We investigated the current-induced spin-orbit torque (SOT) originating from the spin Hall effect in stack systems with perpendicularly magnetized Co/Pt/Ir/Pt/Co synthetic antiferromagnetic (AFM) structures which exhibit nearly compensated magnetization and interlayer exchange coupling of $J_{\mathrm{ex}}=0.11\mathrm{mJ}/{\mathrm{m}}^2$. The results were compared with ferromagnetic stack systems with perpendicularly magnetized Pt/Co and (Ir/Pt)-multilayer/Co structures. The magnetizations of the two Co layers in the Co/Pt/Ir/Pt/Co synthetic AFMs can be switched between two antiparallel states simultaneously by SOT. By this switching mechanism, the current to spin-current conversion and spin-torque efficiencies in a synthetic AFM layer stack based on a Pt/Ir/Pt spacer layer are about twice as high as those of a ferromagnetic stack using a Pt heavy metal electrode. The efficient switching of compensated synthetic AFMs would advance magnetic memory devices with high density, high speed, and low power consumption. We expect the Pt/Ir/Pt spacer layer paves the way to AFM spintronics based on multilayer systems.

We study the effects of a periodically varying electric field on the Hubbard model at half filling on a triangular lattice. The electric field is incorporated through the phase of the nearest-neighbor hopping amplitude via the Peierls prescription. When the on-site interaction $U$ is much larger than the hopping, the effective Hamiltonian $H_{\text{eff}}$ describing the spin sector can be found using a Floquet perturbation theory. To third order in the hopping, $H_{\text{eff}}$ is found to have the form of a Heisenberg antiferromagnet with three different nearest-neighbor couplings $(J_{\alpha },J_{\beta },J_{\gamma })$ on bonds lying along the different directions. Remarkably, when the periodic driving does not have time-reversal symmetry, $H_{\text{eff}}$ can also have a chiral three-spin interaction in each triangle, with the coefficient $C$ of the interaction having opposite signs on up- and down-pointing triangles. Thus periodic driving which breaks time-reversal symmetry can simulate the effect of a perpendicular magnetic flux which is known to generate such a chiral term in the spin sector, even though our model does not have a magnetic flux. The four parameters $(J_{\alpha },J_{\beta },J_{\gamma },C)$ depend on the amplitude, frequency, and direction of the oscillating electric field. We then study the spin model as a function of these parameters using exact diagonalization and find a rich phase diagram of the ground state with seven different phases consisting of two kinds of ordered phases (collinear and coplanar) and disordered phases. Thus periodic driving of the Hubbard model on the triangular lattice can lead to an effective spin model whose couplings can be tuned over a range of values thereby producing a variety of interesting phases.

We propose using maximum coherence (${\mathrm{QC}}_{\max }$) to study quantum phase transition (QPT). We investigate several well-known models, such as the XXZ model, $J_1\text{−}{J}_2$ model, and one-dimensional spin Kitaev model. The results show that ${\mathrm{QC}}_{\max }$ can be used to detect different types of QPTs, including the Berezinskii-Kosterlitz-Thouless and topological types. In addition, ${\mathrm{QC}}_{\max }$ is more robust against interferences, such as thermal fluctuations and measurement interferences, than any existing detector. This property enables ${\mathrm{QC}}_{\max }$ to identify QPTs in experiments, where temperature effects and measurement interferences always exist. Thus, ${\mathrm{QC}}_{\max }$ might be an ideal tool for studying QPTs because of its measurability, universality, and robustness against interferences.

