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ABSTRACT: We study nonlinear inter-subband microwave absorption of electrons bound to
the liquid helium surface. Already for a comparatively low radiation intensity,
resonant absorption due to transitions between the two lowest subbands is
accompanied by electron overheating. The overheating results in a significant
population of higher subbands. The Coulomb interaction between electrons causes
a shift of the resonant frequency, which depends on the population of the
excited states and thus on the electron temperature $T_e$. The latter is
determined experimentally from the electron photoconductivity. The
experimentally established relationship between the frequency shift and $T_e$
is in reasonable agreement with the theory. The dependence of the shift on the
radiation intensity introduces nonlinearity into the rate of the inter-subband
absorption resulting in bistability and hysteresis of the resonant response.
The hysteresis of the response explains the behavior in the regime of frequency
modulation, which we observe for electrons on liquid $^3$He and which was
previously seen for electrons on liquid $^4$He.
01/2012;
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ABSTRACT: Charge offsets and two-level fluctuators are common in single-electron transistors with a typical magnitude of |ΔQ|≪0.1e . We present measurements in a 2e -periodic single-Cooper-pair transistor which exhibited hysteretic charge offsets close to 1e . The real-time capture and escape of individual electrons in metastable trapped states was measured at very low temperatures. This enabled the dynamics of the transitions to be investigated in detail, demonstrating thermal excitation to a hysteretic tunneling transition. We show that, allowing for the hysteresis, the metastable states are in thermal equilibrium with each other. The observed temperature dependence and hysteresis can be explained by the coupling of a two-level fluctuator to a quasiparticle trap.
Journal of Applied Physics 01/2010; · 2.17 Impact Factor
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ABSTRACT: We show that electrons on liquid helium display intrinsic bistability of resonant intersubband absorption. The bistability occurs for comparatively weak microwave power. The underlying giant nonlinearity of the many-electron response results from the interplay of the strong short-range electron correlations, the long relaxation time, and the multisubband character of the electron energy spectrum.
Physical Review Letters 08/2009; 103(9):096801. · 7.37 Impact Factor
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ABSTRACT: The microwave (MW) absorption resonance in 2D electrons bound to the surface of liquid 3He is studied at high MW powers. In our experiment, we induce quantum transitions between two lowest surface states of electrons by letting them interact with the resonant MW radiation. Under the conditions of the experiment, the resonant absorption induces strong heating of the electron system. The electron temperature can be accurately determined by measuring the variation of the electron magneto-resistivity at the resonance. Electron heating causes a shift in the resonance frequency, which is measured as a function of the electron temperature. The shift is compared with a theory that takes into account strong electron-electron correlation, and a reasonable agreement is found. When the shift exceeds the width of the absorption line, their emerges bistability of the nonlinear response and hysteresis. Our result demonstrate the occurrence of a new nonlinear optical effect due to strong correlations in the many-electron system on liquid helium.
Journal of Physics Conference Series 03/2009; 150(2):022046.
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ABSTRACT: Metastable electron traps and two-level systems (TLSs) are common in solid-state devices and lead to background charge movement and charge noise in single-electron and single-Cooper-pair transistors. We present measurements of the real-time capture and escape of individual electrons in metastable trapped states at very low temperatures, leading to charge offsets close to 1e. The charge movement exhibits thermal excitation to a hysteretic tunneling transition. The temperature dependence and hysteresis can be explained by the coupling of a TLS to a quasiparticle trap.
Applied Physics Letters 10/2008; 93(17):173508-173508-3. · 3.84 Impact Factor
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ABSTRACT: The a.c. Hall effect has been measured directly in a 2D sheet of free electrons above the surface of liquid helium at frequencies from 1.5 to 35 kHz in a magnetic field B up to 4 T. For small B the normal Hall effect is observed but at higher fields finite frequency effects occur as the 2D skin depth becomes less than the sample size. Calculations using the magneto-conductivity tensor for a 2D transmission line agree well with experiment, except in the high-field limit as quantum effects become significant.
