Philip Kim

Sacroiliac (SI) joint pain is a widely prevalent, and frequent cause of chronic low back pain. Therefore, this review aimed to evaluate current evidence on the investigation and treatment of SI joint injections and radiofrequency ablation (RFA), outline the comparative effectiveness, and future treatments. Clinical studies were collected from databases, such as Scopus, MEDLINE, PubMed, EMBASE, Cochrane Library, Web of Science, Google Scholar, ClinicalTrials.gov, and CINAHL. Image-guided diagnostic injections are the reference standard for confirming the SI joint pain. Therapeutic steroid injections offer only temporary benefit, whereas RFA, in particular, cooled or bipolar methods offer longer-lasting benefit, lasting up to 6 months to 12 months. Comparative experimental studies showed better performance of RFA than injections in a well-selected population. There are fewer invasive options that include regenerative treatments, including using platelet-rich plasma and mesenchymal stem cells, which are on the horizon, but the evidence presented in the studies is limited. The pain in the SI joint ought to be managed in a multimodal and evidence-based pain management approach that focuses on the correct diagnosis. RFA remains the most widely supported intervention in offering long-term relief, and biologic and neuro-modulation therapies are areas where research can potentially improve in the future.

Abstract Niobium diselenide (NbSe 2 ) has garnered significant attention due to the coexistence of superconductivity and charge density waves (CDWs) down to the monolayer limit. However, realistic modeling of CDWs—capturing effects such as layer number, twist angle, and strain—remains challenging due to the high computational cost of first-principles methods. Here, we develop a physically informed workflow for training machine-learning interatomic potentials (MLIPs) based on the E(3)-equivariant Allegro architecture, tailored to capture the subtle structural and dynamical signatures of CDWs in mono- and bilayer NbSe 2 . We find that while CDW lattice distortions are relatively easy to learn, modeling vibrational properties remains more challenging. It requires targeted dataset design and careful hyperparameter tuning, pushing the boundaries and testing the extensibility of current MLIP frameworks. Our MLIPs enable reliable simulations of commensurate and incommensurate CDW phases, including their sensitivity to dimensionality and stacking, as well as CDW dynamics, phonons, and transition temperatures estimated via the stochastic self-consistent harmonic approximation. This work opens new possibilities for studying and tuning CDWs in NbSe 2 and other two-dimensional systems, with implications for electron-phonon coupling, superconductivity, and advanced materials design.

Room-temperature superconductivity is arguably the greatest challenge in condensed matter physics, with significant practical and commercial implications if it can be solved. There are no physical laws preventing this from occurring; indeed, superconductivity has been observed in so many different materials under so many different conditions that it is almost a "generic" property of nonmagnetic metals. This guides our viewpoint that high-temperature superconductivity is possible, if difficult to realize. Here, we lay out two grand challenges facing the field, titled the Prediction Challenge and the Engineering Challenge, and put forward a programmatic approach for overcoming them. The Prediction Challenge addresses the fact that our ability to predict new conventional superconductors has dramatically advanced in recent years, but most predicted materials are not experimentally synthesizable. To address this challenge, we propose a shift from modeling the superconducting critical temperature and dynamic stability toward high-throughput ab initio and predictive thermodynamics/synthesis modeling. The Engineering Challenge describes how we can control superconductivity with various "knobs," including pressure, nanostructuring, and light. However, our ability to predict how a specific knob will modify a given superconductor is limited, making it difficult to fully exploit them. We describe the current status and identify areas where additional work is needed to fully exploit six of the most common knobs. Progress in both of these grand challenges, while closely integrating theory and experiment into a continuous feedback loop and incorporating insights from fields beyond physics and materials science, could unlock the underlying keys to room-temperature superconductivity.

We present Coulomb-drag measurements on a heterostructure comprising two Bernal-stacked bilayer graphene (BLG) sheets separated by a 2.5 nm hexagonal boron nitride (hBN) spacer in the quantum Hall (QH) regime. Using top and bottom gate control, together with an interlayer bias, we independently tune the two BLG layers into either the lowest (N=0) or second (N=1) Landau level (LL) orbital and probe their interlayer QH states. When both layers occupy the N=0 orbital, we observe both interlayer exciton condensates (ECs) at integer total filling and interlayer fractional QH states, echoing the results in double monolayer graphene. In contrast to previous studies, however, when both BLG layers occupy the N=1 orbital, we also observe quantized drag signals, signifying an interlayer exciton condensate formed between the second LLs. By tuning the layer degree of freedom, we find that this N=1 EC state arises only when the N=1 wave function in each BLG is polarized toward the hBN interface to maximize the interlayer Coulomb interaction.

