Few-site Kitaev chains are promising for realizing Majorana zero modes without topological protection but fully nonlocal, which are known as poor man's Majorana modes. While several signatures have already been reported both theoretically and experimentally, it still remains unknown what is the nature of superconducting correlations in the presence of poor man's Majorana modes. In this paper, we study few-site Kitaev chains and demonstrate that they host pair correlations with distinct symmetries, entirely determined by the underlying quantum numbers. In particular, we find that a two-site Kitaev chain hosts local (odd-frequency) and nonlocal (odd- and even-frequency) pair correlations, both spin polarized and highly tunable by the system parameters. Interestingly, the odd-frequency pair correlations exhibit a divergent behavior around zero frequency when the nonlocal $p$-wave pair potential and electron tunneling are of the same order, an effect that can be controlled by the on-site energies. Since a divergent odd-frequency pairing is directly connected to the intrinsic spatial nonlocality of Majorana zero modes in topological superconductors, the divergent odd-frequency pairing here reflects the intrinsic Majorana nonlocality of poor man's Majorana modes but without any relation to topology. Our findings could help understanding the emergent pair correlations in few-site Kitaev chains.

We present a numerical simulation of x-ray magnetic circular dichroism (XMCD) at the $L_{2,3}$ edge of Mn in a representative rutile altermagnet ${\mathrm{MnF}}_2$ using a combination of density functional theory plus exact diagonalization of the atomic model. We explore how the dichroic spectra vary with the orientation of the light propagation vector and the Néel vector. An exact relationship between the XMCD spectra for different orientations of the Néel vector, valid in the absence of the valence spin-orbit coupling and core-valence multipole interaction, is derived and its approximate validity for the full Hamiltonian verified by numerical calculation. This relationship allows one to determine the in-plane orientation of the Néel vector using the XMCD spectra alone.

We reassess the structure of the effective action and quantum critical singularities of two-dimensional Fermi systems characterized by the ordering wave vector $\vec{Q}=\vec{0}$. By employing infrared cutoffs on all the massless degrees of freedom, we derive a generalized form of the Hertz action, which does not suffer from problems of singular effective interactions. We demonstrate that the Wilsonian momentum-shell renormalization group (RG) theory capturing the infrared scaling should be formulated keeping $\vec{Q}$ as a flowing, scale-dependent quantity. At the quantum critical point, scaling controlled by the dynamical exponent $z=3$ is overshadowed by a broad scaling regime characterized by a lower value of $z\approx 2$. This, in particular, offers an explanation of the results of quantum Monte Carlo simulations pertinent to the electronic nematic quantum critical point.

There has been much recent interest and progress on topological structures of the non-Hermitian Bloch bands. Here, we study the topological structures of non-Bloch bands of non-Hermitian multiband quantum systems under open boundary conditions, which has received limited attention in prior studies. Using a continuity criterion and an efficient sub-generalized Brillouin zone (sub-GBZ) algorithm, we establish a homotopic characterization—braiding topology, e.g., characterized by the band's total vorticity—for open-boundary bands and sub-GBZs. Such topological identification is robust without topological transition and emergent degenerate points, such as exceptional points. We further analyze the transition's impact on bands and spectral flows, including interesting properties unique to open boundaries, and numerically demonstrate our conclusions with tight-binding model examples. We unveil a crucial insight that open-boundary bands interchange their portions after encountering certain exceptional points. Our results enrich the foundational understanding of topological characterizations for generic non-Hermitian quantum systems.

