New State Of Matter Research Articles

Magnetic Monopoles, Dyons and Confinement in Quantum Matter

We show that magnetic monopoles appear naturally in granular quantum matter. Their condensation leads to a new state of matter, superinsulation, in which Cooper pairs are bound into purely electric pions by strings of electric flux. These electric flux tubes, the dual of Abrikosov vortices, prevent the separation of charge–hole pairs, thereby causing an infinite resistance, even at finite temperatures, the dual behaviour of superconductors. We will discuss the electric Meissner effect, asymptotic freedom and their measurements and describe the recent direct detection of a linear, confining potential by dynamic relaxation experiments. Finally, we consider dyons, excitations carrying both a magnetic and an electric charge, and show that a condensate of such dyons leads to a possible solution of the mysteries of the pseudogap state of high-Tc cuprates.

Review on Developments and Progress in Nickelate‐Based Heterostructure Composites and Superconducting Thin Films

AbstractIn the past decade, the rapid development of modern heterointerface growth and characterization techniques has stimulated great effort to research and design the extraordinary physical properties of transition metal heterostructure composite materials. Here, new physics originates from the rearrangement of orbital, charge, spin, and lattice and the resulting rebalancing of their mutual interactions. In this paper, recent experimental and theoretical progress in the design, preparation, characterization, and physical property measurement of LaNiO3‐based heterostructure composites and the infinite‐layer Ni1 + nickelate superconducting thin films on (001) SrTiO3 substrate is reviewed, mainly by the methods of various X‐ray spectroscopy measurements, scanning transmission electron microscopy, and magneto‐transport measurements. In these materials, the electronic structure and orbital occupation around the Fermi level are modified, enabling nickelate‐based composite materials to exhibit new states of matter and physical phenomena, which are absent in the bulk constituents. Their confined structures, superconductivity, orbital polarization, charge transfer, electronic structures, magnetic properties, and X‐ray spectroscopic analysis, are therefore highlighted, aiming at understanding unconventional superconducting mechanisms and designing new high‐Tc superconducting low‐dimensional materials for device applications.

Time-dependent exchange creates the time-frustrated state of matter

Magnetic systems governed by exchange interactions between magnetic moments harbor frustration that leads to ground state degeneracy and results in the new topological state often referred to as a frustrated state of matter (FSM). The frustration in the commonly discussed magnetic systems has a spatial origin. Here we demonstrate that an array of nanomagnets coupled by the real retarded exchange interactions develops a new state of matter, time frustrated matter (TFM). In a spin system with the time-dependent retarded exchange interaction, a single spin-flip influences other spins not instantly but after some delay. This implies that the sign of the exchange interaction changes, leading to either ferro- or antiferromagnetic interaction, depends on time. As a result, the system’s temporal evolution is essentially non-Markovian. The emerging competition between different magnetic orders leads to a new kind of time-core frustration. To establish this paradigmatic shift, we focus on the exemplary system, a granular multiferroic, where the exchange transferring medium has a pronounced frequency dispersion and hence develops the TFM.

Three-dimensional quantum droplets in spin-orbit-coupled Bose-Einstein condensates

Quantum droplets (QDs) are a recently discovered new state of matter in ultracold atoms. We study three-dimensional (3D) self-trapped modes in spinor Bose-Einstein condensates with spin-orbit coupling (SOC), described by coupled Gross-Pitaevskii equations including beyond-mean-field Lee-Huang-Yang terms. The 3D QDs, semi-vortex and mixed-mode states, of a large size with an anisotropic density profile, exist with a wide large values of the norm as the Lee-Huang-Yang terms eliminate the collapse. The effect of the intra- and inter-component of the nonlinearity and SOC on characteristics of the QDs is systematically addressed. Using the linear-stability analysis and direct simulations, we have checked the stability of all the 3D QDs states, stressing they are stable against small perturbations in propagation in limited scales. The present analysis opens a new way for creating multidimensional solitary waves, and may be developed in other directions, including nonlinear optics, not only in conservative, but also in dissipative systems.

A machine learning photon detection algorithm for coherent x-ray ultrafast fluctuation analysis.