We report the effect of Pt doping on the superconductivity in ${\mathrm{CuRh}}_2{\mathrm{Se}}_4$ spinel using a combined experimental and theoretical study. Our x-ray diffraction results reveal that the $\mathrm{Cu}{\left({\mathrm{Rh}}_{1\text{−}x}{\mathrm{Pt}}_x\right)}_2{\mathrm{Se}}_4 (0\le x\le 0.35)$ crystallizes in the structure with a space group of $Fd\overline{3}m$ (No. 227), and the lattice parameter $a$ increases with Pt doping. The resistivity and magnetic susceptibility measurement results verify that the superconducting transition temperature ($T_c$) forms a domelike shape with a maximum value of 3.84 K at $x=0.06$. It is also observed that the Pt doping slightly reduces the lower critical magnetic field from 220 Oe in ${\mathrm{CuRh}}_2{\mathrm{Se}}_4$ to 168 Oe in $\mathrm{Cu}{\left({\mathrm{Rh}}_{0.94}{\mathrm{Pt}}_{0.06}\right)}_2{\mathrm{Se}}_4$, while it significantly enhances the upper critical magnetic field, reaching the maximum of 4.93 T in the $\mathrm{Cu}{\left({\mathrm{Rh}}_{0.94}{\mathrm{Pt}}_{0.06}\right)}_2{\mathrm{Se}}_4$ sample. The heat capacity result indicates that the sample $\mathrm{Cu}{\left({{\mathrm{Rh}}_{0.}}_{91}{{\mathrm{Pt}}_{0.0}}_9\right)}_2{\mathrm{Se}}_4$ is a bulk superconductor. First-principles calculations suggest that the Pt doping leads to a redshift of a density of state peak near the Fermi level, consistent with the domelike $T_{\mathrm{c}}$ observed experimentally.

The origin of the charge density wave in ${\mathrm{TaTe}}_4$ is discussed on the basis of a first-principles density functional theory analysis of the Fermi surface, electron-hole response function, phonon band structure of the average structure, and structural optimization of the modulated phase. Analysis of the band structure and Fermi surface of the average structure clearly proves that despite the presence of $\mathrm{Ta}{\mathrm{Te}}_4$ chains in the crystal structure, $\mathrm{Ta}{\mathrm{Te}}_4$ is in fact a 3D material as far as the electronic structure near the Fermi level is concerned. A Fermi surface nesting mechanism is dismissed as the origin of the $2a\times 2a\times 3c$ structural modulation. The optimized $2a\times 2a\times 3c$ structure, which is found to be the more stable modulation in agreement with the experimental observations, can be obtained directly from a soft-phonon mode computed for the undistorted structure. Our results suggest that the driving force for the distortion is the maximization of Ta-Ta metal-metal bonding subject to inducing the minimum bonding decrease in the Te sublattice.

The polar antiferromagnet ${\mathrm{Co}}_2{\mathrm{Mo}}_3{\mathrm{O}}_8$ was recently reported as a new multiferroic material exhibiting remarkable second-order magnetoelectric (ME) coupling effect while no other metamagnetic transitions occurred at low magnetic field. Herein, we have investigated the ME phenomena under high magnetic field (up to 60 T) in ${\mathrm{Co}}_2{\mathrm{Mo}}_3{\mathrm{O}}_8$ single crystals and observed unique ME response associated with the changes in the hidden magnetic moment on the honeycomb lattice. Two spin-flop transitions are unambiguously defined at $H_{c1}\sim 27\mathrm{T}$ and $H_{c2}\sim 31\mathrm{T}$ under $H$ along the $c$ axis at 1.7 K, accompanied by two successive colossal changes of electric polarization. The results on the anisotropy of magnetoelectricity as well as the angular-dependent polarization are well consistent with the ME tensor prediction, providing a better approach to understand the evolution of magnetic structures under high magnetic field. Therefore, the hidden magnetic transitions and distinctive magnetoelectricity provide a unique platform on which the ME coupling mechanism in the presence of rich magnetic phase transitions can be explored in this 238 family.

