We demonstrate an efficient and accurate, general-purpose first-principles blueprint for calculating anharmonic vibrational free energy and predicting structural phase transition temperatures of solids including those involving dynamic instability. Thermodynamic integration is performed using $\lambda$-dependent ensembles ($0\le \lambda \le 1$) constructed directly from a statistical sampling of atomic displacements under $\lambda$-dependent potentials while completely avoiding molecular dynamics of any kind. The underlying statistical distributions of the dynamically unstable Born-Oppenheimer potential ($\lambda =1$), temperature-dependent effective harmonic potential ($\lambda =0$), and all intermediate-$\lambda$ potentials are formulated using only the information from interatomic force constants. Our approach enables a faster thermodynamic integration by four orders of magnitude over the traditional route via AIMD. Experimental phase transition temperatures of a variety of strongly anharmonic materials with dynamical instabilities including shape-memory alloys are recovered to largely within 25% error. Such a combination of speed and accuracy enables the method to be deployed at a large scale for predictive mapping of phase transition temperatures.

${\mathrm{LaNiGa}}_2$ is superconductor that has been shown to break time-reversal symmetry in the superconducting state without any known nearby magnetism. Recently, single crystals of ${\mathrm{LaNiGa}}_2$ have been synthesized, revealing a nonsymmorphic Cmcm space group. Here, we report on measurements of the electronic structure of ${\mathrm{LaNiGa}}_2$ throughout the three-dimensional Brillouin zone (BZ) using angle-resolved photoemission spectroscopy. Our findings show broad consistency with density functional theory calculations and provide evidence for degeneracies in the electronic structure that are predicted from the space group symmetry. We report evidence for those predicted symmetry-enforced degeneracies as well as accidental near degeneracies throughout the BZ. These degeneracies and near degeneracies may play a role in the pairing mechanism of ${\mathrm{LaNiGa}}_2$. Our results provide insight into the interplay between structure, fermiology, and superconductivity in unconventional superconductors with nonsymmorphic space group.

We make lattice generalization of two well-known zero-dimensional models of quantum spin glass, Sachdev-Ye (SY) and spherical quantum $p$-spin glass model, to one dimension for studying crossovers in nonlocal scrambling dynamics because of glass transition, complex dynamics, and quantum and thermal fluctuations in paramagnetic (PM) and spin glass (SG) phases. In the SY chain of quantum dots, each described by infinite-range random Heisenberg model of $N$ spin-$SSU\left(M\right)$ spins, we obtain the quantum Lyapunov exponent ${\lambda }_{\mathrm{L}}$ and butterfly velocity $v_B$ as a function of temperature $T$ and the quantum parameter $S$ across the PM-SG phase boundary using a bosonic spinon representation in the large-$N,M$ limit. In particular, we extract asymptotic $T$ and $S$ dependence, e.g., power laws, for ${\lambda }_{\mathrm{L}}$ and $v_B$ in different regions deep inside the phases and near the replica symmetry breaking SG transition. We find the chaos to be nonmaximal almost over the entire phase diagram. Very similar results for chaos indicators are found for the $p$-spin glass chain as a function of temperature and a suitable quantum parameter $\mathrm{\Gamma }$, with some important qualitative differences. In particular, ${\lambda }_{\mathrm{L}}$ and $v_B$ exhibit a maximum, coinciding with onset of complex glassy relaxation, above the glass transition as a function of $T$ and $\mathrm{\Gamma }$ in the PM phase of the $p$-spin glass model. In contrast, the maximum is only observed as a function of $S$, but not with temperature, in the PM phase of SY model. The maximum originates from enhanced chaos caused by maximal complexity in the glassy landscape. Thus, the results in the SY model indicate very different evolution of glassy complexity with quantum and thermal fluctuations.

