Showing 1–50 of 63 results for author: Meng, T

Quantum control of Hubbard excitons

Authors: D. R. Baykusheva, D. P. Carmichael, C. S. Weber, I-T. Lu, F. Glerean, T. Meng, P. B. M. De Oliveira, C. C. Homes, I. A. Zaliznyak, G. D. Gu, M. P. M. Dean, A. Rubio, D. M. Kennes, M. Claassen, M. Mitrano

Abstract: Quantum control of the many-body wavefunction is a central challenge in quantum materials research, as it could yield a precise control knob to manipulate emergent phenomena. Floquet engineering, the coherent dressing of quantum states with periodic non-resonant optical fields, has become an important strategy for quantum control. Most applications to solid-state systems have targeted weakly inter… ▽ More Quantum control of the many-body wavefunction is a central challenge in quantum materials research, as it could yield a precise control knob to manipulate emergent phenomena. Floquet engineering, the coherent dressing of quantum states with periodic non-resonant optical fields, has become an important strategy for quantum control. Most applications to solid-state systems have targeted weakly interacting or single-ion states, leaving the manipulation of many-body wavefunctions largely unexplored. Here, we use Floquet engineering to achieve quantum control of a strongly correlated Hubbard exciton in the one-dimensional Mott insulator Sr$_2$CuO$_3$. A nonresonant midinfrared optical field coherently dresses the exciton wavefunction, driving its rotation between bright and dark states. We use resonant third-harmonic generation to quantify ultrafast $π/2$ rotations on the Bloch sphere spanned by these exciton states. Our work advances the quest towards programmable control of correlated states and exciton-based quantum sensing. △ Less

Submitted 27 January, 2026; originally announced January 2026.

Comments: main+supplementary, 43 pages, 12 figures

Journal ref: Nat. Mater. 25, 937-943 (2026)

Quantum geometry in the dynamics of band-projected operators

Authors: Chen Xu, Andreas Haller, Suraj Hegde, Tobias Meng, Thomas L. Schmidt

Abstract: We study the dynamics of electrons in crystalline solids in the presence of inhomogeneous external electric and magnetic fields. We present a manifestly gauge-invariant operator-based approach without relying on a semiclassical wavepacket construction, and derive the field-induced corrections to the equations of motion at the operator level. This includes the Berry curvature induced anomalous velo… ▽ More We study the dynamics of electrons in crystalline solids in the presence of inhomogeneous external electric and magnetic fields. We present a manifestly gauge-invariant operator-based approach without relying on a semiclassical wavepacket construction, and derive the field-induced corrections to the equations of motion at the operator level. This includes the Berry curvature induced anomalous velocity and contributions arising from the quantum geometry of the Bloch bands. We show explicitly how these multi-band effects are manifested in an effective single band approximation. We present a formalism that allows for a systematic expansion to an arbitrary order in the inhomogeneity of the applied fields, as well as a way to compute the matrix elements in Bloch basis. △ Less

Submitted 14 March, 2025; originally announced March 2025.

Comments: 6 pages, 11 pages of supplemental material

Chiral damping with persistent edge states: interplay of spectral topology and band topology in open quantum systems

Authors: Ronika Sarkar, Suraj S. Hegde, Awadhesh Narayan, Tobias Meng

Abstract: We study the dynamical consequences of combining the non-Hermitian skin effect with topological edge states. Focusing on the paradigmatic dissipative Hofstadter model, we find that the time-dependent particle density exhibits both chiral damping (due to the non-Hermitian skin effect) and edge-selective extremal damping (rooted in persistent topological edge states). We find that the time scales of… ▽ More We study the dynamical consequences of combining the non-Hermitian skin effect with topological edge states. Focusing on the paradigmatic dissipative Hofstadter model, we find that the time-dependent particle density exhibits both chiral damping (due to the non-Hermitian skin effect) and edge-selective extremal damping (rooted in persistent topological edge states). We find that the time scales of chiral damping and edge-selective extremal damping decouple due to boundary-induced spectral topology, thus allowing observation of both effects under dynamics. We identify intermediate magnetic fields as the most favorable regime, since chiral damping is then partially recovered. More generally, our work sheds light on how open quantum systems are impacted by the combined presence of spectral and band topologies, and how their interplay can be probed directly. △ Less

Submitted 10 March, 2025; originally announced March 2025.

Comments: 6 pages, 4 figures

Magnetotransport in a graphite cylinder under quantizing fields

Authors: N. Kunchur, S. Galeski, F. Menges, R. Wawrzyńczak, C. Felser, T. Meng, J. Gooth

Abstract: We analyze the transport properties of curved, three-dimensional graphite samples in strong magnetic fields. Focusing on a millimeter-scale graphite cylinder as a prototypical curved object, we perform longitudinal and Hall voltage measurements while applying quantizing magnetic fields. These measurements are investigated as a function of field strength and angles. Most importantly, we find that a… ▽ More We analyze the transport properties of curved, three-dimensional graphite samples in strong magnetic fields. Focusing on a millimeter-scale graphite cylinder as a prototypical curved object, we perform longitudinal and Hall voltage measurements while applying quantizing magnetic fields. These measurements are investigated as a function of field strength and angles. Most importantly, we find that angle-dependent Shubnikov-de Hass oscillations are superimposed with angle-independent features. Reproducing the experimental observations, we introduce a network model that accounts for the cylindrical geometry effect by conceptualizing the cylinder as composed of strips of planar graphite in an effectively inhomogeneous magnetic field. Our work highlights how the interplay between geometric curvature and quantizing magnetic fields can be leveraged to engineer tunable spatial current densities within solid-state systems, and paves the way for understanding transport properties of curved and bent three-dimensional samples more generally. △ Less

Submitted 19 July, 2024; originally announced July 2024.

Giant quantum oscillations in thermal transport in low-density metals via electron absorption of phonons

Authors: B. Bermond, R. Wawrzynczak, S. Zherlitsyn, T. Kotte, T. Helm, D. Gorbunov, G. D. Gu, Q. Li, F. Janasz, T. Meng, F. Menges, C. Felser, J. Wosnitza, Adolfo G. Grushin, David Carpentier, J. Gooth, S. Galeski

Abstract: Oscillations of conductance observed in strong magnetic fields are a striking manifestation of the quantum dynamics of charge carriers in solids. The large charge carrier density in typical metals sets the scale of oscillations in both electrical and thermal conductivity, which characterize the Fermi surface. In semimetals, thermal transport at low-charge carrier density is expected to be phonon d… ▽ More Oscillations of conductance observed in strong magnetic fields are a striking manifestation of the quantum dynamics of charge carriers in solids. The large charge carrier density in typical metals sets the scale of oscillations in both electrical and thermal conductivity, which characterize the Fermi surface. In semimetals, thermal transport at low-charge carrier density is expected to be phonon dominated, yet several experiments observe giant quantum oscillations in thermal transport. This raises the question of whether there is an overarching mechanism leading to sizable oscillations that survives in phonon-dominated semimetals. In this work, we show that such a mechanism exists. It relies on the peculiar phase-space allowed for phonon scattering by electrons when only a few Landau levels are filled. Our measurements on the Dirac semimetal ZrTe5 support this counter-intuitive mechanism through observation of pronounced thermal quantum oscillations, since they occur in similar magnitude and phase in directions parallel and transverse to the magnetic field. Our phase-space argument applies to all low-density semimetals, topological or not, including graphene and bismuth. Our work illustrates that phonon absorption can be leveraged to reveal degrees of freedom through their imprint on longitudinal thermal transport. △ Less

Submitted 26 February, 2024; originally announced February 2024.

Journal ref: Proc. Natl. Acad. Sci. 122 (10) e2408546122, (2025)

Deciphering Interphase Instability of Lithium Metal Batteries with Localized High-Concentration Electrolytes at Elevated Temperatures

Authors: Tao Meng, Shanshan Yang, Yitong Peng, Xiwei Lan, Pingan Li, Kangjia Hu, Xianluo Hu

Abstract: Lithium metal batteries (LMBs), when coupled with a localized high-concentration electrolyte and a high-voltage nickel-rich cathode, offer a solution to the increasing demand for high energy density and long cycle life. However, the aggressive electrode chemistry poses safety risks to LMBs at higher temperatures and cutoff voltages. Here, we decipher the interphase instability in LHCE-based LMBs w… ▽ More Lithium metal batteries (LMBs), when coupled with a localized high-concentration electrolyte and a high-voltage nickel-rich cathode, offer a solution to the increasing demand for high energy density and long cycle life. However, the aggressive electrode chemistry poses safety risks to LMBs at higher temperatures and cutoff voltages. Here, we decipher the interphase instability in LHCE-based LMBs with a Ni0.8Co0.1Mn0.1O2 cathode at elevated temperatures. Our findings reveal that the generation of fluorine radicals in the electrolyte induces the solvent decomposition and consequent chain reactions, thereby reconstructing the cathode electrolyte interphase (CEI) and degrading battery cyclability. As further evidenced, introducing an acid scavenger of dimethoxydimethylsilane (DODSi) significantly boosts CEI stability with suppressed microcracking. A Ni0.8Co0.1Mn0.1O2||Li cell with this DODSi-functionalized LHCE achieves an unprecedented capacity retention of 93.0% after 100 cycles at 80 °C. This research provides insights into electrolyte engineering for practical LMBs with high safety under extreme temperatures. △ Less

Submitted 11 January, 2024; originally announced January 2024.

