Condensed-matter physics

  • Article
    | Open Access

    It is difficult to find magnetoelectric low-dimensional structures partly due to the lack of experimental techniques locally probing their physical nature. Here, the authors observe multiferroic ribbon-like domains in a non-multiferroic environment in MnWO4 by optical second harmonic generation.

    • Shingo Toyoda
    • , Manfred Fiebig
    •  & Naoki Ogawa
  • Article
    | Open Access

    Transition metal oxides exhibit a variety of correlated phases in their bulk form; however, they typically become insulators in the monolayer limit. Here, the authors report a correlated metallic state in a single-atomic layer of epitaxial SrRuO3, realized in epitaxial oxide heterostructure.

    • Byungmin Sohn
    • , Jeong Rae Kim
    •  & Changyoung Kim
  • Article
    | Open Access

    The mechanism of the charge density wave transition in quasi one-dimensional blue bronzes is still debated. Here, the authors report evidence of a Luttinger liquid in the normal state of blue bronzes and Holstein polarons below the transition temperature, revealing the important role of electron-phonon coupling in the transition.

    • L. Kang
    • , X. Du
    •  & L. X. Yang
  • Article
    | Open Access

    An exciton polaron is a quasiparticle composed of an exciton dressed with an electron-hole cloud, and this concept has been used to explain the ground excitonic states in charged monolayer transition metal dichalcogenides. Here the authors present experimental and theoretical evidence of exciton-polaron Rydberg states in monolayer MoSe2 and WSe2.

    • Erfu Liu
    • , Jeremiah van Baren
    •  & Chun Hung Lui
  • Article
    | Open Access

    The pseudogap phase in cuprate superconductors is predicted to be a pair density wave state (PDW) but experimental evidence has been lacking. Here, the authors detect the temperature evolution of energy gap modulations and scattering interference signature suggesting the Bi2Sr2CaDyCu2O8 pseudogap phase contains a PDW.

    • Shuqiu Wang
    • , Peayush Choubey
    •  & J. C. Séamus Davis
  • Article
    | Open Access

    While multiband superconductivity is the subject of extensive studies, the possibility of multiband charge density waves (CDW) remains elusive. Here, the authors report evidence of gap opening on both inner and outer bands by a CDW state in 2H-NbSe2, suggesting a possible multiband CDW.

    • Árpád Pásztor
    • , Alessandro Scarfato
    •  & Christoph Renner
  • Article
    | Open Access

    Single molecules on metal surfaces are paradigmatic systems for the study of many-body phenomena. Here, the authors show that several spectroscopic experiments on iron phthalocyanine on Au(111) surface can be described in a unified way in terms of a strongly interacting topologically non-trivial (non-Landau) Fermi liquid.

    • R. Žitko
    • , G. G. Blesio
    •  & A. A. Aligia
  • Article
    | Open Access

    A space-time crystal (STC) is a nonequilibrium phase of matter displaying long-range order in both space and time. Here, the authors propose that the high-Tc cuprate superconductor Bi2Sr2CaCu2O8+x is a candidate of a classical discrete STC, when a parametric modulation periodic in time and uniform in space is applied.

    • Reinhold Kleiner
    • , Xianjing Zhou
    •  & Dafei Jin
  • Article
    | Open Access

    The Kondo effect has been observed in a variety of systems, including carbon nanotube quantum dots and graphene in the presence of impurities. Here, the authors report the observation of the Kondo effect in bilayer graphene quantum dots and study its interplay with weak spin-orbit coupling.

    • Annika Kurzmann
    • , Yaakov Kleeorin
    •  & Klaus Ensslin
  • Article
    | Open Access

    The local variation of grain boundary atomic structure and chemistry caused by segregation of impurities influences the macroscopic properties of polycrystalline materials. Here, the effect of co-segregation of carbon and boron on the depletion of aluminum in a α − Fe grain boundary is shown.

    • A. Ahmadian
    • , D. Scheiber
    •  & G. Dehm
  • Article
    | Open Access

    Skyrmions, a topological spin texture, have been found in a variety of magnetic systems, including quantum hall ferromagnets. Here, Yang et al demonstrate the existence of skyrmions in domain walls in a quantum Hall ferromagnet, and suggest that these skyrmions form a 1D Wigner crystal.