Room-temperature superconductivity is arguably the greatest challenge in condensed matter physics, with significant practical and commercial implications if it can be solved. There are no physical laws preventing this from occurring; indeed, superconductivity has been observed in so many different materials under so many different conditions that it is almost a "generic" property of nonmagnetic metals. This guides our viewpoint that high-temperature superconductivity is possible, if difficult to realize. Here, we lay out two grand challenges facing the field, titled the Prediction Challenge and the Engineering Challenge, and put forward a programmatic approach for overcoming them. The Prediction Challenge addresses the fact that our ability to predict new conventional superconductors has dramatically advanced in recent years, but most predicted materials are not experimentally synthesizable. To address this challenge, we propose a shift from modeling the superconducting critical temperature and dynamic stability toward high-throughput ab initio and predictive thermodynamics/synthesis modeling. The Engineering Challenge describes how we can control superconductivity with various "knobs," including pressure, nanostructuring, and light. However, our ability to predict how a specific knob will modify a given superconductor is limited, making it difficult to fully exploit them. We describe the current status and identify areas where additional work is needed to fully exploit six of the most common knobs. Progress in both of these grand challenges, while closely integrating theory and experiment into a continuous feedback loop and incorporating insights from fields beyond physics and materials science, could unlock the underlying keys to room-temperature superconductivity.

OBJECTIVES: Recent advancements in spinal cord stimulation (SCS) technologies have focused on improving device performance and therapeutic effectiveness. However, SCS implant status and postimplant therapeutic utilization have historically been poorly monitored, with limited outcomes reported, primarily owing to inherent limitations of legacy technology and clinic-based data collection. The recent emergence of SCS remote monitoring enables daily, objective tracking of device use, establishing reliable longitudinal data integrity. This advancement supports a new standard for long-term surveillance of SCS implant status and therapy utilization and enables benchmarking against previously reported estimates. MATERIALS AND METHODS: After institutional review board exemption, deidentified data were extracted from a manufacturer database for the first 500 consecutive US patients implanted with a remote monitoring-capable SCS system to retrospectively analyze rates of real-world SCS therapy utilization, explant, and virtual explant. RESULTS: In total, 493 patients met the eligibility criteria, with a median age of 67 years; 58.8% were female. At a median SCS implant duration of 364 days, 95.1% remained implanted, whereas 4.9% were explanted. The most common reason for explant was surgical complications, including infection and pocket-site pain. Among patients implanted, 96.8% were actively using SCS; 2.3% were not actively using SCS, and 0.9% were considered virtual explants owing to prolonged SCS inactivity. CONCLUSIONS: Automated SCS remote monitoring offers targeted enhancements to therapeutic care and may support longitudinal accountability and data integrity through daily transmission of objective device data. Unlike traditional methods for assessing device explant, which underestimate SCS discontinuation rates, real-time monitoring enables first-of-its-kind detection of inactive users and virtual explants for a more comprehensive assessment of real-world outcomes. The high rate of SCS usage in these results indicates the potential value of remote care and provides support for the adoption of remote monitoring as a new standard for postimplant device management and long-term surveillance.

Abstract Highly doped semiconductor quantum wells (QWs) exhibit strong intersubband transitions resulting from nanoscale electron confinement. Coupling photons to these collective dipoles in this anisotropic quantum structure enables intersubband polaritons with strong nonlinear optical response and hyperbolicity. Analogous to epitaxially grown multi-quantum wells, two-dimensional (2D) van der Waals (vdW) semiconductor heterostructures provide a compelling alternative platform, offering additional degrees of freedom and exceptional optoelectronic properties. Here we report intersubband polaritons in multilayer vdW WSe 2 QWs with broadband tunability. By oxidizing the top WSe 2 layer into a self-limiting native oxide, we activate charge transfer–induced efficient, high-density doping, enabling strong intersubband transitions and directly visualized polariton propagation. Lithographically defined nanostructures reveal their hyperbolic nature and sub-diffractional confinement, while electrostatic gating offers dynamic dispersion control. These results position vdW multilayers as a highly adaptable platform for tunable mid-infrared nanophotonics and integrated polaritonic circuits, detectors, and light sources.