X-ray free electron laser experiments have brought unique capabilities and opened new directions in research, such as creating new states of matter or directly measuring atomic motion. One such area is the ability to use finely spaced sets of coherent x-ray pulses to be compared after scattering from a dynamic system at different times. This enables the study of fluctuations in many-body quantum systems at the level of the ultrafast pulse durations, but this method has been limited to a select number of examples and required complex and advanced analytical tools. By applying a new methodology to this problem, we have made qualitative advances in three separate areas that will likely also find application to new fields. As compared to the “droplet-type” models, which typically are used to estimate the photon distributions on pixelated detectors to obtain the coherent x-ray speckle patterns, our algorithm achieves an order of magnitude speedup on CPU hardware and two orders of magnitude improvement on GPU hardware. We also find that it retains accuracy in low-contrast conditions, which is the typical regime for many experiments in structural dynamics. Finally, it can predict photon distributions in high average-intensity applications, a regime which up until now has not been accessible. Our artificial intelligence-assisted algorithm will enable a wider adoption of x-ray coherence spectroscopies, by both automating previously challenging analyses and enabling new experiments that were not otherwise feasible without the developments described in this work.

Chiral SO(4) spin-valley density wave and degenerate topological superconductivity in magic-angle twisted bilayer graphene

Starting from a realistic extended Hubbard model for a ${p}_{x,y}$-orbital tight-binding model on the Honeycomb lattice, we perform a thorough investigation of the possible electron instabilities in magic-angle twisted bilayer graphene near the van Hove (VH) dopings. Here we focus on the interplay between the two symmetries of the system. One is the approximate $\mathrm{SU}(2)\ifmmode\times\else\texttimes\fi{}\mathrm{SU}(2)$ symmetry which leads to the degeneracy between the intervalley spin density wave (SDW) and valley density wave (VDW) as well as that between the intervalley singlet and triplet superconductivities (SCs). The other is the ${D}_{3}$ symmetry which leads to the degeneracy among the three symmetry-related wave vectors of the density-wave (DW) orders, originating from the Fermi-surface nesting. The interplay between these two degeneracies leads to intriguing quantum states relevant to recent experiments, as revealed by our systematic random-phase-approximation based calculations followed by a succeeding mean-field energy minimization for the groundstate energy. At the $\mathrm{SU}(2)\ifmmode\times\else\texttimes\fi{}\mathrm{SU}(2)$ symmetric point, the degenerate intervalley SDW and VDW are mixed into a new state of matter dubbed as the chiral SO(4) spin-valley DW. This state simultaneously hosts three four-component vectorial spin-valley DW orders with each adopting one wave vector, and the polarization directions of the three DW orders are mutually perpendicular to one another. In the presence of a tiny intervalley exchange interaction with coefficient ${J}_{H}\ensuremath{\rightarrow}{0}^{\ensuremath{-}}$ which breaks the $\mathrm{SU}(2)\ifmmode\times\else\texttimes\fi{}\mathrm{SU}(2)$ symmetry, a pure chiral SDW state is obtained. In the case of ${J}_{H}\ensuremath{\rightarrow}{0}^{+}$, although a nematic VDW order is favored, the two SDW orders with equal amplitudes are accompanied simultaneously. This nematic $\mathrm{VDW}+\mathrm{SDW}$ state possesses a stripy distribution of the charge density, consistent with the recent STM observations. On the aspect of SC, while the triplet $p+ip$ and singlet $d+id$ topological SCs are degenerate at ${J}_{H}=0$ near the VH dopings, the former (latter) is favored for ${J}_{H}\ensuremath{\rightarrow}{0}^{\ensuremath{-}}$ (${J}_{H}\ensuremath{\rightarrow}{0}^{+}$). In addition, the two asymmetric doping-dependent behaviors of the obtained pairing phase diagram are well consistent with experiments.

Symmetry progression and possible polar metallicity in NiPS3 under pressure

van der Waals solids are ideal platforms for the discovery of new states of matter and emergent properties under external stimuli. Under pressure, complex chalcogenides like MPS3 (M = Mn, Ni, Co, V) host sliding and structural transitions, insulator-to-metal transitions, the possibility of an orbitally-selective Mott state, piezochromism, and superconductivity. In this work, we bring together diamond anvil cell techniques, infrared and Raman scattering spectroscopies, and X-ray diffraction with a detailed symmetry analysis and first-principles calculations to uncover a series of high-pressure phases in NiPS3. Remarkably, we find five different states of matter between ambient conditions and 39 GPa—quite different than in the other MPS3 materials. Even more strikingly, infrared spectroscopy and X-ray diffraction combined with a symmetry analysis reveal both metallicity and loss of the inversion center above ~23 GPa suggesting that NiPS3 may be a polar metal with a P3m1 space group under these conditions and P1 symmetry under maximum compression. In addition to identifying a candidate polar metal ripe for further inquiry, we suggest that pressure may tune other complex chalcogenides into this elusive state.

