The physical properties of the noncentrosymmetric and quasi-two-dimensional canted antiferromagnetic material ${\mathrm{CoTeMoO}}_6$ (CTMO) are studied. We unravel a spectrum of intriguing phenomena, including a correlated short-range-ordered Griffiths-like phase near $T_G\sim 64\mathrm{K}$, a sharp step-like metamagnetic behavior of isothermal magnetization induced by a spin-flop transition at a critical magnetic field $H_{\mathrm{c}}\sim 1.2\mathrm{T}$, a strong dielectric anomaly, a pronounced magnetodielectric effect, and the associated weak magnetoelectric coupling at its magnetic transition temperature, $T_N\sim 23.4\mathrm{K}$. The crucial roles played by spin canting in CTMO are revealed in the aforementioned strongly entangled behavior of the spin and dipolar order parameters. The observed magnetostriction effect coupled with spin-phonon coupling seems to be a key factor in influencing the observed magnetodielectric effect. In addition, our theoretical first-principles calculations predict an insulating state with a canted antiferromagnetic spin configuration that matches well with the experimental results.

Fermion-exciton condensation in which both fermion-pair (i.e., superconductivity) and exciton condensations occur simultaneously in a single coherent quantum state has recently been conjectured to exist. Here, we capture the fermion-exciton condensation through a model Hamiltonian that can recreate the physics of this new class of highly correlated condensation phenomena. We demonstrate that the Hamiltonian generates the large-eigenvalue signatures of fermion-pair and exciton condensations for a series of states with increasing particle numbers. The results confirm that the dual-condensate wave function arises from the entanglement of fermion-pair and exciton wave functions, which we previously predicted in the thermodynamic limit. This model Hamiltonian—generalizing well-known model Hamiltonians for either superconductivity or exciton condensation—can explore a wide variety of condensation behavior. It provides significant insights into the required forces for generating a fermion-exciton condensate, which will likely be invaluable for realizing such condensations in realistic materials with applications from superconductors to excitonic materials.

Neutral excitations in a fractional quantum Hall droplet define the incompressibility gap of the topological phase. In this paper, we derive a set of analytical results for the energy gap of the graviton modes with two-body and three-body Hamiltonians in both the long-wavelength and the thermodynamic limit. These allow us to construct model Hamiltonians for the graviton modes in different FQH phases, and to elucidate a hierarchical structure of conformal Hilbert spaces (null spaces of model Hamiltonians) with respect to the graviton modes and their corresponding ground states. Using the analytical tools developed, we perform numerical analysis with a particular focus on the Laughlin $\nu =1/5$ and the Gaffnian $\nu =2/5$ phases. Our calculation shows that for gapped phases, low-lying neutral excitations can undergo a “phase transition” even when the ground state is invariant. We discuss the compressibility of the Gaffnian phase, the possibility of multiple graviton modes, and the transition from the graviton modes to the “hollow-core” modes, as well as their experimental consequences.

In frustrated spin-1/2 chains the competition between the nearest- and next-nearest-neighbor exchange interactions leads to a rich phase diagram that becomes even richer in the presence of perturbations in their material realizations. These effects are still largely unexplored, so that new insight into static and dynamic magnetism, in particular by sensitive local probes, is highly desired. Here we present a comprehensive ${}^{17}\mathrm{O}$ nuclear magnetic resonance study of $\beta \text{−}{\mathrm{TeVO}}_4$, where the anisotropy of the main exchange interactions and additional weak interchain exchange interactions complement the theoretical phase diagram. Our results confirm the dynamical nature of the intriguing spin-stripe phase that has been reported in previous studies. In addition, we find that the magnetic order in the high-field phase, which develops just below the magnetization saturation, is consistent with an unusual type of spin-density-wave (SDW) order with different alignments of the magnetic moments on the neighboring chains. This is reminiscent of the ordering in the SDW phase, realized in the absence of the magnetic field, and is thus most likely stabilized by magnetic anisotropy.

