Strong Transverse Field Research Articles

Halobenzene Adducts of a Dysprosocenium Single-Molecule Magnet.

Dysprosium complexes with strong axial crystal fields are promising candidates for single-molecule magnets (SMMs), which could be used for high-density data storage. Isolated dysprosocenium cations, [Dy(CpR)2]+ (CpR = substituted cyclopentadienyl), have recently shown magnetic hysteresis (a memory effect) above the temperature of liquid nitrogen. Synthetic efforts have focused on reducing strong transverse ligand fields in these systems as they are known to enhance magnetic relaxation by spin-phonon mechanisms. Here we show that equatorial coordination of the halobenzenes PhX (X = F, Cl, Br) and o-C6H4F2 to the cation of a recently reported dysprosocenium complex [Dy(Cpttt)(Cp*)][Al{OC(CF3)3}4] (Cpttt = C5H2tBu3-1,2,4; Cp* = C5Me5) reduces magnetic hysteresis temperatures compared to that of the parent cation. We find that this is due to increased effectiveness of both one- (Orbach) and two-phonon (Raman) relaxation mechanisms, which correlate with the electronegativity and number of interactions with the halide despite κ1-coordination of a single halobenzene having a minimal effect on the metrical parameters of [Dy(Cpttt)(Cp*)(PhX-κ1-X)]+ cations vs the isolated [Dy(Cpttt)(Cp*)]+ cation. We observe unusual divergent behavior of relaxation rates at low temperatures in [Dy(Cpttt)(Cp*)(PhX)][Al{OC(CF3)3}4], which we attribute to a phonon bottleneck effect. We find that, despite the transverse fields introduced by the monohalobenzenes in these cations, the interactions are sufficiently weak that the effective barriers to magnetization reversal remain above 1000 cm-1, being only ca. 100 cm-1 lower than for the parent complex, [Dy(Cpttt)(Cp*)][Al{OC(CF3)3}4].

Electro-optic properties of liquid crystal cells with nanowall electrodes

This work fabricates a nanowall electrode for achieving advanced liquid crystal (LC) devices and improving LC displays. The nanowall electrode consists of indium–tin–oxide (ITO) sheets stacked with nanowalls, and the nanowalls have a height and thickness of 4 µm and 500 nm, respectively. The high aspect ratio (8.0) of the nanowalls sets the nanowall electrode apart from previous electrodes. A flat electrode that comprises only ITO sheets is used to evaluate the nanowall electrode. The LC cell with the nanowall electrode exhibits better electro-optic properties than the LC cell with the flat electrode due to the strong transverse electric field and small subelectrode gap of the nanowall electrode. Especially, the operating voltage (3.7 V) of the nanowall cell is 36% smaller than that (5.8 V) of the flat cell. Therefore, nanowall electrodes have potential in LC lenses, LC antennas, metaverse displays, and digital optics.

Evaluation of the transfer matrix of a plasma ramp with squared cosine shape via an approximate solution of Mathieu differential equation

The high longitudinal electric fields generated in plasma wakefields are very attractive for a new generation of high gradient plasma based accelerators. On the other hand, the strong transverse fields increase the demand for a proper matching device in order to avoid the spoiling of beam transverse quality. A solution can be provided by the use of a plasma ramp, a region at the plasma injection/extraction with smoothly increasing/decreasing plasma density. The transport of a beam inside a plasma ramp, beside its parameters, depends on the profile of the ramp itself. Establishing the transfer matrix for a plasma ramp represent a very useful tool in order to evaluate the beam evolution in the plasma. In this paper a study of a cosine squared ramp is presented. An approximate solution of the transverse equation of motion is evaluated and exploited to provide a simple transfer matrix for the plasma ramp. The transfer matrix is then employed to demonstrate that this kind of ramp has the effect to minimize the emittance growth due to betatron dephasing. The behavior of a squared cosine plasma ramp will be compared with an experimentally measured plasma ramp profile in order to validate the applicability of the transfer matrix to real cases.

Resonant silicon waveguide with strong transverse electric field rotation for magnetic-field-induced non-reciprocity.