In this study we present results of the dynamic compression of $\alpha$-cristobalite up to a pressure of 106 GPa with the use of the dynamic diamond anvil cell. X-ray diffraction images were recorded at different ramp compression and decompression rates to investigate in situ the high-pressure phase transitions of $\alpha$-cristobalite. Our results suggest that the pressure onset of the phase transformation of $\alpha$-cristobalite to cristobalite II, cristobalite X-I, and ultimately to seifertite ($\alpha \text{−}{\mathrm{PbO}}_2$ type ${\mathrm{SiO}}_2$) is dependent on the applied compression rates and stress conditions of the experiment. Increasing compression rates in general shift the studied phase transitions to higher pressures. Furthermore, our results indicate for single crystals under hydrostatic conditions a suppression of a phase transition from cristobalite X-I to seifertite at pressures of up to 82 GPa.

We study the dynamics of entanglement in the quantum Ising chain with dephasing dissipation in a Lindblad master equation form. We consider two unravelings which preserve the Gaussian form of the state, allowing us to address large system sizes. The first unraveling gives rise to a quantum-state-diffusion dynamics, while the second one describes a specific form of quantum-jump evolution, suitably constructed to preserve Gaussianity. In the first case we find a crossover from area-law to logarithm-law entanglement scaling and draw the related phase diagram. In the second case we only find logarithm-law scaling, remarking on the different entanglement behavior for different unravelings of the same Lindblad equation. Finally, we compare these outcomes with the predictions of a non-Hermitian Hamiltonian evolution, finding conflicting results.

Parallel (P) and antiparallel (AP) configurations are widely applied in magnetic heterostructures and have significant impacts on the spin-wave transmission in magnonic devices. In the present study, a theoretical investigation was conducted into the transmission of exchange-dominated spin waves with nanoscale wavelengths in a type of heterostructure including two magnetic media, of which the magnetization state can be set to the P (AP) configuration by ferromagnetic (antiferromagnetic) interfacial exchange coupling (IEC). The boundary conditions in P and AP cases were derived, by which the transmission and reflection coefficients of spin waves were analytically given and numerically calculated. In the P configuration, a critical angle ${\theta }_{\text{c}}$ always exists and has a significant influence on the transmission. Spin waves are refracted and reflected when the incident angle ${\theta }_{\text{i}}$ is smaller than the critical angle (${\theta }_{\text{i}}<{\theta }_{\text{c}}$), while total reflection occurs as ${\theta }_{\text{i}}\ge {\theta }_{\text{c}}$. In the AP configuration, the spin-wave polarizations of mediums 1 and 2 are inverse, that is, right handed (RH) and left handed (LH), leading to the total reflection being independent of ${\theta }_{\text{i}}$. As demonstrated by the difference in spin-wave transmission properties between the P (${\theta }_{\text{i}}<{\theta }_{\text{c}}$) and AP cases, there is a polarization-dependent scattering. However, as ${\theta }_{\text{i}}$ exceeds ${\theta }_{\text{c}}$, the P (${\theta }_{\text{i}}>{\theta }_{\text{c}}$) case exhibits similarities with the AP case, where the transmitted waves are found to be evanescent in medium 2 and their decay lengths are investigated. In both the P (${\theta }_{\text{i}}>{\theta }_{\text{c}}$) and AP cases, the Goos-Hänchen (GH) shift of the total reflection waves are calculated and shown as a function of the frequency and incident angle. The relationship between the decay lengths and GH shifts is also explored. Furthermore, as the number of media exceeds two, spin waves are scattered by multiple interfaces, resulting in the resonant transmission effect in the P (${\theta }_{\text{i}}<{\theta }_{\text{c}}$) case. At the same time, there is a tunneling effect and a resonant tunneling effect in the P (${\theta }_{\text{i}}>{\theta }_{\text{c}}$) and AP cases, which are attributed to the evanescent waves. The influences of the IEC strength on all of the aforementioned findings are investigated in detail. The present study provides a comprehensive guide for the transmission of spin waves in the magnetic systems with either P or AP configuration and is helpful for the design of future magnonic devices.

