We propose an orbital magnetothermal effect wherein a temperature gradient generates an orbital magnetization (OM) for Bloch electrons, and we present a unified theory for electrically and thermally induced OM, valid for both metals and insulators. We reveal that there exists an intrinsic response of OM, for which the susceptibilities are completely determined by the band geometric quantities such as interband Berry connections, interband orbital moments, and the quantum metric. The theory can be readily combined with first-principles calculations to study real materials. As an example, we calculate the OM response in ${\mathrm{CrI}}_3$ bilayers, where the intrinsic contribution dominates. The temperature scaling of intrinsic and extrinsic responses, the effect of phonon drag, and the phonon angular momentum contribution to OM are discussed.

We report the observation of resistivity saturation in lightly doped ($x=0.08)$ as-grown samples of the electron-doped cuprate ${\mathrm{La}}_{2-x}{\mathrm{Ce}}_x{\mathrm{CuO}}_4$. The saturation occurs at resistivity values roughly consistent with the phenomenological Mott-Ioffe-Regel criterion once the low effective carrier density of these materials is included in the analysis. These results imply that, at least for light doping, the high-temperature metallic phase of these materials is not necessarily strange and may be understood as simply a low-density metal.

We point out that in non-Hermitian systems, Jordan decomposition should replace eigendecomposition so that all “good approximate eigenstates” of the system are identified. These states can be resonantly excited. As a concrete example, we study the location and field distribution of zero-energy corner states in a non-Hermitian quadrupole insulator (QI) and split the parameter space into three distinct regimes according to properties of the corner states: near-Hermitian QI, intermediate phase, and trivial insulator. In the newly discovered intermediate phase, the Hamiltonian becomes defective, and the counterintuitive and delicate response of the system to external drives can be perfectly explained by the Jordan decomposition.

The Raman exponent of single molecular magnetic relaxation may take various unexpected values because of rich phonon spectra and spin-phonon coupling of molecular crystals. We systematically examine the origins of different abnormalities and clarify misunderstandings of the past, particularly the appropriateness of the fitting procedures for the exponents. We find that exponential laws raised by optical phonons can yield spurious power laws with low exponents. This observation indicates long-standing misunderstandings of the origins of low Raman exponents in a large bulk of single molecule magnets. Resulting from spin-lattice coupling with optical modes, the presence of these exponents suggests the importance of the local dynamical environment for the magnetic relaxation in this regime.

Interest in creating magnetic metamaterials has led to methods for growing superstructures of magnetic nanoparticles. Mesoscopic crystals of maghemite ($\gamma {\text{-Fe}}_2{\text{O}}_3$) nanoparticles can be arranged into highly ordered body-centered tetragonal lattices of up to a few micrometers. Although measurements on disordered ensembles have been carried out, determining the magnetic properties of individual mesoscopic crystals is challenging due to their small total magnetic moment. Here, we overcome these challenges by utilizing sensitive dynamic cantilever magnetometry to study individual micrometer-sized $\gamma {\text{-Fe}}_2{\text{O}}_3$ mesocrystals. These measurements reveal an unambiguous cubic anisotropy, resulting from the crystalline anisotropy of the constituent maghemite nanoparticles and their alignment within the mesoscopic lattice. The signatures of anisotropy and its origins come to light because we combine the self-assembly of highly ordered mesocrystals with the ability to resolve their individual magnetism. This combination is promising for future studies of the magnetic anisotropy of other nanoparticles, which are too small to investigate individually.

The pairing of two electrons on a Fermi surface due to an infinitesimal attraction between them always results in a superconducting instability at zero temperature ($T=0$). The equivalent question of pairing instability on a Luttinger surface (LS)—190a contour of zeros of the propagator—instead leads to a quantum critical point (QCP) that separates a non-Fermi liquid and superconductor. A surprising and little understood aspect of pair fluctuations at this QCP is that their thermodynamics maps to that of the Sachdev-Ye-Kitaev (SYK) model in the strong coupling limit. Here, we offer a simple justification for this mapping by demonstrating that (i) LS models share the reparametrization symmetry of the $q\to \infty$ SYK model with $q$-body interactions close to the LS, and (ii) the enforcement of gauge invariance results in a $\frac{1}{\sqrt{\tau }}$ ($\tau \sim T^{-1}$) behavior of the fluctuation propagator near the QCP, as is the feature of SYK conformal Green functions, but leaves the overall form of the free energy map robust.