The Weyl semimetal ${\mathrm{Co}}_2\mathrm{MnGa}$ (CMG) has recently attracted significant attention in the field of condensed matter physics because of its unique topological features along with the simultaneous presence of ferromagnetism at room temperature. Utilizing these remarkable properties of CMG for the spintronic applications will be of great interest both from fundamental as well as technological viewpoints. However, the investigation of spin pumping by means of the inverse spin Hall effect (ISHE) is not yet explored in this material. Here, we report the spin generation, spin propagation, and detection of the efficiency of spin-to-charge conversion (SCC) from CMG to different nonmagnetic (NM) layers such as heavy metals like Pt and W and topological materials like ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ through ISHE. The ferromagnetic resonance analyses clearly revealed the dependence of spin relaxation on the spin-orbit coupling strength of the nonmagnets and the concerned interface quality. A large spin mixing conductance of $\sim 1.8\times {10}^{19}{\mathrm{m}}^{-2}$ is observed for W and a quite high value of spin Hall angle of ∼1.5 is evidenced for ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ in these CMG based heterostructures. Importantly, a correlation is also established between the interfacial spin transport efficiency and the SCC efficiency with the quality of the NM layer as well as the associated interface. The findings obtained are fortified by the longitudinal spin Seebeck effect (LSSE) measurements. The anomalous Nernst contribution is separated from the spin Seebeck contribution by employing measurements in both in-plane magnetized and out-of-plane magnetized configurations. The anomalous Nernst coefficient for a 20-nm polycrystalline CMG film is found to be independent of measurement geometry with a value estimated to be 0.41 µV/K. The results of the LSSE are coherent with the ISHE measurements obtained for different CMG/NM bilayers. This detailed analysis is fundamentally very vital regarding the underlying principles of spin transport and SCC, and is expected to provide key insights for the strategic fabrication and optimization of spintronic devices.

Quantum long-range models at zero temperature can be described by fractional Lifshitz field theories, that is, anisotropic models whose actions are short range in time and long range in space. In this paper, we study the renormalization of fractional Lifshitz field theories with weakly relevant cubic or quartic self-interactions. Their nontrivial infrared fixed points exhibit Lifshitz scale invariance and we compute the lowest-order corrections to the dynamic critical exponent.

The main features of the nonlinear pulse propagated in iron-yttrium-garnet magnonic crystal with thickness 100 nm and a periodic system of grooves on the surface are studied. We have demonstrated the possibility of the formation of gap solitons at a frequency inside the band gap of the magnonic crystal when the input signal power is increased. A further increase in the duration and power of the input pulse leads to the formation a series of gap solitons with a duration of about 10 ns. We have discovered that the threshold power of the gap solitons' generation is determined by the magnitude of the magnetic field.

The conformal anomaly indicates the breaking of conformal symmetry (angle-preserving transformations) in quantum theory by quantum fluctuations, and is a close cousin of the gravitational anomaly. We show that the conformal anomaly controls the variance of the local magnetization $M_{\mathrm{loc}}$ at finite temperatures in spin chains and spin ladders. This effect is predicted to appear at constant and variable temperature across the sample. The change of $M_{\mathrm{loc}}$ induced by the conformal anomaly is of the order of 3–5% of angular momentum $\hslash /2$ at 1 K for ${\left({\mathrm{C}}_7{\mathrm{H}}_{10}\mathrm{N}\right)}_2{\mathrm{CuBr}}_4$ (DIMPY) or copper pyrazine nitrate (CuPzN) and increases linearly with temperature. Further, for a temperature gradient of 10% across the sample, the time relaxation of the nonequilibrium $M_{\mathrm{loc}}$ is of the order of nanoseconds. Thus, we believe that experimental techniques such as neutron scattering, nuclear magnetic resonance (NMR), spin noise, and ultrafast laser pumping should determine the presence of the conformal anomaly. Therefore, we outline a method to detect the conformal anomaly in spin observables of strongly interacting low-dimensional magnets.

Usually, traditional magneto-optical (MO) applications demand high magneto-optic figures of merit, which results in limited available materials. Tunable MO applications concerning polarization states and magnetic orientations have been proposed with the discovery of large MO effects in anisotropic low-dimensional materials. Recently, a van der Waals ferrimagnet ${\mathrm{Mn}}_3{\mathrm{Si}}_2{\mathrm{Te}}_6$ exhibits colossal spin orientation-dependent magnetoresistance and magnetizability by comparing these properties between the in-plane ([100]) and out-of-plane ([001]) spin configurations. Thus exploring potential MO performances of ${\mathrm{Mn}}_3{\mathrm{Si}}_2{\mathrm{Te}}_6$ in detail is of importance. By utilizing first-principles calculations together with group theory analyses, we systematically investigate the electronic, optical, and MO properties of ${\mathrm{Mn}}_3{\mathrm{Si}}_2{\mathrm{Te}}_6$. An insulator-metal transition occurs between these two spin configurations. In addition, the maximal Kerr MO rotation angles of $\sim 0.{41}^{\circ }$ for the metal state are comparable to those of best-known MO materials, while the maximal Schäfer-Hubert rotation angle of the insulated state is nearly one-tenth. We find that the spin-orbital coupling on Te atoms makes a dominant contribution to the MO anisotropy. Based on the large MO performances and their tunability of magnetic orientation and intensity, we suggest that ${\mathrm{Mn}}_3{\mathrm{Si}}_2{\mathrm{Te}}_6$ could serve as a promising MO material.

