scholarly journals Lattice fluctuation induced pseudogap in quasi-one-dimensional Ta2NiSe5

2021 ◽  
Author(s):  
Yu He ◽  
Cheng Chen ◽  
Xiang Chen ◽  
Weichen Tang ◽  
Zhenglu Li ◽  
...  
Keyword(s):  
Energy Gap ◽  
Density Wave ◽  
Spectral Weight ◽  
Global Symmetry ◽  
Model Calculations ◽  
Lattice Contribution ◽  
Strongly Correlated Materials ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Charge Localization ◽  
Low Dimensional

Abstract In conventional solid-state systems, the development of an energy gap is often associated with a broken symmetry. However, strongly correlated materials can exhibit energy gaps without any global symmetry breaking -- the so-called pseudogap, most notably in the Mott insulating state1 and the fluctuating superconducting or charge density wave states. To date, lattice induced pseudogap remains elusive. With angle-resolved photoemission spectroscopy (ARPES) and single crystal x-ray diffraction, we identify a pseudogap in the quasi-1D excitonic insulator candidate Ta2NiSe5. Strong lattice contribution is revealed by the pervasive diffuse scattering well above the transition temperature and the negative electronic compressibility in the pseudogap state. Combining first-principles and microscopic model calculations, we show that inter-band electron-phonon coupling can create fluctuating phonon-mediated electron-hole pairing or hybridization. This suppresses the spectral weight on the Fermi surface, causing a metal-to-insulator-like transition without breaking the global symmetry. Our work establishes the precedence of a pseudogap with a lattice origin, highlighting Ta2NiSe5 as a room-temperature platform to study lattice-induced charge localization and low dimensional fluctuations.

scholarly journals Unveiling the electronic transformations in the semi-metallic correlated-electron transitional oxide Mo8O23

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
V. Nasretdinova ◽  
Ya. A. Gerasimenko ◽  
J. Mravlje ◽  
G. Gatti ◽  
P. Sutar ◽  
...  
Keyword(s):  
Density Functional ◽  
Density Wave ◽  
Functional Materials ◽  
Functional Theory ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Correlated Electron ◽  
Carrier Scattering ◽  
Gap Opening ◽  
Metal To Insulator Transition ◽  
Low Dimensional

Abstract Mo8O23 is a low-dimensional chemically robust transition metal oxide coming from a prospective family of functional materials, MoO3−x, ranging from a wide gap insulator (x = 0) to a metal (x = 1). The large number of stoichometric compounds with intermediate x have widely different properties. In Mo8O23, an unusual charge density wave transition has been suggested to occur above room temperature, but its low temperature behaviour is particularly enigmatic. We present a comprehensive experimental study of the electronic structure associated with various ordering phenomena in this compound, complemented by theory. Density-functional theory (DFT) calculations reveal a cross-over from a semi-metal with vanishing band overlap to narrow-gap semiconductor behaviour with decreasing temperature. A buried Dirac crossing at the zone boundary is confirmed by angle-resolved photoemission spectroscopy (ARPES). Tunnelling spectroscopy (STS) reveals a gradual gap opening corresponding to a metal-to-insulator transition at 343 K in resistivity, consistent with CDW formation and DFT results, but with large non-thermal smearing of the spectra implying strong carrier scattering. At low temperatures, the CDW picture is negated by the observation of a metallic Hall contribution, a non-trivial gap structure in STS below ∼170 K and ARPES spectra, that together represent evidence for the onset of the correlated state at 70 K and the rapid increase of gap size below ∼30 K. The intricate interplay between electronic correlations and the presence of multiple narrow bands near the Fermi level set the stage for metastability and suggest suitability for memristor applications.

scholarly journals Incommensurate two-dimensional checkerboard charge density wave in the low-dimensional superconductor Ta4Pd3Te16

2020 ◽  
Vol 2 (4) ◽  
Author(s):  
Zhenzhong Shi ◽  
S. J. Kuhn ◽  
F. Flicker ◽  
T. Helm ◽  
J. Lee ◽  
...  
Keyword(s):  
Charge Density ◽  
Charge Density Wave ◽  
Density Wave ◽  
Two Dimensional ◽  
Low Dimensional

scholarly journals Global symmetry, Euclidean gravity, and the black hole information problem

2021 ◽  
Vol 2021 (4) ◽  
Author(s):  
Daniel Harlow ◽  
Edgar Shaghoulian
Keyword(s):  
Black Hole ◽  
Quantum Gravity ◽  
Global Symmetries ◽  
Close Connection ◽  
Usual Sense ◽  
Global Symmetry ◽  
Recent Argument ◽  
Black Hole Information ◽  
Information Problem ◽  
Low Dimensional

Abstract In this paper we argue for a close connection between the non-existence of global symmetries in quantum gravity and a unitary resolution of the black hole information problem. In particular we show how the essential ingredients of recent calculations of the Page curve of an evaporating black hole can be used to generalize a recent argument against global symmetries beyond the AdS/CFT correspondence to more realistic theories of quantum gravity. We also give several low-dimensional examples of quantum gravity theories which do not have a unitary resolution of the black hole information problem in the usual sense, and which therefore can and do have global symmetries. Motivated by this discussion, we conjecture that in a certain sense Euclidean quantum gravity is equivalent to holography.