Non-reciprocal devices suitable for on-chip implementation are of high importance in modern photonics. In most cases, non-reciprocity is caused by the magneto-optical effect. At the same time, the external magnetic field is convenient to apply in the normal direction to the chip plane, which leads to Voigt geometry and modes with in-plane transverse rotations of the electric field. Here, we propose two resonant magnetic material-free silicon waveguides supporting such modes. The first one is a rectangular waveguide with air holes inside, whose modes have higher rotations at the telecom wavelength, but the silicon thickness is non-standard. The second one is based on a 220-nm-thick silicon waveguide compatible with commercially available silicon-on-insulator wafers. We also propose the scheme of an optical isolator based on a Mach-Zehnder interferometer with a rotation elements delay in its arms.

Pyroelectric deflector of relativistic electron beam

Deflection of a relativistic electron beam by means of the pyroelectric deflector is demonstrated experimentally for the first time. The operating principle of the pyroelectric deflector is based on the generation of a strong transverse electric field in a vacuum in the gap between a pair of pyroelectric crystals due to the pyroelectric effect. The experiments on observation of deflection of 7 MeV electron beam for 26 mrad in the transverse electric field with a strength of about 100 kV/cm arising at a variation of the temperature of a pair of pyroelectric crystals in vacuum are described. The possibility for application of the installed sequentially pyroelectric deflectors in pyroelectric undulator for production of undulator radiation by relativistic electron beam without any external high voltage power supply is discussed.

Van Allen Probes Observations of Symmetric Stormtime Compressional ULF Waves.

Previous spacecraft studies showed that stormtime poloidal ultralow‐frequency (ULF) waves in the ring current region have an antisymmetric (second harmonic) mode structure about the magnetic equator. This paper reports Van Allen Probes observations of symmetric ULF waves in the postnoon sector during a moderate geomagnetic storm. The mode structure is determined from the presence of purely compressional magnetic field oscillations at the equator accompanied by strong transverse electric field perturbations. Antisymmetric waves were also detected but only very late in the recovery phase. The symmetric waves were detected outside the plasmasphere at L = 3.0–5.5 and had peak power at 4–10 mHz, lower than the frequency of the local fundamental toroidal standing Alfvén wave. During the wave events, the flux of protons was enhanced at energies below ∼5 keV, which appears to be a prerequisite for the waves. The protons may provide free energies to waves through drift resonance instability or drift compressional instability, which occur in the presence of radial gradients of plasma parameters.

Quantum simulation of lattice gauge theories on superconducting circuits: Quantum phase transition and quench dynamics

Recently, quantum simulation of low-dimensional lattice gauge theories (LGTs) has attracted many interests, which may improve our understanding of strongly correlated quantum many-body systems. Here, we propose an implementation to approximate ℤ2 LGT on superconducting quantum circuits, where the effective theory is a mixture of a LGT and a gauge-broken term. By using matrix product state based methods, both the ground state properties and quench dynamics are systematically investigated. With an increase of the transverse (electric) field, the system displays a quantum phase transition from a disordered phase to a translational symmetry breaking phase. In the ordered phase, an approximate Gauss law of the ℤ2 LGT emerges in the ground state. Moreover, to shed light on the experiments, we also study the quench dynamics, where there is a dynamical signature of the spontaneous translational symmetry breaking. The spreading of the single particle of matter degree is diffusive under the weak transverse field, while it is ballistic with small velocity for the strong field. Furthermore, due to the emergent Gauss law under the strong transverse field, the matter degree can also exhibit confinement dynamics which leads to a strong suppression of the nearest-neighbor hopping. Our results pave the way for simulating the LGT on superconducting circuits, including the quantum phase transition and quench dynamics.

Nanomaterials Based Nanoplasmonic Accelerators and Light-Sources Driven by Particle-Beams

Unprecedented tens of TVm−1 fields are modeled to be realizable using novel nanoplasmonic surface crunch-in modes in nanomaterials. These relativistic nonlinear surface modes are accessible due to advances in nanofabrication and quasi-solid density sub-micron particle bunch compression. Proof of principle of TVm−1 plasmonics is provided using three-dimensional computational and analytical modeling of GeV scale energy gain in sub-millimeter long tubes having nanomaterial walls with controllable free-electron densities, $n_{\mathrm t}\sim 10^{22-24}\mathrm {cm^{-3}}$ and hundreds of nanometer core radius driven by quasi-solid electron beams, $n_{\mathrm b}\sim 0.01n_{\mathrm t}$ . Besides the tens of TeVm−1 acceleration gradients, equally strong transverse fields lead to self-focusing and nanomodulation of the beam which drive extreme beam compression to ultra-solid peak densities increasing the crunch-in field strength. Apart from ultra-solid particle beams, extreme focusing also opens up a nano-wiggler like tunable coherent $\mathrm {\mathcal {O}(100MeV)}$ ultra-dense photon source.

