We propose a nonchemical intrinsic Janus configuration and identify it in a pure $s{p}^2$ hybridized carbon monolayer, termed Janus graphene. The spontaneous unilateral growth of carbon atoms drives the nonchemical Janus configuration in Janus graphene, which is totally different from the chemical effect in common Janus materials such as MoSSe. A structure-independent half-auxetic behavior is mapped in Janus graphene, that the structure maintains expansion whether stretched or compressed, which lies in the key role of the $p_z$ orbital. With the unique half-auxeticity that emerged in the nonchemical Janus configuration, Janus graphene enriches the functional carbon family as a promising candidate for micro/nanoelectronic device applications.

A universal topological marker has been proposed recently to map the topological invariants of Dirac models in any dimension and symmetry class to lattice sites. Using this topological marker, we examine the conditions under which the global topological order, represented by the spatially averaged topological marker, remains unchanged in the presence of disorder for 1D and 2D systems. We find that if an impurity corresponds to varying a nonzero-matrix element of the lattice Hamiltonian, regardless the element represents hopping, chemical potential, pairing, etc., then the average topological marker is conserved. However, if there are many strong impurities and the average distance between them is shorter than a correlation length, then the average marker is no longer conserved. In addition, strong and dense impurities can be used to continuously interpolate between one topological phase and another. A number of prototype lattice models including Su-Schrieffer-Heeger model, Kitaev chain, Chern insulators, Bernevig-Hughes-Zhang model, and chiral $p$-wave superconductors are used to elaborate the ubiquity of these statements.

The magnetic and structural phase transitions occurring in ${\mathrm{K}}_2{\mathrm{ReCl}}_6$ were studied by macroscopic and microscopic techniques. Structural phase transitions associated with rotations of the ${\mathrm{ReCl}}_6$ octahedra lower the symmetry from cubic to monoclinic, form ferroelastic domains, and are visible in susceptibility, specific heat, and thermal expansion measurements. In the antiferromagnetically ordered state slightly below $T_{\mathrm{N}}=12\mathrm{K}$ these domains can be rearranged by a magnetic field inducing a relative elongation of the polydomain crystal parallel to the field of 0.6%. At zero field the magnetic structure in ${\mathrm{K}}_2{\mathrm{ReCl}}_6$ does not exhibit a weak ferromagnetic component, but at large magnetic field a distinct magnetic structure with a finite weak ferromagnetic component is stabilized. High magnetic fields rearrange the domains in the crystal to align the weak ferromagnetic moment parallel to the field. The altered domain structure with the crystal elongation is abruptly suppressed at lower temperature but persists upon heating to well above $T_{\mathrm{N}}$. However, heating above the lowest structural phase transition and successive cooling restore the initial shape.

The phenomenon of temperature induced magnetization-reversal, giving rise to negative magnetization (NM) in several rare-earth chromates, has been revisited through magnetization studies on $\mathrm{G}{\mathrm{d}}_{1-x}{\mathrm{Y}}_x\mathrm{Cr}{\mathrm{O}}_3$. The study re-examines the well accepted explanation of NM, i.e., the antiparallel polarization of the paramagnetic rare-earth $\left({\mathrm{R}}^{3+}\right)$ moments against the weak magnetization $\left(M_{\mathrm{Cr}}\right)$ of the canted antiferromagnetically ordered $\mathrm{C}{\mathrm{r}}^{3+}$ moment subsystem and compares the results with a relatively new explanation invoking frustration of the $\mathrm{G}{\mathrm{d}}^{3+}$ moment subsystem at temperatures as high as 170 K [Phys. Rev. B 99, 014422 (2019)]. Keeping in view the highly localized nature of f electrons the invoked frustration appears unphysical. We find that the magnitude of the NM increases with increasing concentration of nonmagnetic ${\mathrm{Y}}^{3+}$ ion. This is attributed to increased antiparallel polarization of the $\mathrm{G}{\mathrm{d}}^{3+}$ moments against increased $M_{\mathrm{Cr}}$ due to structural modifications in $\mathrm{G}{\mathrm{d}}_{1-x}{\mathrm{Y}}_x\mathrm{Cr}{\mathrm{O}}_3$ with increasing ${\mathrm{Y}}^{3+}$ content. This observation strongly contradicts the interpretation for NM based on the frustration of $\mathrm{G}{\mathrm{d}}^{3+}$ moments. The temperature induced negative to positive magnetization jump (TMJ) is observed and is attributed to the minimization of the Zeeman-energy against an energy barrier. A phenomenological comparative study of the modified Curie-Weiss fitting to M($T$) indicates that TMJ in polycrystalline $\mathrm{G}{\mathrm{d}}_{1-x}{\mathrm{Y}}_x\mathrm{Cr}{\mathrm{O}}_3$ is an outcome of cascaded individual flips of $\mathrm{G}{\mathrm{d}}^{3+}$ moments occurring over random sites having homogeneously distributed barrier energy. In our analysis the M($T$) data is fitted using modified Curie-Weiss treating $M_{\mathrm{Cr}}$ to be temperature dependent, i.e., $M_{\mathrm{Cr}}\left(T\right)=M\left(0\right)$.${\left[1-{\left(T/T_C\right)}^{\alpha }\right]}^{\beta }$.

