The ontology of Bohmian mechanics includes both the universal wave function (living in 3N-dimensional configuration space) and particles (living in ordinary 3-dimensional physical space). Proposals for understanding the physical significance of the wave function in this theory have included the idea of regarding it as a physicallyreal field in its 3N-dimensional space, as well as the idea of regarding it as a law of nature. Here we introduce and explore a third possibility in which the configuration space wave function is simply eliminated-replaced by a set of single-particle pilotwave fields living in ordinary physical space. Such a re-formulation of the Bohmian pilot-wave theory can exactly reproduce the statistical predictions of ordinary quantum theory. But this comes at the rather high ontological price of introducing an infinite network of interacting potential fields (living in 3-dimensional space) which influence the particles' motion through the pilot-wave fields. We thus introduce an alternative approach which aims at achieving empirical adequacy (like that enjoyed by GRW type theories) with a more modest ontological complexity, and provide some preliminary evidence for optimism regarding the (once popular but prematurely-abandoned) program of trying to replace the (philosophically puzzling) configuration space wave function with a (totally unproblematic) set of fields in ordinary physical space.

In this paper we propose two transistor concepts based on lateral heterostructures of monolayer MoS2, composed of adjacent regions of 1T (metallic) and 2H (semiconducting) phases, inspired by recent research showing the possibility to obtain such heterostructures by electron beam irradiation. The first concept, the lateral heterostructure field-effect transistor, exhibits potential of better performance with respect to the foreseen evolution of CMOS technology, both for high performance and low power applications. Performance potential has been evaluated by means of detailed multi-scale materials and device simulations. The second concept, the planar barristor, also exhibits potential competitive performance with CMOS, and an improvement of orders of magnitude in terms of the main figures of merit with respect to the recently proposed vertical barristor.

Weak values allow the measurement of observables associated with noncommuting operators. Up to now, position-momentum weak values have been mainly developed for (relativistic) photons. In this Letter, a proposal for the measurement of such weak values in typical electronic devices is presented. Inspired by the Ramo-Shockley-Pellegrini theorem that provides a relation between current and electron velocity, it is shown that the displacement current measured in multiterminal configurations can provide either a weak measurement of the momentum or strong measurement of position. This proposal opens new opportunities for fundamental and applied physics with state-ofthe-art electronic technology. As an example, a setup for the measurement of the Bohmian velocity of (nonrelativistic) electrons is presented and tested with numerical experiments.Introduction.-Nowadays, there is a rapidly growing interest in weak measurements and weak values [1-4], both from fundamental and applied points of view. Since weak values (a weak measurement postselected by a strong measurement) provide information on incompatible observables associated with noncommuting operators, relevant topics of quantum mechanics, such as the tunneling times [5], Hardy's paradox [6,7], Leggett-Garg inequalities [8,9], and quantum amplification [10][11][12], are being revisited. Especially attractive is the simultaneous measurement of position and momentum: a set of weak measurements of position postselected by a strong measurement of momentum is proportional to the wave function of the system [13,14], while a weak measurement of momentum postselected by a strong measurement of position gives the local velocity of a quantum particle [15,16].Most experimental techniques for weak values are developed for photons, whose technology is not easily transferable to industry based on electronics. The few proposals dealing with weak measurements in solid-state systems [17-22] use particle current measurement (i.e., electron charge detection). Instead, we propose measuring displacement current (i.e. time dependent variations of the electric field) to get information on the position and momentum of a quantum state. Similar to Landauer's proposal [23] which demonstrates that the measured dc current provides information of the quantum transmission coefficient, here, we show that the weak measurement of the ac current flowing through a (properly prepared multiterminal) electron device provides information on the whole quantum state. This new proposal opens original routes to study, both, fundamental physics and quantum engineering.As an example of the potentialities of our proposal, inspired by the old classical works of Shockley and Ramo [24,25], we discuss the measurement of the local (Bohmian) velocity (i.e. the current density divided by the modulus of the wave function) for an electron. Such velocity is obtained from a weak value constructed from two measurements of the displacement current on two different metallic surfaces belonging to a multiterminal

Without access to the full quantum state, modeling dissipation in an open system requires approximations. The physical soundness of such approximations relies on using realistic microscopic models of dissipation that satisfy completely positive dynamical maps. Here we present an approach based on the use of the Bohmian conditional wave function that, by construction, ensures a completely positive dynamical map for either Markovian or non-Markovian scenarios, while allowing the implementation of realistic dissipation sources. Our approach is applied to compute the current-voltage characteristic of a resonant tunneling device with a parabolic-band structure, including electron-lattice interactions. A stochastic Schrödinger equation is solved for the conditional wave function of each simulated electron. We also extend our approach to (graphene-like) materials with a linear band-structure using Bohmian conditional spinors for a stochastic Dirac equation.

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Two-particle scattering probabilities in tunneling scenarios with exchange interaction are analyzed with quasi-particle wave packets. Two initial one-particle wave packets (with opposite central momentums) are spatially localized at each side of a barrier. After impinging upon a tunneling barrier, each wave packet splits into transmitted and reflected components. When the initial two-particle anti-symmetrical state is defined as a Slater determinant of any type of (normalizable) one-particle wave packet, it is shown that the probability of detecting two (identically injected) electrons at the same side of the barrier is different from zero in very common (single or double barrier) scenarios. In some particular scenarios, the transmitted and reflected components become orthogonal and the mentioned probabilities reproduce those values associated to distinguishable particles. These unexpected non-zero probabilities are still present when non-separable Coulomb interaction or non-symmetrical potentials are considered. On the other hand, for initial wave packets close to Hamiltonian eigenstates, the usual zero two-particle probability for electrons at the same side of the barrier found in the literature is recovered. The generalization to many-particle scattering probabilities with quasi-particle wave packets for low and high phase-space density are also analyzed. The far-reaching consequences of these non-zero probabilities in the accurate evaluation of quantum noise in mesoscopic systems are briefly indicated.