Probing eigenstate thermalization in quantum simulators via fluctuation-dissipation relations

The eigenstate thermalization hypothesis (ETH) offers a universal mechanism for the approach to equilibrium of closed quantum many-body systems. So far, however, experimental studies have focused on the relaxation dynamics of observables as described by the diagonal part of ETH, whose verification requires substantial numerical input. This leaves many of the general assumptions of ETH untested. Here, we propose a theory-independent route to probe the full ETH in quantum simulators by observing the emergence of fluctuation-dissipation relations, which directly probe the off-diagonal part of ETH. We discuss and propose protocols to independently measure fluctuations and dissipations as well as higher-order time ordered correlation functions. We first show how the emergence of fluctuation dissipation relations from a nonequilibrium initial state can be observed for the 2D Bose-Hubbard model in superconducting qubits or quantum gas microscopes. Then we focus on the long-range transverse field Ising model (LTFI), which can be realized with trapped ions. The LTFI exhibits rich thermalization phenomena: For strong transverse fields, we observe prethermalization to an effective magnetization-conserving Hamiltonian in the fluctuation dissipation relations. For weak transverse fields, confined excitations lead to non-thermal features resulting in a violation of the fluctuation-dissipation relations up to long times. Moreover, in an integrable region of the LTFI, thermalization to a generalized Gibbs ensemble occurs and the fluctuation-dissipation relations enable an experimental diagonalization of the Hamiltonian. Our work presents a theory-independent way to characterize thermalization in quantum simulators and paves the way to quantum simulate condensed matter pump-probe experiments.

Diffusion of heavy quarks in the early stage of high-energy nuclear collisions at energies available at the BNL Relativistic Heavy Ion Collider and at the CERN Large Hadron Collider

We study the diffusion of charm and beauty in the early stage of high energy nuclear collisions at RHIC and LHC energies, considering the interaction of these heavy quarks with the evolving Glasma by means of the Wong equations. In comparison with previous works, we add the longitudinal expansion as well as we estimate the effect of energy loss due to gluon radiation. We find that heavy quarks diffuse in the strong transverse color fields in the very early stage (0.2-0.3 fm/c) and this leads to a suppression at low $p_T$ and enhancement at intermediate low $p_T$. The shape of the observed nuclear suppression factor obtained within our calculations is in qualitative agreement with the experimental results of the same quantity for $D-$mesons in proton-nucleus collisions. We compute the nuclear suppression factor in nucleus-nucleus collisions as well, for both charm and beauty, finding a substantial impact of the evolving Glasma phase on these, suggesting that initialization of heavy quarks spectra in the quark-gluon plasma phase should not neglect the early evolution in the strong gluon fields.

Transverse field effects on the competition between antiferromagnetic and cluster spin-glass phases.

We investigate a disordered cluster Ising antiferromagnet in the presence of a transverse field. By adopting a replica cluster mean-field framework, we analyze the role of quantum fluctuations in a model with competing short-range antiferromagnetic and intercluster disordered interactions. The model exhibits paramagnetic (PM), antiferromagnetic (AF), and cluster spin-glass (CSG) phases, which are separated by thermal and quantum phase transitions. A scenario of strong competition between AF and CSG unveils a number of interesting phenomena induced by quantum fluctuations, including a quantum PM state and quantum driven criticality. The latter occurs when the thermally driven PM-AF discontinuous phase transition becomes continuous at strong transverse fields. Analogous phenomena have been reported in a number of systems, but a description of underlying mechanisms is still required. Our results indicate that quantum driven criticality can be found in a highly competitive regime of disordered antiferromagnets, which is in consonance with recent findings in spin models with competing interactions.

Gully quantum Hall ferromagnetism in biased trilayer graphene

Multilayer graphene lattices allow for an additional tunability of the band structure by the strong perpendicular electric field. In particular, the emergence of the new multiple Dirac points in ABA stacked trilayer graphene subject to strong transverse electric fields was proposed theoretically and confirmed experimentally. These new Dirac points dubbed ``gullies'' emerge from the interplay between strong electric field and trigonal warping. In this work we first characterize the properties of new emergent Dirac points and show that the electric field can be used to tune the distance between gullies in the momentum space. We demonstrate that the band structure has multiple Lifshitz transitions and higher-order singularity of ``monkey saddle'' type. Following the characterization of the band structure, we consider the spectrum of Landau levels and structure of their wave functions. In the limit of strong electric fields when gullies are well separated in momentum space, they give rise to triply degenerate Landau levels. In the second part of this work, we investigate how degeneracy between three gully Landau levels is lifted in presence of interactions. Within the Hartree-Fock approximation we show that the symmetry breaking state interpolates between fully gully polarized state that breaks $C_3$ symmetry at high displacement field, and the gully symmetric state when the electric field is decreased. The discontinuous transition between these two states is driven by enhanced inter-gully tunneling and exchange. We conclude by outlining specific experimental predictions for the existence of such a symmetry-breaking state.