The concept of scattering length density tuning for improved polarization is investigated for Fe/${}^{11}\mathrm{B}_4\mathrm{CTi}$ multilayers and compared to the commonly used Fe/Si system in polarizing multilayer neutron optics. X-ray and neutron reflectivity, magnetization, and neutron polarization were measured on such multilayers, highlighting differences from conventional Fe/Si multilayers. The multilayer systems were deposited with 25 Å period thickness, a layer thickness ratio of 0.35, and 20 periods using ion-assisted dc magnetron sputtering. Replacing Si with ${}^{11}\mathrm{B}_4\mathrm{CTi}$ for these multilayers showed an increase in reflectivity due to a reduction in interface width. Tuning the ratio between ${}^{11}\mathrm{B}_4\mathrm{C}$ and Ti in the nonmagnetic layers enabled a wide range of scattering length density contrasting and matching for spin-down neutrons, which in turn led to an improved polarization. These findings demonstrate the potential of Fe/${}^{11}\mathrm{B}_4\mathrm{CTi}$ multilayers as a promising option for polarizing neutron optics and highlight the concept of scattering length density tuning in a large range using ${}^{11}\mathrm{B}_4\mathrm{CTi}$.

We show that one-dimensional lattice models exhibit superdiffusive transport in the presence of random nodal impurities in the absence of interaction. Here a nodal impurity is defined as a localized state, the wave function of which has zeros (nodes) in the momentum representation. The dynamics exponent $z$, a defining quantity for transport behaviors, is computed to establish this result. To be specific, in a disordered system having only nodal impurities, the dynamical exponent $z=4n/(4n-1)$, where $n$ is the order of the node. If the system has time reversal, the nodes appear in pairs and the dynamical exponent can be enhanced to $z=8n/(8n-1)$. As $1<z<2$, both cases indicate superdiffusive transport.

The application of high pressure is a formidable tool in condensed matter physics, capable of unveiling hidden quantum phases and dramatically altering the magnetic and electronic landscape of materials. Here, we present a comprehensive study on the pressure-induced enhancement of antiferromagnetic (AFM) order in DySbTe, a material characterized by its rich interplay between magnetism and topology. Under pressures reaching up to 66 GPa, we observe an initial reduction in resistivity, reflective of enhanced electronic bandwidth, followed by a conspicuous resistivity upturn beyond 15 GPa. The upturn coincides with the simultaneous observation of a distinctive kink in the resistivity-temperature profile around 9 K, signaling a pressure-amplified AFM phase transition. The intensification of this kink with increasing pressure underscores the stabilization and amplification of AFM interactions under extreme conditions. Fermi-liquid analysis reveals a critical temperature crossover, characterized by a pressure-dependent suppression followed by a resurgence near 10 GPa, indicating that AFM enhancement is intricately entangled with quasiparticle scattering effects, underscoring a deep-seated correlation that likely amplifies electron-electron interactions and profoundly influences coherent transport properties. Concurrent magnetoresistance (MR) measurements expose spin canting phenomena, with pronounced peaks around 3 T across the pressure regime, and an upward shift in spin-flop and spin-flip fields above 10 GPa, corroborating the reinforcement of AFM coupling. These results illuminate the complex interdependence of pressure, magnetism, and electronic transport in DySbTe, providing pivotal insights into the manipulation of magnetic states under extreme conditions and advancing our understanding of magnetic topological quantum materials.

A family of molecular Mott insulators on triangular lattice has provided a few $S=1/2$ triangular quantum spin liquid candidates, with $\kappa \text{−}{\left(\mathrm{BEDT}\text{−}\mathrm{TTF}\right)}_2{\mathrm{Cu}}_2{\left(\mathrm{CN}\right)}_3$ being the most studied material of this group. The large number of experimental works present a conflicting set of evidence, with some suggesting spin liquid behavior, while others pointing towards a valence bond solid with orphan spins. In this work we use Raman scattering spectroscopy to probe both local charge on molecular sites and lattice phonons as a function of temperature down to 6 K. Based on the analysis of the line shape of the BEDT-TTF charge sensitive vibration ${\nu }_2$ on cooling below 40 K, we suggest the development of disordered fluctuating charge disproportionation on $(\mathrm{BEDT}\text{−}{\mathrm{TTF})}_2$ dimers of amplitude as small as $0.05e$. The lattice phonons show strong anomalous broadening on cooling only in the (c,c) scattering channel, associated with the developing charge disproportionation. We suggest an interpretation, where the coupling of disordered charge dipoles on dimers to the lattice results in anisotropic modulation of charge transfer integrals between dimer lattice sites. Such fluctuations would result in modulation of magnetic coupling between spins which can produce fluctuating charge ordered spin-singlet pairs.