A two-dimensional electron gas (2DEG) in two-valley semiconductors has two discrete degrees of freedom given by the spin and valley quantum numbers. We analyze the zero-temperature magnetic instabilities of two-valley semiconductors with SOI, in-plane magnetic field, and electron-electron interaction. The interplay of an applied in-plane magnetic field and the SOI results in noncollinear spin quantization in different valleys. Together with the exchange intervalley interaction this results in a rich phase diagram containing four nontrivial magnetic phases. The negative nonanalytic cubic correction to the free energy, which is always present in an interacting 2DEG, is responsible for first order phase transitions. Here, we show that nonzero ground state values of the order parameters can cut this cubic nonanalyticity and drive certain magnetic phase transitions second order. We also find two tricritical points at zero temperature which together with the line of second order phase transitions constitute the quantum critical sector of the phase diagram. The predicted magnetic phases can be observed in a monolayer $\mathrm{Mo}{\mathrm{S}}_2$ at electron densities $n\lesssim 5\times {10}^{12}{\mathrm{cm}}^{-2}$.

We employed inelastic neutron scattering (INS), specific heat, and magnetization analysis to study the magnetism in a synthetic polymorph of the quasi-two-dimensional natural metal-organic framework material, stepanovite $\mathrm{Na}\mathrm{Mg}\mathrm{Fe}{\left({\mathrm{C}}_2{\mathrm{O}}_4\right)}_3·9{\mathrm{H}}_2\mathrm{O}$. No long-range magnetic order can be observed down to 0.5 K. The INS spectra show two dispersionless excitations at energy transfer 0.028(1) and 0.050(1) meV at base temperature, which are derived from the magnetic transitions between zero-field splitting (ZFS) of $S=5/2$ ground state multiplets of ${\mathrm{Fe}}^{3+}$ ion. Further analysis of the INS results shows that the ${\mathrm{Fe}}^{3+}$ ion has an easy-axis anisotropy with axial ZFS parameter $D=-0.0128\left(5\right)$ meV and rhombic parameter $E=0.0014\left(5\right)$ meV. The upward behavior at zero field and Schottky-like peak under magnetic field of the low-temperature magnetic specific heat further support the INS results. Our results clearly reveal the magnetic ground and excited state of this stepanovite polymorph.

We study the dynamical spin excitations of the one-dimensional $S=1$ Heisenberg antiferromagnetic chain with single-ion anisotropy by using quantum Monte Carlo simulations and stochastic analytic continuation of imaginary-time correlation function. Using the transverse dynamic spin structure factor, we observe the quantum phase transition with a critical point between the topological Haldane gapped phase and the trivial phase. At the quantum critical point, we find a broad continuum characterized by the Tomonaga-Luttinger liquid, and its dynamical signatures are similar to a $S=1/2$ Heisenberg antiferromagnetic chain. The broad continuum can be seen as a dynamical signature of spinons. We further identify that the elementary excitations are fractionalized spinons in the critical state.

We present a cyclic and helical symmetry-adapted formulation and large-scale parallel implementation of real-space Kohn-Sham density functional theory for one-dimensional (1D) nanostructures, with application to the mechanical and electronic response of carbon nanotubes subject to torsional deformations. Specifically, employing a semilocal exchange correlation and a local formulation of the electrostatics, we derive symmetry-adapted variants for the energy functional, variational problem governing the electronic ground state, Kohn-Sham equations, atomic forces, and axial stress, all posed on the fundamental domain. In addition, we develop a representation for twisted nanotubes of arbitrary chirality within this framework. We also develop a high-order finite-difference parallel implementation capable of performing accurate cyclic and helical symmetry-adapted Kohn-Sham calculations in both the static and dynamic settings, and verify it through numerical tests and comparisons with established codes. We use this implementation to perform twist-controlled simulations for a representative set of achiral and chiral carbon nanotubes, in both the small and large deformation regimes. In the linear regime, we find that the torsional moduli are proportional to the cube of the diameter; metallic nanotubes undergo metal-insulator transitions; and both the band gap as well as effective mass of charge carriers are proportional to the shear strain and sine of three times the chiral angle. In the nonlinear regime, we find that there is significant Poynting effect, particularly at the ultimate strain, the value of which is determined by the chiral angle; torsional deformations provide a possible mechanism for the irreversible phase transformation from armchair to zigzag nanotubes; and both the band gap as well as effective mass have an oscillatory behavior, with the period for metal-insulator transitions being inversely proportional to the square of the diameter and sine of three times the chiral angle. Wherever available, the results are in good agreement with experimental observations and measurements. Overall, this opens an avenue for the highly accurate and efficient first-principles study of 1D nanostructures that have cyclic and/or helical symmetry, as well as their response to torsional deformations.