Quasicrystals (QCs) host long-range order without translational symmetry, a regime in which the very foundations of BCS theory are not straightforwardly applicable, yet experiments on QCs and their approximant crystals (ACs) point to conventional, $s$-wave, electron-phonon coupled superconductivity. Here we test the predictive power of the electron-phonon framework in a representative decagonal AC from first principles. Using state-of-the-art \textit{ab initio} methods, we compute the superconducting properties of the recently discovered AC Al$_{13}$Os$_4$ and quantitatively reproduce its bulk $T_\text{c}$. This constitutes, to our knowledge, the first \textit{ab initio} determination of $T_\text{c}$ for an AC and establishes that the electron-phonon framework is predictive in these systems as well. Using the generalized quasichemical approximation for alloy modeling in the decagonal Al--Os family, we predict tunable superconductivity in Al$_{13}$Os$_{4-x}$Re$_x$ and Al$_{13}$Os$_{4-x}$Ir$_x$; in particular, Al$_{13}$Re$_4$ is dynamically stable and estimated to have a $T_\text{c}$ about 30% above Al$_{13}$Os$_4$. Finally, we discuss the role of ACs as high-fidelity proxies for their parent QCs. Although long-range quasiperiodicity may introduce subtle electronic features, our findings indicate that the key ingredients for superconductivity are already encoded in the local structural motifs preserved by the AC. This places the Al--Os and Al--Re families among the most promising candidates for the highest-$T_\text{c}$ quasicrystalline superconductivity.

Van der Waals (vdW) superconductors remain superconducting down to the monolayer limit, enabling the exploration of emergent physical phenomena and functionality driven by reduced dimensionality. Here, we report the characterization of the kinetic inductance of atomically thin NbSe$_2$, a two-dimensional van der Waals superconductor, using superconducting coplanar waveguides and microwave measurement techniques familiar to circuit quantum electrodynamics (cQED). The kinetic inductance scales inversely with the number of NbSe$_2$ layers, reaching 1.2 nH/$\Box$ in the monolayer limit. Furthermore, the measured kinetic inductance exhibits a thickness-dependent crossover from clean- to dirty-limit behavior, with enhanced dirty-limit contributions emerging in the ultra-thin regime. These effects are likely driven by increased surface scattering, multi-band superconductivity, and geometric confinement. Additionally, the self-Kerr nonlinearity of the NbSe$_2$ films ranges from $K/2π$ = -0.008 to -14.7 Hz/photon, indicating its strong potential in applications requiring compact, nearly linear, high-inductance superconducting quantum devices and detectors. The fabrication and characterization techniques demonstrated here are extensible to the investigation of other two-dimensional superconductors.

Abstract Emergent strongly correlated electronic phenomena in atomically thin transition-metal dichalcogenides are an exciting frontier in condensed matter physics, with examples ranging from bilayer superconductivity and electronic Wigner crystals to the ongoing search for exciton condensation. Here we take a step towards the latter by reporting experimental signatures of unconventional hybridization of the excitons with opposing dipoles consistent with coherence between interlayer electrons in a transition-metal dichalcogenide bilayer. We investigate naturally grown MoS 2 homobilayers integrated in a dual-gate device structure allowing independent control of the electron density and out-of-plane electric field. By electron doping the bilayer when electron tunnelling between the layers is negligible, we observe that the two interlayer excitons hybridize, displaying unusual behaviour distinct from both conventional level crossing and anti-crossing. We show that these observations can be explained by quasi-static random coupling between the excitons, which increases with electron density and decreases with temperature. We argue that this phenomenon is indicative of a spatially fluctuating order parameter in the form of interlayer electron coherence, a theoretically predicted many-body state that has yet to be unambiguously established experimentally outside of the quantum Hall regime.

