Shape Analysis of the Level Spacing Distribution around the Metal Insulator Transition in the Three Dimensional Anderson Model

We present a new method for the numerical treatment of second order phase transitions using the level spacing distribution function $P(s)$. We show that the quantities introduced originally for the shape analysis of eigenvectors can be properly applied for the description of the eigenvalues as well. The position of the metal--insulator transition (MIT) of the three dimensional Anderson model and the critical exponent are evaluated. The shape analysis of $P(s)$ obtained numerically shows that near the MIT $P(s)$ is clearly different from both the Brody distribution and from Izrailev's formula, and the best description is of the form $P(s)=c_1\,s\exp(-c_2\,s^{1+\beta})$, with $\beta\approx 0.2$. This is in good agreement with recent analytical results.Comment: 14 pages in plain TeX, 6 figures upon reques

Polaronic slowing of fermionic impurities in lattice Bose-Fermi mixtures

We generalize the application of small polaron theory to ultracold gases of Ref. [\onlinecite{jaksch_njp1}] to the case of Bose-Fermi mixtures, where both components are loaded into an optical lattice. In a suitable range of parameters, the mixture can be described within a Bogoliubov approach in the presence of fermionic (dynamic) impurities and an effective description in terms of polarons applies. In the dilute limit of the slow impurity regime, the hopping of fermionic particles is exponentially renormalized due to polaron formation, regardless of the sign of the Bose-Fermi interaction. This should lead to clear experimental signatures of polaronic effects, once the regime of interest is reached. The validity of our approach is analyzed in the light of currently available experiments. We provide results for the hopping renormalization factor for different values of temperature, density and Bose-Fermi interaction for three-dimensional $^{87}\rm{Rb}-^{40}\rm{K}$ mixtures in optical lattice.Comment: 13 pages, 5 figure

Photofrin II as an efficient radiosensitizing agent in an experimental tumor

Background and Objective: The use of ionizing irradiation as radiation therapy (RT) for tumor treatment represents a well-established method. The use of photodynamic therapy (PDT), especially with Photofrin II, for tumor treatment is also known. Chemical modifiers enhancing the action of radiation therapy are well known and widely used in medicine. None of these compounds, however, is a selective radiosensitizer. Materials and Methods: Several series of animal experiments were performed, The highly differentiated human bladder cancer cell line RT4 was implanted subcutaneously in nude mice. The mice were injected 10 mg/kg Photofrin II and irradiated with 5 Gy. Results: Photofrin II has proved to be a chemical modifier of ionizing irradiation, enhancing the tumor doubling time (tumor growth) from 6.2 to 10.9 days in the control group with the use of irradiation and injection of porphyrin. Conclusion: Photofrin II shows a high activity as radiosensitizer and, in the future, can be used as a selective radiosensitizer for tumor treatment with ionizing radiation

Magnetism and domain formation in SU(3)-symmetric multi-species Fermi mixtures

We study the phase diagram of an SU(3)-symmetric mixture of three-component ultracold fermions with attractive interactions in an optical lattice, including the additional effect on the mixture of an effective three-body constraint induced by three-body losses. We address the properties of the system in $D \geq 2$ by using dynamical mean-field theory and variational Monte Carlo techniques. The phase diagram of the model shows a strong interplay between magnetism and superfluidity. In the absence of the three-body constraint (no losses), the system undergoes a phase transition from a color superfluid phase to a trionic phase, which shows additional particle density modulations at half-filling. Away from the particle-hole symmetric point the color superfluid phase is always spontaneously magnetized, leading to the formation of different color superfluid domains in systems where the total number of particles of each species is conserved. This can be seen as the SU(3) symmetric realization of a more general tendency to phase-separation in three-component Fermi mixtures. The three-body constraint strongly disfavors the trionic phase, stabilizing a (fully magnetized) color superfluid also at strong coupling. With increasing temperature we observe a transition to a non-magnetized SU(3) Fermi liquid phase.Comment: 36 pages, 17 figures; Corrected typo

Wet etch methods for InAs nanowire patterning and self-aligned electrical contacts