Atomic steps are typically assumed to only influence surface phenomena of solids. In contrast, here we show, using in situ atomic-resolution electron microscopy observations and atomistic modeling, the pronounced effect from surface steps in inducing compositional and structural evolution in the subsurface of a Cu(Au) solid solution. We find that Au surface segregation results in a stacked sequence of Cu-Au ordered phases in the subsurface. The presence of a monatomic step at the surface induces the formation of an antiphase boundary that extends from the surface step to deeper layers by maintaining the same composition profile associated with each terrace. The bunching of surface steps induces chemical disordering of the Cu-Au ordered phases in the subsurface region of the bunched steps. These results demonstrate the instant propagation of surface dynamics of atomic steps into the subsurface region and can find broader applicability in utilizing surface defects to tune the composition and structure in the subsurface of alloys.

We have investigated the electronic structure and the topological property of a Ce Kondo system, ${\mathrm{CeFe}}_2{\mathrm{Al}}_{10}$, employing the first-principles density functional theory (DFT) and dynamical mean-field theory (DMFT) band calculations. Based on the DMFT band calculation, we have found that, upon cooling, Ce $4f$ electrons in ${\mathrm{CeFe}}_2{\mathrm{Al}}_{10}$ become coherent at $T\approx 150$ K, so as to form coherent bands revealing the hybridization pseudogap near the Fermi level ($E_{\text{F}}$). We have checked that the band structure near $E_{\text{F}}$ and the Fermi surface from the DMFT at low $T$ are almost identical with those from the renormalized DFT. We have explored the topological nature based on the DFT band structure and found that ${\mathrm{CeFe}}_2{\mathrm{Al}}_{10}$ has a topological Kondo insulating nature with $Z_4=1$. Therefore, our finding reveals that ${\mathrm{CeFe}}_2{\mathrm{Al}}_{10}$ would display $T$-dependent topological phase transition from a topological Kondo insulating phase at low $T$ to a trivial semimetallic phase at high $T$. The analysis of $T$-dependent local magnetic susceptibility obtained from the DMFT calculation confirms the Kondo coherence mechanism upon cooling in ${\mathrm{CeFe}}_2{\mathrm{Al}}_{10}$.

We investigate the effects of stripe-charge ordering on the thermoelectric power of ${\mathrm{IrTe}}_2$, together with other transport properties, including the resistivity, thermal conductivity, and Hall effect. At the stripe-charge ordering transitions, clear transport anomalies such as abrupt changes in the thermoelectric power and Hall effect are observed and attributed to multiband conduction due to stripe-order-driven Fermi surface (FS) reconstruction. This FS reconstruction depends sensitively on intralayer charge modulations and interlayer staircaselike arrangements, leading to complex sign changes in the thermoelectric power. These results are in good agreement with the Boltzmann transport calculations based on the reconstructed FS and confirm the strong impact of the stripe charge order on the intrinsic charge conduction in ${\mathrm{IrTe}}_2$.

We investigate the electronic structure of nickelate superconductor ${\mathrm{NdNiO}}_2$ upon hole doping, by means of density-functional theory and dynamical mean-field theory. We demonstrate the strong intrinsic hybridization between strongly correlated states formed by Ni-$3d_{x^2-y^2}$ orbital and itinerant electrons due to Nd-$5d$ and Ni-$3d_{z^2}$ orbitals, producing a valence-fluctuating correlated metal as the normal state of hole-doped ${\mathrm{NdNiO}}_2$. The Hund's rule appears to play a dominating role on multiorbital physics in the lightly doped compound, while its effect is gradually reduced by increasing the doping level. Crucially, the hole-doping leads to intricate effects on Ni-$3d$ orbitals, such as a nonmonotonic change of electron occupation in lightly doped level, and a flipping orbital configuration in the overdoped regime. Additionally, we also map out the topology of Fermi surface at different doping levels. These findings render a preferred window to peek into electron pairing and superconductivity.

