Phase separation in the two-dimensional electron liquid in MOSFETs

We show that the existence of an intermediate phase between the Fermi liquid and the Wigner crystal phases is a generic property of the two-dimensional pure electron liqd in MOSFET's at zero temperature. The physical reason for the existence of these phases is a partial separation of the uniform phases. We discuss properties of these phases and a possible explanation of experimental results on transport properties of low density electron gas in Si MOSFET's. We also argue that in certain range of parameters the partial phase separation corresponds to a supersolid phas e discussed in [AndreevLifshitz].Comment: 11 pages, 3 figure

Destruction of diagonal and off-diagonal long range order by disorder in two-dimensional hard core boson systems

We use quantum Monte Carlo simulations to study the effect of disorder, in the form of a disordered chemical potential, on the phase diagram of the hard core bosonic Hubbard model in two dimensions. We find numerical evidence that in two dimensions, no matter how weak the disorder, it will always destroy the long range density wave order (checkerboard solid) present at half filling and strong nearest neighbor repulsion and replace it with a bose glass phase. We study the properties of this glassy phase including the superfluid density, energy gaps and the full Green's function. We also study the possibility of other localized phases at weak nearest neighbor repulsion, i.e. Anderson localization. We find that such a phase does not truly exist: The disorder must exceed a threshold before the bosons (at weak nn repulsion) are localized. The phase diagram for hard core bosons with disorder cannot be obtained easily from the soft core phase diagram discussed in the literature.Comment: 7 pages, 10 eps figures include

A system for polymer film irradiation with heavy ions accelerated to the energy of 1 MeV/u

At the Kharkov heavy ion linear accelerator MILAC experimental investigations on irradiation polymer films with heavy ion beams are carried out with the aim of obtaining track-etched membranes. Presently, the MILAC prestripping section accelerates tripled-charged Ar₄₀³⁺ ions to the energy of 1 MeV/u with the intensity of 10⁹…10¹⁰ particles/s. To provide uniform track distribution with the specified density and orientation in the polymer film a system of ion irradiation was developed on the basis of electrostatic scanning deviceНа Харьковском линейном ускорителе тяжелых ионов ЛУМЗИ проводятся экспериментальные исследования по облучению пучками тяжелых ионов полимерной пленки для получения трековых мембран. В настоящее время предобдирочная секция ускорителя ЛУМЗИ ускоряет трехзарядные ионы аргона Ar₄₀³⁺ до энергии 1 МэВ/нуклон с интенсивностью 10⁹…10¹⁰ част./с. Для обеспечения равномерного распределения треков в полимерной пленке с заданной плотностью и направленностью треков разработана система ионного облучения. Работа выполнена по гранту №2476.На Харківському лінійному прискорювачі важких іонів ЛУМЗІ проводяться експериментальні дослідження по опроміненню пучками важких іонів полімерної плівки для одержання трекових мембран. На цей час передобдиркова секція прискорювача ЛУМЗІ прискорює тризарядні іони аргону Ar₄₀³⁺ до енергії 1 МеВ/нуклон з інтенсивністю 10⁹…10¹⁰ част./с. Для забезпечення рівномірного розподілу треків у полімерній плівці із заданою щільністю и спрямованістю треків розроблена система іонного опромінення. Робота виконана по гранту №2476

Critical velocities in two-component superfluid Bose gases

On the ground of the Landau criterion we study the behavior of critical velocities in a superfluid two-component Bose gas. It is found that under motion of the components with different velocities the velocity of each component should not be lower than a minimum phase velocity of elementary excitations (s_). The Landau criterion yields a relation between the critical velocities of the components (v_{c1}, v_{c2}). The velocity of one or even both components may exceed s_. The maximum value of the critical velocity of a given component can be reached when the other component does not move. The approach is generalized for a two-component condensate confined in a cylindrical harmonic potential. PACS numbers: 03.75.Kk,03.75.MnComment: 6 pages, 1 figure

Non-zero temperature transport near quantum critical points

We describe the nature of charge transport at non-zero temperatures ($T$) above the two-dimensional ($d$) superfluid-insulator quantum critical point. We argue that the transport is characterized by inelastic collisions among thermally excited carriers at a rate of order $k_B T/\hbar$. This implies that the transport at frequencies $\omega \ll k_B T/\hbar$ is in the hydrodynamic, collision-dominated (or `incoherent') regime, while $\omega \gg k_B T/\hbar$ is the collisionless (or `phase-coherent') regime. The conductivity is argued to be $e^2 / h$ times a non-trivial universal scaling function of $\hbar \omega / k_B T$, and not independent of $\hbar \omega/k_B T$, as has been previously claimed, or implicitly assumed. The experimentally measured d.c. conductivity is the hydrodynamic $\hbar \omega/k_B T \to 0$ limit of this function, and is a universal number times $e^2 / h$, even though the transport is incoherent. Previous work determined the conductivity by incorrectly assuming it was also equal to the collisionless $\hbar \omega/k_B T \to \infty$ limit of the scaling function, which actually describes phase-coherent transport with a conductivity given by a different universal number times $e^2 / h$. We provide the first computation of the universal d.c. conductivity in a disorder-free boson model, along with explicit crossover functions, using a quantum Boltzmann equation and an expansion in $\epsilon=3-d$. The case of spin transport near quantum critical points in antiferromagnets is also discussed. Similar ideas should apply to the transitions in quantum Hall systems and to metal-insulator transitions. We suggest experimental tests of our picture and speculate on a new route to self-duality at two-dimensional quantum critical points.Comment: Feedback incorporated into numerous clarifying remarks; additional appendix discusses relationship to transport in dissipative quantum mechanics and quantum Hall edge state tunnelling problems, stimulated by discussions with E. Fradki

