Electrodynamics of a Coulomb glass in n-type silicon

Measurements of the complex frequency dependent conductivity of uncompensated n-type silicon are reported. The experiments are done in the quantum limit, variant Planck's over 2pi omega>k(B)T, across a broad doping range on the insulating side of the metal-insulator transition. The low energy linear frequency dependence is consistent with theories of a Coulomb glass, but discrepancies exist in the relative magnitudes of the complex components. At higher energies we observe a crossover to a quadratic frequency dependence that is sharper than expected. The concentration dependence gives evidence that the Coulomb interaction energy is the energy scale that determines this crossover.     

Behavior features of phononless hopping conductivity in the vicinity of the crossover from the linear to quadratic frequency dependence

It was shown that the Coulomb interaction between electrons of “active” (resonance) pairs plays a major role in a wide frequency range. Therefore, the conventional approach to the calculation of the super-linearity of the frequency dependence of ac conductivity, based on the single-particle density of states with a Coulomb gap, is inapplicable to the calculation of high-frequency phononless conductivity. The observed superlinearity of the frequency dependence of the phononless hopping conductivity can manifest itself immediately in the region of the crossover from the linear to quadratic frequency dependence of the conductivity.     

Compressibility crossover and quantum opening of a gap for two-dimensional disordered clusters with Coulomb repulsion

Using Hartree-Fock orbitals with residual Coulomb repulsion, we study spinless fermions in a two-dimensional random potential. When we increase the system size L at fixed particle density, the size dependence of the average inverse compressibility exhibits a smooth crossover from a 1/L ² towards a 1/L decay when the Coulomb energy to Fermi energy ratio increases from 0 to 3. In contrast, the distribution of the first energy excitation displays a sharp Poisson-Wigner-like transition at . Received 13 March 2000     

The special features of the frequency dependence of phononless hopping conduction

Within the framework of perturbation theory the imaginary part of the phononless conduction of a lightly doped compensated semiconductor is calculated. It is shown that when the basis of localized atomic-like functions is used, the superlinear frequency dependence of the real part of the conduction corresponds to the approximately linear frequency dependence of the imaginary part of the conductivity. It has been found that at frequencies below the transition (crossover) frequency ??_cr from the linear to quadratic frequency dependence of the real part of conductivity, the dielectric loss tangent depends weakly on the frequency and it is determined by the relationship of ???_cr to the width of the impurity band. It is shown that measurements of the dielectric loss tangent can provide information on the localization radius of impurity states.     

The effect of a magnetic field on the crossover from the linear to quadratic frequency dependence of phononless hopping conductivity in disordered systems

The effect of an external magnetic field on the frequency dependence of phononless hopping conductivity in disordered system is studied. The dependence of the low-temperature phononless conductivity on the applied magnetic field is established. It is shown that in the limit of a strong magnetic field, the frequency of the transition (crossover) from linear to quadratic frequency dependence of phononless conductivity grows logarithmically with the value of a magnetic field.     

Frequency dependence of low-temperature phononless conductivity in disordered systems

The frequency dependence of resonant phononless hopping conductivity in disordered systems with pointlike centers of localization in the low-temperature limit is considered within the framework of the pair approximation. It is shown that the existing theory that predicts the power-mode frequency dependence of the low-frequency phononless hopping conductivity σ(ω) and a transition from linear to quadratic dependence (crossover) when frequency increases may become invalid, and the quadratic frequency dependence may never manifest itself at all.     

Nonlocal Coulomb correlations in metals close to a charge order insulator transition

The charge ordering transition induced by the nearest-neighbor Coulomb repulsion V in the 1/4-filled extended Hubbard model is investigated using cellular dynamical mean-field theory. We find a transition to a strongly renormalized charge ordered Fermi liquid at V(CO) and a metal-to-insulator transition at V(MI)>V(CO). Short range antiferromagnetism occurs concomitantly with the CO transition. Approaching the charge ordered insulator, V approximately 相似文献   

Strong correlation, electron-phonon interaction and critical fluctuations: isotope effect, pseudogap formation, and phase diagram of the cuprates

Within the Hubbard-Holstein model with long-range Coulomb forces, we revisit the charge-ordering (CO) scenario for the superconducting cuprates and account for the presence or the absence of a formed stripe phase in different classes of cuprates. We also evaluate the mean-field and the fluctuation-corrected critical lines for CO and we relate them with the various pseudogap crossover lines occurring in the cuprates and we discuss a mechanism for their peculiar isotopic dependence. Considering the dynamical nature of the CO transition, we explain the spread of T∗ and of its isotopic shift, obtained with experimental probes with different characteristic time scales.     