Comments: 10 pages, 8 figures

Nonlinear response functions and disorder: the case of photogalvanic effect

Authors: Konstantinos Ladovrechis, Tobias Meng

Abstract: We investigate the impact of disorder in the form of impurity scattering on a generalized version of the circular photogalvanic effect (CPGE) in Weyl semimetals where the frequency detuning between the two orthogonally polarized beams is nonzero. Considering a minimal model with two Weyl nodes at different energies, we employ the self-consistent Born approximation to unravel the dependence of the… ▽ More We investigate the impact of disorder in the form of impurity scattering on a generalized version of the circular photogalvanic effect (CPGE) in Weyl semimetals where the frequency detuning between the two orthogonally polarized beams is nonzero. Considering a minimal model with two Weyl nodes at different energies, we employ the self-consistent Born approximation to unravel the dependence of the associated two-point retarded Green's function on the strength of intra- and internode scattering, frequency detuning, and energy difference between the two Weyl nodes. In the case of intranode scattering only, the second-order current density acquires Drude-like features, which we elucidate further by introducing an effective scattering strength. The Drude-like theory can even describe the second-order response in the presence of strong internode scattering, provided the latter has a linear interdependence with the intranode scattering. By properly adjusting the frequency detuning, we also find the real part of the two-point retarded Green's function to be reminiscent of a "quantized CPGE"-like form, although the imaginary part of the latter function is in general finite, and the second-order current density oscillates with time due to the finite frequency detuning. We finally conclude with an outlook on possible experimental consequences. △ Less

Submitted 9 October, 2025; v1 submitted 27 September, 2023; originally announced September 2023.

Comments: 15 pages, 12 figures

Journal ref: Phys. Rev. Research 7, 033291 (2025)

Anomalous Shubnikov-de Haas effect and observation of the Bloch-Grüneisen temperature in the Dirac semimetal ZrTe5

Authors: S. Galeski, K. Araki, O. K. Forslund, R. Wawrzynczak, H. F. Legg, P. K. Sivakumar, U. Miniotaite, F. Elson, M. Månsson, C. Witteveen, F. O. von Rohr, A. Q. R. Baron, D. Ishikawa, Q. Li, G. Gu, L. X. Zhao, W. L. Zhu, G. F. Chen, Y. Wang, S. S. P. Parkin, D. Gorbunov, S. Zherlitsyn, B. Vlaar, D. H. Nguyen, S. Paschen , et al. (7 additional authors not shown)

Abstract: Appearance of quantum oscillations (QO) in both thermodynamic and transport properties of metals at low temperatures is the most striking experimental consequence of the existence of a Fermi surface (FS). The frequency of these oscillations and the temperature dependence of their amplitude provides essential information about the FS topology and fermionic quasiparticle properties. Here, we report… ▽ More Appearance of quantum oscillations (QO) in both thermodynamic and transport properties of metals at low temperatures is the most striking experimental consequence of the existence of a Fermi surface (FS). The frequency of these oscillations and the temperature dependence of their amplitude provides essential information about the FS topology and fermionic quasiparticle properties. Here, we report the observation of an anomalous suppression of the QO amplitude seen in resistivity (Shubnikov de-Haas effect) at sub-kelvin temperatures in ZrTe5 samples with a single small FS sheet comprising less than 5% of the first Brillouin zone. By comparing these results with measurements of the magneto-acoustic QO and the recovery of the usual Lifshitz-Kosevich behavior of the Shubnikov de-Haas (SdH) effect in ZrTe$_5$ samples with a multi-sheet FS, we show that the suppression of the SdH effect originates from a decoupling of the electron liquid from the lattice. On crossing the so-called Bloch-Grüneisen temperature, T$_BG$, electron-phonon scattering becomes strongly suppressed and in the absence of Umklapp scattering the electronic liquid regains Galilean invariance. In addition, we show, using a combination of zero-field electrical conductivity and ultrasonic-absorption measurements, that entering this regime leads to an abrupt increase of electronic viscosity. △ Less

Submitted 31 January, 2024; v1 submitted 19 September, 2023; originally announced September 2023.

Edge-selective extremal damping from topological heritage of dissipative Chern insulators

Authors: Suraj S. Hegde, Toni Ehmcke, Tobias Meng

Abstract: One of the most important practical hallmarks of topological matter is the presence of topologically protected, exponentially localised edge states at interfaces of regions characterised by unequal topological invariants. Here, we show that even when driven far from their equilibrium ground state, Chern insulators can inherit topological edge features from their parent Hamiltonian. In particular,… ▽ More One of the most important practical hallmarks of topological matter is the presence of topologically protected, exponentially localised edge states at interfaces of regions characterised by unequal topological invariants. Here, we show that even when driven far from their equilibrium ground state, Chern insulators can inherit topological edge features from their parent Hamiltonian. In particular, we show that the asymptotic long-time approach of the non-equilibrium steady state, governed by a Lindblad Master equation, can exhibit edge-selective extremal damping. This phenomenon derives from edge states of non-Hermitian extensions of the parent Chern insulator Hamiltonian. The combination of (non-Hermitian) topology and dissipation hence allows to design topologically robust, spatially localised damping patterns. △ Less

Submitted 29 December, 2023; v1 submitted 18 April, 2023; originally announced April 2023.

Comments: 4pages, 6 figures + Supplemental material. Published in Phys. Rev. Lett

Journal ref: Phys. Rev. Lett. 131, 256601(2023)

Quantum-Hall physics and three dimensions

Authors: Johannes Gooth, Stanislaw Galeski, Tobias Meng

Abstract: The discovery of the quantum Hall effect (QHE) in 1980 marked a turning point in condensed matter physics: given appropriate experimental conditions, the Hall conductivity σ_xy of a two-dimensional (2D) electron system is exactly quantized. But what happens to the QHE in three dimensions (3D)? Experiments over the past 40 years showed that some of the remarkable physics of the QHE, in particular p… ▽ More The discovery of the quantum Hall effect (QHE) in 1980 marked a turning point in condensed matter physics: given appropriate experimental conditions, the Hall conductivity σ_xy of a two-dimensional (2D) electron system is exactly quantized. But what happens to the QHE in three dimensions (3D)? Experiments over the past 40 years showed that some of the remarkable physics of the QHE, in particular plateau-like Hall conductivities σ_xy accompanied by minima in the longitudinal resistivity \r{ho}_xx, can also be found in 3D materials. However, since typically \r{ho}_xx remains finite and a quantitative relation between σ_xy and the conductance quantum e^2/h could not be established, the role of quantum Hall physics in 3D remains unsettled. Following a recent series of exciting experiments, the QHE in 3D has now returned to the centre stage. Here, we summarize the leap in understanding of 3D matter in magnetic fields emerging from these experiments. △ Less

Submitted 11 November, 2022; originally announced November 2022.

Journal ref: Rep. Prog. Phys. 86, 044501 (2023)

Black hole mirages: electron lensing and Berry curvature effects in inhomogeneously tilted Weyl semimetals

Authors: Andreas Haller, Suraj Hegde, Chen Xu, Christophe De Beule, Thomas L. Schmidt, Tobias Meng

Abstract: We study electronic transport in Weyl semimetals with spatially varying nodal tilt profiles. We find that the flow of electrons can be guided precisely by judiciously chosen tilt profiles. In a broad regime of parameters, we show that electron flow is described well by semiclassical equations of motion similar to the ones governing gravitational attraction. This analogy provides a physically trans… ▽ More We study electronic transport in Weyl semimetals with spatially varying nodal tilt profiles. We find that the flow of electrons can be guided precisely by judiciously chosen tilt profiles. In a broad regime of parameters, we show that electron flow is described well by semiclassical equations of motion similar to the ones governing gravitational attraction. This analogy provides a physically transparent tool for designing tiltronic devices like electronic lenses. The analogy to gravity circumvents the notoriously difficult full-fledged description of inhomogeneous solids. A comparison to microscopic lattice simulations shows that it is only valid for trajectories sufficiently far from analogue black holes. We finally comment on the Berry curvature-driven transverse motion and relate the latter to spin precession physics. △ Less

Submitted 20 February, 2023; v1 submitted 28 October, 2022; originally announced October 2022.

Comments: Replaced with revised version for SciPost resubmission. 38 pages, 12 figures

Journal ref: SciPost Phys. 14, 119 (2023)

Gross-Neveu-Heisenberg criticality from $2+\boldsymbolε$ expansion

Authors: Konstantinos Ladovrechis, Shouryya Ray, Tobias Meng, Lukas Janssen

Abstract: The Gross-Neveu-Heisenberg universality class describes a continuous quantum phase transition between a Dirac semimetal and an antiferromagnetic insulator. Such quantum critical points have originally been discussed in the context of Hubbard models on $π$-flux and honeycomb lattices, but more recently also in Bernal-stacked bilayer models, of potential relevance for bilayer graphene. Here, we demo… ▽ More The Gross-Neveu-Heisenberg universality class describes a continuous quantum phase transition between a Dirac semimetal and an antiferromagnetic insulator. Such quantum critical points have originally been discussed in the context of Hubbard models on $π$-flux and honeycomb lattices, but more recently also in Bernal-stacked bilayer models, of potential relevance for bilayer graphene. Here, we demonstrate how the critical behavior of this fermionic universality class can be computed within an $ε$ expansion around the lower critical space-time dimension of two. This approach is complementary to the previously studied expansion around the upper critical dimension of four. The crucial technical novelty near the lower critical dimension is the presence of different four-fermion interaction channels at the critical point, which we take into account in a Fierz-complete way. By interpolating between the lower and upper critical dimensions, we obtain improved estimates for the critical exponents in 2+1 space-time dimensions. For the situation relevant to single-layer graphene, we find an unusually small leading-correction-to-scaling exponent, arising from the competition between different interaction channels. This suggests that corrections to scaling may need to be taken into account when comparing analytical estimates with numerical data from finite-size extrapolations. △ Less

Submitted 3 February, 2023; v1 submitted 6 September, 2022; originally announced September 2022.