A recent paper on the insulating state of monolayer $\text{W}{\text{Te}}_2$ reported the observation of large oscillations in the conductivity that are periodic in $1/B$, resembling quantum oscillations in metals. This remarkable observation has inspired suggestions of exotic physics such as spin-charge separation. We show that a rather more conventional but still nontrivial explanation in terms of gap modulation may be possible in a model of an excitonic insulator subject to a magnetic field.

We theoretically investigate the second harmonic generation (SHG) of Dirac or Weyl semimetals under parallel DC electric and strong magnetic fields using the Boltzmann equation approach. The DC current-induced SHG process originates from the optical intraband transitions of the Landau subbands. It is a remarkable fingerprint of three-dimensional Dirac or Weyl dispersions and absent in other materials. An analytical formula for the SHG tensor is derived, and it shows chirality independence. The second-order nonlinear optical susceptibility is proportional to the DC field, giving strong optical nonlinearity up to ${10}^5\mathrm{pm}/\mathrm{V}$ with THz light, which is several orders larger than that of the usual materials. More interesting, the second harmonic conductivity is found to exhibit periodicity in magnetic field $1/B$ oscillations, which are similar to the Shubnikov–de Haas oscillations. Thus our work proposes another approach for SHG and potential applications of Dirac or Weyl semimetals in nonlinear optics.

Here, we report an irreversible cubic-to-monoclinic structural transition in cubic $c\text{−}{\mathrm{Sc}}_2{\mathrm{O}}_3$ nanocrystals which occur at pressures above $\sim 8.9\mathrm{GPa}$ upon nonhydrostatic compression in association with a pronounced volume collapse. This phase-transition–induced anomaly is further confirmed by our experimental Raman spectroscopy measurements and theoretical predictions. After annealing, however, this high-pressure monoclinic $m\text{−}{\mathrm{Sc}}_2{\mathrm{O}}_3$ phase undergoes a reversible back-transformation to the cubic counterpart at $\sim 1123\mathrm{K}$ and 9.0 GPa. Our observed transition pressure of $\sim 8.9\mathrm{GPa}$ for the cubic-to-monoclinic structural evolution is significantly lower than that from the previously diamond-anvil-cell–based hydrostatic x-ray experiments because of the existence of internal microscopic stress and/or high-stress concentration in the specimen caused by grain-to-grain contacts upon nonhydrostatic compression, which promoted the cubic-to-monoclinic structural transition. Moreover, we have reported new thermoelastic properties of $c\text{−}{\mathrm{Sc}}_2{\mathrm{O}}_3$ nanocrystals at simultaneous high-pressure and high-temperature conditions. These findings/results may have significant implications for the design of phase-switching devices and for the exploration of the structural relationship among sesquioxides for their uses in extreme environments.

The complex metallic alloy ${\mathrm{Mn}}_3\mathrm{In}$ has recently attracted attention for being a probable candidate for the fully compensated half-metallic ferrimagnet. The compound is associated with a rather unusual negative coefficient of resistivity approximately above the ferrimagnetic, $T_C=80\mathrm{K}$. Our investigation indicates that that the ground state of the alloy is spin-glass like, which possibly coexists with the ferrimagnetic state. The carrier density obtained from the Hall-effect measurement shows a jump below $T_C$; afterward, it gradually increases with lowering temperature and shows a saturating tendency at the lowest temperature. The electronic structure calculations indicate that, at the Fermi energy, dominant contributions come from minority-spin channels with larger bandwidth. In contrast, very weak but nonzero states arise from the majority-spin channel, and half metallicity can be ruled out. The calculations also found that the antiferromagnetic alignment of Mn spins with nonzero resultant magnetic moment confirms the ferrimagnetic nature consistent with the experimental results. The high-temperature phase with negative temperature coefficient of resistivity can be related to the localization of charge carriers through electron-phonon interactions.