| 1. |
- Revelli, A., et al.
(författare)
-
Quasimolecular electronic structure of the spin-liquid candidate Ba3 InIr2 O9
- 2022
-
Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 106:15
-
Tidskriftsartikel (refereegranskat)abstract
- The mixed-valent iridate Ba3InIr2O9 has been discussed as a promising candidate for quantum spin-liquid behavior. The compound exhibits Ir4.5+ ions in face-sharing IrO6 octahedra forming Ir2O9 dimers with three t2g holes per dimer. Our results establish Ba3InIr2O9 as a cluster Mott insulator. Strong intradimer hopping delocalizes the three t2g holes in quasimolecular dimer states while interdimer charge fluctuations are suppressed by Coulomb repulsion. The magnetism of Ba3InIr2O9 emerges from spin-orbit entangled quasimolecular moments with yet unexplored interactions, opening up a new route to unconventional magnetic properties of 5d compounds. Using single-crystal x-ray diffraction we find the monoclinic space group C2/c already at room temperature. Dielectric spectroscopy shows insulating behavior. Resonant inelastic x-ray scattering reveals a rich excitation spectrum below 1.5 eV with a sinusoidal dynamical structure factor that unambiguously demonstrates the quasimolecular character of the electronic states. Below 0.3 eV, we observe a series of excitations. According to exact diagonalization calculations, such low-energy excitations reflect the proximity of Ba3InIr2O9 to a hopping-induced phase transition based on the condensation of a quasimolecular spin-orbit exciton. The dimer ground state roughly hosts two holes in a bonding j=1/2 orbital and the third hole in a bonding j=3/2 orbital.
|
|
| 2. |
- Bergholtz, Emil Johansson, et al.
(författare)
-
Microscopic theory of the quantum Hall hierarchy
- 2007
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 99:25, s. 256803-1-256803-4
-
Tidskriftsartikel (refereegranskat)abstract
- We solve the quantum Hall problem exactly in a limit and show that the ground states can be organized in a fractal pattern consistent with the Haldane-Halperin hierarchy, and with the global phase diagram. We present wave functions for a large family of states, including those of Laughlin and Jain and also for states recently observed by Pan et al., and show that they coincide with the exact ones in the solvable limit. We submit that they establish an adiabatic continuation of our exact results to the experimentally accessible regime, thus providing a unified approach to the hierarchy states.
|
|
| 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. |
- Hermanns, Maria, 1980-
(författare)
-
Quasielectrons in Abelian and non-Abelian Quantum Hall States
- 2010
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Strongly correlated electron systems continue to attract a lot of interest. Especially two-dimensional electron systems have shown many surprising behaviours. A fascinating example is the quantum Hall effect, which arises when electrons are confined to two dimensions, subjected to a very large magnetic field, and cooled to very low temperatures. Under these conditions, the electrons form new states of matter - the strongly correlated quantum Hall liquids. A hallmark of these quantum liquids is the precise quantization of the Hall conductance, but in recent years more attention has been focused on their exotic excitations. These have fractional electric charge, and fractional exchange statistics. The latter implies that the wave function is multiplied by a phase factor containing a fractional phase when two quasiparticles are moved around each other. Thus, they are neither bosons nor fermions, but so-called anyons. In recent years, there has accumulated theoretical and experimental evidence for some of the quantum Hall liquids having even more exotic excitations with not only fractional but non-Abelian exchange statistics. The quasiparticles of such systems could be used to build topologically protected quantum bits, which are much more robust than presently available quantum bits; they would be the ideal building blocks of a quantum computer. We use conformal field theory to describe the quantum Hall liquids, as well as their excitations. In particular, we represent the electrons and quasiparticles by conformal field theory operators. Even though the operator description for quasiholes is very well understood, it was for a long time unclear how to describe their antiparticles, the quasielectrons. We found an operator that describes quasielectron excitations correctly and shares many of the useful properties of the corresponding quasihole operator. For instance, many of the topological properties of the particles are manifest in the operator. This not only adds a missing piece to the quantum Hall puzzle, but it also opens up new and exciting possibilities. For instance, we were able to extend this construction to the non-Abelian states. A highly non-trivial application of our approach is the condensation of non-Abelian quasielectrons, which yields new non-Abelian quantum Hall states with non-Abelian properties that differ from those of their parent states.
|
|
| 5. |
- Rødland, Lukas, 1993-, et al.