The competition between scrambling and projective measurements can lead to measurement-induced entanglement phase transitions (MIPT). In this work, we show that the universality class of the MIPT can be drastically altered when the system has a diffusing conserved density. As a numerical tractable model of this, we study a $1+\mathrm{1d}$ random Clifford circuit locally monitored by classically diffusing particles (“measurers”). The resulting diffusive correlations in the measurement density are a relevant perturbation to the usual space-time random MIPT critical point, producing a new universality class for this phase transition. We find “Griffiths-like” effects due to rare space-time regions where, e.g., the diffusive measurers have a low or high density, but these are considerably weaker than the Griffiths effects that occur with quenched randomness that produce rare spatial regions with infinite lifetime.

The putative Kitaev material ${\mathrm{Na}}_2{\mathrm{Co}}_2{\mathrm{TeO}}_6$ has recently been proposed to enter a quantum spin disordered state when magnetic fields are applied in parallel to the honeycomb layers. In this Letter we uncover signatures of a quantum critical endpoint (QCEP) associated with the assumed order-disorder transition by means of high-resolution capacitance dilatometry. At the critical field $B_{\mathrm{C}}$ $\simeq 6 \mathrm{T}$, a sign change of the out-of-plane thermal expansion coefficient ${\alpha }_{\mathrm{c}}$ indicates the accumulation of entropy upon crossing the phase boundary. The proportional relationship between isothermal magnetization and magnetostriction signals that the QCEP can be tuned by magnetic field and pressure simultaneously. The presented results expand the material classes that exhibit metamagnetic quantum criticality to honeycomb antiferromagnets with possible Kitaev interactions.

We analyze the transition into the most favorable ordered state for a system of 2D fermions with spin and valley degrees of freedom. We show that for a range of rotationally invariant dispersions, the ordering transition is highly unconventional: The associated susceptibility diverges (or almost diverges) at the transition, yet, immediately below it, the system jumps discontinuously into a fully polarized state. We analyze the dispersion of the longitudinal and transverse collective modes in different parameter regimes above and below the transition. Additionally, we consider ordering in a system with full $\mathrm{SU}\left(4\right)$ symmetry and show that there is a cascade of discontinuous transitions into a set of states, which includes a quarter-metal, a half-metal, and a three-quarter metal. We compare our results with the data for biased bilayer and trilayer graphene.

Recent quantum Hall experiments have observed “daughter states” next to several plateaus at half-integer filling factors in various platforms. These states were first proposed based on model wave functions for the Moore-Read state by Levin and Halperin. We show that these daughters and their parents belong to an extensive family tree that encompasses all pairing channels and permits a unified description in terms of weakly interacting composite fermions. Each daughter represents a bosonic integer quantum Hall state formed by composite-fermion pairs. The pairing of the parent dictates an additional number of filled composite-fermion Landau levels. We support our field-theoretic composite-fermion treatment by using the $K$-matrix formalism, analysis of trial wave functions, and a coupled-wire construction. Our analysis yields the topological orders, quantum numbers, and experimental signatures of all daughters of paired states at half-filling and “next-generation” even denominators. Crucially, no two daughters share the same two parents. The unique parentage implies that Hall conductance measurements alone could pinpoint the topological order of even-denominator plateaus. Additionally, we propose a numerically suitable trial wave function for one daughter of the $\mathrm{SU}{\left(2\right)}_2$ topological order, which arises at filling factor $\nu =\frac{6}{11}$. Finally, our insights explain experimentally observed features of transitions in wide-quantum wells, such as suppression of the Jain states with the simultaneous development of half-filled and daughter states.

Emerging two-dimensional (2D) materials bring unprecedented opportunities for electronic applications. The design of high-performance devices requires an accurate prediction of carrier mobility in 2D materials, which can be obtained using state-of-the-art ab initio calculations. However, various factors impact the computational accuracy, leading to contradictory estimations for the mobility. Targeting accurate and efficient ab initio calculations for nonmagnetic materials, transport properties in III-V monolayers are reported using the Boltzmann transport equation, and the influences of the pseudopotential, quadrupole correction, Berry connection, and spin-orbit coupling (SOC) on mobilities are systematically investigated in this work. Our findings are as follows: (1) The inclusion of semicore states in pseudopotentials is important to obtain accurate calculations. (2) The variations induced by dynamical quadrupole and Berry connection when treating long-range fields can be 40% and 10%, respectively. (3) The impact of SOC can reach up to 100% for materials with multipeak bands. Importantly, although SOC notably modifies the electronic wave functions, it negligibly impacts the dynamical matrices and scattering potential variations. As a result, the combination of a fully relativistic electron calculation and a scalar-relativistic phonon calculation can strike a good balance between accuracy and cost. This work compares computational methodologies, providing guidelines for accurate and efficient calculations of mobilities in 2D semiconductors.

