Fig. 3 Re ﬂection of the quasiparticle wave functions at the step edge. a Filled-state scanning tunneling microscopy (STM) image (I = 100 pA, V = − 0.5 V) presenting an atomically perfect surface area near the step edge at Ge(001)-c(4 × 2). b Series of empty-state constant-current dI/dV maps (100 pA) obtained on the atomically perfect Ge(001)-c(4 × 2) surface area marked in a by the blue box. White bar is 2 nm. c Cross-sections of dI/dV maps obtained along dashed lines presented in b. Interference patterns related to re ﬂection of electronic waves on the step-edge potential are clearly seen. d Single-point scanning tunnelingspectroscopy dI/dV data obtained in positions marked by white points in a. Brighter contrast represents higher intensity of dI/dV signal. e Left: computed density of states of a twelve-layer Ge(001)-c(4 × 2) slab (broadened by η = 0.015 eV) as a function of energy and k y (i.e., integrating the contribution for all k x at each point, see equation 3 in the Supplementary Note 9). Right: one-dimensional Fourier transform of the data presented in
PILLET, JOYEZ, ˇ ZITKO, AND GOFFMAN PHYSICAL REVIEW B 88, 045101 (2013)
FIG. 1. (Color online) (a) Color-enhanced scanning electron micrograph (scale bar: 500 nm) of a device fabricated for the tunnelingspectroscopy of a carbon nanotube (CNT). The substrate consists of highly doped silicon serving as a back gate (BG), shown here in cyan, with a 1 μm surface oxide layer. A second gate electrode [side gate (SG)] is used to electrostatically influence the left part the CNT. A grounded aluminum fork (green) is well connected to the CNT. The measurement of dI /dV through the tunnel probe (red) gives access to the DOS in the CNT. (b) Schematic representation of the system: the presence of the tunnel probe electrode likely acts as a scatterer splitting the CNT into two QDs.
Keywords: STM, scanning tunnelingspectroscopy, silicon dangling bond, charge state transition, silicon atomic quantum dot
We report the study of single dangling bonds (DBs) on a hydrogen-terminated silicon (100) surface using a low-temperature scanning tunneling microscope. By investigating samples prepared with different annealing temperatures, we establish the critical role of subsurface arsenic dopants on the DB electronic properties. We show that when the near-surface concentration of dopants is depleted as a result of 1250 °C ﬂash anneals, a single DB exhibits a sharp conduction step in its I(V) spectroscopy that is not due to a density of states effect but rather corresponds to a DB charge state transition. The voltage position of this transition is perfectly correlated with bias-dependent changes in the STM images of the DB at different charge states. Density functional theory calculations further highlight the role of subsurface dopants on DB properties by showing the inﬂuence of the DB-dopant distance on the DB state. We discuss possible theoretical models of electronic transport through the DB that could account for our experimental observations.
supercurrent is mainly transmitted by discrete entangled electron-hole states confined to the nanotube, called Andreev Bound States (ABS). These states are a key concept in mesoscopic superconductivity as they provide a universal description of Josephson-like effects in quantum-coherent nanostructures (e.g. molecules, nanowires, magnetic or normal metallic layers) connected to super- conducting leads . We report here the first tunnelingspectroscopy of indi- vidually resolved ABS, in a nanotube-superconductor device. Analyzing the evolution of the ABS spectrum with a gate voltage, we show that the ABS arise from the discrete electronic levels of the molecule and that they reveal detailed information about the energies of these levels, their relative spin orientation and the coupling to the leads. Such measurements hence constitute a power- ful new spectroscopic technique capable of elucidating the electronic structure of CNT-based devices, including those with well-coupled leads. This is rele- vant for conventional applications (e.g. superconducting or normal transistors, SQUIDs ) and quantum information processing (e.g. entangled electron pairs generation [6, 7], ABS-based qubits  ). Finally, our device is a new type of dc-measurable SQUID.
In this Letter we report on low temperature tunnelingspectroscopy and vortex images of superconducting hole-
doped diamond films. These measurements, which probe the quasiparticule excitations near the Fermi energy, show a clear BCS local density of states (LDOS) consistent with weak coupling. Contrary to what is expected for a dirty superconductor [10,11], a significant density of localized resonant states is found below the gap in the vortex core.
One of the most fabulous potentials of the STM is to enable the acquisition of spectro- scopic data with a spatial resolution better than the nanometre. As we will see, scanning tunnelingspectroscopy (STS) is a very powerful tool to directly probe the local density of states (LDOS) of a sample. Different techniques to study the superconducting state of our sample with STS will be reviewed in this chapter. First of all, the most classical case with the use of a normal tip will be theoretically described and tunneling measurements on normal-insulator-superconductor (NIS) junctions will be interpreted and discussed. The second section will be dedicated to measurements in the point-contact mode, i.e. with a very low resistance of the junction, when the tip is in contact with the sample surface. This technique enables to transfer two charge carriers to the superconducting condensate by a process called Andreev reflection, and could give access to new energy scales. Finally, we will present a third spectroscopy technique based on the use of a superconducting tip and we will see what kind of new information we can extract from the collected data.