Comments: 14 pages, 15 figures

Journal ref: Phys. Rev. B 107, 035151 (2023)

Engineering a pure Dirac regime in ZrTe$_5$

Authors: Jorge I. Facio, Elisabetta Nocerino, Ion Cosma Fulga, Rafal Wawrzynczak, Joanna Brown, Genda Gu, Qiang Li, Martin Mansson, Yasmine Sassa, Oleh Ivashko, Martin v. Zimmermann, Felix Mende, Johannes Gooth, Stanislaw Galeski, Jeroen van den Brink, Tobias Meng

Abstract: Real-world topological semimetals typically exhibit Dirac and Weyl nodes that coexist with trivial Fermi pockets. This tends to mask the physics of the relativistic quasiparticles. Using the example of ZrTe5, we show that strain provides a powerful tool for in-situ tuning of the band structure such that all trivial pockets are pushed far away from the Fermi energy, but only for a certain range of… ▽ More Real-world topological semimetals typically exhibit Dirac and Weyl nodes that coexist with trivial Fermi pockets. This tends to mask the physics of the relativistic quasiparticles. Using the example of ZrTe5, we show that strain provides a powerful tool for in-situ tuning of the band structure such that all trivial pockets are pushed far away from the Fermi energy, but only for a certain range of Van der Waals gaps. Our results naturally reconcile contradicting reports on the presence or absence of additional pockets in ZrTe$_5$, and provide a clear map of where to find a pure three-dimensional Dirac semimetallic phase in the structural parameter space of the material. △ Less

Submitted 5 December, 2022; v1 submitted 28 June, 2022; originally announced June 2022.

Comments: 17 pages

Journal ref: SciPost Phys. 14, 066 (2023)

Signatures of a magnetic-field-induced Lifshitz transition in the ultra-quantum limit of the topological semimetal ZrTe$_5$

Authors: S. Galeski, H. F. Legg, R. Wawrzyńczak, T. Förster, S. Zherlitsyn, D. Gorbunov, P. M. Lozano, Q. Li, G. D. Gu, C. Felser, J. Wosnitza, T. Meng, J Gooth

Abstract: The quantum limit (QL) of an electron liquid, realised at strong magnetic fields, has long been proposed to host a wealth of strongly correlated states of matter. Electronic states in the QL are, for example, quasi-one dimensional (1D), which implies perfectly nested Fermi surfaces prone to instabilities. Whereas the QL typically requires unreachably strong magnetic fields, the topological semimet… ▽ More The quantum limit (QL) of an electron liquid, realised at strong magnetic fields, has long been proposed to host a wealth of strongly correlated states of matter. Electronic states in the QL are, for example, quasi-one dimensional (1D), which implies perfectly nested Fermi surfaces prone to instabilities. Whereas the QL typically requires unreachably strong magnetic fields, the topological semimetal ZrTe$_5$ has been shown to reach the QL at fields of only a few Tesla. Here, we characterize the QL of ZrTe$_5$ at fields up to 64 T by a combination of electrical-transport and ultrasound measurements. We find that the Zeeman effect in ZrTe$_5$ enables an efficient tuning of the 1D Landau band structure with magnetic field. This results in a Lifshitz transition to a 1D Weyl regime in which perfect charge neutrality can be achieved. Since no instability-driven phase transitions destabilise the 1D electron liquid for the investigated field strengths and temperatures, our analysis establishes ZrTe$_5$ as a thoroughly understood platform for potentially inducing more exotic interaction-driven phases at lower temperatures. △ Less

Submitted 25 April, 2022; originally announced April 2022.

Journal ref: Nature Communications 13, 7418 (2022)

Steering Majorana braiding via skyrmion-vortex pairs: a scalable platform

Authors: Jonas Nothhelfer, Sebastián A. Díaz, Stephan Kessler, Tobias Meng, Matteo Rizzi, Kjetil M. D. Hals, Karin Everschor-Sitte

Abstract: Majorana zero modes are quasiparticles that hold promise as building blocks for topological quantum computing. However, the litmus test for their detection, the observation of exotic non-abelian statistics revealed by braiding, has so far eluded experimental efforts. Here we take advantage of the fact that skyrmion-vortex pairs in superconductor-ferromagnet heterostructures harboring Majorana zero… ▽ More Majorana zero modes are quasiparticles that hold promise as building blocks for topological quantum computing. However, the litmus test for their detection, the observation of exotic non-abelian statistics revealed by braiding, has so far eluded experimental efforts. Here we take advantage of the fact that skyrmion-vortex pairs in superconductor-ferromagnet heterostructures harboring Majorana zero modes can be easily manipulated in two spatial dimensions. We adiabatically braid the hybrid topological structures and explicitly confirm the non-abelian statistics of the Majorana zero modes numerically using a self-consistent calculation of the superconducting order parameter. Our proposal of controlling skyrmion-vortex pairs provides the necessary leeway toward a scalable topological quantum computing platform. △ Less

Submitted 26 October, 2021; originally announced October 2021.

Comments: 9 pages, 7 figures

Journal ref: Phys. Rev. B 105, 224509 (2022)

Renormalization approach to the superconducting Kondo model

Authors: Steffen Sykora, Tobias Meng

Abstract: An approach to bound states based on unitary transformations of Hamiltonians is presented. The method is applied to study the interaction between electrons in a BCS $s$-wave superconductor and a quantum spin. It is shown that known results from the t-matrix method and numerical studies are reproduced by this new method. As a main advantage, the method can straightforwardly be extended to study the… ▽ More An approach to bound states based on unitary transformations of Hamiltonians is presented. The method is applied to study the interaction between electrons in a BCS $s$-wave superconductor and a quantum spin. It is shown that known results from the t-matrix method and numerical studies are reproduced by this new method. As a main advantage, the method can straightforwardly be extended to study the topological properties of combined bound states in chains of many magnetic impurities. It also provides a uniform picture of the interplay between the Yu-Shiba-Rusinov (YSR) bound states and the Kondo singlet state. △ Less

Submitted 24 March, 2022; v1 submitted 24 September, 2021; originally announced September 2021.

Comments: 29 pages, 7 figures, Submission to SciPost

Journal ref: SciPost Phys. 13, 016 (2022)

Propagation of longitudinal acoustic phonons in ZrTe$_{\boldsymbol{5}}$ exposed to a quantizing magnetic field

Authors: Toni Ehmcke, Stanislaw Galeski, Denis Gorbunov, Sergei Zherlitsyn, Joachim Wosnitza, Johannes Gooth, Tobias Meng

Abstract: The compound ZrTe$_5$ has recently been connected to a charge-density-wave (CDW) state with intriguing transport properties. Here, we investigate quantum oscillations in ultrasound measurements that microscopically originate from electron-phonon coupling and analyze how these would be affected by the presence or absence of a CDW. We calculate the phonon self-energy due to electron-phonon coupling,… ▽ More The compound ZrTe$_5$ has recently been connected to a charge-density-wave (CDW) state with intriguing transport properties. Here, we investigate quantum oscillations in ultrasound measurements that microscopically originate from electron-phonon coupling and analyze how these would be affected by the presence or absence of a CDW. We calculate the phonon self-energy due to electron-phonon coupling, and from there deduce the sound-velocity renormalization and sound attenuation. We find that the theoretical predictions for a metallic Dirac model resemble the experimental data on a quantitative level for magnetic fields up to the quantum-limit regime. △ Less

Submitted 22 November, 2021; v1 submitted 8 September, 2021; originally announced September 2021.

Comments: 14 pages, 7 figures

Journal ref: Phys. Rev. B 104, 245117 (2021)

Artificial event horizons in Weyl semimetal heterostructures and their non-equilibrium signatures

Authors: Christophe De Beule, Solofo Groenendijk, Tobias Meng, Thomas L. Schmidt

Abstract: We investigate transport in type-I/type-II Weyl semi\-metal heterostructures that realize effective black- or white-hole event horizons. We provide an exact solution to the scattering problem at normal incidence and low energies, both for a sharp and a slowly-varying Weyl cone tilt profile. In the latter case, we find two channels with transmission amplitudes analog to those of Hawking radiation.… ▽ More We investigate transport in type-I/type-II Weyl semi\-metal heterostructures that realize effective black- or white-hole event horizons. We provide an exact solution to the scattering problem at normal incidence and low energies, both for a sharp and a slowly-varying Weyl cone tilt profile. In the latter case, we find two channels with transmission amplitudes analog to those of Hawking radiation. Whereas the Hawking-like signatures of these two channels cancel in equilibrium, we demonstrate that one can favor the contribution of either channel using a non-equilibrium state, either by irradiating the type-II region or by coupling it to a magnetic lead. This in turn gives rise to a peak in the two-terminal differential conductance which can serve as an experimental indicator of the artificial event horizon. △ Less

Submitted 23 November, 2021; v1 submitted 28 June, 2021; originally announced June 2021.