(författare)
-
Disorder and non-Hermiticity in Kitaev spin liquids with a Majorana Fermi surface
- 2024
-
Ingår i: Physical Review B. - 2469-9950 .- 2469-9969. ; 109:15
-
Tidskriftsartikel (refereegranskat)abstract
- We study the effect of disorder on ?2 quantum spin liquids with a Majorana Fermi line (respectively a surface in three dimensions), and we show that depending on the symmetries that are preserved on average, qualitatively different scenarios will occur. In particular, we identify the relevant non-Hermitian symmetries for which disorder will effectively split the Fermi line into two exceptional lines, with Re(?)=0 states filling the area in between. We demonstrate the different scenarios using both toy models as well as large-scale numerical simulations.
|
|
| 6. |
- Vergara, I., et al.
(författare)
-
Spin-orbit coupling and crystal-field splitting in Ti-doped Ca2RuO4 studied by ellipsometry
- 2022
-
Ingår i: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 106:8
-
Tidskriftsartikel (refereegranskat)abstract
- In Ca2RuO4, the competition of spin-orbit coupling ζ and tetragonal crystal-field splitting ΔCF has been discussed controversially for many years. The orbital occupation depends on ΔCF/ζ, which allows us to address this ratio via the optical spectral weights of the lowest intersite Mott-Hubbard excitations. We study the optical conductivity of Ca2Ru0.99Ti0.01O4 in the range of 0.75-5 eV by ellipsometry, using the large single crystals that can be grown for small Ti concentrations. Based on a local multiplet calculation, our analysis results in 2.4≤ΔCF/ζ≲4 at 15 K. The dominant crystal field yields a ground state close to xy orbital order but spin-orbit coupling is essential for a quantitative description of the properties. Furthermore, we observe a pronounced decrease of ΔCF with increasing temperature, as expected based on the reduction of octahedral distortions.
|
|
| 7. |
- Warzanowski, P., et al.
(författare)
-
Spin-orbit coupling in a half-filled ?2? shell : The case of 5?3 K2ReCl6
- 2024
-
Ingår i: Physical Review B. - 2469-9950 .- 2469-9969. ; 109:15
-
Tidskriftsartikel (refereegranskat)abstract
- The half-filled ?2? shell of the configuration usually, in ?? coupling, hosts a ?=3/2 ground state with quenched orbital moment. This state is not Jahn-Teller active. Sufficiently large spin-orbit coupling ? has been predicted to change this picture by mixing in orbital moment, giving rise to a sizable Jahn-Teller distortion. In 5?3K2ReCl6 we study the electronic excitations using resonant inelastic x-ray scattering and optical spectroscopy. We observe on-site intra-?2? excitations below 2 eV and corresponding overtones with two intra-?2? excitations on adjacent sites, the Mott gap at 2.7 eV, ?2?-to-?? excitations above 3 eV, and charge-transfer excitations at still higher energy. The intra-?2? excitation energies are a sensitive measure of ? and Hund's coupling ?H. The sizable value of ?≈0.29eV places K2ReCl6 into the intermediate coupling regime, but ?/?H≈0.6 is not sufficiently large to drive a pronounced Jahn-Teller effect. We discuss the ground state wave function in a Kanamori picture and find that the ?=3/2 multiplet still carries about 97% of the weight. However, the finite admixture of orbital moment allows for subtle effects. We discuss small temperature-induced changes of the optical data and find evidence for a lowering of the ground state by about 3 meV below the structural phase transitions.
|
|