In this study, we investigate the magnetic susceptibility, entropy, and isothermal magnetization curve of the spin-1/2 Heisenberg model on an anisotropic triangular lattice using the orthogonalized finite-temperature Lanczos method. In addition, we investigate the adiabatic magnetization curve and magnetocaloric effect. We estimate these physical quantities with sufficient accuracy in the thermodynamic limit, except at low temperatures. We observe a 1/3 magnetization plateau in the isothermal magnetization process, whereas the plateau is observed to have a slope in the adiabatic process. We show that the magnetocaloric effect can be used to detect the signature of phase transitions. We believe that these results will be useful for understanding the magnetism of anisotropic triangular lattice compounds through a comparison with experimental results in the future.

Liquid helium under negative pressure represents a unique possibility for studying the macroscopic quantum nucleation phenomena in condensed media. We analyze the quantum cavitation rate of single electron bubbles at low temperatures down to absolute zero. The energy dissipation and sound emission processes result in the different temperature behavior of quantum cavitation rate in normal fluid ${}^3\mathrm{He}$ and superfluid ${}^4\mathrm{He}$ below the thermal-quantum crossover temperature. The position of the rapid nucleation line in the temperature-pressure phase diagram is discussed as well.

After half a century of debate, superconductivity in doped ${\mathrm{SrTiO}}_3$ has come to the fore again with the discovery of interfacial superconductivity in the ${\mathrm{LaAlO}}_3 /{\mathrm{SrTiO}}_3$ heterostructures. While these interfaces share the interesting properties of bulk ${\mathrm{SrTiO}}_3$ , quantum confinement generates a complex band structure involving bands with different orbital symmetries whose occupancy is tunable by electrostating doping. Multigap superconductivity has been predicted to emerge in ${\mathrm{LaAlO}}_3 /{\mathrm{SrTiO}}_3$ at large doping, with a Bose-Einstein condensation character at the Lifshtiz transition. In this article, we report on the measurement of the upper critical magnetic field ${\mathrm{H}}_{\mathrm{c}2}$ of superconducting (110)-oriented ${\mathrm{LaAlO}}_3 /{\mathrm{SrTiO}}_3$ heterostructures and evidence a two-gap superconducting regime at high doping. Our results are quantitatively explained by a theoretical model based on the formation of an unconventional ${\mathrm{s}}_{\pm }$-wave superconducting state with a repulsive coupling between the two condensates.

Electronic nematicity in iron pnictide materials has been extensively studied by various experimental techniques, yet its heat capacity anomaly at the phase transition has not been examined quantitatively. In this paper, we review the thermodynamic description of nematicity in $\mathrm{Ba}{\left({\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x\right)}_2{\mathrm{As}}_2$ using the Landau free energy, which defines the behavior of three thermodynamic quantities: the structural orthorhombicity that develops below the nematic transition, the softening shear modulus above the transition, and the discontinuous heat capacity at the transition. We derive a quantitative relationship between these three quantities, which is found to hold for a range of dopings. This result shows that the nematic transition is exceedingly well described by a mean-field model in the underdoped regime of the phase diagram.

We study the magnetic-field dependence of the vortex-core charge in the Abrikosov lattice of an $s$-wave superconductor based on the augmented quasiclassical equations, where we incorporate the pair-potential gradient (PPG) terms characteristic of charging in superconductors besides the well-known Lorentz force. Our numerical results at $T=0.2T_{\mathrm{c}}$ and $0.5T_{\mathrm{c}}$ reveal that periodic charge redistribution is superimposed on the magnetic flux-line lattice with different spatial patterns at different fields. The PPG terms are dominant at weak fields over the Lorentz force for accumulating charge in the vortex cores, whereas the Lorentz force prevails at higher fields to give rise to a peak structure in the core charge around $H\sim \frac{1}{2}{H}_{\mathrm{c}2}$. We estimate the peak value of the core charge at $T=0.2T_{\mathrm{c}}$ using parameters appropriate for cuprates to obtain a large value of $Q\sim {10}^{-2}\left|e\right|$ in the core region of radius $0.2{\xi }_0$ in the $ab$ plane and length $1\mathrm{nm}$ along the $c$ axis.