We investigate the origin of spin-orbit torques (SOTs) in archetypical Pt/Co/MgO thin films structures by performing harmonic Hall measurements. The behavior of the dampinglike (DL) effective field ($h_{\mathrm{DL}})$ with varying the Pt layer thickness and the Co layer thickness indicates that bulk spin-Hall effect (SHE) in Pt is mainly responsible for DL-SOT. The insertion of a Pd ultrathin layer at the Pt/Co interface leads to a step decrease in $h_{\mathrm{DL}}$, attributed to the modification of interfacial spin transparency. Further increase in Pd thickness leads to a reduction of the interfacial spin-orbit coupling (iSOC) quantified by the decrease in the surface magnetic anisotropy. The consistent insensitivity of $h_{\mathrm{DL}}$ to variations in iSOC at the bottom Pt/Co interface and oxidation at the top Co/MgO interface provides additional evidence for the bulk SHE origin of DL-SOT. The strong reduction in the fieldlike (FL) torque effective field ($h_{\mathrm{FL}})$ with decreasing iSOC at the Pt/Co interface points to the interfacial nature of FL-SOT, either due to iSOC-induced interfacial spin currents or to the Rashba-Edelstein effect at the Pt/Co interface. Furthermore, we demonstrate that a FL-SOT develops at the top Co/MgO interface opposing the one generated at the bottom Pt/Co interface, the strength of which increases with Co/MgO interfacial oxidation, and is attributed to the Rashba-Edelstein effect.

Core losses of amorphous and nanocrystalline soft magnetic ribbons with a range of saturation magnetostriction constants (${\lambda }_{\mathrm{s}}$) from near zero to $+38\times {10}^{-6}$ have been investigated experimentally with complementary micromagnetic simulations in order to clarify the effect of magnetostriction on the excess loss, i.e., the core loss component unaccounted for by the hysteresis and classical eddy-current losses. The excess loss at 400 Hz and a peak polarization of 1.0 T ($P_{\mathrm{ev}}$) has been found to increase linearly with ${\lambda }_{\mathrm{s}}$, and $P_{\mathrm{ev}}$ varies considerably between $0.27\mathrm{k}\mathrm{W}/{\mathrm{m}}^3$ for near zero-magnetostrictive nc-$\mathrm{F}{\mathrm{e}}_{85}\mathrm{N}{\mathrm{b}}_6{\mathrm{B}}_9$ and $11.0\mathrm{k}\mathrm{W}/{\mathrm{m}}^3$ for amorphous $\mathrm{F}{\mathrm{e}}_{80}\mathrm{S}{\mathrm{i}}_{11}{\mathrm{B}}_9$ with ${\lambda }_{\mathrm{s}}=+38\times {10}^{-6}$. By substituting the domain wall damping coefficient (${\beta }_{\mathrm{dw}}$) for the eddy current one in Bertotti's statistical model of core losses, the excess loss is predicted to be proportional to $\sqrt{{\beta }_{\mathrm{dw}}}$, indicating that the observed linear increase of $P_{\mathrm{ev}}$ is caused by mechanisms where ${\beta }_{\mathrm{dw}}$ increases with ${\lambda }_{\mathrm{s}}^2$. Such a quadratic relationship is confirmed by modeling a free wall damping process with lattice anelasticity, suggesting that the anelastic lattice relaxation mediated by magnetostriction could be a potential mechanism. However, the absolute value of ${\beta }_{\mathrm{dw}}$ remains open because of the uncertainty of the viscosity, and further investigation is needed to validate the mechanism of the excess loss induced by magnetostriction. Our results show that magnetostriction plays a significant role in determining the excess loss in the exchange-softened magnetic materials, and lowering the saturation magnetostriction is crucial for reducing the wall damping effect and the core loss at high frequencies.