Transient reflectivity spectroscopy is widely used to study ultrafast carrier and phonon dynamics in semiconductors. In their heterostructures, it is often not straightforward to distinguish contributions to the signal from the various layers. In this work, we perform transient reflectivity measurements on lattice-matched GaP/Si(001) using a near-infrared pulse, to which GaP is transparent. The pump laser pulse can generate coherent longitudinal-optical phonons both in the GaP overlayer as well as in the Si substrate, which have distinct frequencies. This enables us to track the amplitude of the respective signal contributions as a function of the GaP layer thickness $d$. The Si phonon signal exhibits a drastic amplitude decrease and a sign change with increasing $d$, which can be quantitatively explained by the interference of the probe light reflected at the GaP/Si interface. Based on this knowledge, we can separate the interface contribution and the substrate contribution in the carrier-induced nonoscillatory transient reflectivity signal. The obtained signals reveal interfacial carrier dynamics that is dependent on the GaP layer thickness.

Recent Raman scattering experiments have revealed a quasielastic peak in ${\mathrm{FeSe}}_{1-\mathrm{x}}{\mathrm{S}}_{\mathrm{x}}$ near an Ising-nematic quantum critical point (QCP) [Zhang et al., PNAS 118, 20 (2021)]. Notably, the peak occurs at subtemperature frequencies, and softens as $T^{\alpha }$ when temperature is decreased toward the QCP, with $\alpha >1$. This temperature dependence is inconsistent with an impurity scattering scenario, and suggests that quantum critical fluctuations play an important role. In this work,we incorporate these effects in the framework of a memory matrix approach. The quasielastic peak is associated with the relaxation of an Ising-nematic deformation of the Fermi surface. We identify the dynamical scattering rate ${\tau }^{-1}$ of this deformation as the product of the quasielastic peak frequency $\mathrm{\Gamma }$ and the Ising-nematic thermodynamic susceptibility $\chi$. Over a broad temperature regime, we find that ${\tau }^{-1}\left(T\right)$ exhibits a quasilinear dependence on temperature, in qualitative agreement with experiments. This behavior reflects a crossover from quantum critical scaling to a regime where the lifetime is governed by scattering from quasielastic thermal fluctuations. At frequencies larger than the temperature, we find that the Raman response is proportional to ${\omega }^{1/3}$, consistently with earlier theoretical predictions.

By using electrochemical etching, we fabricated conductive ultrathin ${\mathrm{SrVO}}_3$ (SVO) films that exhibited metallic behavior down to 3 monolayers (ML). From an observed systematic change in transport properties with decreasing film thickness, it was found that the disorder in the films remained nearly unchanged during etching, and only the thickness was reduced. This is in contrast to the insulating behavior found for as-deposited SVO ultrathin films. For the etched films, the electron mobility at 200 K decreased with decreasing film thickness below 10 ML, originating from an increased scattering rate and electron effective mass near the metal-insulator transition. A slight upturn in the resistivity and a positive magnetoresistance at low temperatures were typically observed for the etched films down to 3 ML, which was explained by weak antilocalization of electrons in a weakly disordered metal.

The Floquet Hamiltonian has often been used to describe a time-periodic system. Nevertheless, because the Floquet Hamiltonian depends on a micromotion parameter, the Floquet Hamiltonian with a fixed micromotion parameter cannot faithfully represent a time-periodic system, which manifests as the anomalous edge states. Here we show that an accurate description of a Floquet system requires a set of Hamiltonian spanning all values of the micromotion parameter, and this micromotion parameter can be viewed as an extra synthetic dimension of the system. Therefore we show that a $d$-dimensional Floquet system can be described by a $d+1$-dimensional static Hamiltonian, and the advantage of this representation is that the periodic boundary condition is automatically imposed along the extra dimension, which enables a straightforward definition of topological invariants. The topological invariant in the $d+1$-dimensional system can ensure a $d-1$-dimensional edge state of the $d$-dimensional Floquet system. We show two examples where the topological invariant is defined as the three-dimensional Hopf invariant.