Incompressible paired hall state, stripe order, and the composite fermion liquid phase in half-filled landau levels

We consider the two lowest Landau levels at half filling. In the higher Landau level (nu = 5/2), we find a first-order phase transition separating a compressible striped phase from a paired quantum Hall state, which is identified as the Moore-Read state. The critical point is very near the Coulomb potential and the transition can be driven by increasing the width of the electron layer. We find a much weaker transition (either second-order or a crossover) from pairing to the composite fermion Fermi-liquid behavior. A very similar picture is obtained for the lowest Landau level, but the transition point is not near the Coulomb potential.     

Precise measurement of a weak radio frequency electric field using a resonant atomic probe

We present a precise measurement of a weak radio frequency electric field with a frequency of ■3 GHz employing a resonant atomic probe that is constituted with a Rydberg cascade three-level atom, including a cesium ground state |6S(1/2)〉,an excited state |6P(3/2)〉, and Rydberg state |nD(5/2)〉. Two radio frequency(RF) electric fields, noted as local and signal fields, couple the nearby Rydberg transition. The two-photon resonant Rydberg electromagnetically induced transparency(Rydberg-EIT) is employed to directly read out the weak signal field having hundreds of k Hz difference between the local and signal fields that is encoded in the resonant microwave-dressed Rydberg atoms. The minimum detectable signal fields of ESmin= 1.36 ± 0.04 mV/m for 2.18 GHz coupling |68D(5/2)〉→ |69P(3/2)〉 transition and 1.33 ± 0.02 mV/m for 1.32 GHz coupling |80D(5/2)〉→ |81P(3/2)〉 transition are obtained, respectively. The bandwidth dependence is also investigated by varying the signal field frequency and corresponding -3 dB bandwidth of 3 MHz is attained. This method can be employed to perform a rapid and precise measurement of the weak electric field, which is important for the atom-based microwave metrology.     

Quantum clock synchronization based on shared prior entanglement

We consider theoretically the formation and stability of quasi-one-dimensional many-body excitons in GaAs quantum wire structures under external photoexcitation conditions by solving the dynamically screened Bethe-Salpeter equation for realistic Coulomb interaction. In agreement with several recent experimental findings the calculated excitonic peak shows weak carrier-density dependence up to (and even above) the Mott transition density, nc approximately 3 x 10(5) cm(-1). Above nc we find considerable optical gain demonstrating compellingly the possibility of a one-dimensional quantum wire laser operation.     

Multiphoton transitions between energy levels in a current-biased Josephson tunnel junction

The escape of a current-biased Josephson tunnel junction from the zero-voltage state in the presence of weak microwave radiation is investigated experimentally at low temperatures. The measurements of the junction switching current distribution indicate the macroscopic quantum tunneling of the phase below a crossover temperature of T small star, filled approximately 280 mK. At temperatures below T small star, filled we observe both single-photon and multiphoton transitions between the junction energy levels by applying microwave radiation in the frequency range between 10 and 38 GHz to the junction. These observations reflect the anharmonicity of the junction potential containing only a small number of levels.     

Critical dielectric relaxation of highly deuterated betaine arsenate at microwave frequencies

The dielectric behavior of highly deuterated betaine arsenate in the frequency range up to 11 GHz is described by a Cole-Davidson relaxation. The characteristic dynamics show a critical slowing down near the para-antiferroelectric phase transition. The temperature dependence of the dielectric constant is analyzed in terms of a pseudo-one-dimensional Ising model. Evidence is given for a dependence of antiferroelectric coupling on deuteration which can explain the change from a ferro- to an antiferroelectric ordering on deuteration. Measurements of the dielectric relaxation under a dc bias field parallel to the critical axis elucidate the unusual phase transition behavior at low temperatures. A multicritical point appears in theE-T-phase diagram. Frustration effects due to competing ferro- and antiferroelectric interactions are not seen.     