A hole injected into a Mott insulator will gain an internal structure as recently identified by exact numerics, which is characterized by a nontrivial quantum number whose nature is of central importance in understanding the Mott physics. In this work, we show that a spin texture associated with such an internal degree of freedom can explicitly manifest after the spin degeneracy is lifted by a weak Rashba spin-orbit coupling (SOC). It is described by an emergent angular momentum $J_z=\pm \frac{3}{2}$ as shown by both exact diagonalization and variational Monte Carlo calculations, which are in good agreement with each other at a finite size. In particular, as the internal structure such a spin texture is generally present in the hole composite even at high excited energies, such that a corresponding texture in momentum space, extending deep inside the Brillouin zone, can be directly probed by the spin-polarized angle-resolved photoemission spectroscopy (ARPES). This is in contrast to a Landau quasiparticle under the SOC, in which the spin texture induced by SOC will not be protected once the excited energy is larger than the weak SOC coupling strength, away from the Fermi energy. We point out that the spin texture due to the SOC should be monotonically enhanced with reducing spin-spin correlation length in the superconducting-pseudogap phase at finite doping. A brief discussion of a recent experiment of the spin-polarized ARPES will be made.

Magnetic materials with pyrochlore crystal structure form exotic magnetic states due to the high lattice frustration. In this work we follow the effects of coupling of the lattice and electronic and magnetic degrees of freedom in two praseodymium-based pyrochlores ${\mathrm{Pr}}_2{\mathrm{Zr}}_2{\mathrm{O}}_7$ and ${\mathrm{Pr}}_2{\mathrm{Ir}}_2{\mathrm{O}}_7$. In either of these materials, the presence of magnetic interactions does not lead to magnetically ordered low temperature states; however, their electronic properties are different. A comparison of Raman phonon spectra of ${\mathrm{Pr}}_2{\mathrm{Zr}}_2{\mathrm{O}}_7$ and ${\mathrm{Pr}}_2{\mathrm{Ir}}_2{\mathrm{O}}_7$ allows us to identify magnetoelastic coupling in ${\mathrm{Pr}}_2{\mathrm{Zr}}_2{\mathrm{O}}_7$ that elucidates its magnetic properties at intermediate temperatures and allows us to characterize phonon-electron scattering in the semimetallic ${\mathrm{Pr}}_2{\mathrm{Ir}}_2{\mathrm{O}}_7$. We also show that the effects of random disorder on the Raman phonon spectra is small.

Erbium nitride (ErN) is an emerging rocksalt rare-earth semiconducting pnictide and has attracted significant interest in recent years for its potential applications in thermoelectric energy conversion, spintronic devices, and for the Gifford-McMahon cryocoolers. Due to the Er intra-$4f$ electronic transition, Er-doped III-nitride semiconductors such as GaN, InGaN, etc. exhibit strong emission in the retina-safe and fiber optical communication wavelength window of 1.54 μm that is researched extensively for developing solid-state lasers, amplifiers, and light-emitting devices. However, due to ErN's propensity for oxidation in ambient, high-quality ErN thin film growth has been challenging and an in-depth understanding of its electronic structure remains unanswered. In this work, the valence band electronic structure of ErN thin films is measured with normal as well as with resonant synchrotron-radiation photoemission spectroscopy. Photoemission measurements show a valence band maximum and Fermi energy difference of ∼2.3 eV in ErN. First-principles density functional theory (DFT) calculations are performed not only to explain the valence band electronic structure but also to determine transport properties such as effective mass and deformation potentials. Strong localized Er-$4f$ states are observed ∼6–8 eV below the valence band maxima and the valence band edge is found to exhibit N-$2p$ character. Resonant photoemission data corroborates the DFT calculations. To accurately capture the electronic structure in modeling, beyond generalized gradient approximation (GGA) methods such as (a) Heyd-Scuseria-Ernzerhof hybrid functional and (b) GGA+U Hubbard correction schemes are utilized. Determination of the electronic structure of ErN marks significant progress in developing ErN-based electronic, optoelectronic, and thermoelectric devices.

