| 1. |
- Behrends, J., et al.
(författare)
-
Anomalous conductance scaling in strained Weyl semimetals
- 2019
-
Ingår i: Physical Review Research. - : American Physical Society (APS). - 2643-1564. ; 1:3
-
Tidskriftsartikel (refereegranskat)abstract
- Magnetotransport provides key experimental signatures in Weyl semimetals. The longitudinal magnetoresistance is linked to the chiral anomaly and the transversal magnetoresistance to the dominant charge relaxation mechanism. Axial magnetic fields that act with opposite sign on opposite chiralities facilitate new transport experiments that probe the low-energy Weyl nodes. As recently realized, these axial fields can be achieved by straining samples or adding inhomogeneities to them. Here, we identify a robust signature of axial magnetic fields: an anomalous scaling of the conductance in the diffusive ultraquantum regime. In particular, we demonstrate that the longitudinal conductivity in the ultraquantum regime of a disordered Weyl semimetal subjected to an axial magnetic field increases with both the field strength and sample width due to a spatial separation of charge carriers. We contrast axial magnetic with real magnetic fields to clearly distinguish the different behavior of the conductance. Our results rely on numerical tight-binding simulations and are supported by analytical arguments. We argue that the spatial separation of charge carriers can be used for directed currents in microstructured electronic devices.
|
|
| 2. |
- Eschmann, T., et al.
(författare)
-
Thermodynamics of a gauge-frustrated Kitaev spin liquid
- 2019
-
Ingår i: Physical Review Research. - : American Physical Society (APS). - 2643-1564. ; 1:3
-
Tidskriftsartikel (refereegranskat)abstract
- Two- and three-dimensional Kitaev magnets are prototypical frustrated quantum spin systems, in which the original spin degrees of freedom fractionalize into Majorana fermions and a Z2 gauge field—a purely local phenomenon that reveals itself as a thermodynamic crossover at a temperature scale set by the strength of the bond-directional interactions. For conventional Kitaev magnets, the low-temperature thermodynamics reveals a second transition at which the Z2 gauge field orders and the system enters a spin-liquid ground state. Here, we discuss an explicit example that goes beyond this paradigmatic scenario—the Z2 gauge field is found to be subject to geometric frustration, the thermal ordering transition is suppressed, and an extensive residual entropy arises. Deep in the quantum regime, at temperatures of the order of one per mil of the interaction strength, the degeneracy in the gauge sector is lifted by a subtle interplay between the gauge field and the Majorana fermions, resulting in the formation of a Majorana metal. We discuss the thermodynamic signatures of this physics obtained from large-scale, sign-free quantum Monte Carlo simulations.
|
|
| 3. |
- Eschmann, T., et al.
(författare)
-
Thermodynamics of a gauge-frustrated Kitaev spin liquid
- 2019
-
Ingår i: Physical Review Research. - : American Physical Society (APS). - 2643-1564. ; 1:3
-
Tidskriftsartikel (refereegranskat)abstract
- Two- and three-dimensional Kitaev magnets are prototypical frustrated quantum spin systems, in which the original spin degrees of freedom fractionalize into Majorana fermions and a Z2 gauge field - a purely local phenomenon that reveals itself as a thermodynamic crossover at a temperature scale set by the strength of the bond-directional interactions. For conventional Kitaev magnets, the low-temperature thermodynamics reveals a second transition at which the Z2 gauge field orders and the system enters a spin-liquid ground state. Here, we discuss an explicit example that goes beyond this paradigmatic scenario - the Z2 gauge field is found to be subject to geometric frustration, the thermal ordering transition is suppressed, and an extensive residual entropy arises. Deep in the quantum regime, at temperatures of the order of one per mil of the interaction strength, the degeneracy in the gauge sector is lifted by a subtle interplay between the gauge field and the Majorana fermions, resulting in the formation of a Majorana metal. We discuss the thermodynamic signatures of this physics obtained from large-scale, sign-free quantum Monte Carlo simulations.
|
|
| 4. |
- Johansson, Magnus, et al.
(författare)
-
Stability analysis of numerically exact time-periodic breathers in the Lugiato-Lefever equation: Discrete vs continuum
- 2019
-
Ingår i: Physical Review Research. - : American Physical Society. - 2643-1564. ; 1:3, s. 1-9
-
Tidskriftsartikel (refereegranskat)abstract
- We describe a framework for numerical calculation of time-periodically oscillating (breather) solutions to the discretized Lugiato-Lefever equation (LLE), as well as their linear stability as obtained from numerical Floquet analysis. Compared to earlier approaches, our work allows for the following conclusions: (i) The complete families of solutions are obtained also in regimes of instability; (ii) analysis of Floquet spectra and the corresponding eigenvectors show clearly the nature of the various Hopf and period-doubling bifurcations; (iii) properties of breather solutions to the continuous LLE are connected to corresponding oscillating solutions of the discrete LLE, which is of interest in its own right modeling coupled nonlinear cavities. In particular, we show that the oscillating discrete cavity solitons found in earlier work can be viewed as lattice versions of the continuous LLE breathers, as there is a smooth continuation in parameter space connecting them. Moreover, we confirm the existence of stable breathers at large detunings that was recently observed experimentally and describe their appearance from bifurcations.
|
|
| 5. |
- Nag, T., et al.