Comments: 28 pages, 7 figures; published version

Journal ref: SciPost Phys. 11, 095 (2021)

Hawking fragmentation and Hawking attenuation in Weyl semimetals

Authors: Daniel Sabsovich, Paul Wunderlich, Victor Fleurov, Dmitry I. Pikulin, Roni Ilan, Tobias Meng

Abstract: We study black and white hole analogues in Weyl semimetals with inhomogenous nodal tilts. We study how the presence of a microscopic lattice, giving rise to low-energy fermion doubler states at large momenta that are not present for elementary particles, affects the analogy between Weyl Hamiltonians and general relativity. Using a microscopic tight-binding lattice model, we find the doubler states… ▽ More We study black and white hole analogues in Weyl semimetals with inhomogenous nodal tilts. We study how the presence of a microscopic lattice, giving rise to low-energy fermion doubler states at large momenta that are not present for elementary particles, affects the analogy between Weyl Hamiltonians and general relativity. Using a microscopic tight-binding lattice model, we find the doubler states to give rise to Hawking fragmentation and Hawking attenuation of wavepackets by the analogue event horizon. These phenomena depend on an analogue Hawking temperature, and can be measured in metamaterials and solids, as we confirm by numerical simulations. △ Less

Submitted 3 November, 2021; v1 submitted 28 June, 2021; originally announced June 2021.

Comments: 12 pages, 6 figures

Journal ref: Phys. Rev. Research 4, 013055 (2022)

Competing magnetic orders and multipolar Weyl fermions in 227 pyrochlore iridates

Authors: Konstantinos Ladovrechis, Tobias Meng, Bitan Roy

Abstract: Owing to comparably strong spin-orbit coupling and Hubbard interaction, iridium based 227 pyrochlore oxides harbor a rich confluence of competing magnetic orders and emergent multipolar Weyl quasiparticles. Here we show that this family of materials is predominantly susceptible toward the nucleation of electronic noncoplanar all-in all-out (AIAO) and three-in one-out (3I1O) orders, respectively tr… ▽ More Owing to comparably strong spin-orbit coupling and Hubbard interaction, iridium based 227 pyrochlore oxides harbor a rich confluence of competing magnetic orders and emergent multipolar Weyl quasiparticles. Here we show that this family of materials is predominantly susceptible toward the nucleation of electronic noncoplanar all-in all-out (AIAO) and three-in one-out (3I1O) orders, respectively transforming under the singlet $A_{2u}$ and triplet $T_{1u}$ representations, supporting octupolar and dipolar Weyl fermions, and favored by strong on-site Hubbard and nearest-neighbor ferromagnetic interaction. Furthermore, a coplanar magnetic order generically appears as an intermediate phase between them. This order transforms under the triplet $T_{2u}$ representation and also hosts octupolar Weyl fermions. With the AIAO and 3I1O phases possibly being realized in (Nd$_{1-x}$Pr$_{x}$)$_2$Ir$_2$O$_7$ when $x=0$ and 1, respectively, the intervening $T_{2u}$ order can in principle be found at an intermediate doping ($0<x<1$) or in pressured (hydrostatic) Nd$_2$Ir$_2$O$_7$. △ Less

Submitted 25 June, 2021; v1 submitted 18 December, 2020; originally announced December 2020.

Comments: Published version: 6 Pages, 3 Figures (Supplemental Materials: As ancillary file)

Journal ref: Phys. Rev. B 103, 241116 (2021)

Universal Hall conductance scaling in non-Hermitian Chern insulators

Authors: Solofo Groenendijk, Thomas L. Schmidt, Tobias Meng

Abstract: We investigate the Hall conductance of a two-dimensional Chern insulator coupled to an environment causing gain and loss. Introducing a biorthogonal linear response theory, we show that sufficiently strong gain and loss lead to a characteristic non-analytical contribution to the Hall conductance. Near its onset, this contribution exhibits a universal power-law with a power 3/2 as a function of Dir… ▽ More We investigate the Hall conductance of a two-dimensional Chern insulator coupled to an environment causing gain and loss. Introducing a biorthogonal linear response theory, we show that sufficiently strong gain and loss lead to a characteristic non-analytical contribution to the Hall conductance. Near its onset, this contribution exhibits a universal power-law with a power 3/2 as a function of Dirac mass, chemical potential and gain strength. Our results pave the way for the study of non-Hermitian topology in electronic transport experiments. △ Less

Submitted 22 September, 2020; originally announced September 2020.

Comments: 5+3 pages, 2 figures

Journal ref: Phys. Rev. Research 3, 023001 (2021)

Origin of the quasi-quantized Hall effect in ZrTe5

Authors: Stanislaw Galeski, Toni Ehmcke, Rafal Wawrzynczak, Pedro Mercado Lozano, Kyungjune Cho, Ankit Sharma, Souvik Das, Felix Kuster, Paolo Sessi, Manuel Brando, Robert Kuchler, Anastasios Markou, Markus Konig, Claudia Felser, Yasmine Sassa, Qiang Li, Genda Gu, Peter Swekis, Martin Zimmermann, Oleh Ivashko, Dennis I. Gorbunov, Sergei Zherlitsyn, Tobias Forster, Stuart Parkin, Joachim Wosnitza , et al. (2 additional authors not shown)

Abstract: The quantum Hall effect (QHE) is traditionally considered a purely two-dimensional (2D) phenomenon. Recently, a three-dimensional (3D) version of the QHE has been reported in the Dirac semimetal ZrTe5. It was proposed to arise from a magnetic-field-driven Fermi surface instability, transforming the original 3D electron system into a stack of 2D sheets. Here, we report thermodynamic, thermoelectric… ▽ More The quantum Hall effect (QHE) is traditionally considered a purely two-dimensional (2D) phenomenon. Recently, a three-dimensional (3D) version of the QHE has been reported in the Dirac semimetal ZrTe5. It was proposed to arise from a magnetic-field-driven Fermi surface instability, transforming the original 3D electron system into a stack of 2D sheets. Here, we report thermodynamic, thermoelectric and charge transport measurements on ZrTe5 in the quantum Hall regime. The measured thermodynamic properties: magnetization and ultrasound propagation, show no signatures of a Fermi surface instability, consistent with in-field single crystal X-ray diffraction. Instead, a direct comparison of the experimental data with linear response calculations based on an effective 3D Dirac Hamiltonian suggests that the quasi-quantization of the observed Hall response is an intrinsic property of the 3D electronic structure. Our findings render the Hall effect in ZrTe5 a truly 3D counterpart of the QHE in 2D systems. △ Less

Submitted 22 February, 2021; v1 submitted 26 May, 2020; originally announced May 2020.

Journal ref: Nature Communications 12, 3197 (2021)

Bosonization in 2+1 dimensions via Chern-Simons bosonic particle-vortex duality

Authors: Oguz Turker, Jeroen van den Brink, Tobias Meng, Flavio S. Nogueira

Abstract: Dualities provide deep insight into physics by relating two seemingly distinct theories. Here we consider a duality between lattice fermions and bosons in (2+1) spacetime dimensions, relating free massive Dirac fermions to Abelian Chern-Simons Higgs (ACSH) bosons. To establish the duality we represent the exact partition function of the lattice fermions in terms of the writhe of fermionic worldlin… ▽ More Dualities provide deep insight into physics by relating two seemingly distinct theories. Here we consider a duality between lattice fermions and bosons in (2+1) spacetime dimensions, relating free massive Dirac fermions to Abelian Chern-Simons Higgs (ACSH) bosons. To establish the duality we represent the exact partition function of the lattice fermions in terms of the writhe of fermionic worldlines. On the bosonic side the partition function is expressed in the writhe of the vortex loops of the particle-vortex dual of the ACSH Lagrangian. In the continuum and scaling limit we show these to be identical. This result can be understood from the closed fermionic worldlines being direct mappings of the ACSH vortex loops, with the writhe keeping track of particle statistics. △ Less

Submitted 27 October, 2020; v1 submitted 22 April, 2020; originally announced April 2020.

Comments: 13 pages, 4 figures; v2 matches published version

Journal ref: Phys. Rev. D 102, 034506 (2020)

Unconventional Hall response in the quantum limit of HfTe5

Authors: S. Galeski, X. Zhao, R. Wawrzyńczak, T. Meng, T. Förster, P. M. Lozano, S. Honnali, N. Lamba, T. Ehmcke, A. Markou, Q. Li, G. Gu, W. Zhu, J. Wosnitza, C. Felser, G. F. Chen, J. Gooth

Abstract: Interacting electrons confined to their lowest Landau level in a high magnetic field can form a variety of correlated states, some of which manifest themselves in a Hall effect. Although such states have been predicted to occur in three dimensional semimetals, a corresponding Hall response has not yet been experimentally observed. Here, we report the observation of an unconventional Hall response… ▽ More Interacting electrons confined to their lowest Landau level in a high magnetic field can form a variety of correlated states, some of which manifest themselves in a Hall effect. Although such states have been predicted to occur in three dimensional semimetals, a corresponding Hall response has not yet been experimentally observed. Here, we report the observation of an unconventional Hall response in the quantum limit of the bulk semimetal HfTe5, adjacent to the three-dimensional quantum Hall effect of a single electron band at low magnetic fields. The additional plateau-like feature in the Hall conductivity of the lowest Landau level is accompanied by a Shubnikov-de Haas minimum in the longitudinal electrical resistivity and its magnitude relates as 3/5 to the height of the last plateau of the three-dimensional quantum Hall effect. Our findings are consistent with strong electron-electron interactions, stabilizing an unconventional variant of the Hall effect in a three-dimensional material in the quantum limit. △ Less

Submitted 19 October, 2020; v1 submitted 16 March, 2020; originally announced March 2020.