To explore phonon-mediated superconductors with critical temperature ($T_c$) exceeding the liquid-nitrogen temperature under ambient pressure, two pure carbon structures ${\mathrm{C}}_6$ and ${\mathrm{C}}_{10}$ with a carbon-cage-network are designed and their superconductivity is investigated. By shifting the Fermi level by hole doping, we successfully obtain the metallized $s{p}^3$-hybridized covalent $\sigma$-bonding bands, which generally show strong coupling with phonons. Based on first-principles calculations and the Wannier interpolation technique, the lattice dynamics, mechanical properties, electronic structures, and electron-phonon coupling of hole-doped ${\mathrm{C}}_6$ and ${\mathrm{C}}_{10}$ clathrates are investigated. Both the enlarged density of states at the Fermi level and the softened phonons play significant roles in the enhancement of electron-phonon coupling. By solving the anisotropic Eliashberg equations, we find that the $T_c$ of hole-doped ${\mathrm{C}}_6$ and ${\mathrm{C}}_{10}$ clathrates can reach about 43 K and 150 K, respectively. Additionally, pristine ${\mathrm{C}}_6$ and ${\mathrm{C}}_{10}$ clathrates exhibit ultrahigh hardness simultaneously. This study suggests that a carbon-cage-network is another direction to explore materials simultaneously possessing high-temperature superconductivity and ultrahigh hardness.

We perform a systematic ab initio study on phonon-mediated superconductivity in the transition-metal-based superconductors ${\mathrm{Sc}}_{6}M{\mathrm{Te}}_2(M=\mathrm{Fe},\mathrm{Co},\mathrm{Ni})$. Firstly, our charge analysis reveals significant electron transfer from Sc to $M$ because of the substantial difference in the electronegativity, filling the $3d$ orbitals of $M$ and suppressing magnetic instability. Secondly, we show that ${\mathrm{Sc}}_6{\mathrm{FeTe}}_2$ exhibits strong lattice anharmonicity. Moreover, for $M=\mathrm{Fe}$ and Co, we find low-frequency soft phonon bands of $M$, which can be interpreted as “rattling phonons” in the framework formed by Sc. While not observed in the case of $M=\mathrm{Ni}$, the rattling phonons give rise to a prominent peak or plateau in the Eliashberg spectral function and enhance the pairing instability. By reproducing the experimental trend of superconducting transition temperatures, our study underscores the potential of designing phonon-mediated superconductors by strategically combining nonsuperconducting and magnetic transition-metal elements.

All-In-All-Out/All-Out-All-In (AIAO/AOAI) ordering in pyrochlore iridates provides an intriguing platform for investigating exotic phenomena such as the topological Hall effect, Berry curvature-induced spontaneous Hall effect. In this study, we delve into the magnetotransport properties of Weyl Semimetallic (WSM) candidate ${\mathrm{Dy}}_2{\mathrm{Ir}}_2{\mathrm{O}}_7$ (111) single-crystalline epitaxial thin films. Weyl nodes in the WSM system serve as the source and drain of Berry curvature in the electronic band structure. Observed anomalous Hall effect (AHE) in the samples is mediated by Berry curvature-driven intrinsic contribution, leading to spontaneous Hall effect (SHE) in the system. We introduce strain in the system to observe SHE with a significant value ($\sim 30\mu \mathrm{\Omega }\mathrm{cm}$ at 7 K). Additionally, apart from the intrinsic contribution, the AHE signal comprises a topological-like Hall signal. Longitudinal resistivity (${\rho }_{xx}$) measurements confirm ${\mathrm{Ir}}^{4+}$ moment ordering in an antiferromagnetic AIAO/AOAI spin structure around 120 K; consequently ${\mathrm{Dy}}^{3+}$ moments align in an AOAI/AIAO spin configuration through $f\text{−}d$ exchange interaction around 22 K. Magnetoresistance measurements demonstrate that the application of an external magnetic field along the [111] direction interacts with ${\mathrm{Dy}}^{3+}$ moments and modify the spin structure by flipping ${\mathrm{Dy}}^{3+}$ spins, leading to domain imbalance of ${\mathrm{Ir}}^{4+}$ moments. The field-induced modification in the magnetic sublattices contributes to the topological Hall-like AHE signal.