Loop currents in quantum matter

In many quantum materials, strong electron correlations lead to the emergence of new states of matter. In particular, the study in the last decades of the complex phase diagram of high temperature superconducting cuprates highlighted intra-unit-cell electronic instabilities breaking discrete Ising-like symmetries, while preserving the lattice translation invariance. Polarized neutron diffraction experiments have provided compelling evidences supporting a new form of intra-unit-cell magnetism, emerging concomitantly with the so-called pseudogap state of these materials. This observation is currently interpreted as the magnetic hallmark of an intra-unit-cell loop current order, breaking both parity and time-reversal symmetries. More generally, this magneto-electric state is likely to exist in a wider class of quantum materials beyond superconducting cuprates. For instance, it has been already observed in hole-doped Mott insulating iridates or in the spin liquid state of hole-doped 2-leg ladder cuprates.

Observation of fractional spin textures in a Heusler material

Recently a zoology of non-collinear chiral spin textures has been discovered, most of which, such as skyrmions and antiskyrmions, have integer topological charges. Here we report the experimental real-space observation of the formation and stability of fractional antiskyrmions and fractional elliptical skyrmions in a Heusler material. These fractional objects appear, over a wide range of temperature and magnetic field, at the edges of a sample, whose interior is occupied by an array of nano-objects with integer topological charges, in agreement with our simulations. We explore the evolution of these objects in the presence of magnetic fields and show their interconversion to objects with integer topological charges. This means the topological charge can be varied continuously. These fractional spin textures are not just another type of skyrmion, but are essentially a new state of matter that emerges and lives only at the boundary of a magnetic system. The coexistence of both integer and fractionally charged spin textures in the same material makes the Heusler family of compounds unique for the manipulation of the real-space topology of spin textures and thus an exciting platform for spintronic and magnonic applications.

Emergent phenomena at oxide interfaces studied with standing-wave photoelectron spectroscopy

Emergent phenomena at complex-oxide interfaces have become a vibrant field of study in the past two decades due to the rich physics and a wide range of possibilities for creating new states of matter and novel functionalities for potential devices. The electronic-structural characterization of such phenomena presents a unique challenge due to the lack of direct yet nondestructive techniques for probing buried layers and interfaces with the required Ångstrom-level resolution, as well as element and orbital specificity. In this Review, we survey several recent studies wherein soft x-ray standing-wave photoelectron spectroscopy—a relatively newly developed technique—is used to investigate buried oxide interfaces exhibiting emergent phenomena such as metal-insulator transition, interfacial ferromagnetism, and two-dimensional electron gas. The advantages, challenges, and future applications of this methodology are also discussed.

Coulomb bound states and atomic collapse in tilted Dirac materials

Searching for new states of matter and unusual quasi-particles in Dirac materials attracts a significant interest in condensed matter physics. Here we investigate the bound state formation in tilted Dirac materials in the presence of the one- and two-dimensional Coulomb potentials. Based on the exact solution of the Dirac equation, we obtain the energy spectrum of the bound states and the corresponding wave functions in the one-dimensional case. It is shown that the lower-energy bound states dive into the continuum below the band gap with the increase of the tilted parameter. The atomic collapse appears when the strength of the Coulomb potential exceeds the critical value. We show that the tilt of Dirac cone facilitates lowing the critical Coulomb potential strength where atomic collapse happens. Most notably, it is found that the bound states are absent for an overtilted Dirac dispersion. For the two-dimensional Coulomb potential, we perform the second-order perturbation theory to study the effect of band tilting on the bound state formation with a single point-like Coulomb impurity. The result indicates that the ground state becomes more unstable near the critical point for a stronger tilt parameter.

Cavity control of nonlinear phononics

Nonlinear interactions between phonon modes govern the behavior of vibrationally highly excited solids and molecules. Here, we demonstrate theoretically that optical cavities can be used to control the redistribution of energy from a highly excited coherent infrared-active phonon state into the other vibrational degrees of freedom of the system. The hybridization of the infrared-active phonon mode with the fundamental mode of the cavity induces a polaritonic splitting that we use to tune the nonlinear interactions with other vibrational modes in and out of resonance. We show that not only can the efficiency of the redistribution of energy be enhanced or decreased, but also the underlying scattering mechanisms may be changed. This work introduces the concept of cavity control to the field of nonlinear phononics, enabling nonequilibrium quantum optical engineering of new states of matter.