A chiral coordinate Bethe ansatz method is developed to study the periodic XYZ chain. We construct a set of chiral vectors with fixed number of kinks. All vectors are factorized and have simple structures. Under roots of unity conditions, the Hilbert space has an invariant subspace, and our vectors form a basis of this subspace. We propose a Bethe ansatz solely based on the action of the Hamiltonian on the chiral vectors, avoiding the use of transfer matrix techniques. This allows us to parametrize the expansion coefficients and derive the homogeneous Bethe ansatz equations, whose solutions give the exact energies and eigenstates. Our analytic results agree with earlier approaches, notably by Baxter, and are supported by numerical calculations.

A quadratic band crossing (QBC) is a crossing of two bands with quadratic dispersion, which has been intensively investigated due to its appearance in Bernal-stacked bilayer graphene. Here, we study an extension of QBCs, the triply degenerate quadratic band crossing (TQBC), which is a three-band crossing node containing two quadratic dispersing bands and a flat band. We focus on two types of TQBCs. The first type contains a symmetry-protected QBC and a free-electron band, the prototype of which is the AA-stacked bilayer square-octagon lattice. In a magnetic field, such a TQBC exhibits an anomalous Landau level structure, leading to a distinctive quantum Hall effect, which displays an infinite ladder of Hall plateaus when the chemical potential approaches zero. The other type of TQBC can be viewed as a pseudospin-1 extension of the bilayer-graphene QBC. Under perturbations, this type of TQBCs may split into linear pseudospin-1 Dirac-Weyl fermions. When tunneling through a potential barrier, the transmission probability of the first type decays exponentially with the barrier width for any incident angle, similar to the free-electron case, while the second type hosts an all-angle perfect reflection when the energy of the incident particles is equal to half the barrier height.

Recent theoretical calculations have shown that ${\mathrm{Mn}}_3{\mathrm{Sn}}_2$, a well-known magnetocaloric material with multiple magnetic transitions, possesses both nodal lines and nodal surfaces in its electronic structures, making it an excellent platform for studying anomalous transport properties in magnetic topological candidates. In this work, we performed comprehensive electrical, thermal, and thermoelectric measurements on ${\mathrm{Mn}}_3{\mathrm{Sn}}_2$ single crystals. The electrical resistivity $\rho \left(T\right)$ shows an abnormal peak near the Curie temperature, $T_{\mathrm{C}2}\sim 227$ K, and a negative resistivity slope above $T_{\mathrm{C}2}$, which are probably related to a large spin-fluctuation scattering. The Seebeck coefficient $S_{xx}\left(T\right)$ shows a sign reversal below 80 K although the Hall coefficient is always positive, which might be ascribed to the magnon-drag effect. Below $T_{\mathrm{C}1}\sim 262$ K, a significant anomalous Hall effect is observed, and the anomalous Hall resistance $\left({\rho }_{\mathrm{xy}}^A\right)$ peaks at around 7 µΩ cm at 200 K. ${\rho }_{\mathrm{xy}}^A$ exhibits a quadratic dependence on the longitudinal resistivity ${\rho }_{xx}$, and the anomalous Hall conductivity ${\sigma }_{\mathrm{xy}}^A$ remains nearly temperature independent below 200 K, suggesting the dominance of the intrinsic Berry-phase mechanism. Correspondingly, we also detect a large anomalous Nernst effect, with the anomalous Nernst coefficient reaching approximately $1\mu \mathrm{V}{\mathrm{K}}^{-1}$ at 200 K. Despite ${\mathrm{Mn}}_3{\mathrm{Sn}}_2$ exhibiting robust ferromagnetism, its anomalous Hall angle (2.5%), anomalous Nernst angle (6.5%), and large anomalous Nernst coefficient $\left(1.65\mu \mathrm{V}{\mathrm{K}}^{-1}{\mathrm{T}}^{-1}\right)$ surpass those observed in typical ferromagnetic materials. Our results experimentally demonstrate the existence of topologically nontrivial states in ${\mathrm{Mn}}_3{\mathrm{Sn}}_2$.

We present nuclear magnetic (NMR) and quadrupole (NQR) resonance and magnetization data in the normal state of the topological crystalline superconductor ${\mathrm{LaNiGa}}_2$. We find no evidence of significant magnetic fluctuations or enhanced paramagnetism. These results suggest that the time-reversal symmetry breaking previously reported in the superconducting state of this material is not driven by strong electron correlations.