Comments: 26 pages with 4 figures

Journal ref: Nature Communications 11, 5926 (2020)

Pseudo field effects in type II Weyl semimetals: new probes for over tilted cones

Authors: Daniel Sabsovich, Tobias Meng, Dmitry I. Pikulin, Raquel Queiroz, Roni Ilan

Abstract: We study the effects of pseudo-magnetic fields on Weyl semimetals with over-tilted Weyl cones, or type II cones. We compare the phenomenology of the resulting pseudo-Landau levels in the type II Weyl semimetal to the known case of type I cones. We predict that due to the nature of the chiral Landau level resulting from a magnetic field, a pseudo-magnetic field, or their combination, the optical co… ▽ More We study the effects of pseudo-magnetic fields on Weyl semimetals with over-tilted Weyl cones, or type II cones. We compare the phenomenology of the resulting pseudo-Landau levels in the type II Weyl semimetal to the known case of type I cones. We predict that due to the nature of the chiral Landau level resulting from a magnetic field, a pseudo-magnetic field, or their combination, the optical conductivity can be utilized to detect a type II phase and deduce the direction of the tilt. Finally, we discuss ways to engineer homogeneous and inhomogeneous type II semimetals via generalizations of known layered constructions in order to create controlled pseudo-magnetic fields and over-tilted cones. △ Less

Submitted 19 November, 2020; v1 submitted 11 March, 2020; originally announced March 2020.

Comments: 12 pages, 8 figures

Journal ref: Journal of Physics: Condensed Matter 32 ,484002 (2020)

Negative longitudinal magnetoconductance at weak fields in Weyl semimetals

Authors: Andy Knoll, Carsten Timm, Tobias Meng

Abstract: Weyl semimetals are topological materials that provide a condensed-matter realization of the chiral anomaly. A positive longitudinal magnetoconductance quadratic in magnetic field has been promoted as a diagnostic for this anomaly. By solving the Boltzmann equation analytically, we show that the magnetoconductance can become negative in the experimentally relevant semiclassical regime of weak magn… ▽ More Weyl semimetals are topological materials that provide a condensed-matter realization of the chiral anomaly. A positive longitudinal magnetoconductance quadratic in magnetic field has been promoted as a diagnostic for this anomaly. By solving the Boltzmann equation analytically, we show that the magnetoconductance can become negative in the experimentally relevant semiclassical regime of weak magnetic fields. This effect is due to the simultaneous presence of the Berry phase and the orbital magnetic moment of carriers and occurs for sufficiently strong intervalley scattering. △ Less

Submitted 6 May, 2020; v1 submitted 17 December, 2019; originally announced December 2019.

Comments: 5 pages + supplemental material, 2 figures

Journal ref: Phys. Rev. B 101, 201402 (2020)

Microscopic theory of fractional excitations in gapless bilayer quantum Hall states: semi-quantized quantum Hall states

Authors: Oğuz Türker, Tobias Meng

Abstract: We derive the low-energy theory of semi-quantized quantum Hall states, a recently observed class of gapless bilayer fractional quantum Hall states. Our theory shows these states to feature gapless quasiparticles of fractional charge coupled to an emergent Chern-Simons gauge field. These gapless quasiparticles can be understood as composites of electrons and Laughlin-like quasiparticles. We show th… ▽ More We derive the low-energy theory of semi-quantized quantum Hall states, a recently observed class of gapless bilayer fractional quantum Hall states. Our theory shows these states to feature gapless quasiparticles of fractional charge coupled to an emergent Chern-Simons gauge field. These gapless quasiparticles can be understood as composites of electrons and Laughlin-like quasiparticles. We show that semi-quantized quantum Hall states exhibit perfect interlayer drag, host non-Fermi liquid physics, and serve as versatile parent states for fully gapped topological phases hosting anyonic excitations. △ Less

Submitted 12 March, 2020; v1 submitted 23 October, 2019; originally announced October 2019.

Comments: 33 pages

Journal ref: SciPost Phys. 8, 031 (2020)

An exactly soluble model for a fractionalized Weyl semimetal

Authors: Fabian Hotz, Apoorv Tiwari, Oguz Turker, Tobias Meng, Ady Stern, Maciej Koch-Janusz, Titus Neupert

Abstract: We construct an exactly solvable lattice model of a fractional Weyl semimetal (FWS). The low energy theory of this strongly interacting state is that of a Weyl semimetal built out of fractionally charged fermions. We show the existence of a universally quantized and fractional circular photogalvanic effect (CPGE) and a violation of the Wiedemann-Franz law in the system. Together with a spectral ga… ▽ More We construct an exactly solvable lattice model of a fractional Weyl semimetal (FWS). The low energy theory of this strongly interacting state is that of a Weyl semimetal built out of fractionally charged fermions. We show the existence of a universally quantized and fractional circular photogalvanic effect (CPGE) and a violation of the Wiedemann-Franz law in the system. Together with a spectral gap in the single-particle electronic Green's function they provide strong experimental signatures for this exotic gapless state of matter. △ Less

Submitted 17 July, 2019; originally announced July 2019.

Journal ref: Phys. Rev. Research 1, 033029 (2019)

Coupled-wire constructions: a Luttinger liquid approach to topology

Authors: Tobias Meng

Abstract: Coupled-wire constructions use bosonization to analytically tackle the strong interactions underlying fractional topological states of matter. We give an introduction to this technique, discuss its strengths and weaknesses, and provide an overview of the main achievements of coupled-wire constructions. Coupled-wire constructions use bosonization to analytically tackle the strong interactions underlying fractional topological states of matter. We give an introduction to this technique, discuss its strengths and weaknesses, and provide an overview of the main achievements of coupled-wire constructions. △ Less

Submitted 11 February, 2020; v1 submitted 24 June, 2019; originally announced June 2019.

Comments: Short introduction and review on coupled-wire constructions

Journal ref: Eur. Phys. J. Special Topics 229, 527 (2020)

Finite temperature effects on Majorana bound states in chiral $p$-wave superconductors

Authors: Henrik Schou Røising, Roni Ilan, Tobias Meng, Steven H. Simon, Felix Flicker

Abstract: We study Majorana fermions bound to vortex cores in a chiral $p$-wave superconductor at temperatures non-negligible compared to the superconducting gap. Thermal occupation of Caroli de Gennes-Matricon states, below the full gap, causes the free energy difference between the two fermionic parity sectors to decay algebraically with increasing temperature. The power law acquires an additional factor… ▽ More We study Majorana fermions bound to vortex cores in a chiral $p$-wave superconductor at temperatures non-negligible compared to the superconducting gap. Thermal occupation of Caroli de Gennes-Matricon states, below the full gap, causes the free energy difference between the two fermionic parity sectors to decay algebraically with increasing temperature. The power law acquires an additional factor of $T^{-1}$ for each bound state thermally excited. The zero-temperature result is exponentially recovered well below the minigap (lowest-lying CdGM level). Our results suggest that temperatures larger than the minigap may not be disastrous for topological quantum computation. We discuss the prospect of precision measurements of pinning forces on vortices as a readout scheme for Majorana qubits. △ Less

Submitted 8 April, 2019; v1 submitted 28 January, 2019; originally announced January 2019.

Comments: 11 pages, 8 figures; submission to SciPost

Journal ref: SciPost Phys. 6, 055 (2019)

Anisotropic electrical and thermal magnetotransport in the magnetic semimetal GdPtBi

Authors: Clemens Schindler, Stanislaw Galeski, Walter Schnelle, Rafał Wawrzyńczak, Wajdi Abdel-Haq, Satya N. Guin, Johannes Kroder, Nitesh Kumar, Chenguang Fu, Horst Borrmann, Chandra Shekhar, Claudia Felser, Tobias Meng, Adolfo G. Grushin, Yang Zhang, Yan Sun, Johannes Gooth

Abstract: The half-Heusler rare-earth intermetallic GdPtBi has recently gained attention due to peculiar magnetotransport phenomena that have been associated with the possible existence of Weyl fermions, thought to arise from the crossings of spin-split conduction and valence bands. On the other hand, similar magnetotransport phenomena observed in other rare-earth intermetallics have often been attributed t… ▽ More The half-Heusler rare-earth intermetallic GdPtBi has recently gained attention due to peculiar magnetotransport phenomena that have been associated with the possible existence of Weyl fermions, thought to arise from the crossings of spin-split conduction and valence bands. On the other hand, similar magnetotransport phenomena observed in other rare-earth intermetallics have often been attributed to the interaction of itinerant carriers with localized magnetic moments stemming from the $4f$-shell of the rare-earth element. In order to address the origin of the magnetotransport phenomena in GdPtBi, we performed a comprehensive study of the magnetization, electrical and thermal magnetoresistivity on two single-crystalline GdPtBi samples. In addition, we performed an analysis of the Fermi surface via Shubnikov-de Haas oscillations in one of the samples and compared the results to \emph{ab initio} band structure calculations. Our findings indicate that the electrical and thermal magnetotransport in GdPtBi cannot be solely explained by Weyl physics and is strongly influenced by the interaction of both itinerant charge carriers and phonons with localized magnetic Gd-ions and possibly also paramagnetic impurities. △ Less

Submitted 23 March, 2020; v1 submitted 4 October, 2018; originally announced October 2018.