Identifying the two-dimensional (2D) topological insulating (TI) state in new materials and its control are crucial aspects towards the development of voltage-controlled spintronic devices with low power dissipation. Members of the 2D transition metal dichalcogenides (TMDCs) have been recently predicted and experimentally reported as a new class of 2D TI materials, but in most cases edge conduction seems fragile and limited to the monolayer phase fabricated on specified substrates. Here, we realize the controlled patterning of the 1T'-phase embedded into the 2H-phase of thin semiconducting molybdenum-disulfide (MoS2) by laser beam irradiation. Integer fractions of the quantum of resistance, the dependence on laser-irradiation conditions, magnetic field, and temperature, as well as the bulk gap observation by scanning tunneling spectroscopy and theoretical calculations indicate the presence of the quantum spin Hall phase in our patterned 1T' phases.Two-dimensional (2D) topological insulting (TI) states have been mainly investigated in HgTe/CdTe or InAs/GaSb quantum well systems (1-3). In the 2D TI state the quantum spin Hall (QSH) effect emerges thanks to the simultaneous presence of a bulk energy gap and gapless helical edge states protected by time-reversal symmetry, namely, opposite and counter-propagating spin states forming a Kramers doublet. Interestingly, 2D TI states were first theoretically predicted for graphene (4-6), but experimentally reported in only few related systems (7-9) such as low-coverage Bi2Te3 nanoparticle-decorated graphene (8). Moreover, control of the QSH phase in graphene-based systems remains a challenge.Recently, a family of atom-thin transition metal dichalcogenides (TMDCs) materials has also been predicted to exhibit the QSHE (10-12), having its origin in the natural band inversion of the 1T' phase (one of the phases of TMDC; see Supplementary Material (SM) 1) and the spin-orbit coupling (SOC)induced band-gap opening. Moreover, the TI state has been experimentally verified in the case of WTe 2 (13-15) thanks to the stability and high-quality of WTe 2 monolayers carefully formed on bilayer graphene/atom-thin hBN. Various signatures of the TI state have been demonstrated in this 2 material (13,15), including the latest observation of a half-integer quantum value of resistance (RQ/2 = h/2e 2 = 12.9 k, where h is Planck's constant and e is the charge on the electron) (14).However, the TI phenomenon in WTe2 is rather sensitive to the substrates, synthesis process, and the chemical environment, making its controlled use in practical applications challenging. Moreover, although the (metastable) 1T' phase can be found or induced in other TMDCs (23,25), nobody has demonstrated the existence of the QSHE in these other TMDCs. The conditions under which helical edge states can exist at the 1T'-2H interfaces is a crucial problem which should be mastered for both TI physics and its applications. Here, we pattern a metallic 1T'-phase (SM 1) embedded into the nontopological and semiconducting 2H p...

The bandgap dependence on the number of atomic layers of some families of 2Dmaterials, can be exploited to engineer and use lateral heterostructures (LHs) as highperformance Field-Effect Transistors (FET). This option can provide very good lattice matching as well as high heterointerface quality. More importantly, this bandgap modulation with layer stacking can give rise to steep transitions in the density of states (DOS) of the 2D material, that can eventually be used to achieve sub-60 mV/decade subthreshold swing in LH-FETs thanks to an energy-filtering source. We have observed this effect in the case of a PdS 2 LH-FET due to the particular density of states of its bilayer configuration. Our results are based on ab initio and multiscale materials and device modeling, and incite the exploration of the 2D-material design space in order to find more abrupt DOS transitions and better suitable candidates. 1 arXiv:2001.03139v1 [cond-mat.mes-hall] 9 Jan 2020 Semiconductor heterostructures of the III-V and II-VI materials systems have played a fundamental role in the progress of electronics and optoelectronics. Firstly proposed by Kroemer in the 1950s, 1 they have been involved in the invention of quantum-well lasers 2 and high-electron-mobility transistors. 3 The large number of available two-dimensional (2D) materials and the possibility to combine them even in the presence of significant lattice mismatch has led to a new wave of interest in materials engineering based on heterostructures of 2D materials. In particular, 2D materials enable the realization of vertical heterostructures, also called "van der Waals" heterostructures, consisting in the vertical stacking of layers of different 2D materials loosely coupled by van der Waals interactions, 4,5 and of lateral heterostructures (LHs), in which a single 2D layer consists of juxtaposed regions of different lattice-matched 2D materials. 6-9LHs have been shown to be particularly well suited as channel materials in high performance Field-Effect Transistors (FETs) for digital electronics. 10 However, the quality of the heterojunction is one of the major obstacles towards the experimental demonstration of high performance LH-FETs. The possibility of fabricating LHs by modulating the stacking order of a single 2D material provides the opportunity of perfect lattice matching and growth compatibility, and therefore a chance to obtain high materials quality. 11Recently, a particular group of transition metal dichalcogenides (TMDs) involving noble transition metals (Pt, Pd, and Ni), combined with S, Se, and Te, have been predicted 12 and demonstrated to have strong gap dependence on the number of stacked layers. 13 The so-called "noble TMDs" are, thus, promising contenders to build 2D LHs by modulation of the number of layers of adjacent regions of the same material. Indeed, these structures based on noble TMDs -that strictly speaking could be considered homostructures instead of heterostructures-would be easier to realize than those made of different 2D materials.Ab initio ...