We investigate the optical response induced by a dc current flowing in a nonmagnetic material that lacks inversion symmetry. In this class of materials, the flowing current experiences a nonlinear Hall effect and induces a nonequilibrium orbital magnetization, even in the absence of spin-orbit coupling. As a result, an orbital-driven Kerr effect arises that can be used to probe not only the orbital magnetization but also the nonlinear Hall effect. In addition, in the long wavelength limit, the nonlinear Hall effect leads to a rectified current that can be used to detect terahertz radiations. We apply the theory to selected model systems, such as ${\mathrm{WTe}}_2$ bilayer and metallic superlattices. The nonequilibrium orbital Kerr efficiencies obtained in these systems are comparable to the largest values reported experimentally in GaAs and ${\mathrm{MoS}}_2$, exceeding the values reported in metals and suggesting a large terahertz current responsivity.

The studies of high-temperature superconductors raise a fundamental question: Can a small Fermi-surface phase, which violates the Luttinger theorem, exist and give rise to superconductivity? Our work provides a positive answer through a concrete theory based on a bilayer model with strong interlayer spin-spin coupling $\left(J_{\perp }\right)$ but no interlayer hopping $\left(t_{\perp }\right)$. Then small hole doping of the rung-singlet insulator with two electrons per rung naturally leads to small hole pockets with Fermi-surface volume per flavor smaller than the free-fermion result by $\frac{1}{2}$ of the Brillouin zone (BZ). We construct a $t\text{−}J$ model on a bilayer square lattice, so called ESD $t\text{−}J$ model, where ESD stands for empty, singlon, doublon states. Then we employ a generalized slave-boson theory, which captures this small Fermi-surface phase at smallhole doping $x$. This metallic state is an intrinsically strongly correlated Fermi liquid beyond weak coupling theory, violating the perturbative Luttinger theorem but consistent with the Oshikawa's nonperturbative proof. We further show that it transitions into an interlayer paired $s^{\prime }$-wave superconductor at lower temperature through Feshbach resonance with a virtual Cooper pair, with a surprising doping-induced crossover from Bardeen-Cooper-Schrieffer to Bose-Einstein condensation at higher hole doping levels. This leads to a superconducting dome centered around $x=0.5$, with the normal state changing from the conventional Fermi liquid in the $x>0.5$ to the unusual small Fermi-surface state in the $x<0.5$ side. Our theoretical findings including phase diagrams are also confirmed by density matrix renormalization group (DMRG) simulation in quasi-one dimension. Applying our theoretical framework, we provide a plausible scenario for the recently found bilayer nickelate ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ materials.

We study the superconductor/normal region/superconductor $\left(\mathrm{S}\right|\mathrm{N}\left|\mathrm{S}\right)$ Josephson junction formed using superconductors with $d$, $d+i{d}^{\prime }$, and $d+is$ superconducting pairings. We show that the quality factor of the Josephson diode effect and its sign can be substantially tuned by the external magnetic field, the gate voltage, and the length of the junction for all three types of pairings. We also identify the conditions under which the anomalous Josephson and Josephson diode effects can appear in the junction by analyzing appropriate symmetries. In particular, by breaking a $\pi$-rotation symmetry, we show how a large field-free Josephson diode effect can be realized even in the absence of spin-orbit coupling. We also study the role of edge states appearing in the case of chiral superconductor with $d+i{d}^{\prime }$ pairing. Our results demonstrate that the Josephson diode effect in a planar geometry can be used as a signature of unconventional superconducting pairings.