Advanced synthesis of semiconductor nanowires (NWs) enables their application in diverse fields, notably in chemical and electrical sensing, photovoltaics, or quantum electronic devices. In particular, Indium Arsenide (InAs) NWs are an ideal platform for quantum devices, e.g. they may host topological Majorana states. While the synthesis has been continously perfected, only few techniques were developed to tailor individual NWs after growth. Here we present three wet chemical etch methods for the post-growth morphological engineering of InAs NWs on the sub-100 nm scale. The first two methods allow the formation of self-aligned electrical contacts to etched NWs, while the third method results in conical shaped NW profiles ideal for creating smooth electrical potential gradients and shallow barriers. Low temperature experiments show that NWs with etched segments have stable transport characteristics and can serve as building blocks of quantum electronic devices. As an example we report the formation of a single electrically stable quantum dot between two etched NW segments.Comment: 9 pages, 5 figure

An optimized return mapping algorithm for the barcelona basic model

For the most well-known constitutive model for partially saturated soils, the Barcelona Basic Model, an optimized return mapping algorithm is proposed, which is characterized by analytical integration of the hardening law and by solving only a nonlinear scalar equation at the integration point level. To investigate the performance of the proposed algorithm several implicit and explicit stress update algorithms are compared at the integration point level. Finally, the proposed stress update algorithm is applied to a 2D solid-fluid coupled numerical simulation of water flow through a homogeneous embankment dam

Two-stage Kondo effect in a four-electron artificial atom

An artificial atom with four electrons is driven through a singlet-triplet transition by varying the confining potential. In the triplet, a Kondo peak with a narrow dip at drain-source voltage V_ds=0 is observed. The low energy scale V_ds* characterizing the dip is consistent with predictions for the two-stage Kondo effect. The phenomenon is studied as a function of temperature T and magnetic field B, parallel to the two-dimensional electron gas. The low energy scales T* and B* are extracted from the behavior of the zero-bias conductance and are compared to the low energy scale V_ds* obtained from the differential conductance. Good agreement is found between kT* and |g|muB*, but eV_ds* is larger, perhaps because of nonequilibrium effects.Comment: 7 pages, 7 figures. Added labels on Fig. 3f and one referenc

Does a magnetic field modify the critical behaviour at the metal-insulator transition in 3-dimensional disordered systems?

The critical behaviour of 3-dimensional disordered systems with magnetic field is investigated by analyzing the spectral fluctuations of the energy spectrum. We show that in the thermodynamic limit we have two different regimes, one for the metallic side and one for the insulating side with different level statistics. The third statistics which occurs only exactly at the critical point is {\it independent} of the magnetic field. The critical behaviour which is determined by the symmetry of the system {\it at} the critical point should therefore be independent of the magnetic field.Comment: 10 pages, Revtex, 4 PostScript figures in uuencoded compressed tar file are appende

BCS pairing in Fermi systems with several flavors

Motivated by the prospect of Bardeen-Cooper-Schrieffer (BCS) pairing in cold fermionic gases we analyze the superfluid phase of 3 fermionic flavors in the attractive Hubbard model. We show that there are several low--lying collective pairing modes and investigate their damping due to the partially gapless nature of the single-particle spectrum. Furthermore we analyze how these modes show up in the density response of the system. Apart from the Anderson-Bogoliubov phase mode of the pairing between two flavors, the dynamical structure factor contains signatures of the gapless third flavor. This picture is found to be robust against perturbations that break the global SU(3)-symmetry of the Hamiltonian.Comment: 13 pages, 6 figure

Singlet-Triplet Transition in lateral Quantum Dots: A Numerical Renormalization Group Study

We discuss transport through a lateral quantum dot in the vicinity of a singlet-triplet spin transition in its ground state. Extracting the scattering phase shifts from the numerical renormalization group spectra, we determine the linear conductance at zero temperature as a function of a Zeeman field and the splitting of the singlet and triplet states. We find reduced low-energy transport, and a non-monotonic magnetic field dependence both in the singlet and the triplet regime. For a generic set of dot parameters and no Zeeman splitting, the singlet-triplet transition may be identified with the conductance maximum. The conductance is least sensitive to the magnetic field in the region of the transition, where it decreases upon application of a magnetic field. Our results are in good agreement with recent experimental data.Comment: 9 pages Revtex, 10 eps figure