The black hole information paradox has been hotly debated for the last few decades, without full resolution. This makes it desirable to find analogs of this paradox in simple and experimentally accessible systems, whose resolutions may shed light on this long-standing and fundamental problem. Here we identify and resolve an apparent “information paradox” in a quantum Hall interface between the Halperin-331 and Pfaffian states. Information carried by the pseudospin degree of freedom of the Abelian 331 quasiparticles gets scrambled when they cross the interface to enter non-Abelian Pfaffian state and becomes inaccessible to local measurements; in this sense, the Pfaffian region is an analog of black hole interior while the interface plays a role similar to its horizon. We demonstrate that the “lost” information gets recovered once the “black hole” evaporates and the quasiparticles return to the 331 region, albeit in a highly entangled form. Such recovery is quantified by the Page curve of the entropy carried by these quasiparticles, which are analogs of Hawking radiation.

We investigate the effect of band geometric quantities on nonlinear magnetoresistivity, which dictates the quadratic dependence of the nonlinear voltage generated by the applied current. We propose that the interplay of the Berry curvature, the orbital magnetic moment, and the Lorentz force can induce a finite nonlinear resistivity in two-dimensional systems in the presence of a perpendicular magnetic field. The induced nonlinear magnetoresistivity scales linearly with the magnetic field and is purely quantum mechanical in origin. Our proposed transport signature can be used as an additional experimental probe for the geometric quantities in intrinsically time reversal symmetric systems.

Periodic-boundary spectrum, open-boundary spectrum, as well as the generalized Brillouin zone (GBZ) are three essential properties of a one-dimensional non-Hermitian system. In this paper we illustrate that the deep connections between them can be revealed by a series of special similar transformations. This viewpoint closely connects the topological geometry of the open-boundary spectrum with the GBZ and provides an efficient numerical method capable of calculating them accurately. We further extend these connections to non-Hermitian systems in the symplectic symmetry class. We show that if just the open-boundary features of a non-Hermitian system such as the spectrum and the GBZ, are concerned, the relevant symmetry we should consider is not that of the original system itself, but that of one that has higher symmetry and is related to the original system by a similarity transformation.

The formation of the dense amorphous structure of granular materials (formed by equal spheres) under air impact is numerically reproduced by a coupled computational fluid dynamics-discrete element method model. Corresponding dynamics and mechanisms are investigated comprehensively through local structural evolution, interparticle interaction forces, and pore filling behavior. Specifically, the jamming phenomenon induced by the structure characteristics is analyzed. The results are of theoretical and practical significance in the preparation of amorphous materials.

We successfully synthesize ${\mathrm{RuBr}}_3$, which is a candidate material of a Kitaev spin liquid, via a high-pressure synthesis. The material ${\mathrm{RuBr}}_3$ possesses a ${\mathrm{BiI}}_3$-type structure (space group $R\overline{3}$) where ${\mathrm{Ru}}^{3+}$ forms an ideal honeycomb lattice even at room temperature and it does not show a structural transition at low temperatures. ${\mathrm{RuBr}}_3$ has a negative Weiss temperature and it undergoes a zigzag antiferromagnetic transition at $T_{\mathrm{N}}=34$ K, as does $\alpha \text{−}{\mathrm{RuCl}}_3$ $(T_{\mathrm{N}}=7–14\mathrm{K}\mathrm{)}$ which is a promising candidate for a Kitaev spin liquid. Although both compounds of ${\mathrm{RuBr}}_3$ and $\alpha \text{−}{\mathrm{RuCl}}_3$ have a zigzag magnetic order at low temperature, the magnetic order in ${\mathrm{RuBr}}_3$ is more robust than in $\alpha \text{−}{\mathrm{RuCl}}_3$. Our results indicate that the Kitaev and non-Kitaev interactions can be modified in ruthenium trihalides by changing the ligand sites, and will provide another platform for exploring Kitaev spin liquids.

Interfacial spin transport has been studied in a $\mathrm{YIG}/{\mathrm{Cr}}_2{\mathrm{O}}_3/\mathrm{Pt}$ trilayer device via the spin-pumping technique. It is found that the linewidths and the magnitudes of the spin-pumping voltage signals suddenly decrease at just below the Néel temperature of the ${\mathrm{Cr}}_2{\mathrm{O}}_3$ interlayer. A detailed analysis shows that the inner decay in the ${\mathrm{Cr}}_2{\mathrm{O}}_3$ interlayer dominates the interfacial spin transport in a wide temperature range, while the interfacial suppression of pumped spin currents occurs at a temperature slightly lower than the Néel temperature, both of which contribute to the sudden changes of spin-pumping voltage signals around the Néel temperature. This work carries forward the understanding of the spin transport in an antiferromagnetic system, which would serve to inspire, as well as facilitate, further breakthroughs of the limits of spin-based devices.