    • Kaifeng Yang
    • , Katsumi Nagase
    •  & Hongwu Liu
  • Article
    | Open Access

    The band topology of nonmagnetic crystals can be characterized by Topological Quantum Chemistry (TQC), whereas the band topology of magnetic crystals remains unexplored. Here, the authors extend TQC to the magnetic space groups to form a complete, real-space theory of band topology in magnetic and nonmagnetic crystalline solids.

    • Luis Elcoro
    • , Benjamin J. Wieder
    •  & B. Andrei Bernevig
  • Article
    | Open Access

    Previous work has proposed that the anomalous and topological Hall effects, associated with Weyl nodes, should have a signature in optical conductivity. Here, using THz optical spectroscopy, the authors assign these two effects to optical conductivity resonances, arising near band anti-crossings, in thin films of MnGe.

    • Y. Hayashi
    • , Y. Okamura
    •  & Y. Takahashi
  • Article
    | Open Access

    A general theory for Floquet topology applicable to all crystalline symmetry groups is lacking. Here, the authors propose such a theory for noninteracting Floquet crystals and predict an inversion-protected Floquet higher-order topological phase with anomalous chiral hinge modes.

    • Jiabin Yu
    • , Rui-Xing Zhang
    •  & Zhi-Da Song
  • Article
    | Open Access

    An enhanced superconducting pairing temperature (Tg) has only been observed in single-layer FeSe interfaced with TiOx system. Here, the authors construct a new interface composed of single-layer FeSe interfaced with LaFeO3 showing a highest Tg of 80 K among all-known interfacial superconductors.

    • Yuanhe Song
    • , Zheng Chen
    •  & Donglai Feng
  • Article
    | Open Access

    Quasicrystals exhibit long-range order without periodicity. The authors report an approach for quasicrystal fabrication and show through in situ imaging and corresponding simulations the formation of a single decagonal quasicrystal arising from coalescence of multiple quasicrystals in a liquid.

    • Insung Han
    • , Kelly L. Wang
    •  & Ashwin J. Shahani
  • Article
    | Open Access

    Quantum spin liquid states are realized in systems with frustrated magnetic interactions. Here, the authors show that tunable frustrated spin-spin interactions can be induced by coupling a quantum antiferromagnet to the quantized light of a driven optical cavity, giving rise to robust quantum spin liquid states.

    • Alessio Chiocchetta
    • , Dominik Kiese
    •  & Sebastian Diehl
  • Article
    | Open Access

    While magnetism, hyperferroelectricity, and topological phases in the two-dimensional limit have been widely explored, the direct experimental study on bulk photovoltaic effect in 2D materials remains unimplemented. Here, the authors find bulk photovoltaic effect in 2D ferroelectric CuInP2S6.

    • Yue Li
    • , Jun Fu
    •  & Hualing Zeng
  • Article
    | Open Access

    Electron-phonon interaction is essential for understanding electronic and optical properties of lead halide perovskites. Here, using multiphonon Raman scattering and THz time-domain spectroscopy, the authors characterize the full phonon spectrum of CsPbBr3 and identify a single phonon mode that dominates electron-phonon scattering.

    • Claudiu M. Iaru
    • , Annalisa Brodu
    •  & Andrei Yu. Silov
  • Article
    | Open Access

    Sr3Ru2O7 exhibits a quantum critical point tunable by magnetic field and has been widely used in the study of criticality. Here, by using inelastic neutron scattering, the authors measure collective magnetic excitations near the quantum critical point and relate them to thermodynamic properties and spin density wave order.

    • C. Lester
    • , S. Ramos
    •  & S. M. Hayden
  • Article
    | Open Access

    Strontium Ruthenate, Sr2RuO4, displays a remarkable number of intriguing physical phenomena, from superconductivity, to strain-induced ferromagnetism. Here, using low-energy muon spectroscopy, Fittipaldi et al. demonstrate the existence of unconventional magnetism at the surface of Sr2RuO4 in its normal state and without any applied strain.

    • R. Fittipaldi
    • , R. Hartmann
    •  & A. Di Bernardo
  • Article
    | Open Access

    Superconductivity reported in metals driven away from equilibrium via optical pumping has been proposed to arise from nonlinear coupling between electrons and optically excited phonons. The authors use an exact approach to show that here, disorder, which disfavors superconductivity, emerges even though the system is translationally invariant.

    • John Sous
    • , Benedikt Kloss
    •  & Andrew J. Millis
  • Article
    | Open Access

    Assembling nanoparticles on surfaces has great technological potential. Here, Tierno et al demonstrate the confinement of magnetic nanoparticles in traps created by magnetic domain walls. The magnetic gradient and location of the domain walls can be finely tuned, allowing for precise control of the constituent nanoparticles.