The quantum phase transition in Ce-based compounds has attracted significant attention in strongly correlated systems, primarily due to the dual nature of $f$ electrons. Rare-earth nitride (Re-N) compounds are particularly intriguing, as they exhibit major physical mechanisms such as the Kondo effect or mixed-valence behavior. Notably, CeN is anomalously small in lattice parameter compared with other Re-N compounds and there is a structure phase transition from $B\text{1-type}$ (NaCl-type) to $B2\text{−}\mathrm{type}$ (CsCl-type) at approximately 77 GPa. Hence, we study the electronic structures of $B\text{1-type}$ and $B2\text{−}\mathrm{type}$ CeN by tuning stress, employing the $\text{DFT}+\text{DMFT}$ method. Our results clarify the $B\text{1-type}$ CeN is in a mixed-valence state at ambient pressure. However, as the system experiences compression and tension, CeN undergoes multiple quantum phase transitions, transitioning from a mixed-valence state to a Kondo metal and ultimately to an insulator. Importantly, it is observed that the number of occupied $4f$ electrons $n_f$ of Ce increases as the temperature and pressure increase within the mixed-valence regime, contrasting with the behavior observed in the Kondo regime, the $n_f$ is very stable, nearly one. Furthermore, we also investigate the high-pressure phase of $B2\text{−}\mathrm{type}$ CeN, it also presents mixed-valence and Kondo metal phases transition by tuning stress. Our paper illustrates stress as a clean method to tune quantum phase transitions in CeN by changing the states of $f$ electrons and clarifying the physical driving force of phase transitions.

(BEDT-TTF)Cu[N(CN)${}_2{]}_2$ (BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene) is a monomer Mott insulator, in which the BEDT-TTF molecules form a three-dimensional (3D) distorted diamond structure; however, its physical properties resemble those of a quasi-one-dimensional (Q1D) zigzag BEDT-TTF chain structure. We investigated the magnetic ground state of this compound using electron spin resonance (ESR) spectroscopy in the X-band region (9.12 GHz) to confirm the occurrence of a transition to a spin-singlet state. The ESR spectra showed an asymmetric spectral line comprising two Lorentzian components, suggesting different correlations of the two independent 1D zigzag chains of the BEDT-TTF molecules. The spin susceptibility derived from the ESR spectra showed an opening of the spin gap below the transition temperature $T_{\text{c}}\approx$ 25 K possibly due to alternating intrachain interactions in both zigzag chains with different spin correlations.

Quantum thermodynamics with microscopic inelastic scattering processes has been intensively investigated in recent years. Here, we apply quantum master equation combined with full counting statistics approach to investigate the role of quantum coherence on the periodically driven inelastic heat engine. We demonstrate that the inelastic quantum heat engine exhibits dramatic advantage of thermodynamic performance compared to their elastic counterpart. Moreover, it is found that inelastic currents, output work, and the efficiency can be enhanced by quantum coherence. In particular, the geometric effect proves crucial in achieving maximal values of generated output work and energy conversion efficiency. The Berry curvature boosted by quantum coherence unveils the underlying mechanism of a periodically driven inelastic heat engine. Our findings may provide some insights for further understanding and optimizing periodically driven heat engines via quantum coherence resource and inelastic scattering processes.

The metal-insulator transition (MIT) in vanadium dioxide $\left({\mathrm{VO}}_2\right)$ due to V-V dimerization has been extensively discussed for decades. While it is widely acknowledged that electron correlations, Peierls instabilities, and molecular orbital formations are crucial for understanding the MIT of ${\mathrm{VO}}_2$, the primary origin of the MIT remains controversial. In this study, we delve into the crystal structure and orbital state of ${\mathrm{VO}}_2$ through synchrotron x-ray diffraction experiments. The molecular orbital formation corresponding to the V-V dimerization is directly observed in the low-temperature insulating monoclinic phase, called the M1 phase, as indicated by the valence electron density distribution. Moreover, diffuse scattering observed in the high-temperature metal phase of rutile structure suggests the presence of short-range correlation of V displacements, which is not directly attributed to the structural fluctuation of the M1 phase. The short-range order in the rutile phase will be the key to understanding the MIT in this system.

I consider relaxation of the pairing amplitude in a disordered Bardeen-Cooper-Schrieffer (BCS) superconductor in the absence of the two-particle collisions. My main assumption is that nonmagnetic and magnetic disorder scattering rates are much smaller than the value of the superconducting pairing gap ${\mathrm{\Delta }}_0$. I derive a system of nonlinear equations which describe the collisionless relaxation of the pairing amplitude following a quench of the pairing strength. I find that in a superconductor in which scattering on paramagnetic impurities is dominant, the pairing amplitude in a steady state varies periodically with time even for small deviations from equilibrium. It is shown that such a steady state emerges due to scattering on paramagnetic impurities which leads to a decrease in the value of the resonant frequency of the amplitude mode below $2{\mathrm{\Delta }}_0$.