EPL (Europhysics Letters) 07/2007; 7(7):641. · 2.17 Impact Factor
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ABSTRACT: The magnetoresistance ρxx of a two-dimensional electron gas on the surface of liquid helium below 1 K has been measured up to the extreme quantum limit ωc/kT ≤ 20, where ωc is the cyclotron frequency. The resistivity increases almost quadratically with magnetic field, and is compared with a theoretical calculation based on many-electron effects.
EPL (Europhysics Letters) 07/2007; 16(6):575. · 2.17 Impact Factor
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ABSTRACT: We show that small numbers of electrons, including a single electron, can be held in a novel electrostatic trap above the surface of superfluid helium. A potential well is created using microfabricated electrodes in a 5 micron diameter pool of helium. Electrons are injected into the trap from an electron reservoir on a helium microchannel. They are individually detected using a superconducting single-electron transistor (SET) as an electrometer. A Coulomb staircase is observed as electrons leave the trap one-by-one until the trap is empty. A design for a scalable quantum information processor using arrays of electron traps is presented Comment: 15 pages, 5 figures
05/2004;
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ABSTRACT: We present measurements of the resonant microwave excitation of Rydberg energy levels for surface-state electrons on superfluid helium. The temperature-dependent contribution to the linewidth gamma(T) agrees with theoretical predictions and is very small below 700 mK, in the ripplon scattering regime. Absorption saturation and power broadening were observed as the fraction of electrons in the first excited state was increased to 0.49, close to the thermal excitation limit of 0.5. The Rabi frequency Omega was determined as a function of microwave power. High values of the ratio Omega/gamma confirm this system as an excellent candidate for creating qubits.
Physical Review Letters 01/2003; 89(24):245301. · 7.37 Impact Factor
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ABSTRACT: The magnetoresistance of neutron-transmutation-doped (NTD) n-type GaAs has been measured in the variable range hopping regime at temperatures, T = 0.03 to 1.6 K. The negative hopping magnetoresistance (NHM) in small magnetic fields is strongly influenced by at least two positive hopping magnetoresistance (PHM) contributions including the effects of spin alignment. Three new effects are reported: (i) The log R versus T—1/2plots in fixed magnetic field show two well-pronounced linear parts with different slopes forming a kink at a certain temperature Tc which shifts to higher temperatures as the applied magnetic field is increased, occurring at Bc/Tc ≅ 9 T/K. (ii) At the lowest temperatures, we observed with decreasing temperatures a steep decrease and disappearance of the negative hopping magnetoresistance, followed by only (iii) a positive hopping magnetoresistance with two different slopes with ρ(B)/ρ(0) ∝ B2. We interpret this behavior as due to the interplay between the (coherent) quantum interference with a negative sign and different incoherent mechanisms, including spin-effects, which dominate the magnetoresistance at different temperatures.
physica status solidi (b) 11/2001; 203(2):487 - 499. · 1.32 Impact Factor
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ABSTRACT: We present measurements of the conduction of nondegenerate free electrons along a low-dimensional channel at low temperatures, using surface-state electrons on liquid helium in novel microelectronic devices. Above 1 K, the electrons form an ideal classical Drude conductor. Below 1 K, Coulomb interactions produce electronic spatial order, leading to strong non-Ohmic effects and negative differential conductivity. Evidence is presented for self-organized current filaments in the channel, created by a nonequilibrium phase transition. Periodic conductance oscillations suggest an anisotropic spatial order with lines of electrons along the channel edges.
Physical Review Letters 11/2001; 87(17):176802. · 7.37 Impact Factor
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ABSTRACT: The ultrasonic attenuation has been measured from 4 to 270K in single crystals of pure bismuth germanium oxide, Bi12GeO20(BGO) and in crystals doped with Al, Ga, Zn, Pb, Cr, Ga+Cr, P+Ga. The relaxation attenuation peak near 50K in pure BGO is increased in the Cr-doped sample, reduced in the Zn-doped sample and absent in the other samples, and this correlated with the optical absorption measured by Oberschmid (1981). The point defect responsible for the attenuation is shown to have trigonal symmetry and the data are analysed in terms of the deformation tensor of the elastic dipole of the defect. A discussion is given of the possible defects which may produce the optical and acoustic absorptions.