New varieties of helical undulators

A helix magnetized along the axis can be used as an undulator with a fairly strong transverse field. Two such helices with the opposite direction of magnetization and shifted relative to each other create a field that is twice as strong. It has been shown, both theoretically and experimentally, that helical undulator fields can also be created due to the redistribution of the uniform magnetic field of the solenoid by ferromagnetic or well-conducting insertions as well as by various combinations of these elements. Use of such undulators in electron sources of terahertz radiation is promising for a significant enhancement of both emitted power and frequency.

Solid-state tube wakefield accelerator using surface waves in crystals

Solid-state or crystal acceleration has for long been regarded as an attractive frontier in advanced particle acceleration. However, experimental investigations of solid-state acceleration mechanisms which offer [Formula: see text] acceleration gradients have been hampered by several technological constraints. The primary constraint has been the unavailability of attosecond particle or photon sources suitable for excitation of collective modes in bulk crystals. Secondly, there are significant difficulties with direct high-intensity irradiation of bulk solids, such as beam instabilities due to crystal imperfections and collisions etc. Recent advances in ultrafast technology with the advent of submicron long electron bunches and thin-film compressed attosecond x-ray pulses have now made accessible ultrafast sources that are nearly the same order of magnitude in dimensions and energy density as the scales of collective electron oscillations in crystals. Moreover, nanotechnology enabled growth of crystal tube structures not only mitigates the direct high-intensity irradiation of materials, with the most intense part of the ultrafast source propagating within the tube but also enables a high degree of control over the crystal properties. In this work, we model an experimentally practicable solid-state acceleration mechanism using collective electron oscillations in crystals that sustain propagating surface waves. These surface waves are driven in the wake of a submicron long particle beam, ideally also of submicron transverse dimensions, in tube shaped nanostructured crystals with tube wall densities, [Formula: see text]. Particle-In-Cell (PIC) simulations carried out under experimental constraints demonstrate the possibility of accessing average acceleration gradients of several [Formula: see text] using the solid-state tube wakefield acceleration regime. Furthermore, our modeling demonstrates the possibility that as the surface oscillations and resultantly the surface wave transitions into a nonlinear or “crunch-in” regime under [Formula: see text], not only does the average gradient increase but strong transverse focusing fields extend down to the tube axis. This work thus demonstrates the near-term experimental realizability of Solid-State Tube Wakefield Accelerator (SOTWA). The ongoing progress in nanoengineering and attosecond source technology thereby now offers the potential to experimentally realize the promise of solid-state or crystal acceleration, opening up unprecedented pathways in miniaturization of accelerators.

Bounded Entanglement Entropy in the Quantum Ising Model

A rigorous proof is presented of the boundedness of the entanglement entropy of a block of spins for the ground state of the one-dimensional quantum Ising model with sufficiently strong transverse field. This is proved by a refinement of the stochastic geometric arguments in the earlier work by Grimmett et al. (J Stat Phys 131:305–339, 2008). The proof utilises a transformation to a model of classical probability called the continuum random-cluster model. Our method of proof is fairly robust, and applies also to certain disordered systems.

Impact of Glasma on heavy quark observables in nucleus-nucleus collisions at LHC

In the pre-thermal equilibrium stage of relativistic heavy-ion collisions, a strong quasi-classical transverse gluon field emerges at about τ0≃0.1fm/c and evolves together with their longitudinal counterparts according to the classical Yang-Mills (CYM) equations. Recently it has been shown that these fields induce a diffusion of charm quarks in momentum space resulting in a tilt of their spectrum without a significant drag. We find that in nucleus-nucleus collisions at LHC such a novel dynamics of charm quarks leads to an initial enhancement of the nuclear modification factor (RAA) at pT larger than 2GeV/c contrary to the standard lore. Moreover, the same dynamics leads to a larger final elliptic flow (v2) inducing a relation between RAA and v2 that is quite close to the experimental measurements. Our study also shows that such an initial pre-thermal stage is unlikely to be described in terms of a standard drag and diffusion dynamics, because even if one tune such coefficients to reproduce the same RAA(pT) this would imply a significantly smaller v2.