Solid, liquid, gas… and beyond

Physicists can't stop discovering bizarre new states of matter. Are we closing in on a complete collection? Jon Cartwright investigates

Unconventional light-induced states visualized by ultrafast electron diffraction and microscopy

Exciting electrons in solids with intense light pulses offers the possibility of generating new states of matter through nonthermal means and controlling their macroscopic properties on femto- to picosecond timescales. One way to manipulate a solid is by altering its lattice structure, which often underlies the electronic, magnetic and other phases. Here, we review how structures of solids are affected by photoexcitation and how their ultrafast dynamics are captured with time-resolved electron diffraction and microscopy. Specifically, we survey how a strong light pulse has been used to tailor the nonequilibrium characteristics to yield on-demand properties in various material classes. In the existing literature, four main routes have been exploited to control material structures: (i) phase competition, (ii) electronic correlations, (iii) excitation of coherent modes, and (iv) defect generation. In this review, we discuss experiments relevant to all four schemes and finish by speculating about future directions.

Controlled Synthesis of MoxW1-xTe2 Atomic Layers with Emergent Quantum States.

Recently, new states of matter like superconducting or topological quantum states were found in transition metal dichalcogenides (TMDs) and manifested themselves in a series of exotic physical behaviors. Such phenomena have been demonstrated to exist in a series of transition metal tellurides including MoTe2, WTe2, and alloyed MoxW1-xTe2. However, the behaviors in the alloy system have been rarely addressed due to their difficulty in obtaining atomic layers with controlled composition, albeit the alloy offers a great platform to tune the quantum states. Here, we report a facile CVD method to synthesize the MoxW1-xTe2 with controllable thickness and chemical composition ratios. The atomic structure of a monolayer MoxW1-xTe2 alloy was experimentally confirmed by scanning transmission electron microscopy. Importantly, two different transport behaviors including superconducting and Weyl semimetal states were observed in Mo-rich Mo0.8W0.2Te2 and W-rich Mo0.2W0.8Te2 samples, respectively. Our results show that the electrical properties of MoxW1-xTe2 can be tuned by controlling the chemical composition, demonstrating our controllable CVD growth method is an efficient strategy to manipulate the physical properties of TMDCs. Meanwhile, it provides a perspective on further comprehension and sheds light on the design of devices with topological multicomponent TMDC materials.

All-electrical creation and control of spin-galvanic signal in graphene and molybdenum ditelluride heterostructures at room temperature

The ability to engineer new states of matter and control their spintronic properties by electric fields is at the heart of future information technology. Here, we report a gate-tunable spin-galvanic effect in van der Waals heterostructures of graphene with a semimetal of molybdenum ditelluride at room temperature due to an efficient spin-charge conversion process. Measurements in different device geometries with control over the spin orientations exhibit spin-switch and Hanle spin precession behavior, confirming the spin origin of the signal. The control experiments with the pristine graphene channels do not show any such signals. We explain the experimental spin-galvanic signals by theoretical calculations considering the spin-orbit induced spin-splitting in the bands of the graphene in the heterostructure. The calculations also reveal an unusual spin texture in graphene heterostructure with an anisotropic out-of-plane and in-plane spin polarization. These findings open opportunities to utilize graphene-based heterostructures for gate-controlled spintronic devices.

Special volume, preface – 9th International Workshop on Astronomy and Relativistic Astrophysics: From Quarks to Cosmos

AbstractThis special volume includes contributions from some of the most relevant scientists who have participated in the IWARA 2020 Video Conference. The series of meetings known by the acronyms IWARA, STARS, and SMFNS,—more than a congregation of events, students and researchers which in itself would be extremely important for science—became in last years a kind of platform for scientific and academic projects, partnerships and presentation of high‐quality research contributions describing original and unpublished results on several topics related as new phenomena and new states of matter in the Universe, general relativity, gravitation, cosmology, astrophysics, particle and nuclear physics, and topics related. And the scientists participating in this volume, perfectly integrated with this design, bring more than just a glimpse into the technical toolbox of their work, be it theoretical or experimental. In addition to international scientific recognition, these researchers are mentors of students and young researchers, and demonstrate, in these contributions, also glimpses of systematically complex decisions made about the interpretation of data, about which problems are relevant to pursue, thus contributing a lot to the craft of science and its development.