A topological phase can undergo a phase transition driven by anyon condensation. A potential obstruction to such a mechanism could arise if there exists a symmetry between anyons that have nontrivial mutual statistics. Here we consider the toric code subjected to errors that tend to proliferate anyons with nontrivial mutual statistics. Using the Cauchy-Schwarz inequality, we show that in the presence of electromagnetic duality and a partial-transpose symmetry, a decoherence-induced phase transition out of the topological phase must be rather unconventional and lie beyond the standard rules of anyon condensation. To explore such physics, we first subject the toric code to a self-dual quantum channel where Kraus operators are proportional to $X+Z$. We find that the topological phase is stable up to the maximal error rate, when viewing the density matrix as a pure state in the double Hilbert space. To access an unconventional transition, we then consider a perturbed toric code subjected to the self-dual channel and find numerical evidence that beyond a critical error rate, the topological phase is destroyed, resulting in a critical phase where anyons are only power-law condensed.

We introduce “Berry-dipole semimetals”, whose band degeneracies are characterized by quantized Berry dipoles. Through a two-band model constructed by a Hopf map, we reveal that the Berry-dipole semimetals display a multitude of salient properties distinct from other topological semimetals. On the boundary, we find that the first-order Berry-dipole semimetal harbors anomalous paired Fermi arcs with the same spin polarization, even though the layer Chern number is zero, and the second-order Berry-dipole semimetal hosts dispersionless hinge arcs. In the bulk, we find that the low-energy Berry-dipole Hamiltonian near the band node has a quadratic energy dispersion and peculiar Berry curvature, which give rise to rather unique characteristics in the intrinsic anomalous Hall effect, orbital magnetization and Landau levels. Our study shows that Berry-dipole semimetals are a class of topological gapless phases supporting rich intriguing physics.

The manipulation of magnetization via magnetic torques is one of the most important phenomena in spintronics. In thin films, conventionally, a charge current flowing in a heavy metal is used to generate transverse spin currents and to exert torques on the magnetization of an adjacent ferromagnetic thin film layer. Here, in contrast to the typically employed heavy metals, we study spin-to-charge conversion in ferromagnetic heterostructures with large spin-orbit interaction that function as the torque-generating layers. In particular, we chose perpendicular magnetic anisotropy (PMA) multilayers [Co/Ni] and [Co/Pt] as the torque-generating layers and drive magnetization dynamics in metallic ferromagnetic thin film ${\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}$ (CoFeB) layers with in-plane magnetic anisotropy (IMA). We investigate the spin dynamics driven by spin-orbit torque (SOT) and the concomitant charge current generation by the inverse SOT process using an inductive technique based on a vector network analyzer. In our experimental findings, we find that the SOTs generated by our multilayers are of a magnitude comparable to those produced by Pt, consistent with first-principles calculations. Furthermore, we noted a significant correlation between the SOT and the thickness of the CoFeB layer.

Twisted bilayer (2L) two-dimensional transition metal dichalgocenides (TMDCs) exhibit a range of novel phenomena such as the formation of moiré excitons and strongly correlated phases. The coupling between the layers is crucial for the resulting physical properties and depends not just on the twist angle but also on the details of the fabrication process. Here, we present an approach for the analysis of this interlayer coupling via Raman spectroscopy. By exciting the C-exciton resonance of the TMDCs, optical (high-frequency) interlayer Raman modes are activated that are too weak in intensity at excitation energies far below the C exciton. This is due to the wave function of the C exciton, which expands—in contrast to A and B excitons—over both layers and therefore couples the layers electronically. We present optical interlayer Raman modes in twisted 2L TMDCs and show that they can be used as a measure of the interlayer coupling between the individual layers.

We systematically explore the structural and electronic properties of twisted trilayer graphene systems. In general, these systems are characterized by two twist angles ${\theta }_{12}$ and ${\theta }_{23}$, which lead to two incommensurate moiré periods. We show that when the ratio of twist angles is close to a simple fraction, ${\theta }_{12}/{\theta }_{23}=\pm 1$, or $-1/2$, strong lattice relaxation results in the formation of domains of periodic single-moiré structures. For other rational pairs of twist angles, we find that relaxation is weak, leading to incommensurate moiré periods and an overall quasicrystalline structure. We identify experimentally relevant magic angles at which the electronic density of states is sharply peaked and strongly correlated physics is most likely to be realized.