implementation is still limited to a few specific physical systems. Here, we consider a simple circuit of two electrodes exchanging heat through electromagnetic radiation. We theoretically demonstrate that the existence of an optimal condition for power transmission, well known as impedance matching in electronics, provides a natural framework for engineering NDTC: the heat flux is reduced when the temperature increase is associated to an abrupt change of the electrode's impedance. As a case study, we numerically analyze a hybrid structure based on thin-film technology, in which the increased resistance is due to a superconductor-resistive phase transition. For typical metallic superconductors operating below $1\mathrm{K}$, NDTC reflects in a temperature drop of the order of a few mK by increasing the power supplied to the system. Our numerical work draws new routes for implementing a thermal transistor in nanoscale circuits.

Members of the $\mathrm{CaK}{\left({\mathrm{Fe}}_{1-x}{\mathrm{Cr}}_x\right)}_4{\mathrm{As}}_4$ series have been synthesized by high-temperature solution growth in single-crystalline form and characterized by x-ray diffraction, elemental analysis, and magnetic and transport measurements. The effects of Cr substitution on the superconducting and magnetic ground states of ${\mathrm{CaKFe}}_4{\mathrm{As}}_4$ ($T_c=35$ K) have been studied. These measurements show that the superconducting transition temperature decreases monotonically and is finally suppressed below 1.8 K as $x$ is increased from 0 to 0.038. For $x$-values greater than 0.012, signatures of a magnetic transition can be detected in magnetic measurements with the associated features in the transport measurements becoming detectable for $x\ge 0.038$. The magnetic transition temperature increases in a roughly linear manner as Cr substitution increases. A temperature-composition ($T-x$) phase diagram is constructed, revealing a half-dome of superconductivity with the magnetic transition temperature, $T^{*}$, appearing near 22 K for $x\sim 0.017$ and rising slowly up to 60 K for $x\sim 0.077$. The $T-x$ phase diagrams for $\mathrm{CaK}{\left({\mathrm{Fe}}_{1-x}{T}_x\right)}_4{\mathrm{As}}_4$ for $T=\text{Cr}$ and Mn are essentially the same despite the nominally different band filling; this is in marked contrast to $T=\text{Co}$ and Ni series for which the $T-x$ diagrams scale by a factor of 2, consistent with the different changes in band filling Co and Ni would produce when replacing Fe. Superconductivity of $\mathrm{CaK}{\left({\mathrm{Fe}}_{1-x}{\mathrm{Cr}}_x\right)}_4{\mathrm{As}}_4$ is also studied as a function of magnetic field. A clear change in $H_{c2}^{\prime }\left(T\right)/T_c$, where $H_{c2}^{\prime }\left(T\right)$ is $d{H}_{c2}\left(T\right)/dT$, at $x\sim 0.012$ is observed and probably is related to a change of the Fermi surface due to magnetic order. Coherence length and the London penetration depths are also calculated based on $H_{c1}$ and $H_{c2}$ data. Both of them as a function of $x$ show changes near $x=0.012$, again consistent with Fermi surface changes associated with the magnetic ordering seen for higher $x$-values.

In this work, we report x-ray powder diffraction, elemental analysis, electrical resistivity, magnetic susceptibility, specific heat, and electron spin resonance (ESR) in single crystals of ${\mathrm{Sr}}_{1\text{−}x}{\mathrm{Eu}}_x{\mathrm{Fe}}_2{\mathrm{As}}_2$. We observed a breakdown of the previously reported scaling between the ${\mathrm{Eu}}^{2+}$ Korringa relaxation rate obtained from ESR and the spin density wave temperature evolution for Sr-rich samples. This result suggests a distinct evolution of the orbital differentiation of the Fe $3d$ bands along the Sr-based series when compared to the Ba counterpart. We argue that this difference is related to a larger splitting between the structural (tetragonal-to-orthorhombic) and the Fe-driven spin density wave transitions induced by Eu doping in this series. In fact, our results indicate that the two transitions follow an opposite $x$-Eu dependence for Sr-concentrated samples. Our work shows that ${\mathrm{Sr}}_{1\text{−}x}{\mathrm{Eu}}_x{\mathrm{Fe}}_2{\mathrm{As}}_2$ series and the comparison with their Ba-based counterparts are exciting platforms to be explored for understanding the interplay among orbital differentiation, magnetism, and structural distortions in the iron pnictides.