    • Pietro Tierno
    • , Tom H. Johansen
    •  & Arthur V. Straube
  • Article
    | Open Access

    Strain glass is a new glassy state characterized by frozen ferroelastic nanodomains. Here, the authors discover a low-temperature feature in the specific heat of a strain glass, which is similar to the well-known boson peak anomaly of structural glasses, but cannot be explained by existing mechanisms.

    • Shuai Ren
    • , Hong-Xiang Zong
    •  & Wei-Hua Wang
  • Article
    | Open Access

    In classical wetting, the spreading of a drop on a surface is preceded by a bridge directly connecting the drop and the surface, yet it ignores the solubility of the drop phase in the medium. Here, the authors show that dissolved drop fluid from the parent drop can nucleate on the surface as islands, one of which coalesces with the parent drop to effect wetting.

    • Suraj Borkar
    •  & Arun Ramachandran
  • Article
    | Open Access

    The mechanisms responsible for the strongly correlated insulating and superconducting phases in twisted bilayer graphene are still debated. The authors provide a theory for phonon-dominated transport that explains several experimental observations, and contrast it with the Planckian dissipation mechanism.

    • Girish Sharma
    • , Indra Yudhistira
    •  & Shaffique Adam
  • Article
    | Open Access

    Here, the authors investigate the lattice dynamics of twisted hexagonal boron nitride layers via nano-infrared spectroscopy, showing local and stacking-dependent variations of the optical phonon frequencies associated to the interaction with the graphite substrate.

    • S. L. Moore
    • , C. J. Ciccarino
    •  & D. N. Basov
  • Article
    | Open Access

    An interest arises if energetic molecules and molecular ferroelectrics can be integrated together to obtain a chemically driven electricity conversion. Here, the authors explore energetic molecular ferroelectrics consisting of imidazolium cations and perchlorate anions with a high-power density.

    • Yong Hu
    • , Zhiyu Liu
    •  & Shenqiang Ren
  • Article
    | Open Access

    Berghoff et al. discover that polycrystalline MAPbI3 undergoes transient Wannier Stark localization at moderate field strengths, exhibiting substantial optical modulation with a fast response time. Since the polycrystallinity does not hinder the switching behaviour, this low-cost material is promising for light modulation and photonic applications.

    • Daniel Berghoff
    • , Johannes Bühler
    •  & Heejae Kim
  • Article
    | Open Access

    Three-dimensional topological insulators have become a research focal point on topological quantum matter. Here, the authors propose the non-Hermitian analogue, the exceptional topological insulator, with anomalous surface states only existing within the topological bulk embedding.

    • M. Michael Denner
    • , Anastasiia Skurativska
    •  & Titus Neupert
  • Article
    | Open Access

    Twisted van der Waals systems are known to host flat electronic bands, originating from moire potential. Here, the authors predict from purely geometric considerations a new type of nearly dispersionless bands in twisted bilayer MoS2, resulting from destructive interference between effective lattice hopping matrix elements.

    • Lede Xian
    • , Martin Claassen
    •  & Angel Rubio
  • Article
    | Open Access

    Naturally occurring hyperbolic polaritons exist in a class of layered materials. Here, the authors show evidence, via optical spectroscopy, of hyperbolic exciton-polaritons in phosphorene, originating from its in-plane anisotropy and strong exciton resonances.

    • Fanjie Wang
    • , Chong Wang
    •  & Hugen Yan
  • Article
    | Open Access

    Merons and Skyrmions, two topological spin-textures, have attracted a lot of interests due to their potential use in information storage. Here, the authors demonstrate the transformation of Meron pairs into Skyrmions without an applied magnetic field within domain walls of GdFeCo films.

    • Zhuolin Li
    • , Jian Su
    •  & Baogen Shen
  • Article
    | Open Access

    It was predicted that lattice reconstruction can lead to the emergence of multiple ultra-flat electronic bands in twisted bilayer transition metal dichalcogenides. Here, by using scanning tunneling microscopy and spectroscopy, the authors demonstrate such bands in twisted bilayer WSe2.

    • En Li
    • , Jin-Xin Hu
    •  & Nian Lin
  • Article
    | Open Access

    The quantum anomalous Hall effect has so far been limited to temperature of the order of 20 mK. Here, Fijalkowski et al. report the existence of chiral edge channels up to the Curie temperature of bulk ferromagnetism of the magnetic topological insulator with a multi-terminal Corbino geometry.