关see also Fig. 1共b兲 兴, in the single-electron 共elastic兲 resonant- tunneling regime, we can measure the single-particle energy spectrum of the downstream dot by using the 1s-like state of the upstream dot as a probe 共energy filter兲. 12 Energy spectra 共mapping out directly the position of current peaks as ex- plained in Secs. IV and V 兲 of two dots are shown in Fig. 3 . The spectrum in Figs. 3共a兲 and 3共b兲 reveals levels which are almost degenerate within shells at 0 T indicating that the first probed dot 共dot 2 from device I兲 is circular to a high degree. In contrast, for the spectrum in Figs. 3共c兲 and 3共d兲 the levels are now well separated at 0 T, indicating that the second probed dot 共dot 2 from device II兲 has higher ellipticity. 30 Two further key observations are readily apparent on examination of the measured spectra. First, an attractive attribute of ac- quiring energy spectra in the way we do with a vertical double-dot device is that we can easily access the single- particle states over a large energy window, limited only by the onset of longitudinal-optic-phonon emission at ⬃37 meV. 31
imity effect, provided the electrons in the tip are cooled well below the temperature δ/k B .
In order to perform such measurements on nanocir- cuits, which contain large insulating areas on which STMs cannot be operated, we have designed and built a cryogenic dual mode STM-AFM (Atomic Force Micro- scope) [14, 15], operating with a single metallic tip. This local probe sensor consists of an electrochemically sharp- ened tungsten wire  glued on one prong of a miniature piezoelectric quartz tuning fork. The latter is a high qual- ity factor electromechanical resonator, which here serves as the AFM transducer . Other dual mode instru- ments are being developed and used elsewhere [18, 19]. The AFM mode is used to acquire detailed topographic images of the samples which later on allow for accurate positioning of the tip for STM spectroscopy. The mi- croscope is mounted in a table-top dilution refrigerator with a base temperature of ∼35 mK. By itself this is not sufficient to ensure a low electronic temperature T e and
One efficient way to mitigate attentional tunneling is to design cognitive countermeasures. Rather than adding alarms, one solution consists in temporarily removing the information (e.g. display) on which the human operator is excessively focusing and to replace it by an explicit notification in their visual field . Therefore, the user interface acts as a cognitive prosthesis as it performs the attentional disengagement, shifting and re-orientation of attention. These cognitive countermeasures were successfully tested with pilots  and with unmanned vehicle operators during attentional tunneling episodes. However, this design may not be appropriate for all contexts and it should be considered only in extreme cases when there is a need to instigate a change in human operator strategy . Indeed, such countermeasure should not be considered as another form of alert. For instance,  demonstrated that this information removal drastically reduced interruption lag (i.e. reaction time to interrupt the primary task to process the alarm) but led to higher "resumption lag" (recovery time to resume primary task). These considerations demonstrate the complexity of designing appropriate solution to mitigate failure of attention.
“submillimeter spectroscopy”, is also utilised by the molecular astrophysics community. Today, however, the majority of spectroscopists hav e adopted the increasingly fashionable term of “terahertz
spectroscopy”. Still, regardless of which terminology is used, we are basically dealing with the same window in the electromagnetic spectrum that spans the range from 0.3 to 3 THz, or for those who prefer wavenumbers, from 10 to 100 cm −1 and for those who like wavelengths, from 1 to 0.1 mm. A recent query on the search engine Google turned up barely 754,000 entries for the new term of “terahertz spectroscopy”, versus 1,510,000 entries for the old term of “far infrared spectroscopy”, hence the idiom “renaissance” in the title of our article.
Inﬂuence of soil conditioning on ground deformation during longitudinal tunneling
Mingjing Jiang a,1 , Zhen-Yu Yin b,c, ∗ ,2
Soil conditioning is often adopted to facilitate EPB shield tunneling. However, the resulting improvement of soil ﬂuidity and the reduction of friction forces will also raise the ground deformation problem. This paper aims to investigate the inﬂuence of soil conditioning on the ground deformation during longitudinal tunneling. DEM is employed for this study due to its advantages in analyzing large deformations and discontinuous processes. Soil conditioning is modeled by reducing the interparticle friction of soils in a speciﬁc zone around the cutterhead of the tunnel. The tunnel advance with different soil-conditioning treatments is thus modeled. Comparisons are carried out on the ground deformation, i.e. ground surface settlement, vertical and horizontal displacements. The inﬂuence of soil conditioning on the ground deformation is clariﬁed, and is associated with the ﬂuidity from poor to favorite, and the mechanical properties from dilative to contractive are associated with the increase of soil conditioning. The results are helpful to determine the conditioned soils and control ground deformation for real constructions.