Excitons in transition metal dichalcogenides (TMDs) have extremely short, picosecond-scale lifetimes which hinders exciton thermalization, limits the emergence of collective coherence, and reduces exciton transport in optoelectronic devices. In this work, we explore an all-optical pathway to extend exciton lifetimes by placing MoSe$_2$ in a deep-subwavelength Fabry-Perot silver cavity. The cavity structure is designed to suppress radiative recombination from in-plane optical dipoles, such as bright excitons and trions. We observe a consistent decrease in photoluminescence (PL) linewidths of excitons and trions (~1 nm), along with a corresponding lifetime increase (~10 ps). We confirm the experimental observations arise purely from exciton-cavity interactions-etching back the top silver layer returns the PL linewidth and lifetimes return to their original values. Our study offers a pathway to engineer excited state lifetimes in 2D materials which can be utilized for studies of optically dark excitons and have potential applications for novel optoelectronic devices.

A promising approach to attain long-distance coherent spin propagation is accessing topological spin-polarized edge states in graphene. Achieving this without external magnetic fields necessitates engineering graphene band structure, obtainable through proximity effects in van der Waals heterostructures. In particular, proximity-induced staggered potentials and spin-orbit coupling are expected to form a topological bulk gap in graphene with gapless helical edge states that are robust against disorder. In this work, we detect the spin-polarized helical edge transport in graphene at zero external magnetic field, allowed by the proximity of an interlayer antiferromagnet, CrPS4. We show the coexistence of the quantum spin Hall (QSH) states and magnetism in graphene, where the induced spin-orbit and exchange couplings also give rise to a large anomalous Hall (AH) effect. The detection of the QSH states at zero external magnetic field, together with the AH signal that persists up to room temperature, opens the route for practical applications of magnetic graphene in quantum spintronic circuitries. Graphene was one of the first materials proposed to host the quantum spin Hall effect. However, its weak intrinsic spin-orbit interaction means that observing such an effect requires modifying the graphene band structure. Here, Ghiasi et al. combine graphene with CrPS4 and detect quantum spin Hall states at zero magnetic field.

The superconducting gap defines the fundamental energy scale for the emergence of dissipationless transport and collective phenomena in a superconductor. In layered high-temperature cuprate superconductors, where the Cooper pairs are confined to weakly coupled two-dimensional copper-oxygen planes, terahertz (THz) spectroscopy at sub-gap millielectronvolt energies has provided crucial insights into the collective superfluid response perpendicular to the superconducting layers. However, within the copper-oxygen planes the collective superfluid response manifests as plasmonic charge oscillations at energies far exceeding the superconducting gap, obscured by strong dissipation. Here, we present spectroscopic evidence of a below-gap, two-dimensional superfluid plasmon in few-layer Bi2Sr2CaCu2O8+x and spatially resolve its deeply sub-diffractive THz electrodynamics. By placing the superconductor in the near-field of a spintronic THz emitter, we reveal this distinct resonance-absent in bulk samples and observed only in the superconducting phase-and determine its plasmonic nature by mapping the geometric anisotropy and dispersion. Crucially, these measurements offer a direct view of the momentum- and frequency dependent superconducting transition in two dimensions. These results establish a new platform for investigating superfluid phenomena at finite momenta and THz frequencies, highlighting the potential to engineer and visualize superconducting devices operating at ultrafast THz rates.

Imposing incommensurable periodicity on the periodic atomic lattice can lead to complex structural phases consisting of locally periodic structure bounded by topological defects1, 2, 3, 4, 5, 6, 7–8. Twisted trilayer graphene (TTG) is an ideal material platform to study the interplay between different atomic periodicities, which can be tuned by twist angles between the layers, leading to moiré-of-moiré lattices9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25–26. Interlayer and intralayer interactions between two interfaces in TTG transform this moiré-of-moiré lattice into an intricate network of domain structures at small twist angles, which can harbour exotic electronic behaviours9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25–26. Here we report a complete structural phase diagram of TTG with atomic-scale lattice reconstruction. Using transmission electron microscopy (TEM) combined with a new interatomic potential simulation27,28, we show several large-scale moiré lattices, including triangular, kagome and a corner-shared hexagram-shaped domain pattern. Each domain is bounded by a 2D network of domain-wall lattices. In the limit of small twist angles, two competing structural orders—rhombohedral and Bernal stackings—with a slight energy difference cause unconventional lattice reconstruction with spontaneous symmetry breaking (SSB) and nematic instability, highlighting the importance of long-range interlayer interactions across entire van der Waals layers. The diverse tessellation of distinct domains, whose topological network can be tuned by the adjustment of the twist angles, establishes TTG as a platform for exploring the interplay between emerging quantum properties and controllable nontrivial lattices. Examination of a complete structural phase diagram of twisted trilayer graphene shows that several large-scale moiré domain lattices can be formed, the physical properties of which can be tuned by the twist angles between layers.