    • Kajetan M. Fijalkowski
    • , Nan Liu
    •  & Laurens W. Molenkamp
  • Article
    | Open Access

    The X-ray magnetic circular dichroism detection of magnetic octupole moment has not been experimentally demonstrated so far. Here, the authors observe ferroic order of magnetic octupole in Mn3Sn, finding the exotic material functionalities related to the multipole order.

    • Motoi Kimata
    • , Norimasa Sasabe
    •  & Tetsuya Nakamura
  • Article
    | Open Access

    Point defects compromise the electronic performance of hybrid perovskites, yet no experimental identifications have been reported. Here, the authors, for the first time, identify lead monovacancy defect in MAPbI3 using positron annihilation lifetime spectroscopy with the aid of density functional theory.

    • David J. Keeble
    • , Julia Wiktor
    •  & Werner Egger
  • Article
    | Open Access

    Semiconductor microcavities allow engineering of artificial lattices with optical write-in and read-out of information. Here, the authors show an optically imprinted system of exciton-polaritons arranged in a Lieb lattice and reveal a nonequilibrium transition from scattered- to trapped polariton condensates.

    • S. Alyatkin
    • , H. Sigurdsson
    •  & P. G. Lagoudakis
  • Article
    | Open Access

    The behaviour of Tungsten ditelluride (WTe2) in few-layer form is not yet fully characterized. Here the authors use a near-field terahertz microscopy technique to observe the electromagnetic responses of WTe2 flakes from one to several layers and to study their semimetallic/ semiconducting behavior.

    • Ran Jing
    • , Yinming Shao
    •  & D. N. Basov
  • Article
    | Open Access

    The honeycomb lattice with a spin-orbit interaction can give rise to exotic quantum states. With the measurements of bulk properties and inelastic neutron scattering, Lin et al demonstrate the existence of a field induced spin-disordered state in Na2Co2TeO6 and extend the Kitaev model to 3d system.

    • Gaoting Lin
    • , Jaehong Jeong
    •  & Jie Ma
  • Article
    | Open Access

    Graphene nanoribbons are potential systems for engineering topological phases of matter, but the pre-required gapped phases are difficult to find. Here, the authors show that chiral graphene nanoribbons undergo a transition from metallic to topological insulators, and then to trivial band insulators as they are narrowed down to nanometer widths.

    • Jingcheng Li
    • , Sofia Sanz
    •  & Jose Ignacio Pascual
  • Article
    | Open Access

    Resistive switching usually occurs by the formation of conducting filaments in the direction of current flow. Here the authors study an intriguing type of volatile metal-to-insulator resistive switching in (La,Sr)MnO3, which occurs by the formation of an insulating barrier perpendicular to the current.

    • Pavel Salev
    • , Lorenzo Fratino
    •  & Ivan K. Schuller
  • Article
    | Open Access

    Valley anisotropy is proposed theoretically to benefit the electrical transport of thermoelectric materials but it lacks experimental demonstration. Here, the authors demonstrate how to utilize the single anisotropic Fermi pocket in p-type Mg3Sb2 to enhance its thermoelectric properties.

    • Airan Li
    • , Chaoliang Hu
    •  & Tiejun Zhu
  • Article
    | Open Access

    Here, the authors report on evidence of an excitonic species formed by electrons in high-energy conduction band states with a negative effective mass, explaining previous observations of quantum interference phenomena in two-dimensional semiconductors.

    • Kai-Qiang Lin
    • , Chin Shen Ong
    •  & John M. Lupton
  • Article
    | Open Access

    Several hydrides have been observed high-Tc superconductivity under pressure, but a physical-chemical understanding of the properties enhancing Tc is still lacking. Here, the authors propose a magnitude named as networking value, combined with hydrogen fraction and the contribution of hydrogen to the density of states at Fermi level, can predict Tc of all hydrogen-based compounds with an accuracy of about 60 K.

    • Francesco Belli
    • , Trinidad Novoa
    •  & Ion Errea
  • Article
    | Open Access

    Magic-angle twisted bilayer graphene exhibits a quantum anomalous Hall effect at 3/4 filling; however, its mechanism is debated. Here, the authors show that such a phase can be realized in a lattice model of twisted bilayer graphene in the strong coupling limit, and interpret the results in terms of a topological Mott insulator phase.

    • Bin-Bin Chen
    • , Yuan Da Liao
    •  & Zi Yang Meng