scholarly journals Nanostructured and Modulated Low-Dimensional Systems

2013 ◽  
Vol 203-204 ◽  
pp. 42-47
Author(s):  
Albert Prodan ◽  
Herman J.P. van Midden ◽  
Erik Zupanič ◽  
Rok Žitko
Keyword(s):  
Charge Density ◽  
Structural Information ◽  
Density Wave ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Additional Information ◽  
Related Pair ◽  
Good Accord ◽  
Long Range Ordering ◽  
Low Dimensional

Charge density wave (CDW) ordering in NbSe3 and the structurally related quasi one-dimensional compounds is reconsidered. Since the modulated ground state is characterized by unstable nano-domains, the structural information obtained from diffraction experiments is to be supplemented by some additional information from a method, able to reveal details on a unit cell level. Low-temperature (LT) scanning tunneling microscopy (STM) can resolve both, the local atomic structure and the superimposed charge density modulation. It is shown that the established model for NbSe3 with two incommensurate (IC) modes, q1 = (0,0.241,0) and q2 = (0.5,0.260,0.5), locked in at T1=144K and T2=59K and separately confined to two of the three available types of bi-capped trigonal prismatic (BCTP) columns, must be modified. The alternative explanation is based on the existence of modulated layered nano-domains and is in good accord with the available LT STM results. These confirm i.a. the presence of both IC modes above the lower CDW transition temperature. Two BCTP columns, belonging to a symmetry-related pair, are as a rule alternatively modulated by the two modes. Such pairs of columns are ordered into unstable layered nano-domains, whose q1 and q2 sub-layers are easily interchanged. The mutually interchangeable sections of the two unstable IC modes keep a temperature dependent long-range ordering. Both modes can formally be replaced by a single highly inharmonic long-period commensurate CDW.

scholarly journals Emergence of quasiparticles in a doped Mott insulator

2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Yao Wang ◽  
Yu He ◽  
Krzysztof Wohlfeld ◽  
Makoto Hashimoto ◽  
Edwin W. Huang ◽  
...  
Keyword(s):  
Hubbard Model ◽  
Single Layer ◽  
Mott Insulator ◽  
Spectral Weight ◽  
Particle Spectrum ◽  
Electron Hole ◽  
Strong Electron ◽  
Side Band ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Weakly Coupled

AbstractHow a Mott insulator develops into a weakly coupled metal upon doping is a central question to understanding various emergent correlated phenomena. To analyze this evolution and its connection to the high-Tc cuprates, we study the single-particle spectrum for the doped Hubbard model using cluster perturbation theory on superclusters. Starting from extremely low doping, we identify a heavily renormalized quasiparticle dispersion that immediately develops across the Fermi level, and a weakening polaronic side band at higher binding energy. The quasiparticle spectral weight roughly grows at twice the rate of doping in the low doping regime, but this rate is halved at optimal doping. In the heavily doped regime, we find both strong electron-hole asymmetry and a persistent presence of Mott spectral features. Finally, we discuss the applicability of the single-band Hubbard model to describe the evolution of nodal spectra measured by angle-resolved photoemission spectroscopy (ARPES) on the single-layer cuprate La2−xSrxCuO4 (0 ≤ x ≤ 0.15). This work benchmarks the predictive power of the Hubbard model for electronic properties of high-Tc cuprates.

scholarly journals Ultrafast electron calorimetry uncovers a new long-lived metastable state in 1T-TaSe2 mediated by mode-selective electron-phonon coupling

2019 ◽  
Vol 5 (3) ◽  
pp. eaav4449 ◽  
Author(s):  
Xun Shi ◽  
Wenjing You ◽  
Yingchao Zhang ◽  
Zhensheng Tao ◽  
Peter M. Oppeneer ◽  
...  
Keyword(s):  
Heat Capacity ◽  
Metastable State ◽  
Density Wave ◽  
Charge Order ◽  
Phonon Coupling ◽  
Phonon Modes ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Quantum Matter ◽  
Electron Phonon Coupling ◽  
Equilibrium Phases

Quantum materials represent one of the most promising frontiers in the quest for faster, lightweight, energy-efficient technologies. However, their inherent complexity and rich phase landscape make them challenging to understand or manipulate. Here, we present a new ultrafast electron calorimetry technique that can systematically uncover new phases of quantum matter. Using time- and angle-resolved photoemission spectroscopy, we measure the dynamic electron temperature, band structure, and heat capacity. This approach allows us to uncover a new long-lived metastable state in the charge density wave material 1T-TaSe2, which is distinct from all the known equilibrium phases: It is characterized by a substantially reduced effective total heat capacity that is only 30% of the normal value, because of selective electron-phonon coupling to a subset of phonon modes. As a result, less energy is required to melt the charge order and transform the state of the material than under thermal equilibrium conditions.

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