arXiv subjects

J. Jung

Publications and source records attributed to J. Jung.

At least 19 recordsLinked to original sources

arXiv2026

Large-scale real-time signal processing in physics experiments: The ALICE TPC FPGA pipeline

For LHC Run 3, the ALICE Time Projection Chamber was upgraded to operate in continuous readout mode. Interaction rates of up to 50 kHz in Pb-Pb collisions require real-time processing of more than 3 TB/s of raw detector data. This requirement is met by a custom FPGA-based processing pipeline that performs the complete front-end data treatment fully in-stream, including common-mode correction, pedestal subtraction, ion-tail filtering, zero suppression, and dense data packing. A central element of the design is a highly parallel common-mode correction algorithm operating directly on the streaming data. It robustly identifies signal-free readout channels on a time-bin basis and applies pad-dependent scaling to compensate for local variations in capacitive coupling in the GEM readout. In combination with pedestal subtraction and ion-tail filtering, this enables accurate baseline restoration under extreme high-occupancy conditions, preventing signal loss while efficiently suppressing noise prior to zero suppression. The pipeline operates continuously at the full detector bandwidth and reduces the raw input rate to about 900 GB/s for Pb-Pb collisions at the target interaction rate. Overall, it represents a large-scale FPGA-based real-time signal-processing implementation for high-energy physics detector readout.

physics.ins-det↗

arXiv2023

Nuclear Recoil Identification in a Scientific Charge-Coupled Device

Charge-coupled devices (CCDs) are a leading technology in direct dark matter searches because of their eV-scale energy threshold and high spatial resolution. The sensitivity of future CCD experiments could be enhanced by distinguishing nuclear recoil signals from electronic recoil backgrounds in the CCD silicon target. We present a technique for event-by-event identification of nuclear recoils based on the spatial correlation between the primary ionization event and the lattice defect left behind by the recoiling atom, later identified as a localized excess of leakage current under thermal stimulation. By irradiating a CCD with an $^{241}$Am$^{9}$Be neutron source, we demonstrate $>93\%$ identification efficiency for nuclear recoils with energies $>150$ keV, where the ionization events were confirmed to be nuclear recoils from topology. The technique remains fully efficient down to 90 keV, decreasing to 50$\%$ at 8 keV, and reaching ($6\pm2$)$\%$ at 1.5--3.5 keV. Irradiation with a $^{24}$Na $\gamma$-ray source shows no evidence of defect generation by electronic recoils, with the fraction of electronic recoils with energies $<85$ keV that are spatially correlated with defects $<0.1$$\%$.

physics.ins-det↗

arXiv2022

Large even-odd spacing and $g$-factor anisotropy in PbTe quantum dots

PbTe is a semiconductor with promising properties for topological quantum computing applications. Here we characterize quantum dots in PbTe nanowires selectively grown on InP. Charge stability diagrams at zero magnetic field reveal large even-odd spacing between Coulomb blockade peaks, charging energies below 140$~\mathrm{μeV}$ and Kondo peaks in odd Coulomb diamonds. We attribute the large even-odd spacing to the large dielectric constant and small effective electron mass of PbTe. By studying the Zeeman-induced level and Kondo splitting in finite magnetic fields, we extract the electron $g$-factor as a function of magnetic field direction. We find the $g$-factor tensor to be highly anisotropic, with principal $g$-factors ranging from 0.9 to 22.4, and to depend on the electronic configuration of the devices. These results indicate strong Rashba spin-orbit interaction in our PbTe quantum dots.

cond-mat.mes-hall↗

arXiv2021

The upgrade of the ALICE TPC with GEMs and continuous readout

The upgrade of the ALICE TPC will allow the experiment to cope with the high interaction rates foreseen for the forthcoming Run 3 and Run 4 at the CERN LHC. In this article, we describe the design of new readout chambers and front-end electronics, which are driven by the goals of the experiment. Gas Electron Multiplier (GEM) detectors arranged in stacks containing four GEMs each, and continuous readout electronics based on the SAMPA chip, an ALICE development, are replacing the previous elements. The construction of these new elements, together with their associated quality control procedures, is explained in detail. Finally, the readout chamber and front-end electronics cards replacement, together with the commissioning of the detector prior to installation in the experimental cavern, are presented. After a nine-year period of R&D, construction, and assembly, the upgrade of the TPC was completed in 2020.

physics.ins-det↗

arXiv2019

Parity-preserving and magnetic field resilient superconductivity in indium antimonide nanowires with tin shells

We study bottom-up grown semiconductor indium antimonide nanowires that are coated with shells of tin. The shells are uniform in thickness. The interface between Sn and InSb is abrupt and without interdiffusion. Devices for transport are prepared by in-situ shadowing of nanowires using nearby nanowires as well as flakes, resulting in etch-free junctions. Tin is found to induce a hard superconducting gap in the range 600-700 micro-eV. Superconductivity persists up to 4 T in magnetic field. A tin island exhibits the coveted two-electron charging effect, a hallmark of charge parity stability. The findings open avenues for superconducting and topological quantum circuits based on new superconductor-semiconductor combinations.