Magneto-optical Kerr effect spectroscopy has been used to measure the $\mathrm{Land}\acute{\mathrm{e}} g$-factor of excitons in bulk $2H\text{−}{\mathrm{MoS}}_2$. For the ground state $A_{1s}$ exciton, the adjacent interlayer $I{L}_A$ exciton and the ground state $B_{1s}$ exciton we get $g_{A_{1s}}=-3.1\pm 0.2, g_{I{L}_A}=10.9\pm 0.8$ and $g_{B_{1s}}=-3.0\pm 0.4$, similar to previous reports based on other measurement techniques. However on the higher energy side of $B_{1s}$ we find another transition which we label $I{L}_B$, with $g_{I{L}_B}=10.6\pm 1.5$. Its presence is independently verified through the observation of a strong feature at that energy in a laser modulated photoreflectance spectrum. Based on the sign and large magnitude of $g_{I{L}_B}$ and using an approximate model to explain it, we identify this as another interlayer type exciton which predominantly involves the second valence band at the $K$ points of the Brillouin zone. The possible existence of an $I{L}_B$ like exciton state is also indicated by our calculations based on density functional theory including electron-hole Coulomb interaction via the $GW +$ Bethe-Salpeter equation.

We consider a quantum-dot (QD) based minimal Kitaev chain model and study the effects of modulation of QD states on the elastic cotunneling (ECT) and crossed Andreev reflection (CAR) processes. We demonstrate that the ECT amplitudes are strongly dependent on the energies of the QD states and are generally asymmetric, even in the absence of magnetic field, with respect to the chemical potential in the proximitized superconducting nanowire. We calculate the phase diagram of the total electron-number parity of the two QDs in terms of the spin-quantization axis direction in the QDs and the chemical potential in the superconducting nanowire, and also evaluate the precondition to attain a balance between ECT and CAR towards realizing the poor man's Majorana bound states. When the QDs are tuned into the deep Coulomb blockade regime, we predict a controllable anisotropic superexchange interaction between electrons in the two QDs under the combined effect of high-order interdot ECT and CAR processes.

Coherent control under two-color femtosecond laser excitation plays a significant role in atomic, molecular, and semiconductor materials. Recently, terahertz (THz) emission spectroscopy has been employed to characterize the coherent ultrafast photocurrent from semiconductor materials under two-color light excitation. However, distinguishing the contributions of various optical effects to THz radiation under normal- and oblique-incident excitations with two-color light remains a challenge. Herein, we choose the zinc selenide (ZnSe) crystal as a model sample to study the THz radiation at normal and oblique incidences with two-color light excitation. Based on the dependence of the THz signal on the relative phase difference between the fundamental wave (800 nm, ω) and the second harmonic wave (400 nm, 2ω), the contribution ratio of optical rectification (OR) to four-wave mixing (FWM) for THz radiation is calculated as 1:2.3 at normal incidence. Under oblique incidence, the contribution ratios of FWM, OR, and surface depletion field (SDF) for THz radiation are calculated as 1:1.5:6.7. In particular, we have observed the THz time-domain signals from net FWM contribution with polarity reversal at both normal and oblique incidences. This work not only elucidates the THz radiation properties of ZnSe crystal but also reveals the interplay among OR, SDF, and FWM in the coherent control of ultrafast photocurrent under femtosecond laser excitations.

We present an exact solution for the linearized junction array modes of the superconducting qubit fluxonium in the absence of array disorder. This solution holds for arrays of any length and ground capacitance and for both differential and grounded devices. Array mode energies are determined by roots of convex combinations of Chebyshev polynomials, and their spatial profiles are modified plane waves. We also provide a simple, approximate solution which estimates array mode properties over a wide range of circuit parameters and an accompanying Mathematica file that implements both the exact and approximate solutions.

