arXiv subjects

Baruch Horovitz

Publications and source records attributed to Baruch Horovitz.

At least 19 recordsLinked to original sources

arXiv2025

Theory of single molecule NMR detected by real time ESR

In relation to recent experimental data [Y. Manassen et al., J. Mag, Res. {\bf 374}, 107863 (2025)] , we develop a theory framework for demonstrating the feasibility of detecting sharp Nuclear Magnetic Resonance (NMR) oscillations in a real time ESR data. The procedure is to follow real time oscillations of the ESR signal measured at a selected frequency of a hyperfine transition. We study a variety of systems such as a single radical molecule with one or two hyperfine coupled nuclei or two molecules that coexist as either radicals or non-radicals, facilitated by charge transfer. We develop a master equation for describing these scenarios and find parameters for which a sharp NMR line can be observed. We show that in all cases an off-diagonal term in the hyperfine tensor is essential for the observation.

cond-mat.mes-hall↗

arXiv2025

Randomly twisted bilayer graphene -- the cascade transitions

Twisted bilayer graphene (TBG) is known to have disorder in its twist angle. We show that in terms of a Dirac equation with a random gauge potential ${\bf A}({\bf r})$ this disorder becomes huge when the average twist angle is near the magic angle where the Dirac velocity vanishes. The density of states (DOS) then diverges at the Dirac point as $\rho(E)\sim E^{(2/z)-1}$ with $z\gg 1$ and we deduce that all electrons occupy energies very near $E=0$. We prove a sum rule on the disorder averaged eigenfunctions from which we deduce that each added electron contributes equal intraband Coulomb interaction energy. The various bands in TBG are related by either ${\bf A}({\bf r})\rightarrow {\bf A}({-\bf r})$ or ${\bf A}({\bf r})\rightarrow -{\bf A}({\bf r})$ which affects the interband interaction energy. We find, within Hartree-Fock, jumps in the chemical potential at each integer filling, accounting for the cascade transitions.

cond-mat.mes-hall↗

arXiv2024

NMR of a single nuclear spin detected by a scanning tunneling microscope

We demonstrate ionization of a molecule with the bias voltage of a Scanning Tunnelling Microscope (STM) resulting in a coexistence of a neutral and ionic molecules, i.e. radical (paramagnetic) and non-radical (diamagnetic) states. This coexistence may be facilitated by a periodic switching between two bias voltages. The precession of the nucleus in the diamagnetic state modulates the nuclear polarization as well as the hyperfine transitions as seen in electron spin resonance (ESR). We analyze the power spectrum of a selected hyperfine intensity and obtain the nuclear magnetic resonance (NMR) spectrum. We have observed this phenomenon in three types of molecules: TEMPO, toluene and triphenylphosphine, showing NMR of $^{14}$N, $^{13}$C, $^{31}$P and $^1$H nuclei. The spectra are detailed and show signatures of the chemical environment, i.e. chemical shifts. A master equation including off-diagonal hyperfine interactions accounts for these observations.

cond-mat.mes-hall↗

arXiv2022

Electron spin spectroscopy of single TEMPO dimers coupled via interfering tunneling currents

We report the detection of electron spin resonance (ESR) in individual dimers of the stable free radical 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO). ESR is measured by the current fluctuations in a scanning tunnelling microscope (ESR-STM method). The multi-peak power spectra, distinct from macroscopic data, are assigned to dimers having exchange and Dzyaloshinskii-Moriya interactions in presence of spin-orbit coupling. These interactions are generated in our model by interfering electronic tunneling pathways from tip to sample via the dimer's two molecules. This is the first demonstration that tunneling via two spins is a valid mechanism of the ESR-STM method.

cond-mat.mes-hall↗

arXiv2021

Observation of Anomalous Moiré Patterns

Moiré patterns are omnipresent. They are important for any overlapping periodic phenomenon, from vibrational and electromagnetic, to condensed matter. Here we show, both theoretically and via experimental simulations by ultracold atoms, that for one-dimensional finite-size periodic systems, moiré patterns give rise to anomalous features in both classical and quantum systems. In contrast to the standard moiré phenomenon, in which the pattern periodicity is a result of a beat-note between its constituents, we demonstrate moiré patterns formed from constituents with the same periodicity. Surprisingly, we observe, in addition, rigidity and singularities. We furthermore uncover universal properties in the frequency domain, which might serve as a novel probe of emitters. These one-dimensional effects could be relevant to a wide range of periodic phenomena.

quant-ph↗

arXiv2021

Double Quantum Dot scenario for spin resonance in current noise

We show that interference between parallel currents through two quantum dots, in presence of spin orbit interactions and strong on-site Coulomb repulsion, leads to resonances in current noise at the corresponding Larmor frequencies. An additional resonance at the difference of Larmor frequencies is present even without spin-orbit interaction. The resonance lines have strength comparable to the background shot noise and therefore can account for the numerous observations of spin resonance in STM noise with non-polarized leads. We solve also several other models that show similar resonances.