cond-mat.mes-hall↗

arXiv2018

Systematics of electronic and magnetic properties in the transition metal doped Sb$_2$Te$_3$ quantum anomalous Hall platform

The quantum anomalous Hall effect (QAHE) has recently been reported to emerge in magnetically-doped topological insulators. Although its general phenomenology is well established, the microscopic origin is far from being properly understood and controlled. Here we report on a detailed and systematic investigation of transition-metal (TM)-doped Sb$_2$Te$_3$. By combining density functional theory (DFT) calculations with complementary experimental techniques, i.e., scanning tunneling microscopy (STM), resonant photoemission (resPES), and x-ray magnetic circular dichroism (XMCD), we provide a complete spectroscopic characterization of both electronic and magnetic properties. Our results reveal that the TM dopants not only affect the magnetic state of the host material, but also significantly alter the electronic structure by generating impurity-derived energy bands. Our findings demonstrate the existence of a delicate interplay between electronic and magnetic properties in TM-doped TIs. In particular, we find that the fate of the topological surface states critically depends on the specific character of the TM impurity: while V- and Fe-doped Sb$_2$Te$_3$ display resonant impurity states in the vicinity of the Dirac point, Cr and Mn impurities leave the energy gap unaffected. The single-ion magnetic anisotropy energy and easy axis, which control the magnetic gap opening and its stability, are also found to be strongly TM impurity-dependent and can vary from in-plane to out-of-plane depending on the impurity and its distance from the surface. Overall, our results provide general guidelines for the realization of a robust QAHE in TM-doped Sb$_2$Te$_3$ in the ferromagnetic state.

cond-mat.mes-hall↗

arXiv2012

$β$ NMR study of Isolated $^8$Li in the enhanced paramagnet Platinum

We report β detected nuclear magnetic resonance (βNMR) measurements of 8Li+ implanted into high purity Pt. The frequency of the 8Li βNMR resonance and the spin-lattice relaxation rates 1/T1 were measured at temperatures ranging from 3 to 300 K. Remarkably, both the spin-lattice relaxation rate and the Knight shift K depend linearly on temperature T although the bulk susceptibility does not. K is found to scale with the Curie-Weiss dependence of the Pt susceptibility extrapolated to low temperatures. This is attributed to a defect response of the enhanced paramagnetism of Pt, i.e. the presence of the interstitial Li+ locally relieves the tendency for the Curie-Weiss susceptibility to saturate at low T . We propose that the low temperature saturation in \c{hi} of Pt may be related to an interband coupling between the s and d bands that is disrupted locally by the presence of the Li+.

cond-mat.str-el↗

arXiv2011

Transport Spectroscopy of Symmetry-Broken Insulating States in Bilayer Graphene

The flat bands in bilayer graphene(BLG) are sensitive to electric fields E\bot directed between the layers, and magnify the electron-electron interaction effects, thus making BLG an attractive platform for new two-dimensional (2D) electron physics[1-5]. Theories[6-16] have suggested the possibility of a variety of interesting broken symmetry states, some characterized by spontaneous mass gaps, when the electron-density is at the carrier neutrality point (CNP). The theoretically proposed gaps[6,7,10] in bilayer graphene are analogous[17,18] to the masses generated by broken symmetries in particle physics and give rise to large momentum-space Berry curvatures[8,19] accompanied by spontaneous quantum Hall effects[7-9]. Though recent experiments[20-23] have provided convincing evidence of strong electronic correlations near the CNP in BLG, the presence of gaps is difficult to establish because of the lack of direct spectroscopic measurements. Here we present transport measurements in ultra-clean double-gated BLG, using source-drain bias as a spectroscopic tool to resolve a gap of ~2 meV at the CNP. The gap can be closed by an electric field E\bot \sim13 mV/nm but increases monotonically with a magnetic field B, with an apparent particle-hole asymmetry above the gap, thus providing the first mapping of the ground states in BLG.

cond-mat.mes-hall↗

arXiv2009

Magneto-electric coupling in zigzag graphene nanoribbons

Zigzag graphene nanoribbons can have magnetic ground states with ferromagnetic, antiferromagnetic, or canted configurations, depending on carrier density. We show that an electric field directed across the ribbon alters the magnetic state, favoring antiferromagnetic configurations. This property can be used to prepare ribbons with a prescribed spin-orientation on a given edge.

cond-mat.mes-hall↗

arXiv2009

Theory of the Magnetic-Field-Induced Insulator in Neutral Graphene

Recent experiments have demonstrated that neutral graphene sheets have an insulating ground state in the presence of an external magnetic field. We report on a $π$-band tight-binding-model Hartree-Fock calculation which examines the competition between distinct candidate insulating ground states. We conclude that for graphene sheets on substrates the ground state is most likely a field-induced spin-density-wave, and that a charge density wave state is possible for suspended samples. Neither of these density-wave states support gapless edge excitations.