Journal of Physics C Solid State Physics 11/2000; 16(2):247.
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ABSTRACT: We present a critical review of the present state of the critical exponent puzzle of the metal-insulator transition of doped
semiconductors with emphasis on the role of meso-and macroscopic inhomogeneity caused by the disorder of intended or unintended
acceptors and donors in crystals. By using both isotopic engineering and neutron transmutation doping (NTD) of germanium we
found for low compensations (at K=1.4 and 12%) that the critical exponents of the localization length and the dielectric constant are nearly ν=1/2 and ζ=1, which double for medium compensations (at K=38 and 54%) to ν=1 and ζ=2, respectively.
Physics of the Solid State 04/1999; 41(5):757-760. · 0.71 Impact Factor
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ABSTRACT: We report the results of electrical conductivity studies down to 30 mK for barely metallic samples in the vicinity of the metal–insulator transition (MIT). We used isotopically enriched 74Ge crystals and neutron-transmutation doping to produce homogeneously doped n-type germanium with As donors and with compensation degree of about 12%. We found that the temperature dependence of the conductivity obeys a logarithmic-like behavior within the experimental range of temperatures. This implies the existence of another mechanism for the scattering apart from the electron–electron interaction. According to the theory of Fukuyama the ln (T) dependence should be due to some kind of magnetic scattering. Therefore, it is impossible to obtain the scaling behavior of the conductivity at zero temperature as a function of the impurity concentration in the vicinity of the MIT due to the divergence of ln (T) at T → 0.
physica status solidi (b) 01/1999; 205(1):257 - 261. · 1.32 Impact Factor
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ABSTRACT: We measured on the dielectric side, with |N/Nc — 1| ≤ 0.64 the critical indices of the metal–insulator transition (MIT) in n-Ge with low (1.4 and 12%) and medium (38 and 54%) compensation, prepared by neutron-transmutation doping (NTD) of isotopic mixtures of 74Ge and 70Ge. We analyzed from the temperature dependence of hopping resistance in the variable-range hopping (VRH) regime with Coulomb gap the scaling of the localization length a, and of the dielectric constant ϰ. At low compensation we find that the critical indices are ν ≈ 1/2, ζ ≈ 1, which increase up to ν ≈ 1, ζ ≈ 2, for medium compensations.
physica status solidi (b) 01/1999; 205(1):269 - 273. · 1.32 Impact Factor
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ABSTRACT: We present measurements and theory of the magnetoconductivity (B) of the 2D electron fluid and Wigner crystal above the surface of liquid helium. Many-electron effects give rise to (i) Drude behaviour (B)"(0)/(1#B), even in classically strong fields, B1 (is the zero-field mobility), (ii) saturation and density dependence of (B)/(0) above an onset field B , which depends on the fluctuational internal electric field E , (iii) an increase in (B) in quantising fields. Far in the quantum limit, single-particle scattering dominates. For typical electron densities, (B)J¹\ for B'2 T and ¹(0.6 K, which is as expected for ripplon scattering, and does not change at the melting transition at ¹ . In low fields in the Wigner solid on He, (B) is non-linear due to the Bragg—C 7 erenkov radiation of coherent ripplons, which limits the Hall velocity to v , the phase velocity of the ripplons at the first reciprocal lattice vector. Above a threshold drive voltage, (B) decreases sharply. Above ¹ , fluctuations in (B) are observed below a temperature ¹ "(2.8$0.3)¹ indicating that some aspects of the 2D electron solid might persist to well above the melting temperature. 1998 Elsevier Science B.V. All rights reserved.