(författare)
-
Out of equilibrium higher-order topological insulator : Floquet engineering and quench dynamics
- 2019
-
Ingår i: Physical Review Research. - : American Physical Society (APS). - 2643-1564. ; 1:3
-
Tidskriftsartikel (refereegranskat)abstract
- Higher-order topological (HOT) states, hosting topologically protected modes on lower-dimensional boundaries, such as hinges and corners, have recently extended the realm of the static topological phases. Here we demonstrate the possibility of realizing a two-dimensional Floquet second-order topological insulator, featuring corner-localized zero quasienergy modes and characterized by quantized Floquet qudrupolar moment QxyFlq=0.5, by periodically kicking a quantum spin Hall insulator (QSHI) with a discrete fourfold (C4) and time-reversal (T) symmetry breaking Dirac mass perturbation. Furthermore, we show that QxyFlq becomes independent of the choice of origin as the system approaches the thermodynamic limit. We also analyze the dynamics of a corner mode after a sudden quench, when the C4 and T symmetry breaking perturbation is switched off, and find that the corresponding survival probability displays periodic appearances of complete, partial and no revival for long time, encoding the signature of corner modes in a QSHI. Our protocol is sufficiently general to explore the territory of dynamical HOT phases in insulators and gapless systems.
|
|
| 6. |
- Sánchez, Rafael, et al.
(författare)
-
Autonomous conversion of information to work in quantum dots
- 2019
-
Ingår i: Physical Review Research. - 2643-1564. ; 1:3
-
Tidskriftsartikel (refereegranskat)abstract
- We consider an autonomous implementation of Maxwell's demon in a quantum dot architecture acting on a system without changing its number of particles or its energy. As in the original thought experiment, only the second law of thermodynamics is seemingly violated when disregarding the demon. The autonomous architecture allows us to compare descriptions in terms of information to a more traditional, thermoelectric characterization. Our detailed investigation of information-to-work conversion is based on fluctuation relations and second-law-like inequalities in addition to the average heat and charge currents. By introducing a time reversal on the level of individual electrons, we find a fluctuation relation that is not connected to any symmetry of the moment-generating function of heat and particle flows. Furthermore, we show how an effective Markovian master equation with broken detailed balance for the system alone can emerge from a full description, allowing for an investigation of the entropic cost associated with breaking detailed balance. Interestingly, while the entropic cost of performing a perfect measurement diverges, the entropic cost of breaking detailed balance does not. Our results connect various approaches and idealized scenarios found in the literature and can be tested experimentally with present-day technology.
|
|
| 7. |
- Schindler, Frank, et al.
(författare)
-
Fractional corner charges in spin-orbit coupled crystals
- 2019
-
Ingår i: Physical Review Research. - : AMER PHYSICAL SOC. - 2643-1564. ; 1:3
-
Tidskriftsartikel (refereegranskat)abstract
- We study two-dimensional spinful insulating phases of matter that are protected by time-reversal and crystalline symmetries. To characterize these phases, we employ the concept of corner charge fractionalization: corners can carry charges that are fractions of even multiples of the electric charge. The charges are quantized and topologically stable as long as all symmetries are preserved. We classify the different corner charge configurations for all point groups, and match them with the corresponding bulk topology. For this we employ symmetry indicators and (nested) Wilson loop invariants. We provide formulas that allow for a convenient calculation of the corner charge from Bloch wave functions and illustrate our results using the example of arsenic and antimony monolayers. Depending on the degree of structural buckling, these materials can exhibit two distinct obstructed atomic limits. We present density functional theory calculations for open flakes to support our findings.
|
|
| 8. |
- Selig, M., et al.
(författare)
-
Ultrafast dynamics in monolayer transition metal dichalcogenides: Interplay of dark excitons, phonons, and intervalley exchange
- 2019
-
Ingår i: Physical Review Research. - 2643-1564. ; 1:2
-
Tidskriftsartikel (refereegranskat)abstract
- Understanding the ultrafast coupling and relaxation mechanisms between valleys in transition metal dichalcogenide semiconductors is of crucial interest for future valleytronic devices. Recent ultrafast pump-probe experiments showed an unintuitive significant bleaching at the excitonic B transition after optical excitation of the energetically lower excitonic A transition. Here, we present a possible microscopic explanation for this surprising effect. It is based on the joint action of exchange coupling and phonon-mediated thermalization into dark exciton states and does not involve a population of the B exciton. Our work demonstrates how intra- and intervalley coupling on a femtosecond timescale governs the optical valley response of 2D semiconductors.
|
|
| 9. |
- Vinas Boström, Emil, et al.
(författare)
-
Electron-electron versus electron-phonon interactions in lattice models: Screening effects described by a density functional theory approach
- 2019
-
Ingår i: Physical Review Research. - 2643-1564. ; 1:1
-
Tidskriftsartikel (refereegranskat)abstract
- We address the interplay of electron-electron (e-e) and electron-phonon (e-ph) interactions in the Hubbard- Holstein model, using a two-component density functional theory. Exchange-correlation potentials constructed via dynamical mean field theory for a D = ∞ Bethe lattice and analytically for an isolated site give a new perspective on e-ph screening of the e-e interactions and its effect on the charge- and spin-Kondo regimes. Comparisons to exact benchmarks show that the approach is suitable to describe transport properties and real- time dynamics in homogeneous and inhomogeneous lattice systems.
|
|