The magnetic properties of single-crystal ${\mathrm{MnSb}}_2{\mathrm{Te}}_4$ were thoroughly investigated. The $M\left(T\right)$ curves exhibit anisotropic magnetic behaviors with the $c$ axis as the easy axis in low temperature, while Curie-Weiss fitting curves show an isotropic behavior at high temperature. The evaluated Rhodes-Wohlfarth ratio of 2.25 (2.22) for $H//ab$ $(H//c)$ demonstrates an itinerant high-field ferromagnetic state. Critical exponents $\beta =0.441\left(9\right)$ with $T_C=19.4\left(1\right)$ K and $\gamma =1.108\left(13\right)$ with $T_C=19.3\left(1\right)$ K are acquired by the modified Arrott plots, whereas $\delta =3.52\left(1\right)$ is achieved by a critical isotherm analysis at $T_C=19.4 \mathrm{K}$, exhibiting three-dimensional critical behavior and complex magnetic interaction. A detailed $H\text{−}T$ phase diagram containing antiferromagnetic, canted antiferromagnetic, and ferromagnetic states is constructed, where two triple points ($\sim 310$ Oe at 19.4 K and $\sim 1970$ Oe at 19.4 K) are achieved. Additionally, the magnetic entropy change $\mathrm{\Delta }{S}_M$ is evaluated with $-\mathrm{\Delta }{S}_M^{\text{max}}$ reaching 2.20 J ${\mathrm{kg}}^{-1}{\mathrm{K}}^{-1}$ in the $ab$ plane and 2.20 J ${\mathrm{kg}}^{-1}{\mathrm{K}}^{-1}$ along the $c$ axis at $H=70$ kOe. The rotating magnetic entropy change $-\mathrm{\Delta }{S}_M^R(T,H)$ is $\sim 0 \mathrm{J} {\mathrm{kg}}^{-1}{\mathrm{K}}^{-1}$ at $T>$ 39 K, displaying a nearly isotropic behavior well above $T_C$, consistent with the above Curie-Weiss fitting; and $-\mathrm{\Delta }{S}_M^R$ is less than 0.24 J ${\mathrm{kg}}^{-1}{\mathrm{K}}^{-1}$ at low temperature, demonstrating weak anisotropy.

We argue that doped twisted bilayer graphene with magical twist angle can become superconducting. In our theoretical scenario, the superconductivity coexists with the spin-density-wave–like ordering. Numerical mean-field analysis demonstrates that the spin-density-wave order, which is much stronger than the superconductivity, leaves parts of the Fermi surface ungapped. This Fermi surface serves as a host for the superconductivity. Since the magnetic texture at finite doping breaks the point group of the twisted bilayer graphene, the stabilized superconducting order parameter is nematic. We also explore the possibility of a purely Coulomb-based mechanism of superconductivity in the studied system. The screened Coulomb interaction is calculated within the random phase approximation. It is shown that near the half-filling the renormalized Coulomb repulsion indeed induces the superconducting state, with the order parameter possessing two nodes on the Fermi surface. We estimate the superconducting transition temperature, which turns out to be very low. The implications of our proposal are discussed.

The reversible phase transition of two-dimensional material allotropes induced by strain engineering has promising applications in nanoelectromechanical systems and memories. Here, we report a series of black and blue phosphorene superlattice (BBPS) can be formed by reversible phase transition between them. The phase transition is with low-energy barrier and can be well regulated by strain engineering, until black phosphorene phase is fully transformed into blue phosphorene phase under strain of ε = 23%. At room temperature, BBPS exhibits a high phase transition rate of about ${10}^6$ Hz, which enables reversible phase transition rapidly. Beyond, the unique in-plane heterostructure of BBPS suppresses phonon transmission, lowering thermal conductivity to only 25.6% of black phosphorene. Beyond, nonequilibrium Green's function calculations indicate the thermal conductivity crossing the black-blue phosphorene heterojunction suddenly drops to only 1/3 that of black phosphorene. Therefore, strain engineering can not only achieve reversible phase transition but also modulate the thermal conductivity in very large range, which is excellent in the field of heat flow manipulation and thermal management.