cond-mat.mes-hall↗

arXiv2009

Carrier Density and Magnetism in Graphene Zigzag Nanoribbons

The influence of carrier density on magnetism in a zigzag graphene nanoribbon is studied in a $π$-orbital Hubbard-model mean-field approximation. Departures from half-filling alter the magnetism, leading to states with charge density variation across the ribbon and parallel spin-alignment on opposite edges. Finite carrier densities cause the spin-density near the edges to decrease steadily, leading eventually to the absence of magnetism. At low doping densities the system shows a tendency to multiferroic order in which edge charges and spins are simultaneously polarized.

cond-mat.mes-hall↗

arXiv2008

Theory of inter-edge superexchange in zigzag edge magnetism

A graphene nanoribbon with zigzag edges has a gapped magnetic ground state with an antiferromagnetic inter-edge superexchange interaction. We present a theory based on asymptotic properties of the Dirac-model ribbon wavefunction which predicts $W^{-2}$ and $W^{-1}$ ribbon-width dependencies for the superexchange interaction strength and the charge gap respectively. We find that, unlike the case of conventional atomic scale superexchange, opposite spin-orientations on opposite edges of the ribbon are favored by both kinetic and interaction energies.

cond-mat.mes-hall↗

arXiv2007

Ab-initio formulation of the 4-point conductance of interacting electronic systems

We derive an expression for the 4-point conductance of a general quantum junction in terms of the density response function. Our formulation allows us to show that the 4-point conductance of an interacting electronic system possessing either a geometrical constriction and/or an opaque barrier becomes identical to the macroscopically measurable 2-point conductance. Within time-dependent density-functional theory the formulation leads to a direct identification of the functional form of the exchange-correlation kernel that is important for the conductance. We demonstrate the practical implementationof our formula for a metal-vacuum-metal interface.

cond-mat.mtrl-sci↗

arXiv2007

Treatment of electron viscosity in quantum conductance

In a recent paper Sai {\it et al.} [1] identified a correction $R^{dyn}$ to the DC conductance of nanoscale junctions arising from dynamical exchange-correlation ($XC$) effects within time-dependent density functional theory. This quantity contributes to the total resistance through $R=R_{s}+R^{dyn}$ where $R_{s}$ is the resistance evaluated in the absence of dynamical $XC$ effects. In this Comment we show that the numerical estimation of $R^{dyn}$ in example systems of the type they considered should be considerably reduced, once a more appropriate form for the shear electron viscosity $η$ is used.

cond-mat.mtrl-sci↗

arXiv2006

$β$-NMR of Isolated $^{8}$Li$^{+}$ Implanted into a Thin Copper Film

Depth-controlled $β$-NMR was used to study highly spin-polarized $^8$Li in a Cu film of thickness 100 nm deposited onto a MgO substrate. The positive Knight Shifts and spin relaxation data show that $^8$Li occupies two sites at low temperatures, assigned to be the substitutional ($S$) and octahedral ($O$) interstitial sites. Between 50 to 100 K, there is a site change from $O$ to $S$. The temperature dependence of the Knight shifts and spin-lattice relaxation rates at high temperatures, i.e. when all the Li are in the $S$ site, is consistent with the Korringa Law for a simple metal.

cond-mat.str-el↗

arXiv2006

Quantum conductance of homogeneous and inhomogeneous interacting electron systems

We obtain the conductance of a system of electrons connected to leads, within time-dependent density-functional theory, using a direct relation between the conductance and the density response function. Corrections to the non-interacting conductance appear as a consequence of the functional form of the exchange-correlation kernel at small frequencies and wavevectors. The simple adiabatic local-density approximation and non-local density-terms in the kernel both give rise to significant corrections in general. In the homogeneous electron gas, the former correction remains significant, and leads to a failure of linear-response theory for densities below a critical value.

cond-mat.mtrl-sci↗

arXiv2004

Assessment of density functional approximations: long-range correlations and self-interaction effects

The complex nature of electron-electron correlations is made manifest in the very simple but non-trivial problem of two electrons confined within a sphere. The description of highly non-local correlation and self-interaction effects by widely used local and semi-local exchange-correlation energy density functionals is shown to be unsatisfactory in most cases. Even the best such functionals exhibit significant errors in the Kohn-Sham potentials and density profiles.

cond-mat.other↗

arXiv2001

Complementary Theories of Energy Gaps in HTSC

We examine experiments on energy gaps in high temperature superconductors (HTSC) in terms of experimental probes that utilize momentum, position, or neither. Experiments on very high quality mechanical tunnel junctions show a sharp energy gap with a maximum anisotropy of ~ 10%, while ultrahigh precision ARPES experiments show 100% anisotropy (d-wave pairing). We resolve this conbflict by showing that the latter result is caused by the momentum-projective nature of ARPES and glassy orthorhombic dopant correlations. The latter appear to be a universal feature of the intermediate phase tha is responsible for HTSC. Apparent large inconsistencies between position-projective STM gap data and tunnel junction data on severely underdoped BSCCO are also resolved.

cond-mat.supr-con↗