Electrons in low-dimensional materials driven out of equilibrium by a strong electric field exhibit intriguing effects that have direct analogues in high-energy physics. In this work we demonstrate that two of these effects can be observed in graphene, leading to relevant implications for light-matter interactions at the nanoscale. For doped graphene, the Cherenkov emission of phonons caused by the fast flow of out-of-equilibrium electrons was found to induce direction-dependent asymmetric plasmon damping and an unexpected generation of photocurrent. For graphene close to charge neutrality, incident infrared photons were found to disrupt the creation-recombination balance of electron-hole pairs enabled by the condensed matter version of the Schwinger effect, resulting in an excess photocurrent that we term Schwinger photocurrent. Both Schwinger and Cherenkov photocurrents are different from other known light-to-current down conversions scenarios and thus expand the family of photoelectric effects in solid state devices. Through nano-infrared imaging methodology, we provide a more comprehensive view of current-driven nonequilibrium electrodynamics in graphene. Here, the authors report the observation of two solid-state analogues of well-known high-energy physics effects in graphene samples irradiated by infrared photons under non-equilibrium conditions. Depending on the carrier density of graphene, they observed asymmetric plasmon damping, and anomalous photocurrents associated with the condensed matter versions of the Cherenkov and Schwinger effects.

The recent discovery of the van der Waals (vdW) layered heavy fermion antiferromagnetic metal CeSiI offers promising potential for achieving accessible quantum criticality in the two-dimensional (2D) limit. CeSiI exhibits both heavy fermion behavior and antiferromagnetic (AFM) ordering, while the exact magnetic structure and phase diagram are yet to be determined. Here, we investigate the magnetic properties of atomically thin CeSiI devices with thicknesses ranging from 2 to 15 vdW layers. The thickness-dependent magnetotransport measurement reveals the intrinsic 2D nature of heavy fermion behavior and antiferromagnetism. Notably, we also find an isotropic, time-dependent hysteresis in both magnetoresistance and Hall resistance, showing glassy relaxation dynamics. This glassy behavior in magnetic structures may suggest the presence of spin glass phases or multipolar ordering, further establishing CeSiI as an intriguing material system for investigating the interplay between magnetic orders and the Kondo effect.

The search for anyons, quasiparticles with fractional charge and exotic exchange statistics, has inspired decades of condensed matter research. Quantum Hall interferometers enable direct observation of the anyon braiding phase through discrete interference phase jumps when the number of encircled localized quasiparticles changes. In this study, we observed this braiding phase in both the filling factor 1/3 and 4/3 fractional quantum Hall states by probing three-state random telegraph noise (RTN) in real time. We found that the observed RTN stems from anyon quasiparticle number n fluctuations, and we reconstructed three Aharonov-Bohm oscillation signals phase shifted by 2π/3, corresponding to the three possible interference branches from braiding around n (mod 3) anyons. Our methods can be readily extended to interference of non-abelian anyons.

Efficient magnetic switching is a cornerstone for advancing spintronics, particularly for energy-efficient data storage and memory devices. Here, we report the electrical switching of spin-flips in V-doped WSe2 multilayers, a van der Waals (vdW)-layered diluted magnetic semiconductor (DMS), demonstrating ultralow-power switching operation at room temperature. Our study reveals unique linear magnetoresistance and parabolic magnetoresistance states, where electrical modulation induces transitions between interlayered ferromagnetic, ferrimagnetic, and antiferromagnetic configurations. We identify an unconventional linear magnetoresistance hysteresis characterized by electrically driven spin flip/flop switching, distinct from conventional random network disorder or linear band-dispersion mechanisms. Applying an electrical voltage across vertical vdW layered V-doped WSe2 multilayers generates the spin currents at room temperature, driving spin-flip transitions from ferromagnetic to antiferromagnetic states due to a strong spin transfer torque effect. Notably, the critical current density reaches an ultralow value of 10-1Acm-2, accompanied by pico-watt power consumption, a record-low spin current density by a six-order-of-magnitude improvement over conventional spintronic devices. These findings establish the V-doped WSe2 multilayer device as a transformative platform for ultralow power spintronics, underscoring the potential of vdW-layered DMS systems for next generation energy-efficient spintronic technologies.