Comments: 11 figures

Journal ref: Phys. Rev. B 101, 125119 (2020)

Dirac fermions in the heavy-fermion superconductors Ce(Co,Rh,Ir)In$_5$

Authors: Kent R. Shirer, Yan Sun, Maja D. Bachmann, Carsten Putzke, Toni Helm, Laurel E. Winter, Fedor F. Balakirev, Ross D. McDonald, James G. Analytis, Nityan L. Nair, Eric D. Bauer, Filip Ronning, Claudia Felser, Tobias Meng, Binghai Yan, Philip J. W. Moll

Abstract: The Ce(Co,Rh,Ir)In$_5$ family of ``Ce-115'' materials hosts an abundance of correlated electron behavior, including heavy-fermion physics, magnetism, superconductivity and nematicity. The complicated behavior of these entangled phenomena leads to a variety of exotic physical properties, which, despite the seemingly simple crystal structure of these compounds, remain poorly understood. It is genera… ▽ More The Ce(Co,Rh,Ir)In$_5$ family of ``Ce-115'' materials hosts an abundance of correlated electron behavior, including heavy-fermion physics, magnetism, superconductivity and nematicity. The complicated behavior of these entangled phenomena leads to a variety of exotic physical properties, which, despite the seemingly simple crystal structure of these compounds, remain poorly understood. It is generally accepted that the interplay between the itinerant and local character of Ce-$4f$ electrons is the key to their exotic behavior. Here, we report theoretical evidence that the Ce-115 materials are also topological semi-metals, with Dirac fermions around well-separated nodes. Dirac nodes in each compound are present on the $Γ-Z$ plane close to the Fermi level. As the Dirac bands are derived from In-orbitals, they occur in all family members irrespective of the transition metal (Co,Rh,Ir). We present the expected Fermi-arc surface state patterns and show the close proximity of a topological Lifshitz transition, which possibly explains the high field physics of Ce-115 materials. Experimentally, we highlight the surprising similarity of Ce(Co,Rh,Ir)In$_5$ in high magnetic fields, despite the distinctly different states of the Ce-$4f$ electrons. These results raise questions about the role Dirac fermions play in exotic transport behavior, and we propose this class of materials as a prime candidate for unconventional topological superconductivity. △ Less

Submitted 1 August, 2018; originally announced August 2018.

Spatially modulated heavy-fermion superconductivity in CeIrIn5

Authors: Maja D. Bachmann, G. M. Ferguson, Florian Theuss, Tobias Meng, Carsten Putzke, Toni Helm, K. R. Shirer, You-Sheng Li, K. A. Modic, Michael Nicklas, Markus Koenig, D. Low, Sayak Ghosh, Andrew P. Mackenzie, Frank Arnold, Elena Hassinger, Ross D. McDonald, Laurel E. Winter, Eric D. Bauer, Filip Ronning, B. J. Ramshaw, Katja C. Nowack, Philip J. W. Moll

Abstract: The ability to spatially modulate the electronic properties of solids has led to landmark discoveries in condensed matter physics as well as new electronic applications. Although crystals of strongly correlated metals exhibit a diverse set of electronic ground states, few approaches to spatially modulating their properties exist. Here we demonstrate spatial control over the superconducting state i… ▽ More The ability to spatially modulate the electronic properties of solids has led to landmark discoveries in condensed matter physics as well as new electronic applications. Although crystals of strongly correlated metals exhibit a diverse set of electronic ground states, few approaches to spatially modulating their properties exist. Here we demonstrate spatial control over the superconducting state in mesoscale samples of the canonical heavy-fermion superconductor CeIrIn5. We use a focused ion beam (FIB) to pattern crystals on the microscale, which tailors the strain induced by differential thermal contraction into specific areas of the device. The resulting non-uniform strain fields induce complex patterns of superconductivity due to the strong dependence of the transition temperature on the strength and direction of strain. Electrical transport and magnetic imaging of devices with different geometry show that the obtained spatial modulation of superconductivity agrees with predictions based on finite element simulations. These results present a generic approach to manipulating electronic order on micrometer length scales in strongly correlated matter. △ Less

Submitted 21 September, 2018; v1 submitted 13 July, 2018; originally announced July 2018.

Comments: 29 pages, 14 figures

Journal ref: Science 366, 221 (2019)

Unpaired Weyl nodes from Long-Ranged Interactions: Fate of Quantum Anomalies

Authors: Tobias Meng, Jan Carl Budich

Abstract: We study the effect of long-ranged interactions on Weyl semimetals. Such interactions can give rise to unpaired Weyl nodes, which we demonstrate by explicitly constructing a system with just a single node - a situation that is fundamentally forbidden by fermion doubling in non-interacting band structures. Adding a magnetic field, we investigate the fate of the chiral anomaly. Remarkably, as long a… ▽ More We study the effect of long-ranged interactions on Weyl semimetals. Such interactions can give rise to unpaired Weyl nodes, which we demonstrate by explicitly constructing a system with just a single node - a situation that is fundamentally forbidden by fermion doubling in non-interacting band structures. Adding a magnetic field, we investigate the fate of the chiral anomaly. Remarkably, as long as a system exhibits a single Weyl node in the absence of magnetic fields, arbitrarily weak fields qualitatively restore the lowest Landau level structure of a non-interacting Weyl semimetal. This underlines the universality of the chiral anomaly in the context of Weyl semimetals. We furthermore demonstrate how the topologically protected Fermi-arc surface states are modified by long-ranged interactions. △ Less

Submitted 10 December, 2018; v1 submitted 13 April, 2018; originally announced April 2018.

Comments: Supplemental Material available as an ancillary file

Journal ref: Phys. Rev. Lett. 122, 046402 (2019)

Uncovering Weyl Fermions in the Quantum Limit of NbP

Authors: K. A. Modic, Tobias Meng, Filip Ronning, Eric D. Bauer, Philip J. W. Moll, B. J. Ramshaw

Abstract: The Fermi surface topology of a Weyl semimetal (WSM) depends strongly on the position of the chemical potential. If it resides close to the band touching points (Weyl nodes), as it does in TaAs, separate Fermi surfaces of opposite chirality emerge, leading to novel phenomena such as the chiral magnetic effect. If the chemical potential lies too far from the nodes, however, the chiral Fermi surface… ▽ More The Fermi surface topology of a Weyl semimetal (WSM) depends strongly on the position of the chemical potential. If it resides close to the band touching points (Weyl nodes), as it does in TaAs, separate Fermi surfaces of opposite chirality emerge, leading to novel phenomena such as the chiral magnetic effect. If the chemical potential lies too far from the nodes, however, the chiral Fermi surfaces merge into a single large Fermi surface with no net chirality. This is realized in the WSM NbP, where the Weyl nodes lie far below the Fermi energy and where the transport properties in low magnetic fields show no evidence of chiral Fermi surfaces. Here we show that the behavior of NbP in high magnetic fields is nonetheless dominated by the presence of the Weyl nodes. Torque magnetometry up to 60 tesla reveals a change in the slope of $τ/B$ at the quantum limit B$^\star$ ($\approx 32\,\rm{T}$), where the chemical potential enters the $n=0$ Landau level. Numerical simulations show that this behaviour results from the magnetic field pulling the chemical potential to the chiral $n=0$ Landau level belonging to the Weyl nodes. These results show that high magnetic fields can uncover topological singularities in the underlying band structure of a potential WSM, and can recover topologically non-trivial experimental properties, even when the position of the chemical potential precludes their observation in zero magnetic field. △ Less

Submitted 22 February, 2018; originally announced February 2018.

Comments: 6 pages including 5 figures

Journal ref: Scientific Reports 9, Article number: 2095 (2019)

Z4 parafermions in one-dimensional fermionic lattices

Authors: Alessio Calzona, Tobias Meng, Maura Sassetti, Thomas L. Schmidt

Abstract: Parafermions are emergent excitations which generalize Majorana fermions and are potentially relevant to topological quantum computation. Using the concept of Fock parafermions, we present a mapping between lattice $\mathbb{Z}_4$ parafermions and lattice spin-$1/2$ fermions which preserves the locality of operators with $\mathbb{Z}_4$ symmetry. Based on this mapping, we construct an exactly solvab… ▽ More Parafermions are emergent excitations which generalize Majorana fermions and are potentially relevant to topological quantum computation. Using the concept of Fock parafermions, we present a mapping between lattice $\mathbb{Z}_4$ parafermions and lattice spin-$1/2$ fermions which preserves the locality of operators with $\mathbb{Z}_4$ symmetry. Based on this mapping, we construct an exactly solvable, local, and interacting one-dimensional fermionic Hamiltonian which hosts zero-energy modes obeying parafermionic algebra. We numerically show that this parafermionic phase remains stable in a wide range of parameters, and discuss its signatures in the fermionic spectral function. △ Less

Submitted 14 November, 2018; v1 submitted 16 February, 2018; originally announced February 2018.

Comments: 9 pages, 4 figures

Journal ref: Phys. Rev. B 98, 201110 (2018)

Fractionalized Fermi liquids and exotic superconductivity in the Kitaev-Kondo lattice

Authors: Urban F. P. Seifert, Tobias Meng, Matthias Vojta

Abstract: Fractionalized Fermi liquids (FL$^\ast$) have been introduced as non-Fermi-liquid metallic phases, characterized by coexisting electron-like charge carriers and local moments which itself form a fractionalized spin liquid. Here we investigate a Kondo lattice model on the honeycomb lattice with compass interactions among the local moments, a concrete model hosting FL$^\ast$ phases based on Kitaev's… ▽ More Fractionalized Fermi liquids (FL$^\ast$) have been introduced as non-Fermi-liquid metallic phases, characterized by coexisting electron-like charge carriers and local moments which itself form a fractionalized spin liquid. Here we investigate a Kondo lattice model on the honeycomb lattice with compass interactions among the local moments, a concrete model hosting FL$^\ast$ phases based on Kitaev's $\mathbb{Z}_2$ spin liquid. We characterize the FL$^\ast$ phases via perturbation theory, and we employ a Majorana-fermion mean-field theory to map out the full phase diagram. Most remarkably we find triplet superconducting phases which mask the quantum phase transition between fractionalized and conventional Fermi liquid phases. Their pairing structure is inherited from the Kitaev spin liquid, i.e., superconductivity is driven by Majorana glue. △ Less

Submitted 12 February, 2018; v1 submitted 25 October, 2017; originally announced October 2017.