Phase transitions in cold and warm dense matter

We consider the phase transitions, in dense matter, from nuclei to bubbles and from bubbles to uniform matter. A simplified version of the compressible liquid-drop model allows us to discuss analytically the densities at which the free energies of the different phases are equal, and the density discontinuities of the phases in equilibrium. A reasonable agreement with detailed numerical calculations is obtained only if the compressibility of the matter inside nuclei, and particularly outside bubbles, is taken into account. The dependence of the bubbles-uniform matter transition on the various elements of the Coulomb energy is discussed in detail: the transition is actually a first-order one, but it becomes of second order if the lattice Coulomb energy is turned off.The insight into the effect on the transition of the ratio of surface-plus-Coulomb energy to compression modulus allows us to understand the dependence of the transition densities on temperature and on the microscopic model employed.     

Origin of constant loss in ionic conductors

We have analyzed the constant loss contribution to the ac conductivity in the frequency range 10 Hz-1 MHz and temperatures down to 8 K, for two Li ionic conductors, one crystalline (Li(0.18)La(0.61)TiO(3)) and the other glassy (61SiO(2);35Li(2)O.3Al(2)O3.P(2)O(5)). As temperature is increased a crossover is observed from a nearly constant loss to a fractional power law frequency dependence of the ac conductivity. At any fixed frequency omega, this crossover occurs at a temperature T such that omega approximately nu(0)exp(-E(m)/k(B)T), where nu(0) is the attempt frequency and E(m) is identified with the barrier for Li+ ions to leave their wells.     

Quantum critical behavior near a density-wave instability in an isotropic fermi liquid

We study the quantum critical behavior in an isotropic Fermi liquid in the vicinity of a zero-temperature density-wave transition at a finite wave vector qc. We show that, near the transition, the Landau damping of the soft bosonic mode yields a crossover in the fermionic self-energy from Sigma(k,omega) approximately Sigma(k) to Sigma(k,omega) approximately Sigma(omega), where k and omega are momentum and frequency. Because of this self-generated locality, the fermionic effective mass diverges right at the quantum critical point, not before; i.e., the Fermi liquid survives up to the critical point.     

Study of the phase transition in the ionic conductor CuTeBr by millimeter wave spectroscopy

By use of a quasi-optical, broad-banded spectrometer in the frequency range of 40–90 GHz (λ = 7.5 ? 3.3 mm), the temperature dependence of absorption of the ionic conductor CuTeBr has been investigated for the first time. An abrupt and reversible jump in absorption independent of the incident frequency is observed at (69 ± 2)°C. This is attributed to a first order phase transition from an orthorhombic superstructure to a tetragonal structure. The results are discussed in connection with the high ionic conductivity of this material.     

From a simple liquid to a polymer melt: NMR relaxometry study of polybutadiene

We utilize NMR field cycling relaxometry to study the crossover from glassy dynamics (t approximately > tau alpha) through Rouse to reptation behavior in a series of monodisperse polybutadienes with molecular weights M=355 to 817,000 g/mol. We separate characteristic polymer dynamics from the total spectrum dominated by glassy dynamics. The polymer dynamics show typical Rouse relaxation features that grow with M and saturate at high M. Comparing to Rouse theory, we determine the Rouse unit size MR approximately = 500 and entanglement weight Me approximately = 2000; the Rouse spectrum saturates at Mmax approximately = 4000. The local order parameter S approximately 0.11 is relatively large, indicating noticeable local packing already in the Rouse regime. The M dependence of the glass transition temperature Tg, obtained from dielectric relaxation spectra, shows distinctive kinks at MR and Me.     

Disappearance of metal-like behavior in GaAs two-dimensional holes below 30 mK

The zero-field temperature dependence of the resistivity of two-dimensional holes is observed to exhibit two qualitatively different characteristics for a fixed carrier density for which only the metallic behavior of the so-called metal-insulator transition is anticipated. As T is lowered from 150 to 0.5 mK, the sign of the derivative of the resistivity with respect to T changes from being positive to negative when the temperature is lowered below approximately 30 mK and the resistivity continuously rises with cooling down to 0.5 mK, suggesting a crossover from being metal-like to insulatorlike.     

Frequency-tunable transmon in a three-dimensional copper cavity

We have realized a frequency-tunable transmon in a three-dimensional cooper cavity using a direct current superconducting quantum interference device. Both the transition frequency of the transmon and the frequency of the dressed cavity can be varied with the applied external flux bias, which are well consistent with the theoretical model. The range of the variable transition frequency is from 5.188 GHz to 7.756 GHz. The energy relaxation time of the transmon is hundreds of nanoseconds.