Room temperature exciton\u2013polariton Bose\u2013Einstein condensation in organic single-crystal microribbon cavities

Exciton–polariton Bose–Einstein condensation (EP BEC) is of crucial importance for the development of coherent light sources and optical logic elements, as it creates a new state of matter with coherent nature and nonlinear behaviors. The demand for room temperature EP BEC has driven the development of organic polaritons because of the large binding energies of Frenkel excitons in organic materials. However, the reliance on external high-finesse microcavities for organic EP BEC results in poor compactness and integrability of devices, which restricts their practical applications in on-chip integration. Here, we demonstrate room temperature EP BEC in organic single-crystal microribbon natural cavities. The regularly shaped microribbons serve as waveguide Fabry–Pérot microcavities, in which efficient strong coupling between Frenkel excitons and photons leads to the generation of EPs at room temperature. The large exciton–photon coupling strength due to high exciton densities facilitates the achievement of EP BEC. Taking advantages of interactions in EP condensates and dimension confinement effects, we demonstrate the realization of controllable output of coherent light from the microribbons. We hope that the results will provide a useful enlightenment for using organic single crystals to construct miniaturized polaritonic devices.

Excitonic insulator emerging from semiconducting normal state in 1T−TiSe2

A new state of matter, an excitonic insulator (EI) state, was predicted to emerge from Bose-Einstein condensation of electron-hole pairs. Some candidate materials were suggested but it has been elusive to confirm its existence. Recent works gave renewed support for the EI picture of the charge density wave (CDW) state below the critical temperature $T_c \approx 200 $ K of $1T$-TiSe$_{2}$. Yet, an important link to its establishment is to show that a majority fraction of the measured $T_c$ indeed follows from the Coulomb interaction alone, while a quantitative match of the $T_c$ may require assistance from the electron-lattice coupling. This will establish that the CDW is formed predominantly by the Coulomb interaction and help confirm the EI view for TiSe$_2$. Here, we provide such calculations by solving the exciton gap equation with material specific electronic structures. We obtain, with no fitting parameters, $T_c \approx 135 \pm 27$ K for the normal state gap of $E_g \approx 74 \pm 15$ meV. It seems that the calculated $T_c$ from Coulomb interaction gives a majority fraction of experimental $T_c$ for recently determined values of $E_g$. The measured doping dependence of $T_c$ was satisfactorily reproduced as well. Also in agreement with experiments are the same set of calculations of the photoemission spectroscopy and density of states. The semiconducting state above and EI below $T_c$ together should give a coherent picture of $1T$-TiSe$_2$.

Distinct Quantum Anomalous Hall Ground States Induced by Magnetic Disorders

The quantum anomalous Hall (QAH) effect in a magnetic topological insulator (TI) represents a new state of matter originating from the interplay between topology and magnetism. The defining characteristics of the QAH ground state are the quantized Hall resistivity (ρyx) and vanishing longitudinal resistivity (ρxx) in the absence of an external magnetic field. A fundamental question concerning the QAH effect is whether it is merely a zero-magnetic-field quantum Hall (QH) effect or if it can host unique quantum phases and phase transitions that are unavailable elsewhere. The most dramatic departure of the QAH systems from other QH systems lies in the magnetic disorders that induce spatially random magnetization. Because disorder and magnetism play pivotal roles in the phase diagram of two-dimensional electron systems, the high degree of magnetic disorders in QAH systems may create novel phases and quantum critical phenomena. In this work, we perform systematic transport studies of a series of magnetic TIs with varied strength of magnetic disorders. We find that the ground state can be categorized into two distinct classes: the QAH phase and the anomalous Hall (AH) insulator phase, as the zero-magnetic-field counterparts of the QH liquid and Hall insulator phases in the QH systems. In the low-disorder limit of the QAH phase, we observe a universal quantized longitudinal resistance ρxx=h/e2 at the coercive field. In the AH insulator regime, we find that a magnetic field can drive it to the QAH phase through a quantum critical point with scaling behaviors that are distinct from those in the QH phase transition. We propose that the transmission between chiral edge states at domain boundaries, tunable by magnetic disorder and magnetic fields, is the key for determining the QAH ground state.Received 24 March 2020Accepted 29 October 2020DOI:https://doi.org/10.1103/PhysRevX.10.041063Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasQuantum anomalous Hall effectPhysical SystemsTopological insulatorsCondensed Matter, Materials & Applied Physics