Comments: 18 pages, 13 figures, (v3) as published

Journal ref: Phys. Rev. B 97, 085118 (2018)

Missing Shapiro steps and the $8π$-periodic Josephson effect in interacting helical electron systems

Authors: Christopher J. Pedder, Tobias Meng, Rakesh Tiwari, Thomas L. Schmidt

Abstract: Two-particle backscattering in time-reversal invariant interacting helical electron systems can lead to the formation of quasiparticles with charge $e/2$. We propose a way to detect such states by means of the Josephson effect in the presence of proximity-induced superconductivity. In this case, the existence of $e/2$ charges leads to an $8 π$-periodic component of the Josephson current which can… ▽ More Two-particle backscattering in time-reversal invariant interacting helical electron systems can lead to the formation of quasiparticles with charge $e/2$. We propose a way to detect such states by means of the Josephson effect in the presence of proximity-induced superconductivity. In this case, the existence of $e/2$ charges leads to an $8 π$-periodic component of the Josephson current which can be identified through measurement of Shapiro steps in Josephson junctions. In particular, we show that even when there is weak explicit time-reversal symmetry breaking, which causes the two-particle backscattering to be a sub-leading effect at low energies, its presence can still be detected in driven, current-biased Shapiro step measurements. The disappearance of some of these steps as a function of the drive frequency is directly related to the existence of non-Abelian zero-energy states. We suggest that this effect can be measured in current state-of-the-art Rashba wires. △ Less

Submitted 22 May, 2017; v1 submitted 18 May, 2017; originally announced May 2017.

Comments: 9 pages, 5 figures. A new submission extending and expanding our analysis in arXiv:1507.08881. (v2) References added

Journal ref: Phys. Rev. B 96, 165429 (2017)

Experimental signatures of the mixed axial-gravitational anomaly in the Weyl semimetal NbP

Authors: Johannes Gooth, Anna Corinna Niemann, Tobias Meng, Adolfo G. Grushin, Karl Landsteiner, Bernd Gotsmann, Fabian Menges, Marcus Schmidt, Chandra Shekhar, Vicky Sueß, Ruben Huehne, Bernd Rellinghaus, Claudia Felser, Binghai Yan, Kornelius Nielsch

Abstract: Weyl semimetals are materials where electrons behave effectively as a kind of massless relativistic particles known asWeyl fermions. These particles occur in two flavours, or chiralities, and are subject to quantum anomalies, the breaking of a conservation law by quantum fluctuations. For instance, the number of Weyl fermions of each chirality is not independently conserved in parallel electric an… ▽ More Weyl semimetals are materials where electrons behave effectively as a kind of massless relativistic particles known asWeyl fermions. These particles occur in two flavours, or chiralities, and are subject to quantum anomalies, the breaking of a conservation law by quantum fluctuations. For instance, the number of Weyl fermions of each chirality is not independently conserved in parallel electric and magnetic field, a phenomenon known as the chiral anomaly. In addition, an underlying curved spacetime provides a distinct contribution to a chiral imbalance, an effect known as the mixed axial-gravitational anomaly, which remains experimentally elusive. However, the presence of a mixed gauge-gravitational anomaly has recently been tied to thermoelectrical transport in a magnetic field, even in flat spacetime, opening the door to experimentally probe such type of anomalies in Weyl semimetals. Using a temperature gradient, we experimentally observe a positive longitudinal magnetothermoelectric conductance (PMTC) in the Weyl semimetal NbP for collinear temperature gradients and magnetic fields (DT || B) that vanishes in the ultra quantum limit. This observation is consistent with the presence of a mixed axial-gravitational anomaly. Our work provides clear experimental evidence for the existence of a mixed axial-gravitational anomaly of Weyl fermions, an outstanding theoretical concept that has so far eluded experimental detection. △ Less

Submitted 29 March, 2017; originally announced March 2017.

Journal ref: Nature 547, 324 (2017)

Inducing superconductivity in Weyl semi-metal microstructures by selective ion sputtering

Authors: Maja D. Bachmann, Nityan Nair, Felix Flicker, Roni Ilan, Tobias Meng, Nirmal J. Ghimire, Eric D. Bauer, Filip Ronning, James G. Analytis, Philip J. W. Moll

Abstract: By introducing a superconducting gap in Weyl- or Dirac semi-metals, the superconducting state inherits the non-trivial topology of their electronic structure. As a result, Weyl superconductors are expected to host exotic phenomena such as non-zero-momentum pairing due to their chiral node structure, or zero- energy Majorana modes at the surface. These are of fundamental interest to improve our und… ▽ More By introducing a superconducting gap in Weyl- or Dirac semi-metals, the superconducting state inherits the non-trivial topology of their electronic structure. As a result, Weyl superconductors are expected to host exotic phenomena such as non-zero-momentum pairing due to their chiral node structure, or zero- energy Majorana modes at the surface. These are of fundamental interest to improve our understanding of correlated topological systems, and moreover practical applications in phase coherent devices and quantum applications have been proposed. Proximity-induced superconductivity promises to allow such experiments on non-superconducting Weyl semi-metals. Here we show a new route to reliably fabricating superconducting microstructures from the non-superconducting Weyl semi-metal NbAs under ion irradiation. The significant difference in the surface binding energy of Nb and As leads to a natural enrichment of Nb at the surface during ion milling, forming a superconducting surface layer (Tc~3.5K). Being formed from the target crystal itself, the ideal contact between the superconductor and the bulk may enable an effective gapping of the Weyl nodes in the bulk due to the proximity effect. Simple ion irradiation may thus serve as a powerful tool to fabricating topological quantum devices from mono-arsenides, even on an industrial scale. △ Less

Submitted 23 March, 2017; originally announced March 2017.

Comments: accepted by Science Advances

Journal ref: Sci. Adv. Vol. 3, no. 5 (2017)

Dynamic response functions and helical gaps in interacting Rashba nanowires with and without magnetic fields

Authors: Christopher Pedder, Tobias Meng, Rakesh P. Tiwari, Thomas L. Schmidt

Abstract: A partially gapped spectrum due to the application of a magnetic field is one of the main probes of Rashba spin-orbit coupling in nanowires. Such a "helical gap" manifests itself in the linear conductance, as well as in dynamic response functions such as the spectral function, the structure factor, or the tunnelling density of states. In this paper, we investigate theoretically the signature of th… ▽ More A partially gapped spectrum due to the application of a magnetic field is one of the main probes of Rashba spin-orbit coupling in nanowires. Such a "helical gap" manifests itself in the linear conductance, as well as in dynamic response functions such as the spectral function, the structure factor, or the tunnelling density of states. In this paper, we investigate theoretically the signature of the helical gap in these observables with a particular focus on the interplay between Rashba spin-orbit coupling and electron-electron interactions. We show that in a quasi-one-dimensional wire, interactions can open a helical gap even without magnetic field. We calculate the dynamic response functions using bosonization, a renormalization group analysis, and the exact form factors of the emerging sine-Gordon model. For special interaction strengths, we verify our results by refermionization. We show how the two types of helical gaps, caused by magnetic fields or interactions, can be distinguished in experiments. △ Less

Submitted 13 December, 2016; v1 submitted 12 August, 2016; originally announced August 2016.

Comments: 15 pages, 7 figures, v2 refs added

Journal ref: Phys. Rev. B 94, 245414 (2016)

Magneto-electric spectroscopy of Andreev bound states in Josephson quantum dots

Authors: Nils Wentzell, Serge Florens, Tobias Meng, Volker Meden, Sabine Andergassen

Abstract: We theoretically investigate the behavior of Andreev levels in a single-orbital interacting quantum dot in contact to superconducting leads, focusing on the effect of electrostatic gating and applied magnetic field, as relevant for recent experimental spectroscopic studies. In order to account reliably for spin-polarization effects in presence of correlations, we extend here two simple and complem… ▽ More We theoretically investigate the behavior of Andreev levels in a single-orbital interacting quantum dot in contact to superconducting leads, focusing on the effect of electrostatic gating and applied magnetic field, as relevant for recent experimental spectroscopic studies. In order to account reliably for spin-polarization effects in presence of correlations, we extend here two simple and complementary approaches that are tailored to capture effective Andreev levels: the static functional renormalization group (fRG) and the self-consistent Andreev bound states (SCABS) theory. We provide benchmarks against the exact large-gap solution as well as NRG calculations and find good quantitative agreement in the range of validity. The large flexibility of the implemented approaches then allows us to analyze a sizeable parameter space, allowing to get a deeper physical understanding into the Zeeman field, electrostatic gate, and flux dependence of Andreev levels in interacting nanostructures. △ Less

Submitted 11 October, 2016; v1 submitted 30 May, 2016; originally announced May 2016.

Comments: 17 pages, 12 figures

Journal ref: Phys. Rev. B 94, 085151 (2016)

Theory of a 3+1D fractional chiral metal: interacting variant of the Weyl semimetal

Authors: Tobias Meng, Adolfo G. Grushin, Kirill Shtengel, Jens H. Bardarson

Abstract: Formulating consistent theories describing strongly correlated metallic topological phases is an outstanding problem in condensed matter physics. In this work we derive a theory defining a fractionalized analogue of the Weyl semimetal state: the fractional chiral metal. Our approach is to construct a 4+1D quantum Hall insulator by stacking 3+1D Weyl semimetals in a magnetic field. In a strong enou… ▽ More Formulating consistent theories describing strongly correlated metallic topological phases is an outstanding problem in condensed matter physics. In this work we derive a theory defining a fractionalized analogue of the Weyl semimetal state: the fractional chiral metal. Our approach is to construct a 4+1D quantum Hall insulator by stacking 3+1D Weyl semimetals in a magnetic field. In a strong enough field the low-energy physics is determined by the lowest Landau level of each Weyl semimetal, which is highly degenerate and chiral, motivating us to use a coupled-wire approach. The one-dimensional dispersion of the lowest Landau level allows us to model the system as a set of degenerate 1+1D quantum wires that can be bosonized in the presence of electron-electron interactions and coupled such that a gapped phase is obtained, whose response to an electromagnetic field is given in terms of a Chern-Simons field theory. At the boundary of this phase we obtain the field theory of a 3+1D gapless fractional chiral state, which we show is consistent with a previous theory for the surface of a 4+1D Chern-Simons theory. The boundary's response to an external electromagnetic field is determined by a chiral anomaly with a fractionalized coefficient. We suggest that such anomalous response can be taken as a working definition of a fractionalized strongly correlated analogue of the Weyl semimetal state. △ Less

Submitted 25 October, 2016; v1 submitted 29 February, 2016; originally announced February 2016.