Power supply system for the helium ions linac’s injector

This paper presents compact power supply system for the helium ion linac’s injector. The system consists of high-voltage modulator, power supplies of cathode filament, solenoid and arc modulator. It is designed on modern semi-conductor base. Using of the designed power supply system allowed to decrease the power consumption and to get rid of spurious capacitances and pickups. As a result of improving the continuous adjustment modulator and high-voltage pulse stabilization scheme, the accelerated beam current has increased twice.Наведено опис малогабаритної системи живлення інжектора лінійного прискорювача іонів гелію, яка складається з високовольтного модулятора, блоків живлення накалу катода, соленоїда та модулятора дуги. Система виконана з використанням сучасної напівпровідникової елементної бази. Застосування розробленої системи живлення дозволило суттєво знизити енерговитрати, позбавитися паразитних ємностей та наведень. У результаті впровадження схеми стабілізації імпульсу високої напруги струм прискореного пучка збільшився в 2 рази.Приведены принципы построения и описание малогабаритной системы питания инжектора линейного ускорителя ионов гелия, состоящей из высоковольтного модулятора, блоков питания накала катода, соленоида и модулятора дуги, выполненных на современной полупроводниковой элементной базе. Применение разработанной системы питания позволило существенно снизить энергозатраты, избавиться от паразитных емкостей и наводок. Стабилизация амплитуды импульса высокого напряжения позволила увеличить ток ускоренного пучка в 2 раза

Radiation complex on the basis of helium ions linac

The numerical simulation results and experimental investigation of helium ions linear accelerator with output energy 4 MeV and focusing by an RF field are presented. The variant of alternating-phase focusing with a step change in the synchronous phase and increasing amplitude of the RF field in accelerating gaps in the grouping section of the accelerating-focusing tract of the accelerator is used to ensure the radial-phase stability of the accelerated beam. The methods for increasing the accelerated ion beam current, as well as the beam current density on the target, are considered.Представлено результати чисельного та експериментального дослідження лінійного прискорювача іонів гелію з вихідною енергією 4 МеВ і фокусуванням ВЧ-полем. Для забезпечення радіально-фазової стійкості прискореного пучка використано варіант змінно-фазового фокусування з покроковою зміною синхронної фази і наростаючою амплітудою ВЧ-поля в прискорюючих зазорах на групуючій ділянці прискорюючофокусуючого тракту прискорювача. Розглянуто способи збільшення струму прискореного пучка іонів, а також щільності струму пучка на мішені.Приведены результаты численного моделирования и экспериментального исследования линейного ускорителя ионов гелия с выходной энергией 4 МэВ c фокусировкой ВЧ-полем. Для обеспечения радиальнофазовой устойчивости ускоряемого пучка использован вариант переменно-фазовой фокусировки с шаговым изменением синхронной фазы и нарастающей амплитудой ВЧ-поля в ускоряющих зазорах на группирующем участке ускоряюще-фокусирующего тракта ускорителя. Рассмотрены способы увеличения тока ускоряемого пучка ионов, а также плотности тока пучка на мишени

Development of aerogel Cherenkov detectors at Novosibirsk

Abstract The development of aerogel Cherenkov counters with the light collection using a wavelength shifter is described. 80 counters of this type are working in the KEDR detector. A project of similar counters for the SND detector based on "heavy" aerogel with n = 1.13 has been developed. Aerogel with a refractive index of 1.006–1.13 and dimensions of blocks up to 200 × 200 × 50 mm 3 is produced by the Novosibirsk group for use in Cherenkov counters of different types. The Novosibirsk group is participating in the development of LHCb RICH as well as a beam diagnostics for a photo-injector test facility at DESY–Zeuthen. Recently we started development of RICH based on focusing aerogel (FARICH) for the endcap of the SuperBaBar. For the first time in the world the focusing aerogel with layers of different refractive indices has been produced

Development of aerogel Cherenkov counters at Novosibirsk

Abstract The work on aerogel Cherenkov counters was started in Novosibirsk in 1986. Production of aerogels with refractive indices of 1.006–1.13 and thicknesses of blocks up to 50 mm was developed. The light absorption length at 400 nm is 5–7 m, the scattering length is 4–5 cm. By these parameters, the Novosibirsk aerogel is one of the best in the world. The ASHIPH Cherenkov counters with light collection on wavelength shifters have been developed. The ASHIPH system of the KEDR detector contains 1000 l of aerogel. The π / K separation is 4.5 σ . A project of ASHIPH counters for the SND detector has been developed. Aerogel RICH for LHCb gives a possibility to identify hadrons in the momentum range of 2–10 GeV/c. The Novosibirsk group is developing an aerogel RICH for the endcap for the SuperBaBar project. Calculations performed by a group of physicists from Novosibirsk and DESY-Zeuthen have shown that aerogel radiators enable to achieve time resolution up to 20 fs