01/1998;
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ABSTRACT: Cryogenic bolometric sensors made from epitaxially grown Si:As have been tested down to 40 mK. The sensors were grown by chemical
vapour deposition with a doped layer 8.4 μm thick. The dopant concentration was measured using SIMS and was constant, ±1%,
with an excellent box profile. Arsenic concentrations up to 7.5×1018 cm−3 were achieved. Above 100 mK the low power resistanceR(T) followed the variable range hopping law, or Efros-Shklovskii law for a Coulomb gap,R(T)=R
0 exp(T
0/T)1/2 withT
0∼25 K, typically. A double sensor arrangement was used to measure the electronphonon coupling in the sensors and the phonon
coupling to the heat sink. As the dc current bias through a sensor was increased, spontaneous voltage oscillations were observed
across the sensor below 100 mK, which limited the sensitivity of the sensors in this region. These are circuit-limited oscillations
between high and low resistance states. A phase diagram was established for the spatio-temporal coexistence of the two states,
with a critical temperatureT
c=115 mK. We show that this is an intrinsic phase transition within a thermal model of the electron-phonon coupling. For a
resistance-temperature characteristic given by the Efros-Shklovskii law we findT
c=0.00512T
0, independent ofR
0 and the coupling strength. This predictsT
c=115±4 mK in this case. The model gives excellent agreement for the critical voltage and current, by assuming that the breakdown
occurred via the formation of a filamentary region of high current density and high electron temperature. At higher currents,
the response was temperature independent and given byI(E)=I(0) exp{−(E
0/E)1/2} whereE is the average applied electric field andE
0∼380 V/cm, in agreement with a thermal model which includes the phonon-phonon coupling to the heat sink.
Journal of Low Temperature Physics 09/1997; 109(1):107-133. · 1.19 Impact Factor
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ABSTRACT: We use Monte Carlo MC simulations to study the Coulomb forces that drive individual electrons in a two-dimensional normal electron fluid and a Wigner crystal. These forces have been previously shown to determine many-electron magnetoconductivity and cyclotron resonance of nondegenerate electron systems; they are also known to provide an important characteristic of the dynamics of particles that form a fluid. We have calculated the moments of the force distribution that are relevant for electron transport, which will permit a quantitative comparison of the many-electron transport theory with experiment. We have investigated the shape of the force distribution. Far tails of the distribution were analyzed by combining the method of optimal fluctuation with MC calculations, and the results were compared with direct MC results. S0163-18299705424-6
Journal of Physics C Solid State Physics 06/1997; 8:215-221.
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ABSTRACT: An observation of the suppression of negative magnetoresistance in samples of doped CdTe that are far from the metal-insulator
transition as the temperature is lowered in the temperature range 3–0.4 K was previously reported [N. V. Agrinskaya, V. I.
Kozub, and D. V. Shamshur, JETP 80, 1142 (1995)]. The results of an investigation of samples that are closer to the transition in the low-temperature region
below 36 mK are presented. It is discovered that the samples investigated (which do not exhibit the suppression of negative
magnetoresistance at comparatively high temperatures) display this effect at low temperatures and that, as previously, the
suppression of the negative magnetoresistance correlates with the transition to conduction via Coulomb-gap states. A plateau-like
magnetoresistance feature is displayed at low temperatures for the sample that is closest to the metal-insulator transition.
The results obtained are analyzed within existing theoretical models that take into account the role of both the orbital and
spin degrees of freedom. In particular, the low-temperature feature indicated is interpreted as a manifestation of positive
magnetoresistance caused by spin effects. Nevertheless, it is shown within a detailed analysis supplemented by numerical calculations
that the observed suppression of the negative magnetoresistance cannot be attributed only to the appearance of spin positive
magnetoresistance. Moreover, the possibility of observing spin positive magnetoresistance is determined to a certain extent
specifically by the suppression of the negative magnetoresistance competing with it.
Journal of Experimental and Theoretical Physics 01/1997; 84(4):814-822. · 1.03 Impact Factor
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ABSTRACT: The forces on individual electrons in an unscreened nondegenerate electron fluid, due to electron density fluctuations, have been calculated using Monte Carlo simulations and determined experimentally over a broad range of the plasma parameter Gamma. The experimental results are obtained from the magnetoconductivity sigma(B) measured for electrons on liquid helium below 1 K for B \leq 8 T. The magnitude and density dependence of sigma(B) are explained by the many-electron theory of magnetotransport. The internal electric fields found from the experiments are in excellent agreement with the simulations. Comment: 10 pages, LaTeX. 4 Postscript figures
11/1996;