Comments: 15 pages, 6 figures, extended discussion about potential realizations of 3+1D fractional chiral metals, final version

Journal ref: Phys. Rev. B 94, 155136 (2016)

$\mathbb{Z}_4$ Parafermions \& the $8π$-periodic Josephson effect in interacting Rashba nanowires

Authors: Chris J. Pedder, Tobias Meng, Rakesh P. Tiwari, Thomas L. Schmidt

Abstract: We demonstrate the appearance of zero-energy bound states satisfying the $\mathbb{Z}_4$ parafermionic algebra in interacting quantum wires with Rashba spin-orbit coupling and proximity-induced superconductivity. The fourfold degeneracy of these states is protected by time-reversal symmetry and fermion-parity conservation, and leads to an $8 π$ periodicity of the Josephson current due to the tunn… ▽ More We demonstrate the appearance of zero-energy bound states satisfying the $\mathbb{Z}_4$ parafermionic algebra in interacting quantum wires with Rashba spin-orbit coupling and proximity-induced superconductivity. The fourfold degeneracy of these states is protected by time-reversal symmetry and fermion-parity conservation, and leads to an $8 π$ periodicity of the Josephson current due to the tunneling of fractionalized excitations with charge $e/2$. Even in the presence of perturbations, we propose that this periodicity will remain visible in driven, current-biased Shapiro step measurements on current state-of-the-art Rashba wires. △ Less

Submitted 8 February, 2016; v1 submitted 31 July, 2015; originally announced July 2015.

Comments: 13 pages, 5 figures

MSC Class: 82D77

Fractional topological phases in three-dimensional coupled-wire systems

Authors: Tobias Meng

Abstract: It is shown that three-dimensional systems of coupled quantum wires support fractional topological phases composed of closed loops and open planes of two-dimensional fractional quantum Hall subsystems. These phases have topologically protected edge states, and are separated by exotic quantum phase transitions corresponding to a rearrangement of fractional quantum Hall edge modes. Some support for… ▽ More It is shown that three-dimensional systems of coupled quantum wires support fractional topological phases composed of closed loops and open planes of two-dimensional fractional quantum Hall subsystems. These phases have topologically protected edge states, and are separated by exotic quantum phase transitions corresponding to a rearrangement of fractional quantum Hall edge modes. Some support for the existence of an extended exotic critical phase separating the bulk gapped fractional topological phases is given. Without electron-electron interactions, similar but unfractionalized bulk gapped phases based on coupled integer quantum Hall states exist. They are separated by an extended critical Weyl semimetal phase. △ Less

Submitted 12 October, 2015; v1 submitted 3 June, 2015; originally announced June 2015.

Comments: 10 pages, 4 figures

Journal ref: Phys. Rev. B 92, 115152 (2015)

Impurity Induced Quantum Phase Transitions and Magnetic Order in Conventional Superconductors: Competition between Bound and Quasiparticle states

Authors: Silas Hoffman, Jelena Klinovaja, Tobias Meng, Daniel Loss

Abstract: We theoretically study bound states generated by magnetic impurities within conventional $s$-wave superconductors, both analytically and numerically. In determining the effect of the hybridization of two such bound states on the energy spectrum as a function of magnetic exchange coupling, relative angle of magnetization, and distance between impurities, we find that quantum phase transitions can b… ▽ More We theoretically study bound states generated by magnetic impurities within conventional $s$-wave superconductors, both analytically and numerically. In determining the effect of the hybridization of two such bound states on the energy spectrum as a function of magnetic exchange coupling, relative angle of magnetization, and distance between impurities, we find that quantum phase transitions can be modulated by each of these parameters. Accompanying such transitions, there is a change in the preferred spin configuration of the impurities. Although the interaction between the impurity spins is overwhelmingly dominated by the quasiparticle contribution, the ground state of the system is determined by the bound state energies. Self-consistently calculating the superconducting order parameter, we find a discontinuity when the system undergoes a quantum phase transition as indicated by the bound state energies. △ Less

Submitted 30 March, 2015; originally announced March 2015.

Comments: 8 pages, 7 figures

Journal ref: Phys. Rev. B 92, 125422 (2015)

Coupled wire construction of chiral spin liquids

Authors: Tobias Meng, Titus Neupert, Martin Greiter, Ronny Thomale

Abstract: We develop a coupled wire construction of chiral spin liquids. The starting point are individual wires of electrons in the Mott regime that are subject to a Zeeman field and Rashba spin-orbit coupling. Suitable spin-flip couplings between the wires yield an Abelian chiral spin liquid state which supports spinon excitations above a bulk gap, and chiral edge states. The approach generalizes to non-A… ▽ More We develop a coupled wire construction of chiral spin liquids. The starting point are individual wires of electrons in the Mott regime that are subject to a Zeeman field and Rashba spin-orbit coupling. Suitable spin-flip couplings between the wires yield an Abelian chiral spin liquid state which supports spinon excitations above a bulk gap, and chiral edge states. The approach generalizes to non-Abelian chiral spin liquids at level k with parafermionic edge states. △ Less

Submitted 11 August, 2015; v1 submitted 17 March, 2015; originally announced March 2015.

Comments: 5 pages, 1 figure

Journal ref: Phys. Rev. B 91, 241106(R) (2015)

Superconducting Gap Renormalization around two Magnetic Impurities: From Shiba to Andreev Bound States

Authors: Tobias Meng, Jelena Klinovaja, Silas Hoffman, Pascal Simon, Daniel Loss

Abstract: We study the renormalization of the gap of an s-wave superconductor in the presence of two magnetic impurities. For weakly bound Shiba states, we analytically calculate the part of the gap renormalization that is sensitive to the relative orientation of the two impurity spins. For impurities with a strong exchange coupling to the conduction electrons, we solve the gap equation self-consistently by… ▽ More We study the renormalization of the gap of an s-wave superconductor in the presence of two magnetic impurities. For weakly bound Shiba states, we analytically calculate the part of the gap renormalization that is sensitive to the relative orientation of the two impurity spins. For impurities with a strong exchange coupling to the conduction electrons, we solve the gap equation self-consistently by numerics and find that the sub-gap Shiba state turns into a supra-gap Andreev state when the local gap parameter changes sign under the impurities. △ Less

Submitted 10 August, 2015; v1 submitted 30 January, 2015; originally announced January 2015.

Comments: 6 pages, 4 figures - final version

Journal ref: Phys. Rev. B 92, 064503 (2015)

Time reversal symmetry broken fractional topological phases at zero magnetic field

Authors: Tobias Meng, Eran Sela

Abstract: We extend the coupled-wire construction of quantum Hall phases, and search for fractional topological insulating states in models of weakly coupled wires at zero external magnetic field. Focussing on systems beyond double copies of fractional quantum Hall states at opposite fields, we find that spin-spin interactions can stabilize a large family of fractional topological phases with broken time re… ▽ More We extend the coupled-wire construction of quantum Hall phases, and search for fractional topological insulating states in models of weakly coupled wires at zero external magnetic field. Focussing on systems beyond double copies of fractional quantum Hall states at opposite fields, we find that spin-spin interactions can stabilize a large family of fractional topological phases with broken time reversal invariance. The latter is manifest by spontaneous spin polarization, by a finite Hall conductivity, or by both. This suggests the possibility that fractional topological insulators may be unstable to spontaneous symmetry breaking. △ Less

Submitted 16 December, 2014; v1 submitted 10 October, 2014; originally announced October 2014.

Comments: 9+ pages, 7 figures, final version

Journal ref: Phys. Rev. B 90, 235425 (2014)

Strongly Interacting Holes in Ge/Si Nanowires

Authors: Franziska Maier, Tobias Meng, Daniel Loss

Abstract: We consider holes confined to Ge/Si core/shell nanowires subject to strong Rashba spin-orbit interaction and screened Coulomb interaction. Such wires can, for instance, serve as host systems for Majorana bound states. Starting from a microscopic model, we find that the Coulomb interaction strongly influences the properties of experimentally realistic wires. To show this, a Luttinger liquid descrip… ▽ More We consider holes confined to Ge/Si core/shell nanowires subject to strong Rashba spin-orbit interaction and screened Coulomb interaction. Such wires can, for instance, serve as host systems for Majorana bound states. Starting from a microscopic model, we find that the Coulomb interaction strongly influences the properties of experimentally realistic wires. To show this, a Luttinger liquid description is derived based on a renormalization group analysis. This description in turn allows to calculate the scaling exponents of various correlation functions as a function of the microscopic system parameters. It furthermore permits to investigate the effect of Coulomb interaction on a small magnetic field, which opens a strongly anisotropic partial gap. △ Less

Submitted 24 October, 2014; v1 submitted 4 August, 2014; originally announced August 2014.

Journal ref: Phys. Rev. B 90, 155437 (2014)