Successive phase transitions in a rare-earth monoaxial chiral magnet ${\mathrm{DyNi}}_3{\mathrm{Ga}}_9$ have been investigated by resonant x-ray diffraction. Magnetic dipole and electric quadrupole degrees of freedom arising from the large angular moment of $J=15/2$, in combination with the symmetric and antisymmetric exchange interactions and the crystal field anisotropy, give rise to competing ordered phases. We show that the antiferromagnetically coupled Dy moments in the $ab$ plane form an incommensurate helimagnetic order with $\mathit{q}\sim (0,0,0.43)$ just below $T_{\text{N}}=10$ K, which further exhibits successive first-order transitions to the commensurate helimagnetic order with $\mathit{q}=(0,0,0.5)$ at $T_{\text{N}}^{\prime }=9.0$ K, and to the canted antiferromagnetic order with $\mathit{q}=(0,0,0)$ at $T_{\text{N}}^{″}=8.5$ K, both with large coexistence regions. The relation of the magnetic helicity and the crystal chirality in ${\mathrm{DyNi}}_3{\mathrm{Ga}}_9$ is also uniquely determined. Splitting of the (6,0,0) Bragg peak is observed below $T_{\text{N}}^{″}$, reflecting the lattice distortion due to the ferroquadrupole order. In the canted antiferromagnetic phase, a spin-flop transition takes place at 5 K when the temperature is swept in a weak magnetic field. We discuss these transitions from the viewpoint of the competing energies described above.

Temperature-dependent London penetration depth, $\lambda \left(T\right)$, of a high quality optimally doped ${\text{YBa}}_2{\text{Cu}}_3{\text{O}}_{7-\delta }$ single crystal was measured using a tunnel-diode resonator. Controlled artificial disorder was induced at a low temperature of 20 K by 2.5 MeV electron irradiation with the accumulation of large doses of $3.8\times {10}^{19}$ and $5.3\times {10}^{19}$ electrons per ${\text{cm}}^2$. The irradiation caused significant suppression of the superconductor's critical temperature, $T_c$, from 94.6 to 90.0 K and then to 78.7 K, respectively. The low-temperature behavior of $\lambda \left(T\right)$ evolves from a $T\mathrm{linear}$ in pristine state to a $T^2$behavior after the irradiation, expected for a line-nodal $d$-wave superconductor. However, the original theory that explained such behavior had assumed a unitary limit of the scattering potential, whereas usually in normal metals and semiconductors, Born scattering is sufficient to describe the experiment. To estimate the scattering potential strength, we calculated the normalized superfluid density, ${\rho }_s(t=T/T_c)={\lambda }^2\left(0\right)/{\lambda }^2\left(t\right)$, varying the amount and the strength of nonmagnetic scattering using a self-consistent $t$-matrix theory. Fitting the obtained curves to a power law, ${\rho }_s=1-R{t}^n$, and to a polynomial, ${\rho }_s=1-At-B{t}^2$, and comparing the coefficients $n$ in one set and $A$ and $B$ in another with the experimental values, we estimate the phase shift to be around 70 and ${65}^{\circ }$, respectively. We correlate this result with the evolution of the density of states with nonmagnetic disorder.

Atom-in-jellium calculations of the Einstein frequency in condensed matter and of the equation of state were used to predict the variation of shear modulus from zero pressure to $\sim {10}^7\mathrm{g}/{\mathrm{cm}}^3$, for several elements relevant to white dwarf stars and other self-gravitating systems. This is by far the widest range reported electronic structure calculation of shear modulus, spanning from ambient through the one-component plasma to extreme relativistic conditions. The predictions were based on a relationship between the Debye temperature and shear modulus, which we assess to be accurate at the $o(10\%)$ level, and is the first known use of atom-in-jellium theory to calculate a shear modulus. We assessed the overall accuracy of the method by comparing with experimental measurements and more detailed electronic structure calculations at lower pressures.