We propose a scheme to perform stroboscopic Hamiltonian engineering in the low frequency regime using a quantum system with one-dimensional nearest-neighbor coupling that are commonly available in the NISQ era. Computational problems are encoded in the effective Hamiltonian of the quantum systems under the effect of external driving. Our approach is nonperturbative and it does not rely on high-frequency expansions, which are a common tool in Floquet engineering. In our paper, the effective Hamiltonian that we want to engineer is fully tailored through designing the periodic driving. We illustrate how this quantum computation proceeds with two examples, an instance from the 3-SAT problem and the LiH molecule quantum chemistry simulation. In the case of the 3-SAT Hamiltonian, we show that by starting from the ground state of the trivial Hamiltonian, the quantum systems go through an adiabatic process in the stroboscopic picture towards the target Hamiltonian of the problem.

We performed comprehensive theoretical and experimental studies of the electronic structure and the Fermi surface topology of two novel quantum materials, $\mathrm{Mo}{\mathrm{Si}}_2$ and $\mathrm{W}{\mathrm{Si}}_2$. The theoretical predictions of the electronic structure in the vicinity of the Fermi level was verified experimentally by thorough analysis of the observed quantum oscillations in both electrical resistivity and magnetostriction. We established that the Fermi surface sheets in $\mathrm{Mo}{\mathrm{Si}}_2$ and $\mathrm{W}{\mathrm{Si}}_2$ consist of 3D dumbbell-shaped holelike pockets and rosette-shaped electronlike pockets, with nearly equal volumes. Based on this finding, both materials were characterized as almost perfectly compensated semimetals. In conjunction, the magnetoresistance attains giant values of ${10}^4$ and ${10}^5\%$ for $\mathrm{W}{\mathrm{Si}}_2$ and $\mathrm{Mo}{\mathrm{Si}}_2$, respectively. In turn, the anisotropic magnetoresistance achieves $-95\%$ and $-98\%$ at $T=2$ K and in $B=14$ T for $\mathrm{W}{\mathrm{Si}}_2$ and $\mathrm{Mo}{\mathrm{Si}}_2$, respectively. Furthermore, for both compounds we observed the Shoenberg effect in their Shubnikov-de Haas oscillations that persisted at as high temperature as $T=25$ K in $\mathrm{Mo}{\mathrm{Si}}_2$ and $T=12$ K in $\mathrm{W}{\mathrm{Si}}_2$. In addition, we found for $\mathrm{Mo}{\mathrm{Si}}_2$ a rarely observed spin-zero phenomenon. Remarkably, the electronic structure calculations revealed type-II Dirac cones located near 480 and 710 meV above the Fermi level in $\mathrm{Mo}{\mathrm{Si}}_2$ and $\mathrm{W}{\mathrm{Si}}_2$, respectively.

We develop a quantum spin-liquid theory for quantum magnets with easy-plane ferromagnetic exchange. These strongly entangled quantum states are obtained by dimer coverings of two-dimensional (2D) lattices with triplet $S=1,m_z=0$ bonds, forming a triplet resonating valence bond (tRVB) state. We discuss the conditions and the procedure to transfer well-known results from conventional singlet resonating valence bond theory to tRVB. Additionally, we present mean field theories of Abrikosov fermions on 2D triangular and square lattices, which can be controlled in an appropriate large-$N$ limit. We also incorporate the effect of charge doping which stabilizes $(p+ip)$-wave superconductivity. Beyond the pure theoretical interest, our study may help to resolve contradictory statements on certain transition metal chalcogenides, including $1T\text{−}{\mathrm{TaS}}_2$, $1T\text{−}{\mathrm{TaSe}}_2$, as well as ${\mathrm{CrSiTe}}_3$ and ${\mathrm{CrGeTe}}_3$.