The multicomponent oxide solid solution is a versatile platform to tune the delicate balance between competing spin, charge, orbital, and lattice degrees of freedom for materials design and discovery. The development of compositionally complex oxides with superior functional properties has been largely empirical and serendipitous, in part due to the exceedingly complex chemistry and structure of solid solutions that span a range of length scales. The usage of classical molecular dynamics (MD), a powerful statistical method, in computer-aided materials design has not yet reached the same level of sophistication as that in computer-aided drug design because of the limited availability and accuracy of classical force fields for solids. Here, we introduce the strategy of “modular development of deep potential” (ModDP) that enables a systematic development and improvement of deep-neural-network-based model potential, termed as deep potential, for complex solid solutions with minimum human intervention. The converged training database associated with an end-member material is treated as an independent module and is reused to train the deep potential of solid solutions via a concurrent learning procedure. We apply ModDP to obtain classical force fields of two technologically important solid solutions, ${\mathrm{Pb}}_x{\mathrm{Sr}}_{1-x}{\mathrm{TiO}}_3$ and ${\mathrm{Hf}}_x{\mathrm{Zr}}_{1-x}{\mathrm{O}}_2$. For both materials' systems, a single model potential is capable of predicting various properties of solid solutions including temperature-driven and composition-driven phase transitions over a wide range of compositions. In particular, the deep potential of ${\mathrm{Pb}}_x{\mathrm{Sr}}_{1-x}{\mathrm{TiO}}_3$ reproduces a few known topological textures such as polar vortex lattice and electric dipole waves in ${\mathrm{PbTiO}}_3/{\mathrm{SrTiO}}_3$ superlattices, paving the way for MD investigations on the dynamics of topological structures in response to external stimuli. MD simulations of ${\mathrm{Hf}}_x{\mathrm{Zr}}_{1-x}{\mathrm{O}}_2$ reveal a substantial impact of composition variation on both the phase transition temperature and the nature of the high-temperature nonpolar phase.

The development of differentiable invariant descriptors for accurate representations of atomic environments plays a central role in the success of interatomic potentials for chemistry and materials science. We introduce a method to generate fast proper orthogonal descriptors for the construction of many-body interatomic potentials, and we discuss its relation to existing empirical and machine-learning interatomic potentials. A traditional way of implementing the proper orthogonal descriptors has a computational complexity that scales exponentially with the body order in terms of the number of neighbors. We present an algorithm to compute the proper orthogonal descriptors with a computational complexity that scales linearly with the number of neighbors irrespective of the body order. We show that our method can enable a more efficient implementation for a number of existing potentials, and we provide a scalable systematic framework to construct new many-body potentials. The new potentials are demonstrated on a data set of density functional theory calculations for tantalum and compared with other interatomic potentials.

The structure of permanently densified silica glass is investigated by neutron and x-ray diffraction, and by the production of atomistic models that reproduce the diffraction results. The focus is on the nature of the ordering on an intermediate length scale that originates from the formation of $n$-rings, where $n$ is the number of Si or O atoms within a ring. The densification process has a large effect on this ordering, as identified by pronounced changes to the first sharp diffraction peak (FSDP) in the measured structure factors. A clear and systematic dependence of the distribution of ring sizes on the position and shape of the FSDP could not be found, i.e., the ring statistics are not directly encoded into the form of this peak. Instead, a significant contribution to the glass densification originates from compaction of the $n$-rings, a metric that is quantified by the radius of gyration and lifetime of the rings. We thereby uncover and quantify a key densification mechanism in amorphous materials.