cond-mat.mes-hall↗

arXiv2021

Spin entanglement via STM current

We consider a system of two spins under a scanning tunneling microscope bias and derive its master equation. We find that the tunneling elements to the electronic contacts (tip and substrate) generate an exchange interaction between the spins, as well as a Dzyaloshinskii-Moriya interaction in the presence of spin-orbit coupling. The tunnel current spectrum then shows additional lines compared to conventional spin resonance experiments. When the spins have degenerate Larmor frequencies and equal tunneling amplitudes (without spin-orbit), there is a dark state with vanishing decay rate. The coupling to the electronic environment generates significant spin-spin entanglement via the dark state, even if the initial state is non-entangled.

cond-mat.mes-hall↗

arXiv2019

Bridging between Lab and Rotating Frame Master Equations for Open Quantum Systems

The problem of a driven quantum system coupled to a bath and coherently driven is usually treated using either of two approaches: Employing the common secular approximation in the lab frame (as usually done in the context of atomic physics) or in the rotating frame (prevailing in, e.g., the treatment of solid-state qubits). These approaches are applicable in different parts of the parameter space and yield different results. We show how to bridge between these two approaches by working in the rotating frame without employing the secular approximation with respect to the driving amplitude. This allows us to uncover novel behaviors in regimes which were previously inaccessible or inaccurately treated. New features such as the qualitative different evolution of the coherence, population inversion at a lower driving amplitude, and novel structure in the resonance fluorescence spectrum of the system are found. We argue that this generalized approach is essential for analyzing hybrid systems, with components that come from distinctly different regimes which can now be treated simultaneously, giving specific examples from recent experiments on quantum dots coupled to optical cavities, and single-spin electron paramagnetic resonance.

quant-ph↗

arXiv2019

A Generalized Open Quantum System Approach for the Electron Paramagnetic Resonance of Magnetic Atoms

A recent experimental breakthrough allowed to probe electronic parametric resonance of a single magnetic atom in an STM setup. The results present intriguing features, such as an asymmetric lineshape and unusually large ratio of the decoherence and decay rates, which defy standard approaches using the conventional Bloch equations. To address these issues we employ novel generalized Bloch equations, together with proper microscopic modeling of the magnetic adatom, and show how all the experimental features can naturally be accounted for. The proposed approach may also be useful in treating any future similar experiments, as well as next generation hybrid quantum devices.

cond-mat.mes-hall↗

arXiv2018

Fingerprints of single nuclear spin energy levels using STM - ENDOR

We performed STM-ENDOR experiments where the intensity of one of the hyperfine components detected in ESR-STM is recorded while an rf power is irradiated into the tunneling junction and its frequency is swept. When the latter frequency is near a nuclear transition a dip in ESR-STM signal is observed. This experiment was performed in three different systems: near surface SiC vacancies where the electron spin is coupled to a next nearest neighbor 29Si nucleus; Cu deposited on Si(111)7x7 surface, where the unpaired electron of the Cu atom is coupled to the Cu nucleus (63Cu, 65Cu) and on Tempo molecules adsorbed on Au(111), where the unpaired electron is coupled to Nitrogen nucleus (14N). While some of the hyperfine values are unresolved in the ESR-STM data due to linewidth we find that they are accurately determined in the STM-ENDOR data including those from remote nuclei, which are not detected in the ESR-STM spectrum. Furthermore, STM-ENDOR can measure single nuclear Zeeman frequencies, distinguish between isotopes through their different nuclear magnetic moments and detect quadrupole spectra. We also develop and solve a Bloch type equation for the coupled electron-nuclear system that facilitates interpretation of the data. The improved spectral resolution of STM - ENDOR opens many possibilities for nanometric scale chemical analysis.

cond-mat.mes-hall↗

arXiv2016

Semiclassical Landau quantization of spin-orbit coupled systems

A semiclassical quantization condition is derived for Landau levels in general spin-orbit coupled systems. This generalizes the Onsager quantization condition via a matrix-valued phase which describes spin dynamics along the classical cyclotron trajectory. We discuss measurement of the matrix phase via magnetic oscillations and electron spin resonance, which may be used to probe the spin structure of the precessing wavefunction. We compare the resulting semiclassical spectrum with exact results which are obtained for a variety of spin-orbit interactions in 2D systems.

cond-mat.mes-hall↗

arXiv2016

Floquet topological phases coupled to environments and the induced photocurrent

We consider the fate of a helical edge state of a spin Hall insulator and its topological transition in presence of a circularly polarized light when coupled to various forms of environments. A Lindblad type equation is developed to determine the fermion occupation of the Floquet bands. We find by using analytical and numerical methods that non-secular terms, corresponding to 2-photon transitions, lead to a mixing of the band occupations, hence the light induced photocurrent is in general not perfectly quantized in the presence of finite coupling to the environment, although deviations are small in the adiabatic limit. Sharp crossovers are identified at frequencies $Ω$ and $\frac{1}{2}Ω$ ($Ω$ is the strength of light-matter coupling) with the former resembling to a phase transition.