The negatively charged boron vacancy (V_{B}^{-}) in hexagonal boron nitride (hBN) has garnered significant attention among defects in two-dimensional materials. This owes, in part, to its deterministic generation, well-characterized atomic structure, and optical polarizability at room temperature. We investigate the latter through extensive measurements probing both the ground and excited state polarization dynamics. We develop a semiclassical model based on these measurements that predicts a near-unity degree of spin polarization, surpassing other solid-state spin defects under ambient conditions. Building upon our model, we include the presence of nuclear spin degrees of freedom adjacent to the V_{B}^{-} and perform a comprehensive set of Lindbladian numerics to investigate the hyperfine-induced polarization of the nuclear spins. Our simulations predict a number of important features that emerge as a function of magnetic field which are borne out by experiment.

We report electric field-controlled modulation of the Fermi surface topology and explore its effects on the superconducting state in alternating-angle twisted quadrilayer graphene (TQG). The unique combination of flat and dispersive bands in TQG allows us to simultaneously tune the band structure through carrier density, $n$, and displacement field, $D$. From density-dependent Shubnikov-de Haas quantum oscillations and Hall measurements, we quantify the $D$-dependent bandwidth of the flat and dispersive bands and their hybridization. In the high $|D|$ regime, the increased bandwidth favors the single particle bands, which coincides exactly with the vanishing of the superconducting transition temperature $T_c$, showing that superconductivity in TQG is strongly bound to the symmetry-broken state. For a range of lower $|D|$ values, a Lifshitz transition occurs when the flat and dispersive band Fermi surfaces merge within the $ν=+2$ symmetry-broken state. The superconducting state correspondingly shows an enhanced $T_c$, suggesting that the superconducting condensate is strongly dependent on the Fermi surface topology and density of states within this symmetry-broken state.

Plasmon polaritons are formed by coupling light with delocalized electrons. The half-light and half-matter nature of plasmon polaritons endows them with unparalleled tunability via a range of parameters, such as dielectric environments and carrier density. Therefore, plasmon polaritons are expected to be tuned when in proximity to polar materials since the carrier density is tuned by an electrostatic potential; conversely, the plasmon polariton response might enable the sensing of polarization. Here, we use infrared nanoimaging and nanophotocurrent measurements to investigate heterostructures composed of graphene and twisted hexagonal boron nitride (t-BN), with alternating polarization in a triangular network of moiré stacking domains. We observe that the carrier density and the corresponding plasmonic response of graphene are modulated by polar domains in t-BN. In addition, we demonstrate that the nanometer-wide domain walls of graphene moirés superlattices, created by the polar domains of t-BN, provide momenta to assist the plasmonic excitations. Furthermore, our study establishes that the plasmon of graphene could function as a delicate sensor for polarization textures. The evolution of polarization textures in t-BN under uniform electric fields is tomographically examined via plasmonic imaging. Strikingly, no noticeable polarization switching is observed under applied electric fields up to <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mrow> <a:mn>0.21</a:mn> <a:mtext> </a:mtext> <a:mtext> </a:mtext> <a:mi mathvariant="normal">V</a:mi> <a:mo stretchy="false">/</a:mo> <a:mi>nm</a:mi> </a:mrow> </a:math> , at variance with transport reports. Our nanoimages unambiguously reveal that t-BN with triangular domains acts like a ferrielectric rather than a ferroelectric as claimed by many previous studies.