Low-dimensional quantum magnets are a versatile materials platform for studying the emergent many-body physics and collective excitations that can arise even in systems with only short-range interactions. Understanding their low-temperature structure and spin Hamiltonian is key to explaining their magnetic properties, including unconventional quantum phases, phase transitions, and excited states. We study the metal-organic coordination compound ${\left({\mathrm{C}}_5{\mathrm{H}}_9{\mathrm{NH}}_3\right)}_2{\mathrm{CuBr}}_4$ and its deuterated counterpart, which upon its discovery was identified as a candidate two-leg quantum $(S=\frac{1}{2})$ spin ladder in the strong-leg coupling regime. By growing large single crystals and probing them with both bulk and microscopic techniques, we deduce that two previously unknown structural phase transitions take place between 136 and 113 K. The low-temperature structure has a monoclinic unit cell that gives rise to two inequivalent spin ladders. We further confirm the absence of long-range magnetic order down to 30 mK and investigate the implications of this two-ladder structure for the magnetic properties of ${\left({\mathrm{C}}_5{\mathrm{H}}_9{\mathrm{NH}}_3\right)}_2{\mathrm{CuBr}}_4$ by analyzing our own specific-heat and susceptibility data.

Inspired by the recent discovery of a new polar metal ${\mathrm{LiReO}}_3$ by K. Murayama et al, we calculate the temperature ($T$)-dependent crystal structures of $\mathrm{Li}B{\mathrm{O}}_3$ with $B=\mathrm{Ta}$, W, Re, Os, using the self-consistent phonon (SCPH) theory. We have reproduced the experimentally observed polar-nonpolar structural phase transitions and the transition temperatures ($T_c$) of ${\mathrm{LiTaO}}_3, {\mathrm{LiReO}}_3$, and ${\mathrm{LiOsO}}_3$. From the calculation, we predict that ${\mathrm{LiWO}}_3$ is a polar metal, which is yet to be tested experimentally. Upon doping electrons to the insulating ${\mathrm{LiTaO}}_3$, the predicted $T_c$ is quickly suppressed and approaches those of the polar metals. Thus, there is a continuous crossover between ferroelectric insulators and polar metals if we dope electrons to the ferroelectric insulators. Investigating the detailed material dependence of the interatomic force constants (IFCs), we explicitly show that the suppression of $T_c$ in polar metals can be ascribed to the screening of the long-range Li-O interaction, which is caused by the presence of the itinerant electrons. The quantitative finite-temperature calculations do not show signs of unscreened long-range interactions by the weak electron-phonon coupling or enhancement of polar instabilities by carrier doping, as expected in some previous works.

The mystery of the field-independent $T^{1/2}$ behavior of resistivity in single-crystal ${\mathrm{Th}}_2{\mathrm{CoSi}}_3$ is unraveled through the lens of interacting electrons in disordered systems. Consistent with theoretical predictions, our magnetotransport studies illuminate a scenario where a robust spin-orbit interaction renders the triplet term in the diffusion contribution ineffective. As a consequence, the magnetic field exerts no influence on the diffusion correction, giving sole dominance to weak localization and classical effects in shaping the magnetoresistance. In addition, marginal temperature variation of the weak localization at low temperatures results in the $T^{1/2}$ relation being predominantly dictated by the singlet term in the diffusion correction.

Non-Abelian anyons, which correspond to collective excitations possessing multiple fusion channels and noncommuting braiding statistics, serve as the fundamental constituents for topological quantum computation. Here, we reveal the exotic Bloch oscillations (BOs) induced by non-Abelian fusion of Fibonacci anyons. It is shown that the interplay between fusion-dependent internal energy levels and external forces can induce BOs and Bloch-Zener oscillations (BZOs) of coupled fusion degrees with varying periods. In this case, the golden ratio of the fusion matrix can be determined by the period of BOs or BZOs in conjunction with external forces, giving rise to an effective way to unravel non-Abelian fusion. Furthermore, we experimentally simulate non-Abelian fusion BOs by mapping the Schrödinger equation of two Fibonacci anyons onto the dynamical equation of electric circuits. Through the measurement of impedance spectra and voltage evolution, both fusion-dependent BZOs and BOs are simulated. Our findings establish a connection between BOs and non-Abelian fusion, providing a versatile platform for simulating numerous intriguing phenomena associated with non-Abelian physics.