cond-mat.str-el↗

arXiv2015

Interferometric resonance signatures of Majorana bound states

We calculate the current noise power spectrum in a nanoscopic interferometer consisting of a Majorana bound state (MBS) and a localized spin. We show that for large voltage (though less than the superconducting gap) several strong resonance peaks appear at frequencies that depend on the Zeeman splitting of the localized spin and on its tunneling to the localized spin. We also evaluate the differential conductance and find the unitary limit peak $2e^2/h$ at zero voltage as well as peaks at voltages corresponding to the resonances. We propose that detection of the resonances and related peaks in the differential conductance provide a strong support for the presence of an MBS.

cond-mat.mes-hall↗

arXiv2014

Trapping neutral atoms in the field of a vortex pinned by a superconducting nano-disc

Atom chips made of superconducting material can generate magnetic traps with significantly reduced noise. Recently, several designs for superconducting chips have been theoretically analyzed and experimentally tested, for cases with many vortices considered as an average vortex density. Here we show theoretically, for the first time, how the magnetic field of a $\it single$ vortex, pinned by a superconducting nano-disc of radius $\sim$100 nm and combined with an external bias field parallel to the disc surface, yields a closed 3D trap for cold atoms. The size of the trap, and its height above the superconductor surface, are typically tens or hundreds of nanometers. We estimate the average lifetime $τ$ of $^{87}$Rb (rubidium) atoms (subject to thermal escape and Majorana spin flips) in the range 0.05-1.0 ms. Next, we model the trap in a quantum adiabatic approximation and apply Fermi's rule to estimate the lifetime of $^{87}$Rb atoms in the ground state of this trap. We obtain similar lifetimes $τ$ as in the semiclassical estimate, in the range 0.05-3.5 ms. We find that $τ$ depends on the gradient $B_0$ of the vortex's magnetic field according to $τ\sim(B_0)^{-2/3}$.

physics.atom-ph↗

arXiv2013

Nanoscopic interferometer model for spin resonance in current noise

We study a model for the observed phenomenon of electron spin resonance (ESR) at the Zeeman frequency as seen by a scanning tunneling microscope (STM) via its current noise. The model for this ESR-STM phenomenon allows the STM current to flow in two arms of a nanoscopic interferometer, one arm has direct tunneling from the tip to the substrate while the second arm has tunneling through two spin states. We evaluate analytically the noise spectrum for non-polarized leads, as relevant to the experimental setup. We show that spin-orbit interactions allow for an interference of two tunneling paths resulting in a resonance effect.

cond-mat.mes-hall↗

arXiv2013

A model for the ESR-STM phenomenon

We propose a model to account for the observed ESR-like signal at the Larmor frequency in the current noise STM experiments identifying spin centers on various substrates. The theoretical understanding of this phenomenon, which allows for single spin detection on surfaces at room temperature, is not settled for the experimentally relevant case that the tip and substrate are not spin polarized. Our model is based on a direct tip-substrate tunneling in parallel with a current flowing via the spin states. We find a sharp signal at the Larmor frequency even at high temperatures, in good agreement with experimental data. We also evaluate the noise in presence of an ac field near resonance and predict splitting of the signal by the Rabi frequency.

cond-mat.mes-hall↗

arXiv2012

Rings and Coulomb boxes in dissipative environments

We study a particle on a ring in presence of a dissipative Caldeira-Leggett environment and derive its response to a DC field. We show how this non-equilibrium response is related to a flux averaged equilibrium response. We find, through a 2-loop renormalization group analysis, that a large dissipation parameter ηflows to a fixed point η^R=\hbar/2π. We also reexamine the mapping of this problem to that of the Coulomb box and show that the relaxation resistance, of recent interest, is quantized for large η. For finite η>η^R we find that a certain average of the relaxation resistance is quantized. We propose a Coulomb box experiment to measure a quantized noise.

cond-mat.mes-hall↗

arXiv2012

Van der Waals-Casimir-Polder interaction of an atom with a composite surface

We study the dispersion interaction of the van der Waals and Casimir-Polder (vdW-CP) type between a neutral atom and the surface of a metal by allowing for nonlocal electrodynamics, i.e. electron diffusion. We consider two models: (i) bulk diffusion, and (ii) diffusion in a surface charge layer. In both cases the transition to a semiconductor is continuous as a function of the conductivity, unlike the case of a local model. The relevant parameter is the electric screening length and depends on the carrier diffusion constant. We find that for distances comparable to the screening length, vdW-CP data can distinguish between bulk and surface diffusion, hence it can be a sensitive probe for surface states.

physics.atom-ph↗