Atomically thin van der Waals (vdW) films provide a material platform for the epitaxial growth of quantum heterostructures. However, unlike the remote epitaxial growth of three-dimensional bulk crystals, the growth of two-dimensional material heterostructures across atomic layers has been limited due to the weak vdW interaction. Here we report the double-sided epitaxy of vdW layered materials through atomic membranes. We grow vdW topological insulators Sb2Te3 and Bi2Se3 by molecular-beam epitaxy on both surfaces of atomically thin graphene or hexagonal boron nitride, which serve as suspended two-dimensional vdW substrate layers. Both homo- and hetero-double-sided vdW topological insulator tunnel junctions are fabricated, with the atomically thin hexagonal boron nitride acting as a crystal-momentum-conserving tunnelling barrier with abrupt and epitaxial interfaces. By performing field-angle-dependent magneto-tunnelling spectroscopy on these devices, we reveal the energy–momentum–spin resonance of massless Dirac electrons tunnelling between helical Landau levels developed in the topological surface states at the interfaces. Double-sided epitaxy of van der Waals materials through atomic membranes is demonstrated, enabling electrons to resonantly tunnel between aligned topological insulator surfaces with the conservation of energy, momentum and spin helicity.

Motivated by the recent proposals for unconventional emergent physics in twisted bilayers of nodal superconductors, we study the peculiarities of the Josephson effect at the twisted interface between $d$-wave superconductors. We demonstrate that for clean interfaces with a twist angle ${\ensuremath{\theta}}_{0}$ in the range ${0}^{\ensuremath{\circ}}&lt;{\ensuremath{\theta}}_{0}&lt;{45}^{\ensuremath{\circ}}$, the critical current can exhibit nonmonotonic temperature dependence with a maximum at a nonzero temperature as well as a complex dependence on the twist angle at low temperatures. These effects are shown to reflect the destructive interference between the $d$-wave order parameters near the nodes at nonzero twist angle. Close to ${\ensuremath{\theta}}_{0}={45}^{\ensuremath{\circ}}$ we find that the critical current does not vanish due to Cooper pair cotunneling, which can lead to the transition to a time-reversal breaking superconducting $d+id$ phase, which can be suppressed by the interface roughness. We provide a comprehensive theoretical analysis of experiments that can reveal this cotunneling for twisted superconductors close to ${\ensuremath{\theta}}_{0}={45}^{\ensuremath{\circ}}$. In particular, we demonstrate that both the emergence of the Fraunhofer interference pattern near ${\ensuremath{\theta}}_{0}={45}^{\ensuremath{\circ}}$ and fractional Shapiro steps yield unambiguous evidence of Cooper pair cotunneling, necessary for topological superconductivity.

Strongly interacting electronic systems often exhibit a complicated phase diagram that results from the competition between different quantum ground states. One feature of these phase diagrams is the emergence of microemulsion phases, where regions of different phases self-organize across multiple length scales. The experimental characterization of these microemulsions can pose considerable challenges, as the long-range Coulomb interaction microscopically mingles with the competing states. Here we observe the signatures of the microemulsion between an electronic Wigner crystal and an electron liquid in a MoSe2 monolayer using cryogenic reflectance and magneto-optical spectroscopy. We find that the transition into this microemulsion state is marked by anomalies in exciton reflectance, spin susceptibility and umklapp scattering, establishing it as a distinct phase of electronic matter. Competition between different possible ground states of strongly correlated electron systems can lead to the emergence of mixed states called microemulsions. Now this phenomenon is reported at the melting transition of a Wigner crystal.

Since the initial discovery of 2D van der Waals (vdW) materials, significant effort has been made to incorporate the three properties of magnetism, band structure topology, and strong electron correlations-to leverage emergent quantum phenomena and expand their potential applications. However, the discovery of a single vdW material that intrinsically hosts all three ingredients has remained an outstanding challenge. Here, the discovery of a Kondo-interacting topological antiferromagnet is reported in the vdW 5f electron system UOTe. It has a high antiferromagnetic (AFM) transition temperature of 150 K, with a unique AFM configuration that breaks the combined parity and time reversal (PT) symmetry in an even number of layers while maintaining zero net magnetic moment. This angle-resolved photoemission spectroscopy (ARPES) measurements reveal Dirac bands near the Fermi level, which combined with the theoretical calculations demonstrate UOTe as an AFM Dirac semimetal. Within the AFM order, the presence of the Kondo interaction is observed, as evidenced by the emergence of a 5f flat band near the Fermi level below 100 K and hybridization between the Kondo band and the Dirac band. The density functional theory calculations in its bilayer form predict UOTe as a rare example of a fully-compensated AFM Chern insulator.