Performance characteristics of several new types of photomultiplier tubes (PMT) with microchannel plates (MCP) are presented in this paper. They are the MCP-PMT with 6-microm diam channels, MCP-PMT with an S-l photocathode, and MCP-PMT with multi (discrete) anode and gatable MCP-PMT. Important requirements of an optical detector for picosecond lasers, fluorescence measurements, and material analysis are low light detectability, ultrafast time response, and versatile operation including modulation. The basic configuration, characteristics, and practical results of these detectors are described.

Charge-density-waves, which occur mainly in low-dimensional systems, have a macroscopic wave function similar to superfluids and superconductors. Kosterlitz-Thouless transition is observed in superfluids and superconductors, but the presence of Kosterlitz-Thouless transition in ultra-thin charge-density-waves systems has been an open problem. We report the direct realspace observation of charge-density-waves with new order states in mono-layer, bi-layer, and tri-layer 1T-TaS 2 crystals using a low voltage scanning-transmission-electron-microscopy without a substrate. This method is ideal to observe local atomic structures and possible defects. We clearly observed that the mono-layer crystal has a new triclinic stripe charge-density-waves order without satisfying the triple q condition q 1 + q 2 + q 3 = 0. A strong electron-phonon interaction gives rise to new crevasse (line) type defects instead of disclination (point) type defects due to the Kosterlitz-Thouless transition. These results reaffirm the importance of the electron-phonon interaction in mono-layer nanophysics.npj Quantum Materials (2017) 2:22 ; doi:10.1038/s41535-017-0025-8 INTRODUCTION Dimensionality and topology are the most important parameters characterizing physical systems. For example, the integral and fractional quantum Hall effects (QHE) 1, 2 are observed only in two-dimensional systems such as metal-oxide-semiconductor field-effect transistors, GaAs/AlGaAs interfaces, and graphene.

We show that time translation symmetry of a ring system with a macroscopic quantum ground state is broken by decoherence. In particular, we consider a ring-shaped incommensurate charge density wave (ICDW ring) threaded by a fluctuating magnetic flux: the Caldeira-Leggett model is used to model the fluctuating flux as a bath of harmonic oscillators. We show that the charge density expectation value of a quantized ICDW ring coupled to its environment oscillates periodically. The Hamiltonians considered in this model are time independent unlike "Floquet time crystals" considered recently. Our model forms a metastable quantum time crystal with a finite length in space and in time.

Ultrathin sheets of transition metal dichalcogenides (MX 2 ) with charge density waves (cDWs) is increasingly gaining interest as a promising candidate for graphene-like devices. Although experimental data including stripe/quasi-stripe structure and hidden states have been reported, the ground state of ultrathin MX 2 compounds and, in particular, the origin of anisotropic (stripe and quasi-stripe) cDW phases is a long-standing problem. Anisotropic cDW phases have been explained by coulomb interaction between domain walls and inter-layer interaction. However, these models assume that anisotropic domain walls can exist in the first place. Here, we report that anisotropic CDW domain walls can appear naturally without assuming anisotropic interactions: We explain the origin of these phases by topological defect theory (line defects in a two-dimensional plane) and interference between harmonics of macroscopic cDW wave functions. We revisit the McMillan-nakanishi-Shiba model for monolayer 1T-taS 2 and 2H-taSe 2 and show that CDWs with wave vectors that are separated by 120° (i.e. the three-fold rotation symmetry of the underlying lattice) contain a free-energy landscape with many local minima. Then, we remove this 120° constraint and show that free energy local minima corresponding to the stripe and quasi-stripe phases appear. our results imply that coulomb interaction between domain walls and inter-layer interaction may be secondary factors for the appearance of stripe and quasi-stripe CDW phases. Furthermore, this model explains our recent experimental result (appearance of the quasi-stripe structure in monolayer 1T-taS 2 ) and can predict new CDW phases, hence it may become the basis to study cDW further. We anticipate our results to be a starting point for further study in two-dimensional physics, such as explanation of "Hidden CDW states", study the interplay between supersolid symmetry and lattice symmetry, and application to other van der Waals structures.Usually, anisotropic structures such as stripe phases can be explained by anisotropic interaction between the constituent atoms, electrons, or liquid crystal polymers 1 . Anisotropic structures in charge density waves (CDWs) have been explained likewise. CDWs are periodic modulations of electric charge density in low-dimensional conductors 2-6 . The stability of CDWs containing stripe domain walls 7,8 was first studied by free energy theories 9,10 . But these theories assumed that stripe domain walls can exist in the first place, probably due to weak computational facilities at that time. The appearance of stripe domain walls and quasi-stripe (triclinic) domain walls 8,11,12 has been explained by Coulomb interaction between domain walls 13 and three-dimensional stacking 14 . However, are these interactions indispensable? It would be ideal to have rich structures with the least amount of interactions.In this article we report that stripe and quasi-stripe CDW domain walls can appear without anisotropic interactions and explain the origin of these phases by topolo...

We investigate time operators in the context of quantum time crystals in ring systems. A generalized commutation relation called the generalized weak Weyl relation is used to derive a class of self-adjoint time operators for ring systems with a periodic time evolution: The conventional Aharonov-Bohm time operator is obtained by taking the infinite-radius limit. Then, we discuss the connection between time operators, time crystals and real-space topology. We also reveal the relationship between our time operators and a PT -symmetric time operator. These time operators are then used to derive several energy-time uncertainty relations.