Photoconductivity Resonance Tunneling Spectroscopy of the Electron States in the InAs/GaAs Quantum Dot Heterostructures

The electric-field behavior of the resonance features in the photoelectric characteristics of InAs/GaAs heterostructures is studied. We discuss the emission mechanism of the charge carriers excited from InAs quantum dots into the GaAs matrix. It was shown that at the temperature of liquid nitrogen the photocurrent in a strong transverse electric field is only determined by the effect of electron tunneling through the barrier formed at the quantum-dot interfaces. Comparison of the experimental curves with the quasi-classical expression for the tunneling current component and analysis of the potential structure allowed us to specify some parameters of investigated heterostructures. Analysis of the electric-field dependences of the photocurrent-tunneling component revealed resonance peculiarities connected with the local defect states in the vicinity of InAs/GaAs interface.

New effects in and control of exciton systems in quasi-two-dimensional structures

New effects in systems of quantum dipoles are discussed, such as anisotropic superfluidity in external fields, strong correlations, crystallization, and the supersolid phase. Roton instability effects typical of strongly correlated Bose systems but also manifesting themselves in weakly interacting systems of titled dipoles are analyzed. Among the interesting physical realizations of the systems under consideration are dipole excitons in single or coupled quantum wells under a strong transverse electric field and in van der Waals heterostructures of new 2D materials, such as transition metal dichalcogenides (TMDCs). The use at ultralow temperatures of polar molecules or atoms with permanent or external-field-induced dipoles is also interesting, as are Rydberg atoms in an external electric field.

Cathode tube effect: Heavy quarks probing the glasma in p -Pb collisions

We study the propagation of charm quarks in the early stage of high energy proton-lead collision, considering the interaction of these quarks with the evolving glasma by means of the Wong equations. Neglecting quantum fluctuations at the initial time, the glasma is made of longitudinal fields, but the dynamics leads to a quick formation of transverse fields; we estimate such a formation time as $\mathrm{\ensuremath{\Delta}}t\ensuremath{\approx}0.1\text{ }\text{ }\mathrm{fm}/\mathrm{c}$, which is of the same order of the formation time of heavy quark pairs ${t}_{\text{formation}}\ensuremath{\approx}\phantom{\rule{0ex}{0ex}}1/(2m)$. Limiting ourselves to the simple case of a static longitudinal geometry, we find that heavy quarks are accelerated by the strong transverse color fields in the early stage and this leads to a tilting of the $c$-quarks spectrum towards higher ${p}_{T}$ states. This average acceleration can be understood in terms of drag and diffusion of $c$-quarks in a hot medium and appears to be similar to the one felt by the electrons ejected by the electron cannon in a cathode tube: we dub this effect as cathode tube effect. The tilting of the spectrum affects the nuclear modification factor, ${R}_{\mathrm{pPb}}$, suppressing this below one at low ${p}_{T}$ and making it larger than one at intermediate ${p}_{T}$. We compute ${R}_{\mathrm{pPb}}({p}_{T})$ after the evolution of charm quarks in the gluon fields and we find that its shape is in qualitative agreement with the measurements of the same quantity for $D$-mesons in proton-lead collisions.

Electric-Field Behavior of the Resonance Features of the Tunneling Photocurrent Component in InAs(QD)/GaAs Heterostructures

The electric-field behavior of resonance features of the photoelectric characteristics of InAs/GaAs heterostructures is investigated. The emission of carriers excited by light from InAs quantum dots into the GaAs matrix is ​​discussed. It is shown that at the temperature of liquid nitrogen the photocurrent in a strong transverse electric field is only determined by the effect of electron tunneling through a barrier formed at the quantum-dot interfaces. Comparison of the experimental curves with the results obtained using a quasiclassical expression for the tunneling-current component and subsequent analysis of the potential structure made it possible to refine the parameters of the heterostructure under study. The contribution of the resonance component caused by possible electron tunneling through the barrier with the participation of the local defect states to the total tunneling current is analyzed. The influence of the level of excitation of the system on the photocurrent flowing through the InAs/GaAs heterojunction is theoretically studied.