During the excavation of deep tunnels, squeezing ground conditions are often encountered. The squeezing behavior of the ground is characterized by large time-dependent and usually anisotropic convergences that take place at the tunnel wall. The technique of excavation has a strong influence on the tunnel response when it is excavated under squeezing conditions. This phenomenon is illustrated throughout the case study of the Fréjus road tunnel excavated with conventional drill and blast methods and of its safety gallery excavated with a single shield tunneling boring machine. They exhibit a very interesting configuration of two tunnels excavated in parallel under the same geotechnical conditions but with different excavation techniques. Monitored geotechnical data from both tunnels are analyzed and compared. Numerical simulations of both tunnels have been carried out with Flac 3D . An anisotropic creep model which includes weakness planes of given orientation
Introduction.– In recent years there has been consider-
able interest in the quantum simulation of more and more complex problems of solid state physics [1–3]. In this con- text, lattice-based quantum simulation has become a key technique to mimic the periodicity of a crystal structure. In such systems, dynamics is governed by two different types of processes: hopping between sites mediated by tunneling effect and interaction between particles. While there exists several ways to implement long-range inter- actions [4–7], long-range hoppings have been up to now very challenging to simulate. These long-range hoppings however, have aroused great theoretical interest in con- densed matter, as they are associated with important problems such as glassy physics , many-body localiza- tion  or quantum multifractality . In this study we show that such long-range hoppings can be engineered in driven lattices in a moderate regime of modulation.
Raman laser pulses are used to induce coherent tunnelling between neighbouring sites of a vertical 1D optical lattice. Such tunneling occurs when the detuning of a probe laser from the atomic transition frequency matches multiples of the Bloch frequency, allowing for a spectroscopic control of the coupling between Wannier Stark (WS) states. In particular, we prepare coherent superpositions of WS states of adjacent sites, and investigate the coherence time of these superpositions by realizing a spatial interferometer. This scheme provides a powerful tool for coherent manipulation of external degrees of freedom of cold atoms, which is a key issue for quantum information processing.
= 0 . (2.7)
Example 3.5 presents a Markov process which exhibits a tunneling behaviour and fulfills condition (M3’) but violates assumption (M1’). Example 3.7 presents a Markov process with the opposite properties. It fulfills conditions (M1’), (M2), (M3) but violates assumption (M3’). This latter example is very instructive. It shows that the same Markov process may have distinct metastable behaviors at different time scales. This occurs when on one time scale there is an isolated point in the asymptotic Markov dynamics. In longer time scales this metastate is reached by other metastates, previous metastates coalesce in one larger metastate, and a new metastable picture emerges.
focus (k distribution) . Details of the system and our calibration procedure are described in .
We now turn to the predictions that we test. The idea that tunneling could describe multiphoton ionization for long wavelength or high intensity pulses was introduced by Keldysh . Using only three observables, i.e., the light frequency ! L , the laser electric field E, and the particle’s binding energy I p , Keldysh introduced a parameter
¼ ð2I p Þ 1=2 ! L =E (in atomic units, abbreviated a.u.)—now known as the Keldysh parameter. If
1 multiphoton ionization is approximated by tunneling. If
1, the perturbative description of multiphoton ionization is ap- propriate. Here, we will present results covering a range of Keldysh parameters from
¼ 0:58 to
In our recent work we have demonstrated how the time at which the electron leaves the atomic barrier can be directly measured . Specifically, we applied a strong laser field to induce tunneling and a weak probe field to steer the tunneled electron. By monitoring attosecond pulses emitted when the liberated electron re-encounters the parent ion, both ionization times and recollision times were reconstructed. We demonstrated high sensitivity of the measurement by resolving subtle delays in ionization times from two orbitals of a CO2 molecule.
also depend on phase index (29). Note also that the speed of the offset fluctuations —as much as 140 MHz per 220 ns during the perturba- tions, roughly 0.5 Df per 1/Df—would be problematic for conventional techniques, because it implies that the short-term linewidth of a comb tooth greatly exceeds the spacing between comb teeth, a situation gen- erally considered incompatible with dual-comb spectroscopy (5, 7, 9). Stabilization by thermal tuning is out of the question because the per- turbation occurs on time scales that are too short, and even techniques that rely on measuring the beating with a CW laser would require an additional fast detector. Figure 2 (C and D) shows the time-domain multiheterodyne signals before and after the phase and timing cor- rection, both during the instability (Fig. 2C) and away from it (Fig. 2D). During the instability, no clear periodicity or structure is ob- vious in the raw data; away from it, some periodicity is evident. In both cases, the signal predicted by the filter agrees very well with the actual data. As a result, following the phase and timing correction (discussed in Materials and Methods), the periodic comb structure is recovered.
assisted tunneling, with the localization length in po- sition space, dependent on W , analogous to the local- ization length in momentum space of the deterministic model (1), dependent on K and ¯ h. The splitting δ is de- termined by computing the eigenfunctions most strongly overlapping with the first site (due to symmetry, this is equivalent to the last site). The corresponding splitting distributions for this model are shown in Fig. 2a. Strik- ingly, very similar behavior is observed in this disordered model compared to the deterministic model. In partic- ular, we recover the Cauchy distribution at small values of W where the disordered sea has delocalized ergodic states, whereas for large W (localized states) the distri- bution has a log-normal shape, with again an interme- diate behavior at the crossover. In Fig. 2b we show, for both the deterministic and disordered models, the scaling behaviors of δ typ = exp(ln δ), where ln δ denotes the en-